Jul 242015

Aerodynamics is complicated. Let’s just get that out of the way. But it’s not so complicated that we can’t understand what’s going on with just a little patience.

Why 3D?

Every wonder why they call it three dimensions? The reason it’s three is because I (or you) can denote any point in space with only three numbers. For example: a latitude, a longitude and an altitude. Since we’re dealing with much more limited spaces, a simple Cartesian Coordinate system, like this one, usually suffices.


The line that goes out to the point P is a three-dimensional vector. It’s got parts going in the x, y and z directions. By specifying that there is so much in the x-direction, so much in the y-direction and so much in the z-direction, I’ve told you everything you need to reconstruct that vector.

Forces in 3D

A force (a push or a pull) can act in any direction, but in order to understand the effect of that force, it’s easier if we break it down into its components – how much of the force acts in the x-direction, how much acts in the y-direction, etc.

When we do this on a race car, we give the different directions their own fancy names – just to make us seem extra clever. Basically, any force that acts in the opposite direction the car is going is called drag. Any force that pushes the car into the track is called downforce.

When the force acts up instead of down, it’s called lift. Yes, I know it should be called ‘upforce’, but the people who study aeroplanes named it.

Not shown in the picture below is side force, which would be in or out of the page.


Spoiler Alert!

Let’s think about the air acting on the spoiler. Because the spoiler is at an angle, the force on the spoiler is at the same angle (it’s perpendicular to the surface). So some of the force on the spoiler points down and some of the force points horizontally.

Which means some of the air hitting the spoiler creates downforce, and some of the air hitting the spoiler creates drag.


The more area there is for the air molecules to hit, the larger the force. A tall spoiler creates  more force than a short spoiler – but because of what I said up above, the angle of the spoiler is absolutely critical.

The more upright the spoiler, the more of the force is drag and the less of the force is downforce.  If the spoiler were horizontal, you’d get all downforce. If the spoiler were perfectly upright (vertical), all the force would be drag.

Why a Different Package for Indy vs. Kentucky?

In Kentucky, NASCAR went with a shorter spoiler to reduce the downforce. Passing has been a persistent problem at 1.5 mile tracks and the idea was that if the cars weren’t quite so dependent on aerodynamic forces, then the loss of those forces when you get close to another car wouldn’t have such a great impact.

And that strategy seems to have paid off well.

But Indianapolis and Michigan are very different kinds of tracks. At 2.5 miles and 2 miles respectively, they  are closer to superspeedways than they are to 1.5 mile tracks. At Indy and Michigan, the cars get going very fast down the straightaways, which lets the leading car get away from its pursuers. And it’s pretty tough to pass a car if you’re two lengths behind it going into the corner.

So the goal at these almost-superspeedway tracks is to slow down the maximum speeds along the straightaways so that a car can’t get away so easily. This is a little different than the goal at the intermediate tracks.

There’s a couple of ways to slow down a car: the two most obvious are

  • Decreasing horsepower
  • Increasing drag.

Decreasing horsepower introduces its own challenges, as we know from restrictor plate racing, so NASCAR is using the increased drag approach at Indy. And they’re doing that by setting the spoiler height at a pretty astounding 9 inches tall. At Kentucky, the spoiler had been reduced to 3.25 inches.

The best way to understand how much of a difference this is comes from a tweet from JGR Racing, which actually shows you the difference. Extra points for having gotten the product placement in there!


That’s a pretty big honking spoiler, eh?

But, you’re thinking (at least I hope you’re thinking) wait a moment… If they increase the spoiler height to increase the drag, aren’t they also increasing the downforce?

Yep. They are. It would be lovely to have a knob that you could turn and independently change the amount of front and rear downforce, and the amount of drag. But real life isn’t that simple.

Those Poor Engineers… NOT

The spoiler isn’t the only thing that’s changed. The changes in toto are…

  • 9″ spoiler
  • 1″ wickerbill (aka Gurney flap)
  • 2″ splitter
  • 43″ radiator pan width
  • speedway extension on the quarterpanels and rear bumper – the same ones run at the superspeedways.

So you’re thinking – my goodness, pity the engineers. All these changes.

Lemme tell you – the engineers are not upset. They love the opportunity to get ahead of the other teams by being smarter and figuring stuff out before someone else does. This is a chance for a team to get a win simply by understanding the set ups better than anyone else.

And something else to think about. In my column about Kentucky, I showed the changes in the spoiler and radiator pan sizes as a function of time. Well, I’ve updated those.

BSPEED_2015RulesChangesbyTrack_Spoiler BSPEED_2015RulesChangesbyTrack_RadiatorPan

The radiator pan is the exact same size at Indy as it was in 2014. The spoiler is only one inch taller than it was in 2014. And the teams have plenty of experience with the rear aerodynamic extensions from years of racing at Talladega and Daytona.

Yes, it does mean that they have to put those disparate elements together – which they haven’t done before – but the teams with the strongest technical staffs will be in the best position to take advantage of these just-in-time adjustments.

Personally, I’m psyched about track-specific packages. It gives the teams much more of a box to work in, which means they have that much more room to be creative. Looking forward to Indy!


Jul 132015

Someone asked in the comments how much kinetic energy Austin Dillon had when he hit the catchfence at Daytona. I don’t know exactly how fast he was going  (probably was somewhere around 180 to 200 mph), so I figured I’d just make a graph and include a couple reference points in terms of kinetic energy scales.

The left axis is labeled in MegaJoules (MJ), which are millions of Joules. To give you an idea

  • 0.009 MJ = energy contained in a AA alkaline battery
  • 0.038 MJ = energy contained in one gram of fat
  • 0.04-0.05 MJ = energy contained in one gram of gasoline
  • 8.4 MJ =  daily recommended energy intake for a typical active woman  (2000 calories)
  • 110 MJ = energy expended by a typical rider in the Tour de France
  • 122 MJ = energy contained in a gallon of gasoline
  • 1000 MJ = energy of a typical lightening bolt

So without further comment, here’s the kinetic energy of Austin Dillon, where I used his NASCAR official weight of 185 lb and minimum car weight of 3300 lbs. Black cowboy hat not included.


Jul 072015

As some of you know, I was in New York for the weekend celebrating my anniversary, so I’m just now catching up on the weekend’s accident at Daytona. Note: Some basic information about catchfences is modified (and updated) from a blog originally posted on 11/14/11.

And I bet there are some typos, still.

A Brief History of Barriers

Track barriers originally were erected to keep cars separated from spectators.  In addition to concrete walls to prevent the cars from driving off track, debris-spewing accidents necessitated fencing to contain airborne objects.

ChainlinkFenceCatchfences should have the same properties as walls, but they can’t block the view.  Chain link fence is a good compromise: It’s cheap, plentiful, easy to put up and surprisingly strong given its high visibility.

Chain-link fabric is an elastic metal mesh. It can give in two ways: gentle forces cause the mesh to deform.  The diamonds stretch out of shape, but when the force is removed, the fabric springs back to its original shape. The fence can also deform by stretching the wires that make up the mesh. A large-enough force will break the wire entirely.

The mesh must must supported, usually by poles and cables. How much the mesh can stretch depends on how it is supported.  If the frame is too big – meaning that there’s a very large area of mesh between supports — the mesh can stretch too much. How the poles are attached to the mesh is critical, because the attachments allow the load to be shared between the fabric and the poles.  The larger the forces, the more robust the links between the poles and the mesh must be.
Catchfence_Daytona2Race track fencing is stouter in just about every way.  The mesh is made of larger-diameter wire with higher tensile strength.  The links between the poles and the fabric are stronger:  In the picture at right (Daytona), steel cables run horizontally through the mesh and are fixed to the vertical poles using some massive turnbuckle-like fixtures.

Different tracks have different installations.  Some have metal tubing running horizontally as reinforcement. Catchfence improvements have primarily been via stronger mesh, stronger or a greater number of poles, or better links between the poles and the mesh.  But it’s basically the same fundamental design.

The chain-link fence is a motorsports institution, with different sanctioning bodies requiring different standards for debris fencing.  In the FIA test, a 760-kg  (1675 lb) test mass is shot into a fence at a speed of 65 km/h (40 mph) at heights of 1.6 m and 2.5 m (5.25 and 8.2 feet respectively).  While 40 mph seems very slow, they’re taking just about the entire mass of an Indy car and concentrating it in a relatively small sphere.  A real car would impact over a much larger area and spread out the force.


The photo at left shows a Geobrugg fence being tested:  The mesh deforms (a lot!) – but it does not break. Load is transferred to the poles, with the poles nearest the impact bending, but not breaking.  The emphasis, however, is pretty strictly on containment.

Geobrugg, one of the primary catchfence providers for motorsports (and many other things) made the video below that shows a car going into a standard vs. going into one of their fences.

The advances in catchfencing that have been made are huge; however, you are always going to have issues. As long as the fence is permeable, small pieces (and fluids) are going to get through the fence. Some of the people injured in the Carl Edwards crash in Talladega were burned by oil. Unless you use a solid fence, this is a hazard you will never eliminate.

Is Speed a Factor?

We’ve been hearing calls for slowing things down at Daytona. Is speed the issue? It is certainly true that speeds have been increasing.


Here’s the pole speeds at Daytona over its entire history. You have to be a little careful. The idea of group qualifying is very recent, and we know single car speeds are lower than those of cars in a pack, so it’s not quite fair to compare these one one one. But the pack qualifying pole speeds are a good 4mph below the peak single-car pole speed, which means we’re still probably 8-10 mph slower than the highest speeds that have been raced at Daytona.

So maybe it would be helpful to compare speeds at different tracks this year, since single-car speeds aren’t really all that different than race speeds at non-plate tracks.


I put triangles above the plate tracks. You’ll notice that speeds there aren’t that much higher than many of the other tracks – and Michigan was faster than either Talladega or Daytona.

Which led me to wonder about whether this year was just an anomaly. So here’s this year and last year.


Michigan is consistently faster than either Daytona or Talladega. I also wanted to look at the speeds for the Sprint Cup versus the XFINITY series, because the last big accident we had at Daytona was Kyle Larson running in the then-Nationwide series.


You can see that the lower-level series runs at significantly lower speeds (10-15 mph) – and still they’re getting in the air.

So I have a hard time believing that simple reducing speed is going to have a lot of effect on these types of crashes.

Pack Racing

So what’s the big different between Michigan – the fastest track – and Daytona/Talladega? It’s the restrictor plates. Restrictor plates produce a very different type of racing. If you watch the throttle/brake indicators during non-restrictor plate races, you’ll see the drivers easing off the throttle going into the turns, or even braking. The pole speed is an average speed, which means they’re generally traveling faster down the straightaways and slower in the turns.

Not at a plate track. The throttle is full open at all times. The cars are maxed out in terms of their engines.

Remember that, at 204 mph, a car goes a football field a second. Think about that. You’ve seen cars scatter to avoid accidents on other tracks. You can’t do that on a plate track because there is nowhere to go. You’re blocked in on all side.

An accident on a plate track is more likely to involve multiple cars. The last line here is the total number of cars involved in accidents

Michigan 2014 Daytona 2015 July Daytona 2015 Feb Las Vegas 2015 Atlanta 2015
6 1-car accidents
1 9-car accident
5 1-car accidents
1 7-car accident
1 9-car accident
1 11-car accident
2 1-car accidents
2 2-car accidents
2 7-car accidents
3 1-car accidents 2 1-car accidents
1 4-car accidents
1 6-car accidents
15 32* 20 3 12

*Racing-reference.info didn’t mention how many were involved in the end-of-race crash because it wasn’t technically a caution, so the number is much larger.

The numbers are small, so it’s hard to prove this, but my intuition, based on observations and the data we do have, is that more cars involved in an accident at close quarters mean

  • more likelihood of a car spinning (and cars are more likely to become airborne if they are not going straight)
  • more likelihood of a car launching off another car and getting airborne

When all this happens in conjunction with high speeds, you have all the elements for a catastrophic accident.

I am not suggesting we remove restrictor plates – that would be just plain stupid for both the drivers and the fans.

So Let’s Just Make Pack Racing Safer!

Everyone seems to assume that NASCAR will come up with a solution that will allow pack racing to continue the way we’re used to it happening. They’ve done an admirable job of dealing with past issues…


There are limits. I mean, if we could do anything, we’d have cured cancer and found a way to make sure everyone in the world has access to clean drinking water.


If there were an obvious solution to make pack racing safer, NASCAR would have already done it. It is possible that there isn’t a solution and that pack racing will always be inherently more dangerous than other types of racing.

Cars travel just as fast at other tracks and they don’t leave the ground nearly as often as they do at Talladega and Daytona.  Putting on a smaller restrictor plate to decrease speeds will not help. It’s not the speed. It’s the combination of the speed and the pack racing.

Perhaps the best that can be done is to protect spectators and let drivers take their chances. (If you’re wondering whether a Lexan ‘hockey-type wall’ would work, I addressed that elsewhere. (TL;DR: expensive and difficult, especially since you not only have to stop the car and parts from getting into the stands, you have to make sure that you don’t make it more dangerous for the drivers.)

Perhaps you have to make a radical change to the engine so that the drivers have to brake and accelerate around the track and you don’t get pack racing. This would make a lot of fans upset. There is nothing as breathtaking as standing in the infield watching the entire field take the turn.

There is also nothing as breathtaking as that gasp of fear, your heart skipping a beat and the feeling in the pit of your stomach as you whisper a prayer that the driver in the crunched up shell of a car just coming to a stop will climb out and wave and live to race another day.

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.


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.


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?


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).



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.



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.



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.)



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.


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.


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.)



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.


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.


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.


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.


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



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.


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.


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


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.


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.

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.


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.



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:


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.


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.


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.


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.


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).


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.


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?


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 .



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.



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.



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.


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.




%d bloggers like this: