Jul 032015
 

Daytona is an enormous, sweeping track. Two-and-a-half miles, 31-degree banking and corner radii of a thousand feet. The infield by itself is 180 acres. If you’ve ever been there (or Talladega), it really does take your breath away when you first enter. Now, bigger tracks (or rather, tracks with bigger turns) automatically mean higher speeds.

There’s a formula for this that tells you how much force you need to make a car turn under specific conditions.

EQ_CentripetalForceWords

The way to think about this is that it is harder to turn (i.e. you need more force)

  • when you have a heavy car
  • when you’re going fast
  • when you’re trying to make a tight turn

So when you compare a thousand foot turn radius like at a superspeedway with the 250-foot turn radius of Bristol, it’s four times easier to turn at Daytona if all other things are held equal.

The equation above is the equation for centripetal force, which is the force that makes a car turn. The centripetal force tends to confuse people because of its direction. The centripetal force points toward the center if the car is moving in a circle. The way I think of it is if you swing a tennis ball around on a string in a horizontal circle over your head, the thing that keeps it going in a circle is the string – producing a force toward the center.

Well, it’s the exact same thing for a car, except instead of a string, you have tires. The force needed to turn a NASCAR stock car at 130 mph at Bristol is about six tons. Yep, tons.

CarTurningwithEquation

Because Daytona is so much larger, you need about four times less force to turn at the same speed.

But why stop at 130 mph?

When Daytona was being planned in the fifties, Bill France knew he wanted high banks. Why?

Speed.

That’s right, banking equals speed, too. Here’s why. Look at the car on a flat track first. I’ve drawn it so the car is moving away from you and it’s turning left (of course).

BSPEED_Banking_CarFlatTrackMovingAway2

 

The force the track exerts on the car is always perpendicular to the track surface. So none of the force of the track on the car is in the direction that helps the car turn. All of the turning force has to come from the interaction between the tires and the track. If you don’t have enough friction, then you’re going to slide out toward the wall.

Banking helps us turn. Let’s give our track a little banking and see why.

BSPEED_Banking_CarBankedTrackMovingAway

 

Two things change. First, the friction between the tires and the track have also tilted. That means you’re not getting the full force from the tires that you did before; however, the force of the track on the car has also shifted direction.

Now the track is helping the car turn. The higher the banking, the more help the car gets from the track.

If you’ve never been on a track, it’s almost hard to appreciate banking. Here’s me filming for our Science of Speed webvideo series at Texas Motor Speedway. I had this great pair of boots I had planned to wear for this shoot, but it turns out you really can’t wear heels on 24 degrees of banking.

And no, the car is not moving. I am adventurous, but I am not (usually) stupid.

DLPTXTrackBanking

 

Turning on Ice

So one of the questions I sometimes get asks how important friction is in turning corners. So let’s play Einstein here…

Einstein thought up all kinds of very strange and mathematically intense ideas about how the universe – space and time, specifically, work. He couldn’t actually do experiments to test all of his ideas. (Plus, he was a theorist and it’s usually best not to trust them with anything more potentially dangerous than a sharp pencil.)

So he did what are called gedanken experiments. Gedanken is the German verb for ‘to think’. These are thought experiments – but they sound much more impressive if you call them gedanken experiments.

We’re going to imagine that a highly localized ice storm hits Daytona. So localized, in fact, that it just hits turns 3 and 4 of the Daytona International Speedway. It covers them with ice. What happens to the car hurtling in there?

There’s an equation – and if you’re the kind of person who breaks into a cold sweat at the sight of a radical (that’s a square root), then just grab your chair tight for a moment. (If you want to see the details, I suggest the wonderful Hyperphysics site.)

 

EQ_CriticalSpeedBankedTurn

All this says is that it is possible to bank a track highly enough that you can take the turn without ANY FRICTION AT ALL.

So if we plug in the numbers for Daytona… we find that, in the absence of friction, you could go 139 mph around the turn.This shouldn’t be all that surprising – after all, Daytona could be viewed as an overgrown luge or bobsled track, right? Those tracks have very high banks because there’s a minimal amount of steering going on.

Being the mathematically OCD person I am, I graphed the maximum speed as a function of banking degree.

BSPEED_Banking_Daytona_GraphMaxSpeed_NoFriction

Remember that we not only have friction, we have lots of it from the tires interacting with the track – that’s why the cars go much faster than in our frictionless case here.

Interestingly, if a car doesn’t go fast enough around a banked turn, it will actually slide down the track.

This presents a major problem when you’re repaving a very banked track because, as a rule, heavy machinery doesn’t move very quickly. The video below shows the 2010 Daytona repaving (pictures, but mostly video).

You’ll see that the paving trucks are actually being held in place by other equipment because otherwise, they would slide (or worse, tumble), right down the track. And that would make for some pretty sloppy surfaces to race on.

Jun 192015
 

Last Tuesday, NASCAR announced aerodynamic modifications to be implemented for the Kentucky Speedway Sprint Cup race on July 11th. While the changes are (right now) only for that race, there’s every expectation that if they help reduce the dreaded ‘aero push’ problem, they may be extended (or modified) for other 1.5 mile tracks.

The changes are fairly straightforward to make, which is why NASCAR can mandate them without much lead notice. All the parts are bolt-ons, as opposed to changes in the body panels, for example. Here they are:

  1. The rear spoiler will be shortened from 6 inches to 3.5 inches
  2. The front splitter will be shortened by 1-3/4 inches
  3. The radiator panel will be narrowed from 38 inches to 25 inches.

These changes continue in the vein of the changes made at the beginning of the 2015 season. At the start of the season, the spoiler was decreased from 7-1/4 to 6 inches and the radiator pan was narrowed down to 38 inches. So the changes are designed for the same goal: decrease the dependence of the car on aerodynamic forces so that passing isn’t quite as hard as it is now. This translates to decreasing the downforce on the car – depending less on aerodynamic grip than on mechanical grip.

The question I’ve heard the most this week is some variation on being concerned that taking downforce away from the car might lead to the cars being more likely to become airborne. I’ve discussed how cars can take to the air. Let’s look at how aerodynamic forces are generated so we can understand how big a problem this is — or isn’t.

We need to start with Bernoulli’s Principle. It’s a rather complicated principle, but we only need one part of it to apply it to a race car.

BernoullisPrinciple_Words

Here’s how I remember which way it goes. The roof flaps on the car are there because, when the car goes fast, the air moves quickly over the roof of the car and the pressure on the roof decreases. If the car spins, the roof flaps open. That slows down the air, and increases the pressure, keeping the car on the ground. (I’ve also done a pretty complete discussion of roof flaps in a previous blog.)

MWR_AerodynamicsAt right is a computational fluid dynamics diagram generated by Michael Waltrip Racing shown at right. Their color scheme is that the slowest moving air (the highest pressure) is red and the fastest moving (lowest pressure) air is in blue. (It’s a rainbow, except without indigo and violet.)

If you look at the front of the car, you’ll notice that the splitter area is a place where the air slams up against the car and slows way down. And, in fact, that’s why the splitter is there. The splitter generates front downforce. If we looked at the rear of the car, you’d see another area of higher pressure by the spoiler, which is responsible for rear downforce. This diagram also shows you the low-pressure area at the top of the car.

Net Force: Lift vs. Downforce

The classic example of how Bernoulli’s law is harnessed in vehicles is the airplane wing. The wing is shaped such that air moves faster over the top of the wing than under the wing. This means that the force pushing up is greater than the force pushing down, and that creates a net lift. (And if you want to see something really cool, take a look at this new NASA plane that changes wing shape in real time.)

How_a_wing_works

 

If you want downforce instead of lift, you shape the wing differently.

 Splitting Airs

The splitter is so named because it literally splits the air coming at the car into two parts: air that goes over the top or around the car and air that goes under the car. A splitter is a much more tunable device than the old air dam, which provided a vertical surface to direct air around the car, but had no horizontal component.

Splitter_New_wphoto

The air running into the car is slowed down, which creates downforce and the faster moving air gets underneath and creates lift.

The splitter is designed so that you can vary how much of it juts out from the car. This is important because the force you get from any surface is the pressure times the (perpendicular) area of the surface. Having less splitter exposed means less area, which translates into less downforce. But it also means less lift, because the same air stream is creating both the up and the down forces.

At the same time, they’ve made the radiator pan (which is poorly named, because it has nothing whatsoever to do with the radiator) smaller. If the underside of the car is nice and smooth, air flows quickly under the car. The radiator pan is really just a flat panel that covers the pipes, ducting and other complicated shapes and presents the air with a smooth surface.

The larger the radiator pan, the more of a ‘sucking effect’ you get, where the lower pressure actually acts like a vacuum, pulling the car down to the track. NASCAR made the pan even narrower than before, which slows down the air.

I would be very surprised if there were any greater incidence of vehicles going airborne – especially given the lower horsepower we have now relative to 2014. Remember that aerodynamic forces go like the speed squared, so if you’re going slower, you’re not making as much lift or downforce.

Radiator Pan

RadiatorPanThe radiator pan is really just a flat piece of metal that (on a stock car) has nothing to do with the radiator except that it’s located in the general area in which the radiator is located. Its sole purpose is smoothing out the surface underneath the car.

The picture is from a NBC NASCAR America video in which Steve Letarte summarizes the 2015 rules changes. It’s the best overview of the changes and the one I use for reference all the time.

The underside of a race car is sort of a mess. Pipes, tubes, ductwork all snake their way through. Aerodynamically, that rough surface, with all its dips and peaks, slows the air down as it moves under the car.  Putting a smooth sheet of metal on the underside of the car decreases the drag and allows the air to flow more smoothly (which means faster) under the car.

And since faster means less pressure, a smooth undercar surface tends to ‘suck’ the car down to the track, giving you more downforce. There’s another effect, however. If a car does start to get airborne, a huge flat plate provides a really nice surface to generate lift off. Decreasing the size of the plate makes the underside of the car much rougher and would decrease lift in case a car does get airborne.

RadiatorPanChange_2015KentuckyThe plate was narrowed by 10% from 2014 to 2015 and now it’s being narrowed again from 38 inches to 25 inches. If the last change was 10%, then the reduction was by about 5 inches. This makes the radiator pan about 58% the width it was in 2014.

Spoilers

Moving to the  rear of the car, the spoiler is going to be a mere 3.5 inches tall. As in the front of the car, the larger the area, the larger the force. A smaller spoiler doesn’t let as many air molecules bang down on the car, so you get less rear downforce. But there’s more to it than that. The spoiler also produces a stream of ‘dirty air’ at the rear of the car. That turbulent flow is part of what makes it so hard for the trailing car to get close enough to the leading car to pass it. Lowering the spoiler decreases the wake behind the car, which should (in principle) help passing.

SpoilerHeightvsTime

Even without the benefits of cleaning up the car’s wake, they pretty much have to adjust the rear of the car if they’re going to adjust the front. If they decrease front downforce and don’t do anything to the back, you’ve got a car that is going to be tight no matter what you do to it. The rear wheels will stick better that the front, so the car moves forward, just not necessarily in the direction you wanted it to go. It’s really all a matter of balance.

There’s another consequence of shortening the spoiler, and that’s decreasing the drag. While the spoiler supplies rear downforce, it also presents an impediment to the air molecules, creating a force opposite the direction the car is moving

Where Do We Go From Here?

It’s been a bit flip floppy around here, right? First NASCAR said they might use 2016 rules for the All-Star race. Then they decided not only not to try that experiment, but maybe there wouldn’t be any aerodynamics changes. Then we get an announcement that we’re changing the rules for one race in two weeks.

It seems like short notice, but the race teams had pretty good indication of what was coming long before we did. NASCAR did make the point that they didn’t want to give the teams six weeks to camp out at wind tunnels researching the changes. NASCAR has enough experience with the Gen-6 car that they’re pretty certain that the changes they’re making won’t be a disaster (plus, they’ve told the teams they need to be ready to revert back to the ‘old’ package at any time during the Kentucky weekend. If any problems crop up, they’ve got a good fallback.)

NASCAR made a big point that “this is a race, not an experiment”. They have to be cautious about what they say because people tend to jump on things and give disproportionate weight to them. Then if NASCAR changes something, they’re accused of not being honest or trying to mess with fans.

One of the hypotheses going around is that NASCAR would have different aerodynamic specifications for each track. This would reverse the trend toward trying to use the same car at every track, but it would give NASCAR a much better way of keeping the racing exciting by minimizing aeropush. And for those people who think it would be terribly confusing for the teams, trust me. These are really smart people. They’re good at keeping track of things.

You know what I’d like to see? I’d like them to run this same experiment at some of the other 1.5 mile tracks, and then come up with an intermediate track “box” – a range of values for splitter and spoiler so that the teams can have a little play in splitter and spoiler configurations. This would let them tune the car for different drivers much better than they can now – and it’s no secret that some drivers have not had an easy time adapting to the current configuration.

The one unknown in all this, however, is going to be tires. Goodyear already tailors tires to different tracks, so it’s not asking them to do a lot more, but it does mean that they have another round of development to do as rules shift.

 

 

 

 

 

Jun 052015
 

https://www.wylio.com/credits/flickr/3288067069Temperatures at the Dover race were unseasonably high. Kurt Busch’s Stewart-Haas 41 team was told by NASCAR officials to remove “heat shields” from their fuel cans. The cans (shown at right) have an 11-gallon capacity. Not shown in the pictures is a tube that connects the nozzle at the top with the vertical part coming straight up from the can. This attachment recovers overflow fuel – remember when we used to have a ‘catch can man’?

Apparently, Busch’s team was using some type of heat shield on the cans to keep them cool. All of the things I’ve read about NASCAR’s response seem to mention safety. This is an important consideration, especially given the incident we had at Richmond where three people were burned seriously enough by a fuel fire to have to go to the hospital.

What hasn’t been mentioned is whether this is actually a performance issue.

Density

As you probably know from middle school, “dense” means “thick”. But we’re going to use it in its precise scientific meaning.

EQ_density

 

Density has units like grams per liter or pounds per cubic foot.

Simplifying Assumptions

OK – let’s make some simplifications for the purposes of discussion.

1.  Gasoline is made up of a mix of molecules, so there’s really no such things as “a gasoline molecule”. In reality, gasoline contains a bunch of hydrocarbons with four to twelve carbons atoms per molecule.  For you specialists, it’s a mix of alkanes, cycloalkanes and alkenes. For the sake of discussion, I’m going to talking about “a gasoline molecule”.

2. Molecules are absurdly small. and talking about their mass becomes unwieldy.  Octane (one of the hydrocarbons in gasoline) has a molecular weight of 114.22852, which means that if you put Avogadro’s number of octane molecules (which would be 6.023×1023 molecules) on a scale, the scale would read 114.22852 grams.

This means that a single octane molecule weighs 1.897 x 10-22 g. That is  0.00000000000000000000001897 g.  You get the point: they’re very small. So we’re going to talk about density in terms of number of molecules more than their mass. The two are related, of course (mass = number of molecules x mass of one molecule), but I think it’s easier to visualize with number.

3. Finally, there ought to be a couple billion billion billion molecules in the drawings, but I just don’t have the patience to draw them. So we’re using simpler numbers like “10” and “20”.

Density of Gasoline and Temperature

The density of typical gasoline is 6.073 lb/gal at 60°F. Whenever you list a density, you must list the temperature at which the density if measured, because density changes with temperature. If you blow up a balloon, then put it in a freezer, the volume of the balloon shrinks -that’s because molecules slow down when it gets cold (like most of us do).

Most things in an automobile that deal with gasses or liquids work on volume. A fuel injector, for example, is set to let a particular volume of gasoline into the combustion chamber. So let’s think about what the change in density with temperature means in terms of a constant volume.

Most liquids become less dense at the temperature gets warmer. So if you get a gallon of gasoline at a higher temperature, the molecules are spaced out more, which means you get fewer molecules when it’s warm than you do when it’s cold.

Density

How the density of gasoline changes with temperature is pretty well known and shown below. Let’s check the axes here to see the magnitude we’re talking about.  I’ve plotted a 126 degree change in temperature, over which the density changes by about 8 percent. If you’re looking at a ten degree change, say from 60°F to 70°F, you’re talking about a little more than a half a percent change in density.

ChangeinDensitywithTemperature_Gasoline

Combustion works on the basis of a precise chemical equation. Each fuel molecule needs a particular number of oxygen molecules to combust. If there are too few oxygen molecules, then some of the gasoline molecules do not combust. If there are too many oxygen molecules, then some of the oxygen molecules just hang around. Either way, you’re limited by whichever component of the combustion process is smaller.

At high altitudes, or high moisture in the air, you get less power from the engine because there are fewer oxygen molecules in the air coming into the engine.

This is the idea behind turbochargers. Turbochargers compress the air going into the engine, so in a fixed volume of air, you get more oxygen molecules. More oxygen molecules means you can inject a larger volume of gasoline and make more power with each combustion.

The same idea can be used on the fuel side. There are systems on the market you can buy that use compressed gasses to cool the fuel – essentially they’re an air conditional, but for the gasoline. That lets you pack as many fuel molecules as possible into each charge that goes into the cylinder. You can let in more air, and – voila – more power. Of course, you reach a point of diminishing returns. The fuel has to be heated to combust and if the fuel is too cold, it won’t heat fast enough and some of those molecules won’t combust and won’t produce any power.

Is It a Performance Advantage?

Did having heat shields on the fuel cans help Kurt Busch? If we’re just talking mechanical heat shields – metal that reflects heat and keeps it from being absorbed by the can – I don’t see how they could’ve gotten more than a five to (maybe) ten degree decrease in temperature. That’s less than one percent change in density, which is pretty small. But also remember that over a 400-mile race, a typical NASCAR race car will use 100 gallons of gasoline, so you’re getting a 1% advantage over the entire course of the race. And races are determined on very small margins, so it’s not impossible that it’s a performance advantage – but it’s not a huge one.

Is This a Safety Issue?

No. The auto-ignition temperature of gasoline (the temperature at which gasoline will spontaneously ignite) is around 500°F. Cooling the gasoline on pit road will have pretty much zero effect on safety aspects.

What about my car? Do I get cheated when I fill up when it’s hot?

There’s an urban legend that you should always fill up your car in the morning instead of in the evening because you get fewer gas molecules for the price when you’re dispensing warmer gasoline. Maybe on those rare days when you have a 40°F temperature change, but on most days… it’s not going to make a heck of a lot of difference. Consumer Reports actually did the experiment.

But the winter/summer change and the sheer amount of gasoline we use does have an effect. The Today Show had a report a couple years ago (2012) on this very phenomenon. If gas pumps are calibrated in cool weather, then you’re actually getting less gasoline for the dollar when you fill the tank in hot weather.  They cite a 2007 Congressional report that says Americans paid an estimated $1.5 billion extra for gas that summer. That sounds like a really big number, but remember there are 300 million people in the U.S. and we use a lot of gas. If each person in the country gets $1 (edit  – I should never do math in my head…)  less gasoline in the summer, there’s 300 million dollars right there.

A group called for a mandate for gas stations to use equipment that measures the temperature and takes that into account when calculating gas prices. After all, they do it in Canada and have been doing it for a couple decades now.  The problem is that most cost-effectiveness studies show that if the government mandates temperature compensating pumps, the cost for installing and maintaining them gets passed along to the consumer. In the short term, no one would save any money.

Plus, there are a lot more important things to be worrying about in the world, don’t you think?

 

 

 

May 152015
 

The All Star Race, let’s face it, is a series of gimmicks strung together in the cause of entertainment.

Not that there’s anything wrong with doing that. It’s what every sport does. People like home runs? Then let’s have an ‘event’ in which people just try to hit home runs. People want to feel like they play a role? Then let’s make a ballot and let people pick who they want to see.

It’s all O.K. because (as Drew Carey said “What’s My Line”) the points don’t count.

NASCAR had an interesting thought last year. What if we use the All-Star race to test out the proposed 2016 rules package? They’ve since backed off on the idea. It’s asking the teams to do a lot of work for a race with no points, and a public test has few benefits. If the rules don’t work, it’s embarrassing. Even if they do work, getting data from instrumented cars (as could happen at a real “test”) offers a much more controlled way in which to evaluate the new package. (Bob Pockrass has a nice summary of this.)

Not to worry, though, because NASCAR fans are full of ideas about how to spice up the All-Star Race. Let’s move the venue. Let’s have no rules at all and let the teams bring anything they want. Let’s race the haulers instead of the cars. Let’s have everyone bring back a favorite old-time paint scheme.

Let’s run the race backward.

That seems like a pretty simple modification

Chirality

Handedness-ChiralityYour scientific word for today is chirality.

Chirality is a type of asymmetry. Put your hands out in front of you, palms down. Keeping your palms facing down, try to move them in such a way that they exactly match up with each other.

I’ll save you some time. It can’t be done.

Your hands are chiral. Don’t be going getting a big head about it, though. Everyone’s are. So are your feet. But you can toss that you’re chiral into conversation and (some) people will be impressed.

If you look at the way a spiral twists, we say that it is either left-handed or right-handed, as shown in the picture at right.  Your fingers on the appropriate hand curl in the same direction as the spiral.

Not only are your hands and feet chiral, so is you DNA. Imaging taking a long ladder and twisting it into a spiral – that’s what you DNA looks like. It’s commonly described as a twisted helix

Interestingly, it only twists one way. DNA (shown below) is right-handed.

BSPEDED_DoubleHelix

So is NASCAR. Well, if you leave out the road courses. For all but two out of the 26 races in a year, we turn left. (And yes, that makes the trace track right-handed.)

NASCAR is Chiral

Why turn left? If you try to track down the answer, you’ll find a lot of interesting theories about this. The one I see most often is that turning left is safer. Since you’re more likely to spin out and hit an outside wall, you should put the driver so that he or she sits on the side of the car away from the outside wall.

Okay, except for the face that most forms of non-stock car racing have the driver sitting in the center of the car.

So let’s look back at racing’s DNA by considering non-automotive competitions. Most race track designers adopted the conventions used by the closest form of non-car racing: horse racing.

In the U.S., horse races turn left. The USA track and field organization tells us that in 1912, the international governing body of track and field made an arbitrary decision that runners would run counterclockwise and it’s been that way ever since.

But I like this theory better. The Thoroughbred Racing Association says American racetracks were designed to be counterclockwise in 1780 because American breeders were still angry at the British because 1776.

British horses turn right. So in true American tradition, we did the opposite.

Left, Right… Does It Really Matter?

Impact_PitRoadWallEndIn a word, yes.

Tracks are designed to be run in particular direction, which means everything is optimized for that direction. There are some minor issues, like sightlines, pitting from the “wrong” side of the car, etc., but there is one very good reason for not running a track in the opposite direction.
Safety.

I’ve mentioned before that the most dangerous place a car can hit is the end of a wall. If a car hits broadside (leftmost picture at right), the entire side of the car is taking the force of the impact.

If the car hits the end of the pit road, you’re concentrating all that force over a much smaller area. You’re much more likely to rupture the car that way and allow the wall (or parts of the car) to hit the driver.

Mark Martin experienced such a crash involving the pit road wall in Michigan in 2012. He noted it was a freak accident, but that class of hits remains the most serious type of impact a driver can experience.

Ideally, you’d just get rid of breaks in the walls, right? Problem is that it is impossible to make a continuous wall around the inside of the track. Cars have to get in and out of the garage and (more importantly) emergency vehicles have to have ready and immediate access to the track. So there are gaps in the wall in various places.

Let’s think about how we might do this. Simplest idea first. Just put a break in the wall,as shown below. The emergency vehicles can sit just beyond the opening and, if they’re needed, they can be out on the track in a matter of seconds.

BSPEED_GoingBackward_SimpleOpeningwHighlight

Here’s the problem. You’ve now got cars headed toward an unprotected wall end. The cars move from left to right in the picture. Given the momentum toward the right, it’s far more probable that the car would hit something in front of it than behind it.

Fishscales

BSPEED_GoingBackward_CharlotteMotorSpeedwaywHighlight

So if you look carefully the next time you’re at the track, look for the fishscales.

No, not the rap album.

Most tracks have them, so if you know what you’re looking for, they’re pretty easy to find examples of. Thanks to Google Earth, I’m able to show you one from Charlotte Motor Speedway at right. I highlighted the feature of interest.

They’re called fish scales because they overlap and the overlap provides protection while still allowing for motion – the same way the scales on a fish protect the fish, but still allow it to move.

It’s a little easier to see if we change the opening I designed up above to something more like this:

BSPEED_GoingBackward_Fishscale

We’ve put the facing end of the wall pretty much out of reach of the car by overlapping the walls as shown. Now if there’s a hit, it’s on a curved portion of the wall, not an end.

But Wait…

You’re thinking – but the other end of the opening hasn’t changed. It’s still a concrete wall sticking out there.

True, but the probability of a driver hitting it is very small.

Except if you’re running the track in the direction opposite for which it was designed.

I know, you’re thinking this isn’t a big deal. But it was to Gary Terry.

Terry worked for a company that offered driving experiences in ‘exotic’ cars – Lamborghinis and the like at the Walt Disney World track. Terry was riding in the right seat (as a passenger) on April 12th of this year when the car hit the end of a wall. The driver was not seriously injured.

Terry was killed.

A heartfelt post by Jon Miller entitled “Please Stop Killing My Friends” on Jalopnik points out that the car was driving the course backward.

BSPEED_GoingBackward_WaltDisneyWorld

The green arrow shows the direction the track designer intended when he laid it out. The orange arrow shows the direction they were going.

The gofundme.com campaign to pay for funeral and related expenses, and for a college trust fund for Terry’s daughter Taylor. If you have a few dollars for a good cause, please donate: http://www.gofundme.com/garyterrymemorial.

And tell everyone who suggests running a race backward that there’s a really good reason for not doing so.

Another example where something seemingly simple turns out to have much more behind it.

Apr 172015
 

Sounds like an energy drink, right?

Listening to Kyle Busch’s press conference Wednesday was alternately fascinating and cringe-worthy. The fact that he remembers so much about the crash is amazing – it will be a great boon to the safety people who probably will use this as a case study in the future. And best wishes to Kyle to get well soon.

Kyle said he left the track at 176 mph, hit at 90 mph and sustained 90 Gs.  My twitter was flooded with people asking “90Gs? No one could survive that kind of a hit.”

That’s actually not true. Trying to quantify a crash via one number is a nice attempt at simplifying things, but totally wrong.

Warning – I wrote and researched this while flying halfway across the country, so we’re likely to need a re-write when I get back home Monday and have a little more time to make this prettier. But let’s start by clarifying terms.

“Gs”

The ‘G’ is quite possibly the most misunderstood unit in racing.  A ‘G’ measures acceleration, not force.   One ‘G’  is equal to the acceleration of any object due to Earth’s gravity. You are experiencing one ‘G’ right now. The product of your mass times the acceleration due to gravity is your weight.

Acceleration is how fast you change speed. If you go from 0 to 62 mph in 2.8 seconds (like the Lykan HyperSport in the Furious 7 Movie), you’ve got an acceleration of 22.4 mph each second. Every second, your speed increases by 22.4 mph. It’s an acceleration of a little more than 1G. (which, by the way does may the Etihad towers jump possible. I did the math, just thought I’d throw that in.)

Let’s set the scale. The Space Shuttle pulled 3G on launch, Apollo 16 pulled 7G on re-entry. A Formula 1 car pulls about 5-6 G laterally during sharp turns and 4-5G during linear acceleration. I’ve got a story in the Physics of NASCAR book about Texas Motor Speedway having to cancel an open-wheel race at the last moment because the drivers were pulling so many Gs that they were having mini blackouts. A good rollercoaster will give you 2-3G.

Electronics spec’ed for the military for use in shells have to survive 15,000 G.

Weight is the force resulting from the acceleration. Remember F-ma? When you experience ’3Gs’ of acceleration, the force you experience is the number of G’s times your weight.

We use the unit ‘G’ just like a unit like ‘dozen’.  I can express anything in terms of dozens:  a dozen eggs, a dozen jellybeans or a dozen beers.  Likewise, we can use the unit ‘G’ to express the acceleration of anything.  I can measure the acceleration when you step on the gas after stopping at a red light in ‘G’s.   I can measure the acceleration you feel on a rollercoaster in Gs.

Important: Although Earth’s gravity pulls down (toward the center of the Earth), we use ‘G’ to measure acceleration in any direction:  up or down, back or forth, or sideways.

How Many G’s Can a Person Withstand?

Again, this is by no means meant to minimize Kyle’s experience. He had a really hard crash and broke bones in both legs. So don’t interpret what I’m going to say as trying to say he’s lying or wrong or is trying to exaggerate his injury. It was serious.

But it wasn’t as simple as “90 Gs”

I’m pretty sure the numbers Kyle had were the numbers from the car’s transponder. As far as I know, NASCAR hasn’t instituted in-ear accelerometers like IndyCar.

An accelerometer is exactly what is sounds like: a meter for acceleration. Most iPads and iPhones today have one. Especially given the increasing concern about concussion, IndyCar and F1 have both provided drivers with a tiny accelerometer that fits into the ear and thus gives a much more accurate measurement of the actual acceleration of the head. (Remember that the problem with concussion is that the brain actually hits the inside of the skull.)

NASCAR relies on a transponder located near the frame rails (low) in the car. That means it measures what happens to the car, not the driver. A number of safety measures make the driver slow down less quickly than the car. I’ll come back to that.

There are three primary factors in a crash: The change in speed, the time over which the change in speed happens and the direction of the force.

So it’s not only how fast you’re going when you crash, it’s how fast you stop. When the people who study these things talk about crashes, they talk about the “crash pulse”, which incorporates the first two of these factors. Here’s one I drew for illustration.

Forcevstime2

When someone talks about 90G, they mean that was the peak value of the acceleration vs time curve was 90G. In my plot above, both curves show a crash from the same starting speed. The difference is that the red curve was a case in which the force/acceleration was spread out over a longer time. That’s why the peak value is lower.

How many Gs you experience depends on your starting and ending speeds and how long it takes you to stop. In the case of a crash where you go from 90 mph to stopped over 1 second, you experience about 4 Gs. If it happens in a tenth of a second, you experience 4o Gs.

Now let’s look at a real crash pulse.

BSPEED_CrashPulse

Here, you see the crash and you see the backlash – that’s the negative acceleration on the right side of the graph. The details of these graph give you a much fuller picture of a crash because you learn how the force was distributed in time.

Although the peak force was 90G, that 90G was applied for a short time. Lesser accelerations were experienced during the rest of the crash. A peak force is like a snapshot of a dance. You get one impression, but it’s not the whole picture.

Let’s get back to measuring the car vs. measuring the driver. The driver is belted in by 2 to 3-inch-wide belts over the shoulders, around the lap and around the legs. Those belts are designed to stretch when they’re stressed, which means that the driver doesn’t stop as quickly as the car stops.

Same thing with the HANS device. The tethers on the helmet allow the driver’s head to move forward, but they slow the rate at which the head moves. So even if the car experiences 90G, the driver experiences less. How much less would require a lot of assumptions, but if the various safety devices double the time it takes for a driver to stop, it halves the force.

I mentioned direction is important. That’s because any force on your body also is a force on your blood. Pilots who make sharp accelerations up or down (parallel to the spine) have issues because the heart has to work extra hard to pump the blood. The human body can withstand higher accelerations perpendicular to the spine than parallel to it.

No, Really. How Many G’s Before It’s Really Bad.

StappSledYeah. That’s what you’re really asking, isn’t it? What are the limits of the human body? These are difficult questions to answer because you can’t really do the experiment. People don’t volunteer to be accelerated really fast so scientists can see if they survive.

With one exception.

Col John Stapp (Air Force, shown at left) was active in the late 40s and early 50s. We didn’t know how far or how fast airplanes (and rockets) would allow us to go. And even if we could build the machinery, would a pilot or passengers survive?

The military didn’t want to hand over soldiers for him to run experiments on.

So he experimented on himself.

Today, that would never happen because there’d be so much paperwork that he’d die of old age before he got approval. But back in the 50s, people got away with a lot more.

The picture shows a test in 1954 where Stapp accelerated at 15g for 0.6 seconds and reached a peak acceleration of 22 second. His record was 46 g, and he sustained more than 25 g for 1.1 seconds.

This was no 90 G, but whereas a driver might experience that acceleration for a couple hundredths of a second, Stapp did it for tenths or full seconds.

These experiments had consequences. There is one really big problem with acceleration perpendicular to your spine. Your eyes bug out (or in).

No, seriously. Your eyes are held into your skull by a couple muscles and optic nerves. High accelerations (and decelerations) is like putting your peepers on a bungee cord. What finally stopped Stapp’s experiments was that he sustained major damage to his vision. I highly recommend http://www.ejectionsite.com/stapp.htm if you’d like to learn more.

C’Mon. How Many G’s Has a Human Being Sustained Before…

O.K. A paper (Society of Automotive Engineers. Indy racecar crash analysis. Automotive Engineering International, June 1999, pages 87-90) says that IndyCar drivers have survived 100G+ crashes. I don’t know yet whether those are crashes measured with the in-ear accelerometer, so it’s difficult to make a direct comparison with NASCAR.

But remember that even smaller accelerations – if applied in just the wrong way — can have equally catastrophic results for the driver.

Closing note: You know what they use in doing crash research? Yes, Crash Test Dummies, but the human body is so complex and intricate that a dummy can’t tell you everything.

They use cadavers.

 

 

 

 

 

Apr 032015
 

There are three things you don’t mess with in NASCAR: engines, fuel and tires.

Tuesday, NASCAR handed down a P5 penalty – the penultimate penalty on the books – to Ryan Newman’s 31 team. Crew Chief Luke Lambert was suspended six races, fined $125,000, and Newman and his owner Richard Childress were each docked 75 points. The tire specialist and team engineer were suspended for six races as well. RCR is appealing the penalty, but I wager they’ve got an uphill battle.

NASCAR’s made its stand loud and clear in the last few weeks. Tire bleeding will not be allowed. If you persist in trying, they’ll come down hard on you.

 

Why Would You Bleed Tires?

The hotter the gas inside a tire gets, the higher the tire pressure gets (says the ideal gas law).

EQ_IealGasLaw_ConstantMoles

The tire volume changes a little with temperature and pressure, but it’s not a huge change. If you were doing actual calculations to use in a race, you wouldn’t ignore it. For us, it’ll be good enough to approximate that the volume remains constant.  The equation tells us then that the ratio of pressure to temperature has to stay the same. If the temperature goes up, the pressure goes up, and vice-versa.

The video below (from the National Science Foundation) details how and why the tire pressure increases. Steve Letarte is a nice person and a very clear explainer of things. I look forward to seeing how he does when NBC takes over broadcasting NASCAR later this year.

The main problem with changing tire pressures is that grip depends on tire pressure – a lot.  If the tire pressure is too low, you lose energy to rolling resistance. If the tire pressure is too high, the sides of the tread pull away from the track, giving you a smaller contact patch and less grip.

Tire builds can be significant. At some tracks, you might see a 35 psi change in tire pressure. A large build means teams have to start a run with very low tire pressure – 8-10 psi at some tracks. If you look at a car at Martinsville waiting to go out on track, it’ll appear as thought it has flat tires.

Bleeding tires prevents the tire build (increase in pressure) from getting too large by releasing some of the pressure once the tire pressure reaches some value.

Wait… Like a Pop-Off Valve?

This is the same principle teams use in the radiator systems. Put water into a closed metal tube and heat it. We call that “a bomb”. As the liquid gets warm, it turns into gas, the gas pressure increases and eventually the gas inside pushes so hard it breaks the radiator or the tubing in the cooling system.

So we use a little valve called a pop-off valve on the radiator. When you see steam pouring out from near the bottom of the windshield, it means the pop-off valve has popped. The video below explains the pop-off valve in the cooling system.

 

That’s a great idea, right? They ought to make something like that for tires, so that the tires can’t get overinflated.

TireBleedValvesThey do. It’s called a tire bleed valve. Shown at left, you install it in the valve stem of the tire. Most are adjustable between some range of pressures.

An o-ring sits atop a spring. When the pressure is low enough (left), the spring is relaxed. The o-ring forms a seal on the valve seat,which holds in the air.

When the pressure inside the tire increases past a pre-set value, the spring compresses and unseats the o-ring. Notice how by where it says “no seal” the o-ring doesn’t touch the sides of the valve anymore . This gives air a path to escape. As soon as enough air has escaped so that the pressure returns to the maximum value, the spring relaxes and the valve closes. There’s less air in the tire, which allows the pressure to remain lower.

BleedValve

Seems Like the Perfect Solution. So…?

So bleed valves (or tire pressure relief valves) aren’t legal in NASCAR. However much nitrogen you put into the tire is how much you have and the driver is supposed to deal with the changes in the tire pressure. The harder you drive the tire, the hotter it gets, so having a way to relieve pressure gives the driver the option of pushing the car harder than a driver who is limited by the building tire pressure.

The scuttlebutt around the garage is that the tires on the 31 had small holes poked in the sidewalls. Rubber is stretchy enough that you can get a tiny, tiny puncture and it won’t open up a gaping hole that lets all the air out of your tire. The rubber on the sidewall is thinner than the rubber on the tread, so a pin prick or something similar would do the job.

The disadvantage of this method is that it’s totally random. With a bleeder valve, you can set it to go off at 35 psi and you know it won’t let any air out until 35 psi. With something like poking tiny holes in the tire, you have to guess at the number and placement of holes so that you don’t let out too much or too little. There’s also a safety issue, in that your well-intentioned “tiny” hole might actually do more damage than you intended – or noticed until the right front below out going 180 mph into a turn.

Plus, one of the fundamental tenets of NASCAR is that you do not mess with the tires. It’s bad from a sportsmanship angle and from a safety angle.

How would you tell?  The easiest way to find out if there are tiny holes in the tire is to over pressure the tire (maybe fill it up to 50 psi) and toss it in a bathtub or a swimming pool. If there are holes, you’ll see air bubbles coming out from the holes. (We actually used to use this technique to find big leaks in our vacuum chambers.) If you can’t submerge the tire, you can overpressure the tire and then squirt a little soapy water on the suspicious areas. You’ll see bubbles (from the soap) appearing near the holes.

If you want to be really pedantic about it, you can look at the material under a microscope once you’ve narrowed down where you suspect the holes might be located.

Can You Really Be Sure Someone Cheated?

There are a lot of things that could put a hole in a tire. But not the same size/shape hole multiple times in multiple tires. NASCAR is pretty cautious about not nailing people without solid evidence. I will be majorly surprised if RCR wins their appeal. That’s not to say upholding the penalty means there was a plan by the team to cheat the tires that way. It could have been one person thinking they were helping and the folks who got fined knew nothing about it. Science says nothing about intention or motive.

 

Apr 012015
 

The Scariest Part of Racing?

During the XFINITY series race at Richmond, a malfunctioning fuel can spilled a huge amount of gasoline in the pit stall. A spark ignited the fuel, engulfing gasman Josh Wittman and rear tire changer Anthony O’Brien. A crew member for a team pitting nearby (Clifford Turner, working on Eric McClure’s car) was also injured. Although all the men were conscious and moving around immediately after the incident, all three were taken to the hospital. O’Brien wasn’t released from the hospital until Monday following the Friday incident happened.

If you were to poll racecar drivers about safety, I bet the majority of them would say the scariest situation isn’t a crash.

Two fears you have as a race car driver: one is being on fire and two is being T-boned in the driver door – everything else you sort of accept.  –Elliott Sadler

That quote was from before the Gen-5 car brought additional reinforcement to the drivers side door in the form of additional tubing and IMPAXX energy-absorbing foam. But what can you do to minimize the risk due to fire?

Fire

You need three things for fire: BSPEED_FireTriangle Without any one of these three, you don’t get fire. Which is a good thing because we pretty much walk around surrounded by oxygen and fuel all the time. Pretty much any clothing, regardless of whether it’s made of natural or artificial fibers, is fuel. The air is about 21% oxygen, with 78% nitrogen and 1% preservatives and fillers. No, actually the 1% are other gasses, like hydrogen, krypton, neon, etc. and they’re present in such tiny quantities that we don’t care. At all.

Back in The Day…

Way back in the day, drivers and crew wore street clothes and hoped they wouldn’t catch on fire. Then fire-retardant chemicals became available and people would dip their clothing in the chemicals to make it fire-resistant. The problem is that you do tend to want to wash your clothes after driving in a hot car for a couple hours and the chemicals would wash off.

And believe me, after three or four hours in a hot car, you want to wash whatever’s been in there with you.

Polymers = Repeating Molecules

Then we learned how to design polymers. The prefix “poly” means many. Polygon means many sides. Polymer means many units. The unit in this case is a particular arrangement of atoms into a molecule.

For example,  below is a schematic of an ethylene molecule and the polymer polyethylene, which is nothing more than a bunch of ethylene molecules hooked up together.

polymerExamplePONYou can make the polymer long or short by varying how many times you repeat.

Kevlar and Nomex: First Cousin Polymers

Kevlar was discovered by DuPont chemist Stephanie Kwolek, who passed away last June at the age of 90. How Kevlar came to be is an interesting story. A looming expected gasoline shortage led DuPont in the early 1960s to look for strong, yet lightweight fibers for tire manufacturing. One of Kwolek’s attempts at making a liquid that would be spun into a fiber ended up looking rather yuck. It was cloudly and thin, totally unlike what she expected, yet she insisted that it be made into a fiber for testing anyway. 

Her invention was Kevlar, a polymer that is five times stronger than steel by weight. Below is a Kevlar molecule. Grey circles are carbon, Blue are nitrogen, red are oxygen and white are hydrogen. There are actually a bunch more hydrogen atoms in the single molecule that I don’t show because it just makes the picture messy and confusing .

BSPEED_KevlarMonomer

BSPEED_Kevlar_JMol

You’ll notice something very interesting about the Kevlar polymer – it’s very straight. That linearity is a big contributor to its strength. Kevlar chains link with each other in a very orderly way and make a fiber that can be used in bulletproof vests, as well as serving as a reinforcement for tires and carbon fiber pieces.

But Kevlar isn’t a miracle material. It has its limitations. When you heat it up to 900 degrees F, Kevlar literally falls apart. The atoms start letting go of each other.

But check this out.

BSPEED_Nomex_vs_Kevlar2

 

Compare the molecules left to right. Exact same atoms, just arranged differently. Kevlar is this nice straight molecule, but Nomex is… well… Nomex is a little kinky.

That difference in conformation – straight vs. kinked – makes all the difference. Nomex is nowhere near as strong as Kevlar; however, when you heat Nomex, it doesn’t melt and it doesn’t burn.

It chars. While that might seem like a bad thing, it’s actually good.

BSPEED_Nomex_Charring

 

When the Nomex fiber chars, it forms a layer of carbon on the outside. That makes the fiber thicker, which does two things: First, the thicker fabric gives you a little more protection from heat transfer, but second, the thickening of the fibers  closes the air gaps and prevents oxygen from getting through to the skin and feeding the fire.

The video below is one of DuPont’s promoting Nomex. Reminder. Don’t try this at home.

CarbonX

Nomex used to have a monopoly on the market, but recently there’s been a new material making waves. CarbonX is a blend of oxidized polyacrylonitrile and other strengthening fibers and is inherently non-flammable. Polyacrylonitrile is the precursor for 90% of carbon fiber production. One issue is that oxidized PAN is pretty much available in your choice of black or black, so the fibers have to be blended with other fire-resistant fibers to get colors.

One of the things CarbonX has is a very high LOI (Limiting Oxygen Index). That’s the percentage of oxygen that has to be present before the material will combust. CarbonX won’t combust unless 55% of the air is oxygen. Remember oxygen makes up about 21% of normal air, so to some extent, that’s a moot point because anything with a LOI over 21% is going to work about the same as far as motorsports goes.  You can hold it at 2600 F for two minutes and it won’t ignite or burn.

Prices have come way down on CarbonX since I first investigated them. You can get a CarbonX sport bra for about $80 and a CarbonX balaclava for about $65 now. A good Nomex balaclava will cost you almost the same.

The choice of CarbonX vs Nomex comes down to comfort, since they both will protect you in a fire. Drivers worry about the weight of the suit, mobility and breathability. The people I know who have tried both feel like CarbonX suits are heavier, but more breathable and less scratchy.

Can We Fireproof Racing?

FuelingApronPeople are very careful with their terminology when talking about fire safety. Nomex is not fireproof. Nomex firesuits are fire-resistant. Firesuits are made in layers, with the air between the layers also providing insulation against heat. That works the same way the air gaps between double-pane windows works.

SFI, a non-profit foundation that writes specifications and tests motorsports safety equipment, rates firesuits in terms of how long you can be exposed to fire before you’d get a second degree burn. For example, a 3.2A/1 rated firesuit gives you three seconds of protection, while a 3.2A/5 rated suit gives you 10 seconds of protection. (For the curious 3.2A is the SFI specification that deals with fire resistant uniforms).

NASCAR mandates that drivers wear a 3.2A/5 rated firesuit, as well as cover the remaining parts of the body with accessories that meet SFI specifications, including shoes and gloves. Crew members who go over the wall are required to have 3.2A/1-rated suits, although the NASCAR rulebook recommends going to the 3.2A/5.  The exception is that anyone handling gas must have the the 3.2A/5 suit and must wear a fire-resistant apron.

Fire resistant underwear and socks aren’t mandated, but they are recommended. The danger here is that if you close enough to a fire, synthetic fibers like nylon and rayon melt. Then they stick to the skin and are very difficult (and painful) to remove. So for the weekend racers, if you can’t afford a full set of Nomex undies, at least make sure everything else you’re wearing is 100% cotton. And ladies – no metal hooks, clasps or underwires. Metal heats up faster than fabrics and you’ll get burned in particularly bad places.

As you might expect, the higher the level of protection, the more expensive the suits are – although you’d like to think that a couple hundred dollars per suit difference is worth a few days in the hospital – or worse. Used to be the pit crews didn’t wear firesuits or helmets. If a fire similar to the one in Richmond happened then, it would likely be fatal.

Let’s also note that the fire wouldn’t have happened if there hadn’t been a malfunction in the fuel can that allowed a couple gallons of gasoline to flood the pit lane and probably get on the gas man as well. I also want to note that the stuff they use in fire extinguishers is a pretty nasty brew of chemicals that aren’t exactly good for people to breathe – but they’re a lot better than burning to death.

Safety is about protecting people on all fronts. Even though the gas can failed, the safety equipment stepped up to the worst-case scenario. Thank heavens everyone is safe.

 

 

 

Mar 262015
 

Joel asks:

Can racetracks work together to make interchangeable/transportable SAFER barriers? To clarify – could SMI or ISC tracks (politics, blah) standardize wall heights, angles, etc. so that they could use barriers at Michigan to fill in the critical areas and then move the necessary walls to Darlington or Homestead? Or even simpler – could the existing walls be setup to install barriers that could be moved from track to track? In the long term I know this is probably not the most cost effective solution. But in the short-term if there are supply problems or significant cost barriers, I thought this could help?

Thanks for the question, Joel. (And apologies for taking so long to get to answering it.)

Installing SAFER barriers is a little more complex than installing a fence in your yard. SAFER barriers are custom manufactured for each section of the track taking into account the wall height, width and condition, the track banking and width. Even putting aside track politics, having a system of barriers versatile enough that they could move from Michigan to Darlington and be equally effective in both places would probably be cost and time prohibitive. You’d need a dedicated crew of people moving from track to track, trucks to transport the barriers and a procedure in place to inspect and qualify each piece after each race.

Standardizing wall heights could be more expensive and time consuming that it’s worth. Each track has its unique geometry and trying to make a one-size-fits-all barrier might be more trouble than it’s worth — and not as effective as just installing barriers.

Plus, if an area of the track is dangerous, it’s not just dangerous during NASCAR races. No track is going to claim they can’t afford to put more barriers in – especially after Kyle Busch’s accident. And although they do take time to manufacture, there are a growing number of companies certified to fabricate, install and maintain the barriers.

But you’d think there would be a better temporary alternative than a bunch of tires, right?

One of the things the SAFER group was thinking about last time I talked to them was a transportable version of the barrier that could be used for street courses. It’s a formidable challenge. The current barriers are fastened to the track wall, which is pretty firmly in place. How would you anchor something to a street in such a way that it would stay in place, but could be removed without significant damage to the road/sidewalk/parking lot?

Another problem that I haven’t really heard talked about is that it’s impossible to line a track with SAFER barriers inside and out. Emergency vehicles must have free and immediate access to the track (and a way out) when needed. The SAFER group also has investigated hinged barrier that could open and close, but developing a hinge that can take a direct hit from a 200-mph racecar and still open easily is a pretty stout challenge as well.

It all goes back to what I tell Moody (it seems) every week. If it were simple, they’d have already done it.

Thanks again for the question!

Mar 202015
 

When winning means a few hundredths of a second, nothing is too small to be ignored.

I’ve talked a lot about energy and the importance of using it as efficiently as possible in racing. Gasoline provides a certain amount of stored (a.k.a. potential) energy. Everyone gets the same amount of energy. Winning lies in part in how efficiently you can transform the potential energy of the gasoline into kinetic energy (also known as speed).

We’ve talked about friction – anywhere two moving parts touch, you have to use some of the energy from the gasoline to overcome their resistance to rubbing past each other. Friction robs a car of speed.

There’s another way energy is used up: Deformation. Also known colloquially as “Squishing”.  Take a gander at the video below.

This is a common example we use in physics classes to illustrate the conversion of energy from gravitational potential energy (energy of position) to kinetic energy (energy of motion). The ball starts out still, but raised to some height. Its energy it entirely potential. As it falls, it loses potential energy and gains kinetic energy.

If the world were perfect (a phrase that should raise a red flag), the ball would return to it’s original height. All of the kinetic energy would be converted back into potential energy. Hopefully, you noticed that it didn’t. Run the video one more time and look at the overlay (the yellow circle) as the ball hits the floor. I wanted to emphasize what happens when the ball hits the floor.

It squishes. Deforms. Whatever. It changes shape.

Changing shape requires energy. That energy can’t be converted back into potential energy, which is why the ball doesn’t bounce back to its original height.  (Note that there are other places where we lose energy. For example, the ‘plonk’ sound when the ball hits the floor takes energy to create, too.)

In some cases, the fact that it takes energy to deform something is good. For example, some areas of a car are designed to crumple more easily than others so that the energy of the moving car is used to smush the car and not transferred to the people inside.  These are cleverly called “crumple zones”.

In other cases, deformation is not such a good thing. And one place where deformation happens a lot is in the tires of a car. Look at a tire lying on the ground. It’s round. When you put that tire on the car, the weight of the car deforms the tire, creating a flat spot – a deformation. I’ve embedded a video below from Goodyear – it’s part of their modeling package for simulations and it shows how the tires continuously deform as the car moves.

Every time the tire deforms upon hitting the ground, then springs back, you lose energy.

This is called rolling resistance. The United States Department of Energy estimates that 5% to 15% of the energy contained in the gasoline goes to overcoming rolling resistance in passenger cars. In big trucks, that number can be as high as 15% – 30% because the tires are wider and there are a lot more of them.

To put this in perspective: If you lose 20% of your energy to rolling resistance, that means that one out of every five fill-ups is used entirely to overcome the rolling resistance of the tires. (Side note: Once you consider all the friction, all the rolling resistance, the energy used by cooling units, only 12%-20% of the energy contained in the fuel is used to actually make a passenger car move.

GY_FuelSavinTiresIf you go to a tire store (as I did recently, thank you potholes), you’ll find advertising displays that talk about low rolling resistance tires. The grab in these ads is that low rolling resistance tires save you money by decreasing the amount of energy lost to the tires.

This is actually a thing. They run tests and studies to prove that it is true. Now, of course, this only works if you keep your tires properly inflated. Underinflated tires on a car deform a lot more than properly inflated tires.  You can verify this for yourself. As you let the air out of a ball and measure how far it bounces back after dropping it, the more underinflated it is, the lower that bounce-back will be.

Ideally, Goodyear would provide tires with exceptionally low rolling resistance; however, rolling resistance is linked to other parameters. A harder tire doesn’t deform as easily, so it will have lower rolling resistance; however, we also know that harder tires don’t wear much and don’t offer a lot of grip. Softer squishy tires give good grip – but have have higher rolling resistance.

Goodyear (and every other tire manufacturer) does research to find ways to decrease rolling resistance without sacrificing grip. A lot of their work is on the tread compounds. Tread compounds are super top-secret recipes with a huge number of ingredients that include everything from rubber to carbon and/or silica nanoparticles.

Now in NASCAR, all teams get the same tires – and teams are not allowed to make any changes to the tires – at all. So although the tires do affect the fuel mileage, every team gets the same equipment. If Goodyear comes up with a way to make a lower rolling resistance tire, everyone on track benefits.

Small Effects Add Up

You may be thinking that we’re talking pretty small numbers. We are, but they accumulate. If there’s something you can do that save you a penny every mile and you drive 50,000 miles a year, that’s $500.  On a larger scale, research indicates that reducing the rolling resistance by 10% would increase fuel mileage by 1%. That’s tiny, right? Well, in 2014, the U.S. used 136.78 billion gallons of gasoline. Decreasing that by 1% saves over a billion gallons of gas. Little things add up – as I keep telling my husband when he doesn’t turn off the light when he leaves the room.

 

 

 

Mar 062015
 

Jeff Gordon’s decision to step away from full-time NASCAR Sprint Cup racing has resulted in a lot of discussion about aging drivers. We’re on the verge of a turnover as a number of drivers (Johnson, Stewart, Junior, Harvick among others) reach their forties. And what an appropriate topic for this week as I hit one of those milestone birthdays next week myself.

Slowing down is a part of aging. The print on menus shrinks, you wake up with aches and pains you can’t figure out where they came from, and you find that it takes you longer to recover from colds and injuries. Sprint Cup drivers are no different. In fact, it’s probably exacerbated because they subject their bodies to more physical punishment than your average human being.

But there are some advantages to aging. You’ve got more experience.  And… well, I’m sure there are others.

So how does age affect a driver’s career? Let’s look at the numbers. (And while you’re at it, check out Eric Chemi’s blog – he took a different approach, but came up with mostly the same conclusions.)

What Do We Measure?

The challenge in questions like this is what to graph that actually makes some sense.

DriverAges_Stewart The first obvious thing to try is wins (or top 5s or top 10s) vs. age, right? I did this (at right) to look for obvious trends. (Note – you can click on any of these graphs and they should like to a full-size version so you can see details.)

This is pretty useless. Stewart won championships at ages 31, 34 and 40. All years where he won a respectable number of races; however, there are years where he won a lot of races and didn’t win the championship.

I also plotted Top 5s and Top 10s this way and it wasn’t any more enlightening.

So I had to re-think a little. What we’re interested in is whether a driver becomes a worse driver as he or she ages. This got me thinking about cumulative stats.

If you’re staying at the same level, you ought to add the same number of wins each year (on average, of course). So what if I plot the cumulative wins as a function of age. That turned out to yield some interesting information.

Cumulative Statistics

It’s always rewarding when you plot something and you realize you finally found the right thing to measure and graph. As a note, I did not include years at the end of a driver’s career where he (and they’ll all men here) didn’t run all the races that year. A number of drivers ran part-time at the ends of their careers, some for lower-tier teams and I didn’t think that would be a fair representation of their career to include those later years.

Let’s start by looking at stats for someone with a long career that spans a wide age range: Darrell Waltrip.

From top to bottom are cumulative wins, cumulative top 5s and cumulative top 10s. There are some subtle differences between the three graphs, but let’s talka bout what they have in common.

If you look at the later years, the graphs become essentially flat – which means there were no more wins, top 5s or top 10s. But the point at which they plateau changes. The wins flatten out first (no new wins after age 45), then the top 5s (only two more after age 50)  and then top 10s (8 after age 50).

The areas where the slope of the graph is constant over a period of time I would characterize as consistent. They are adding to their record at the same rate. All three of Waltrip’s championships (shown in the highlighted regions) came during that period of time.

DriverAges_Portrait_WaltripAnnotated

DriverAges_Portrait_waltripByOwner2This would seem to suggest that this is a driver who reached a certain age and just couldn’t hack it after that – but there are some extenuating circumstances, namely a crash at age 43 and his transition from Hendrick to becoming a driver-owner shortly after.  I’ve put a thumbnail of the graph to right – click to see it larger.

Just a warning that you have to be careful about the rationale.

A number of drivers have very similar looking graphs: Both Labonte brothers, Dale Jarrett, and Mark Martin. But in those cases, there were also extenuating circumstances in terms of changing to lower-tier teams (Bobby Labonte went from Gibbs to Petty, for example). So let’s look at the drivers who don’t follow this pattern.

DriverAges_Portrait_Stewart

 

Wow. You want to talk consistent? Here’s a man who (until the nightmares of the last two years) is almost one straight line from start to finish. The top 5s and top 10s are almost perfectly straight lines. The wins have a little more scatter – but that’s typical because the overall numbers are smaller. Jimmie Johnson’s graphs look very similar.

When we analyze graphs we like to talk about curvature. There’s no curvature here. If the graph curved up (i.e. looked like a saucer), that means the person was getting better. If the graph curves down (as it does when it plateaus), then the person is getting worse.

And now for one of the the interesting ones. It’s interesting in part because Jeff Gordon has driven for the same company his entire career, which eliminates the question of equipment from the analysis. Here’s the raw data for wins.

DriverAges_GordonWinsRaw

Again, it’s small to save space – click to get a larger version. This is really interesting. You can divide his career into specific segments – see how the slope changes in different ranges of years? My first attempt to explain this was to look at personal events like marriages and children. There might have been a correlation there, but them I looked at his crew chiefs.

DriverAges_Gordon_CrewChiefs

That’s sort of interesting, huh? I didn’t make a line during Steve Letarte’s (I know, I spelled it wrong in the graph) tenure. There was a jump there, then it was pretty flat. But that’s a pretty convincing correlation, I think.

Gordon’s still very consistent when it come to the top 5s and top 10s.

DriverAges_Portrait_Gordon_All

Okay, But Can Older Drivers Compete Against Younger Ones?

I know. I got carried away with the data. I do that.

I made a lot of other plots, but here’s the one I think is the most interesting.DriverAges_Champions

There’s been an influx of younger drivers – they start earlier and one might think that would lead the average age of the Sprint Cup Champion to be going down. Overall, though, it’s not. It’s going up. The most recent “Young” winner is Brad Keselowski – and he was 28 years old.

Conclusions

Don’t count the old folks out yet. Even at the advanced age of (gasp) 40-something, drivers like Tony Stewart (pre the last two years), Jimmie Johnson, and Matt Kenseth are remaining consistent with their performance when they started in the series.

Ever scarier, if you look at Kevin Harvick or Brad Keselowski’s graphs, they’re better than straight lines. These drivers are still improving (even as Harvick approaches 40 and Keselowski 30), which means we probably haven’t seen the best of them yet.

 

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