Sep 152014
 

In the last blog entry, I explained what brake bias was and how it could be used to improve the car’s handling during green-flag runs. This time, let’s look under the hood (or I guess, more accurately, under the dash) and see how this is accomplished.

Let’s start with the schematic from last time:

BrakeBiasinaRaceCar

 

 

WilwodBrakeBiasKnobNow we’re going to look at what happens at that little dial icon in the graphic. We start with a knob in the cockpit. It’s a simple knob, with two directions: front and rear. Turn to the right and more brake force goes toward your rear brakes. Turn to the left and the brakes are biased in favor of the front. The cable runs down to the brake bias bar, which I show below in a schematic drawing first, then a picture of the real thing.

On the left side of the drawing is a threaded rod – the bias bar (running up and down) with a center pivot point and two rods (one at either end) that are used to apply force to the two master cylinders.

 

BrakeBalanceBar_Alcon_Schematic

The next picture shows the entire pedal box assembly for a Rally Car.

BrakeBiasPedalBoxRallyCar

 

When you press on the brake pedal, the bias bar moves to the right, which increases the pressure on the master cylinders. When the bias bar is perfectly centered, meaning that the distance from the center to the left rod and the distance from the center to the right rod are equal, then the force is applied equally to the two cylinders.

Now consider moving the center pivot to the left or the right. This changes the distances from the center to the left and right rods and tilts the bias bar (like is shown in the diagram at top).  Now when you press on the brakes, the force is split between the two master cylinders differently. The side that the pivot is closer to will get a larger fraction of the force.  Instead of a 50:50 split, you can get a 60:40 split, for example.

You can see in the photo immediately above  that the center pivot is already adjusted slightly to the right of the picture, so the right master cylinder is going to get more of the braking force than the left one. Often, because of the inherent weight distribution of the car, the ‘neutral position’ of the brakes is biased a little toward the front or the rear.

And that’s pretty much how it’s done.

Sep 052014
 

With all the talk about giving the drivers the ability to change aspects of the setup from within the car, I thought some comments on what types of changes they can make would be appropriate.  Since the only control they have right now is brake bias, let’s start there.

The first thing you need to know is that the braking system on a race car is different from the one on most passenger cars.  On a  standard passenger car, the brake pedal is connected to a master cylinder – a hydraulic-filled container that transfers force from your foot on the brake pedal to the brakes.

BrakeSystem_NormalCarWhen you press on the brake pedal, the master cylinder exerts force on the fluid that fills your brake lines. That fluid pushes on the brake calipers and slows down the car. In everyday driving, most people don’t push the boundaries of traction or of their braking system, so this works pretty well.

In a race car, however, you’re always on the hairy edge of losing traction. Your goal is to go as fast as possible, so you have to run on the edge. That means the balance of the car is absolutely critical.

I’ll remind you of what I’ve decided to call the zeroth law of racing (we do that in science. When something is so fundamental, we make not the first rule, but the zeroth rule.) That rule would be: You can only go as fast as your least grippy tire. The corollary to this is that you can also only slow down as good as your least grippy tire.  For that reason, racers like to have a little more control over how the brakes are applied.  A NASCAR race car has separate master cylinders for the front and the rear tires.

BrakeBiasinaRaceCar

 

Note the little dial where the brake lines split into front and rear. That’s the brake bias, a device that allows the driver to change the proportion of the force that’s going to the front versus the rear brakes.

You’ve heard drivers talk about cars being loose and tight.  Loose is when the front wheels have more grip than the rear wheels. When you’re going around a corner on an icy road and the rear wheels swing out, that’s loose.  Tight is when the rear wheels have more grip than the front wheels. That’s when you have the steering wheel all the way to the left and the car is still going straight.

Look at the extreme case of doing donuts.  You do donuts  (in a rear-wheel drive car, at least) by holding the front tires still, turning the wheel and powering the rear tires. The forces on the front tires essentially pin the front of the car to the ground, while the rear is free to move. This would be the extreme case of an unbalanced car. Because the front wheels are pinned and the rear wheels aren’t, the car goes in circles.

Back that off a little. Anytime you have unbalanced forces, the car is going to want to rotate. On a dirt track, drivers talk about steering with the throttle – you can turn the car by giving it a burst of power to the rear wheels. The need to steer with the throttle is primarily because of the lack of grip on dirt – the front wheels have less effect on steering. It’s a much smaller effect on asphalt. But the principle is the same. When you have better braking in the front wheels than the real wheels – or vice-versa – the car is going to want to turn. You can use that to your benefit to some extent, but remember the goal is always balance.

Hence the need for brake bias.  Let’s say, for example, that we have a front-heavy car. If we apply the same braking force to the front and the rear, we’re going to lock up the rear brakes before we’ve gotten everything out of the front brakes we need.  We need to bias the brakes so that the front gets more braking force.

Remember that the distribution of the car’s weight on the four tires is always changing, depending on whether the car is speeding up, slowing down or turning a corner. So no one brake bias setting is perfect through an entire corner. You’re generally optimizing for corner entry, so you an be the last car braking into the turn.  You want to build up as much speed as possible down the straightaway. If you can wait a fraction of a second longer than your competitors to put on the brakes, you’ve got an advantage.

Traditionally, set-up changes can only be made during pit stops. The brake bias is the one thing the driver can change from inside the car. (At the moment, at least.) The driver can’t change brake bias through a corner, but think about what changes over the course of a green flag run. There are two biggies.  Tires change in two ways. For the first few laps, they’re underpressured and heating up. After that, they’re wearing. Both things change their grip levels.

Second, you’re going from a full to an empty fuel tank. The fuel tank holds somewhere around 18 gallons.  Gasoline is roughly 7 lb per gallon, so that’s a rear weight change of about 120 lbs. Brake bias allows the driver to compensate for those rather significant changes in weight distribution – and thus need for braking – inbetween pit stops.  There’s a knob in the car that’s allows the driver to dial in how much brake goes to the front and how much goes to the rear.  I’ll get into the details of how that works in the next post.

 

 

 

Aug 222014
 

TurbulentSmokeA persistent motorsports issue (and not only with stock cars) is the aerodynamic passing problem. You can’t pass without grip. Grip is a direct result of downforce. Downforce comes from two places: the weight of the car (mechanical grip) and the billions and billions of air molecules hitting the car (a.k.a aerogrip).

Racecars are designed to take advantage of aerodynamic downforce. Everything from their shape to the aerodynamic appendages added to the car are all optimized to produce downforce. You can play around with mechanical grip some by adjusting the weight on each corner of the car and trying to control how the weight changes as the car turns, brakes and accelerates. Aerodynamic grip is even more subtle.

And complicated.

Aerodynamicists think about fluid flow (fluid meaning liquid or gas) in terms of two extremes. Laminar flow is when the air (or water) moves predictably over a surface in nice, uniform sheets with relatively little variation from sheet to sheet.  In the diagram below explaining how a wing works (an airplane wing; turn your computer upside down if you want to see how a car wing works) the air is represented by nice, neat lines that very politely crowd each other as they work their way around the wing. Changes in pressure and velocity happen gradually.LaminarFlowOveraWing

The other extreme is turbulence – when the air (or water) flows in swirls that are not at all well behaved.  Turbulence is chaotic – large differences in pressure and velocity that change quickly. Turbulence is very difficult to describe mathematically because it’s just so darn complicated.

It’s easier to see experimentally. Pour some cream into your morning coffee and stir it with the back of your spoon. The spoon moves the cream out of the way, creating a gap. The cream swirls around the back of the spoon and fills the gap, forming a lovely swirling pattern.  You can see the same thing in the wake of boat – the water flows back in to fill the gap the front of the boat made. Smoke rising from a cigarette is turbulent as it mixes with the air.  Breaking waves are turbulent.

In turbulent flow, the air molecules end up going in all different directions.  If you’ve ever driven very close to the back of a semi on the expressway, you’ll feel your car buffeted from different directions – that’s the turbulence.

Laminar and turbulent flow are both evident in the aerodynamics of racecars. The front of the car is smooth and sloped.  The cross section of the car (what you’d get if you took a slide of the car perpendicular to the direction the car’s traveling) gets larger and larger as you get further from the front fascia. The car keeps pushing a bigger and bigger hole in the air.

Things change when you reach the B-post.  Now the car needs to push away less air because it’s sloping down. Its cross section is getting smaller. The air starts swirling in around the rear window, becoming turbulent. The wake of a racecar is similar to the wake of a boat. The water’s going in all directions, trying to fill the hole made by the front part of the boat.

A technique called computational fluid dynamics lets engineers visualize the airflow. The diagram here is from Ford Racing and shows the turbulence on the 2013 Ford Fusion.  This visualization shows you where there are big changes in the airflow.  You can see the giant wake behind the car. It’s strongest the closest to the rear of the car, but note that the wake extends almost two car lengths behind the car.

2013_FordFusion_CFDTopandSide

If you want to learn more about Ford’s CFD calculations and the role they play in designing racecars, check out their YouTube video - it’s worth a gander.

The wake creates drag on your car and slows it down just a little, but as the driver of said car, it’s not really a big concern. For the guy running behind me, however, my wake is a really big problem. Laminar air makes downforce. Turbulent air doesn’t.

And that’s the origin of the passing problem. A fast car catches up with the car ahead of it. As the trailing car research the leading car’s back end, the turbulence from the wake of the first car makes the flow over the front of the trailing car turbulent, which means the trailing car loses downforce or becomes ‘aeroloose’. And you can see from the CFD calculation that you don’t have to get so close for aeropush to become a problem.

Right after the Michigan race last week, NASCAR ran a big test (10 teams) to try out some options for possible rules changes for the 2015 season.  In case you think this is a simple problem to solve, they had two approaches: more downforce and less downforce.

On the increase downforce side, the first change was to a bigger splitter – nine inches tall.  The problem with increasing the splitter is that it unbalances the car. One of they key principles in racing is that you can only go as fast as your least grippy tire. Grip is proportional to downforce.  If you increase the rear downforce without making a commensurate change in the front downforce, you get a really tight car.  Lots of grip in the back, but the front tire – the ones that turn the car – don’t have enough grip.

Increasing the front splitter has its own challenges, so NASCAR turned to dive planes. Dive planes have been used for a long time on sports cars. They’re simply small, curved pieces of metal or carbon fiber composite. NASCAR used two dive planes – one above the other – and put one set on each side of the car.  The dive planes started at the front fascia and swoop upward, ending at the front fender. The pictures below are from the twitter feeds of @nateryan (top) and @2spotter (Joey Meier, bottom).
divePlane_NateRyan

DivePlane_Joey

The principle behind the dive plane is that it takes the turbulent air coming onto the front of the car and funnels it to make the flow more laminar.  More laminar flow should translate to more downforce.

NASCAR made the point that the dive planes may not be part of the final rules package; however, having the dive planes allowed them another little benefit – they could put pressure sensors on the dive planes and measure how the downforce changed for the different configurations.

The ‘prime rules package’ that was tested consisted of the larger spoiler, a lower rear differential gear, and decreased horsepower.  They tested 850hp, 800 hp and 750hp.  The second test package was actually a lower downforce package, in which they went with a smaller spoiler and they removed an underbody piece that had been new this year.  The estimate is that these changes decreased the overall downforce by 28-30%.

And (of course) the drivers were not very enthusiastic about the prime rules package. They liked the lower downforce better. Reporting from the track suggested that the prime rules package gave rise to in-line racing, while the lower downforce package got drivers really excited about possibilities for passing.

Unfortunately, there’s no time for another test because NASCAR really needs to have the 2015 rules finalized pretty darn quick so the teams have time to prepare for next season.  Right now, a bunch of NASCAR engineers are sitting back at the R&D Center, trying to make sense of the gigabytes of data they collected during the test. I’m sort of glad I’m not the one who has to make this decision!!

I didn’t mention one of the big changes in this blog post – the ability for the driver to modify the trackbar position from inside the car, but I will comment on that in the near future.

Aug 082014
 

TirePressureIconRunning on underinflated tires can be dangerous.  Underinflated tires they create more friction and more heat, which leads to not only bad handling, but also can produce structural problems.

You may remember the late 1990′s, when Firestone tires had problems with tires blowing out or treads coming off.  The flat tires caused vehicles to roll over and there were more than numerous (Wikipedia says 250, but there’s no source for the stat)  fatalities and many more injuries. The majority (but not all) of the vehicles on which this happened were Ford Explorers. So there’s a rule now that any car made after 2007 has to have tire pressure sensors that warn the driver when a tire is significantly under-inflated. (Significantly means around 25% under pressure.)

Underinflated tires produce high stresses and temperatures. In a correctly inflated tire, the gas inside the tire supports most of the car’s weight. If the tire is underinflated, then there’s not enough gas pressure and the sidewall of the tire has to support the weight.  An underinflated tire flexes a lot as it rolls, which causes two major problems.  One is that it put more stress on the tire, and the second is that it produces more heat. (Graphic from http://www.tirebuyer.com/education/tire-pressure-and-performance.)TireUnderOverInflation

Underinflated tires heat up faster. You need some heat in the tire for it to work right; but there’s a Goldilocks situation here. Too cold and they don’t have any grip. Too hot and they fail. The pressure has to be just right.

Which makes you wonder, how hard can it be to just put the right pressure in the tires in the first place?

When it comes to racing, it’s because street tires are rarely called upon to sustain the extreme conditions race tires endure.  The issue is what we call tire pressure build – the increase in the tire pressure due to the heating of the tire and the gas inside the tire. At it’s most basic, heat is simply the motion of molecules. The faster the molecules are moving, the higher the temperature.

In a tire, the faster the molecules move (i.e. the hotter they get), the harder they hit the walls of the tire and the higher the tire pressure.  This is why your car’s owner manual tells you to measure the air pressure in your tires when the tires are cold. The pressure changes a lot with temperature. The video below, which I did a few years ago with the National Science Foundation, delves a little deeper into the specifics of tires and gas pressure. (And if the video doesn’t embed correctly, then try here.)

For the temperatures passenger car tires reach, a good rule of thumb is that every 10 degrees Fahrenheit corresponds to 1 psi (pounds per square inch) increase in pressure. NASCAR tires routinely change pressure by 20-40 psi from the tire sitting on the pit wall to the time it’s run a couple of laps. So the pressure you put into the tire is no where near the pressure you have three to five laps into the race. For a tire to have the right pressure during a long run, it has to have a much lower pressure when it first goes on the car. It takes a few laps for the tire to heat up, so the tire is really being stressed in the initial part of a run.

It’s a calculated risk teams take in how low they will start their tires.  Goodyear specifies a recommended pressure for each tire. NASCAR officials often check right front tire pressures in the pits.  The idea is that because the tires work in concert, if you the left front is way off, the car won’t be set up well. But there’s plenty of evidence that teams are getting around the recommendations and starting off with very low tire pressures.

Lee Spencer had an article this week suggesting that NASCAR might finally give in and require tire sensors as a way to get around the “shenanigans” (Her word, but one I love using). She uses the example of the left rear tire failures of the 48 car at New Hampshire a couple weeks ago. Johnson swore it wasn’t because of low tire pressure. Goodyear begged to differ.

TirePressureSensor_McLarenSo why not just put tire sensors on all four tires and let NASCAR officials monitor the tire pressure before the tires go on the car? Teams already use sensors during testing. They’re basically replacement caps for the tires that measure and transmit the tire pressure through an RF (radio frequency) link to a data logger on the car.  Places like McLaren (where the picture at right comes from) already have sensors for both inner and outer liners. The technology is pretty much already there to require sensors on the cars.

So why not just go ahead and put sensors on the cars?

Because NASCAR is very careful when it comes to opening cans of worms. Who will you allow to have access to the data?  The pit official? The team? Just before the tires go on the car, or will you allow access to that data during (or even after) the race? A lot of the same issues that arose when NASCAR made the transition to Electronic Fuel Injection will come into play here. How much technical data do we want the teams to have?

Sure enough, the first thing the husband said when I mentioned the idea to him was “That’d be great because then the teams would know when they had a tire going down.”

Do we want to go there? Are you encouraging crew chiefs to try edgier setups because they expect they’ll have a bit of a warning before they lose a tire? Do you want to take the driver’s ability to sense what’s happening with the car out of the picture?  NASCAR historically has had a de facto ‘no real-time telemetry’ rule for a very long time. The science and engineering in NASCAR go into the developing and preparing the car.  At race time, you turn over the majority of the control to the driver.

The other issue that always comes up is how teams will attempt to game the system. When NASCAR allowed for skew in the rear end of the cars, teams kept pushing the skew until NASCAR had to say “enough”. That we’re even talking about tires and tire sensors is because of teams ignoring the recommended pressures. Pushing the envelope is their job.

The discussions, according to Lee Spencer’s interview of Goodyear’s Greg Stucker, are ongoing, but NASCAR has a tendency to spend quite a bit of time thinking through issues like this before taking action.  The problem needs to be addressed, both to protect Goodyear’s reputation and for driver safety.

 

 

 

Jul 292014
 

My friend at the Milwaukee Journal Sentinal, Dave Kallmann (whose online column should be a regular read for race fans) asked about the confiscated firewalls from the Number 11 car at Indy.  That reminded me of the  first NASCAR race I was supposed to attend as research for my book The Physics of NASCAR. That was California in 2007. I was to follow around the number 19 car, at that time driven by Elliott Sadler and crew chiefed by Josh Browne.

VentedScrewsThen Josh and three other crew chiefs got themselves suspended at Daytona for using bolts in the spoilers that had tiny holes drilled all the way through the shanks. I know what these are (and where to find a picture) because we used to use them in the lab in our vacuum systems.  If you put a bolt into a hole, you trap air in the hole. We’re trying to leave on about 1 in every 1,000,000,000,000 molecules in the vacuum chamber, so it’s absolute critical that we can pull them all out.

The reason the team used… excuse me, I mean allegedly used… the bolts is because it gave the air trapped in the trunk of the car a way out and that should decrease drag and thus increase speed. So my first research race turned out to be Atlanta.

During Indy post-race inspection, some rear firewalls from the number 11 car were confiscated. A firewall is a piece of sheet metal that puts a barrier between the driver and anything you don’t want the driver exposed to, which may include fire, hot oil and other fluids, carbon monoxide, smoke, etc.  I’ve indicated the front firewalls on the picture because I couldn’t find a good picture of rear firewalls.

Firewallpic

Apparently the firewalls, or their positioning, was suspicious to the NASCAR inspectors. It’s possible there was just an error in the way the parts were installed (the teams manufacture a lot of cars and sometimes there are mistakes). But there is also the possibility that moving the rear firewalls around does pretty much the same thing that the vented bolts did: they provide a path for air to get out of the car and thus reduce drag and increase speed.

Seems like a pretty minor thing to move a few pieces of sheet metal around just a little; however, the positions of the sheet metal are specified pretty precisely. Modifying the arrangement can compromise drive safety in terms of an opening allowing smoke or fire into the cockpit.

We’ll see this afternoon whether NACSAR comes down hard on the team because this is a safety-associated issue. It may just have been a mistake; however, NASCAR doesn’t consider intention in determining the severity of a penalty.

Incidentally, Dave does an online race chat on Wednesdays at 1 pm Central. It’s not limited to NASCAR, so if you have a chance, join in the chat.

And can you believe it? I’m finally getting back to Milwaukee and it ends up being a week when the Brewers are out of town the entire week.  I’m going to have to just break down and go see them when they come to town and play the Nats.  At least Karl Ratzsch’s is still there.  And the Zoo.

 

 

 

 

Jul 252014
 

One of my favorite memories from Nebraska was coming home from the I-80 Speedway  covered in a dusting of red clay. (Planting in that clay was another question entirely.) But there’s something about dirt tracks you just don’t get at the asphalt ones.

It’s great that NASCAR is bringing a little of that spirit to the Truck Series.  Wednesday’s Mudsummer Classic race at Eldora Speedway was a great show. A dirt track challenges drivers and their crew chiefs who are mostly used to asphalt and an occasional foray into concrete.  A lot changes when you trade surfaces: Set ups, driving approaches, pit strategy and, perhaps most significantly, tires.

Some people made a lot of noise about Goodyear and their ability to produce a tire that would stand up to dirt-track racing, but Goodyear has a long history of equipping cars for the dirt. The tire they developed for NASCAR’s first foray into dirt in 40 years (in 2013) was based on rhwie standard 10-inch wide dirt modified tire. They started testing with that tire with Tony Stewart and the Dillon brothers (that sounds like a gang from the Wild West, doesn’t it?)  at Eldora back in October 2012.   They modified the tire based on that test, making it a wider (11 inches) to help with grip. Trucks, being on the order of a thousand pounds heavier than a typical modified, require greater force to turn.

In addition to the individual tire construction, Goodyear also provided some built-in stagger.  Put a red Solo cup on its side and give it a push. It automatically rolls in a circle because the drinking end has a larger circumference (distance around) than the bottom. The same strategy is used for race vehicles that only turn one direction.  At the 2013 race (I’ve been unable to find the specs for this year), the left-side tires had a circumference of 85.8 inches compared to 88.5 inches on the right.  Teams got four sets of tires for the event.

Goodyear_Wrangler_G23DirtTireRegardless of whether they were left- or right-side tires, the tires used at Eldora have two primary differences compared to the standard truck tire used at the other races.

The first is that dirt-track tires have treads. The Goodyear Wranglers employed for the Eldora race use the G23 tread pattern (shown at left). The treads serve the same purpose they serve on rain tires – they provide a path for loose dirt to move out of the way so that the rubber can grip the track. The edges of the blocks provide bite. The tread compound used is a softer compound, which again improves grip on the dirt surface.

The second difference is that the tires used at Eldora are bias-ply tires, not the radial tires that are standard in NASCAR.  Let’s back up a little and remember a little tire anatomy 101.  The diagram at right is from the Michelin website (the people who led the way in popularizing radial tires way back, just a little after WWII).

Tire_Anatomy_new

The part we’re interested in for the sake of this discussion is the plies.  Plies are a type of fabric made up of layers of rigid cords embedded in rubber. The body plies run from the outer bead to the inner bead. The reinforcing fibers (cords) have been made from materials like cotton, rayon, polyester, steel, fiberglass and aramids like Kevlar.

If you ask Goodyear which materials they use in their race tires, they will neither confirm or deny any particular material or combination of materials they use — which should give you an idea how important the cords are in terms of giving the tire desirable properties..

tirecords_wikipediaIf everything works the way it should, you will never see tire cords. When a driver hears during a race that the tires that were just removed had cord showing, they know there’s either a problem with the setup or with their driving. The cords are there for strength and stability. A tire’s grip comes from the tread – not the cords.

The plies have directionality, depending on how cords are arranged.  They are usually parallel to each other – it you look carefully at the picture to the left, you can see the rows of cording.  Whether a tire is radial or bias-ply depends on the way the cords point.

The first tires appeared in the mid-1800s and were simple pieces of solid rubber. They provided a bumpy, uncomfortable ride. The pneumatic tire was introduced in the mid 1800′s, but a tire made soley of rubber didn’t last very long, nor allow you to go very fast. Tires needed to be stronger and more resistant to road hazards. The idea of using cords in tire plies to increase strength was introduced in the early 1900s. A number of plies was used – two to four was common – to reinforce the rubber in the tread.w

The first tires were bias ply tires, which literally means that the cords in different plies were oriented in alternating directions running between 35-60 degrees with respect to the bead, which increases the strength of the tire, as shown in the diagram below, at right.

radialvsbiasply

In a radial tire, the cords go straight across the tire, as shown in the left picture. The cords are 90 degrees with respect to the direction you’re going. The radial tire was patented in 1915 and, as I mentioned earlier, Michelin really pushed the development of the radial tire starting in 1946.  Radial tires didn’t offer as smooth a ride as bias-ply tires; however, the gasoline crisis of the 1970′s made people value their improved gas mileage (which happens because they have less friction.) Almost all passenger car tires at this point are radials.  Because the radial cords go in one direction, the tire isn’t as strong, which is why radial tires have an additional belt package. Belts made of steel, polyester or Kevlar-type polymers are inserted over the plies and under the tread. Those belts greatly increase the strength of the tire..

Bias-ply tires create more friction and thus more heat and more wear.  A bias ply tire is inherently round, which means that the contact patch is smaller. Extra rubber has to be built up at the shoulders to provide a flat surface. Importantly, the sidewall and the tread on a bias-ply tire are one piece, which means that they move in concert with each other.  As a result, a bias-ply tire will give more in a turn because of the lateral force. The separate belt package in the radial separates the sidewall (the plies) from the tread (the belts) so the sidewall can flex, leaving the tread to hug the ground. Bias ply tires give more and allow better grip on an irregular surface like dirt. Radials would make the racing a lot harder — and not just for the drivers who don’t have much prior experience on dirt!

Many lower level series, as well as weekend racers, use bias-ply tires for another very important reason: they’re (in general) cheaper than radial race tires. This doesn’t mean they’re cheap, but it does help cut costs a little, which means more money to put toward going faster.

 

Jul 112014
 

Doug Yates was  guest on Dave Moody’s SiriusXM Speedway last week. He brought up a conversion you hear a lot in the week before Daytona and Talladega.  Every 25 horsepower in the engine translates to about a 1 second decrease in lap times. Dave did the math: Removing the plates would increase the engine by 450 horsepower. Four hundred and fifty more horsepower equates to 18 seconds off the lap time, assuming all other things equal.  That last part was a very important qualification. It will come back to haunt us in a moment.

David Gilliland got the pole at Daytona with a lap speed of 45.153 seconds, translating to a speed of 199.322 miles per hour. Using the above argument, his lap time would decrease to 27.153 seconds.  That translates to a speed of 331.456 mph.In 2004, Rusty Wallace ran 228 mph at Talladega in an unrestricted engine. That’s almost 100 mph slower than our theoretical max speed. Let’s ignore the concerns that NASCAR racecars tend to get aerodynamically unstable if they turn around at high speeds and think only about straight line speed.

So let’s look at what limits how fast a car can go.  We’re considering two major forces: the force the engine makes, which propels the car forward, and the drag force, which pushes the car backward.

 

DragandForceActingonCars

It’s exactly like a tug of war. Which ever is pulling harder, that’s the direct the car is going to go. (That’s because force is, as your physical teacher no doubt repeated over and over, a vector.DragandForceVectorSumsAt most tracks, if you want to pass someone, you step on the gas, the engine produces more force and you accelerate.  Daytona and Talladega are unique in that engine power is limited to about 450 hp. The pedals on the floor the whole way around. You’re perennially in the last situation, in which the car moves at a constant (a terminal) speed, which is the fastest speed you can get. The engine is doing all it can.

So here’s the catch – the reason why the phrase “all other things equal” causes problems.  All other things are not equal. Specifically, drag. Drag is simply the force of the air molecules pushing on the car, but that force increases quadratically, just like downforce. If the car goes twice as fast, you get four time (two squared) the drag.  It’s not fair: you have to work four times harder to get twice as fast. But that’s physics for you.

The argument above relied on the assumption that the drag remained constant – and it definitely doesn’t. It gets worse, because power depends on velocity cubed. So to go twice as fast, you have to overcome four times as much drag and you need eight times (2x2x2) the power.

You can estimate the terminal velocity of a racecar using some simple physics. The terminal velocity is the ratio of the power (P) to the drag (D):

EQ_TerminalVelocityPowerDrag

The maximum drag you can have is proportional to the terminal velocity squared:

EQ_terminalvelocityvsPower

Which means that the terminal velocity ends up depending on the cube root of the power!

EQ_TerminalVelocityPowerCubeRoot

If the power of an engine doubles, the terminal velocity only increases by the cube root of two, which is 1.26. If we take 200 mph as a nice round terminal velocity for a restricted engine, removing the plates and doubling the engine power to 900 hp would only increase the terminal velocity for the unrestricted engine to 252 mph.  That’s pretty surprising – you double the engine power and you only get 50 mph more.  Such is the power of cube roots.

If nature were linear, it would be a whole lot less interesting.

Many thanks to my friends Josh Browne and Andy Randolph, both excellent engineers and always willing to let me bounce ideas off them and verify that I’m not crazy.  Not, at least, when it comes to physics.

Jul 082014
 

Given all the rain at Daytona this weekend, there was plenty of time to think about auxiliary NASCAR issues.  Regular readers know that I’m a huge fan of the racing-reference.info website because they have a trove of data just waiting to be analyzed.  The spouse asked about payouts and whether it really made much of a difference for a team to get back on the track, so I plotted up some data.

I’m showing below for the Nationwide and Sprint Cup Series, the winnings as a function of position. The line is not monotonic (decreasing with each point) because of all the contingency plans, sponsor deals, etc, but the data work pretty well in terms of overall trends. I’ve plotted both races in 2014 – July (red) and February (green).

BSPEED_DaytonaWinningsNWide

Two things surprised me here:  first,  how quickly the prize money goes down and second, how small the money is in the first place, especially relative to the Sprint Cup.  You’re talking about $20,000 for finishing in the upper 30s in the July race and $40,000 in the February race. If you consider how expensive it is to just build a racecar, much less hire a driver and people for the track, that’s not a whole lot of money.

If you look at the drop off, it’s huge for the first five places. From 1st to 2nd in February, we’re talking a drop of almost $30,000. When you get out to 21st compared to 22nd, it’s less than a thousand dollars.

I thought the difference in prize money between February and July was interesting as well.  It’s even more pronounced in the Sprint Cup, as shown below.BSPEED_DaytonaWinningsThe first thing to notice is the huge difference in purse from the 500 to the 400.  The money for first place is four times as much for winning in February versus July. From first to second for the Daytona 500, you’re talking $357,000, but for the July race, it’s “only” $134,000.  If you come in dead last in February, you take home $292k, whereas last weekend, poor A.J. Allmendinger went home with a little under $70k for finishing 43rd.

That outlier at position 32 for the 500 is Paul Menard. I double checked the data at my other favorite source of racing information, jayski.com, and they have the same information. (UPDATE: as @nuggie99 points out in the comments, there was that $200,000 bonus for leading at halfway.) I have no explanation for why he’d make $200,000 more than the guys who finished immediately in front of and behind him.

For both series, though, you can see why it makes sense for teams that aren’t running all the races, or teams with limited resources, to disproportionately focus attention on the restrictor plate races. With the wild card nature of the races, getting a top five can make a huge difference in the money you take home – and thus your ability to build a more competitive team.

 

 

Jun 242014
 

This weekend, we learned that the real weather challenge for the NASCAR Nationwide Series isn’t rain. It’s not enough rain. It wasn’t raining hard enough to put on rain tires, but it wasn’t quite dry enough to safely race on slicks. (I’ve written before about why racing in the rain is hard.) But they managed to pull it off, put on a great show and @Brendan62 finally got that long-sought-after win.

When the teams switched to rain tires, the crew chiefs had to remind the drivers that their tach readings for maintaining pit road speed would be different .  I’ve written quite a bit about tach readings and speed limits:

If you know the  gear ratios in the transmission and the rear end, you can convert the engine speed (in revolutions per minute) to the rotation rate at the wheels.  How far the car moves each revolution of the axle depends on the distance around: the bigger the tire, the further the car moves. This is why your odometer and speedometer get screwed up if you don’t use the right size tire on your car.  You can check this out yourself using two tumblers with different sizes.  If you lie them on their sides and start at the same place, they roll them each one revolution, the larger tumbler will have gone further.

Rain tires have thicker tread and a larger circumference. The car moves further along with each rotation of the tires. If you don’t compensate for this in your tach readings for pit road speed, you’ll end up with a speeding penalty, even though you would have been fine at the same tach readings with the slicks on.

I couldn’t find the difference in the circumferences, but remember that teams are always pushing to get as close to the pit road speed limit as possible, so even a relatively small change in the relationship between speed and circumference can put you at the tail end of the longest line.

Jun 202014
 

 

Brad Keselowski, that never ending source of material on slow news days, had a few words about the state of American Motorsports Engineering. These quotes are from an article by Mike Pryson in Autoweek.com.

“It’s probably a larger story in itself that the American engineering pool is very shallow right now,” said Keselowski after he qualified sixth at Michigan International Speedway on Friday for Sunday’s Quicken Loans 400 NASCAR Sprint Cup Series race. “Penske is moving to any other country [to find them]. We’ve hired multiple engineers from Europe over the last three or four years and we’re pilfering everyone we can in the great country of Canada, so if you know any of them, send them our way.

“It’s just very hard to get engineers with the educational background and commitment that we need to be successful at this level from the United States. There’s certainly a shortage, not just at Penske, but throughout the garage.”

His comments (here and in the last few days) have to be interpreted in the context of their being responses to questions about why Ford (and Penske) were struggling compared to Chevy (and Hendrick in particular).  The mainstream motorsports media (try saying that fast five times) tend to want a simple answer, like “They have more horsepower”. As we know, racing is a holistic enterprise and often it’s the interplay of things and not just the things that is most critical.  And people want to reduce answers to more provocative things like “Keselowski hates American Engineers”.

I know a lot of racing engineers who found his comments derogatory. It reminded me of being in grad school and always hearing the professors complain that they needed “More and better graduate students”. When I finally called on on this and told him it bothered us, he looked at me blankly. “We don’t mean you guys. You guys are great. It’s our applicant pool…”

Sometimes a little clarification makes a huge difference to the people involved. The big thing I got out of it after reading all the media reports I could find about Keselowski’s comments was that he said that Penske got a very small number of applications from highly qualified American engineers.

Let’s look at the numbers. In 2012, according to the American Society for Engineering Education, 88,176 bachelor’s level and 49,372 masters level engineering degrees were handed out.  There were 1.7 million bachelor’s degrees in all fields, which means that engineering degrees make up only 5% of all bachelor’s level degrees. Compare that with Japan and Chine where engineering degrees are 50% of the degrees granted.  That’s for all fields of engineering. Most people working in motorsports have degrees in mechanical engineering (few schools offer a dedicated motorsports engineering degree), which is somewhere around 20,000 degrees at the bachelor’s level and 6,o00 master’s level degrees. (85- 90% of mechanical engineering degrees are earned by men, incidentally).

The schools that offer motorsports engineering degrees are schools like Indiana University – Purdue University at Indiana (IUPUI), UNC-Charlotte and the University of Northern Ohio.  In fact, UNC-Charlotte boasts that 10% of NASCAR engineers come from UNC-Charlotte.  Other schools, like the University of Colorado – Denver offer motorsports specializations within mechanical engineering. Nothing against these schools. But if I look at the engineers I know who are successful in NASCAR, they’ve got degrees from places like Northwestern, Duke, Penn State, Stanford, Carnegie Mellon.  Newman went to Purdue. Those universities attract a different level of student. Nothing against folks who went to a small state school. I did. But if you want the best and the brightest, you’ve got a higher likelihood of finding them at the elite engineering schools.

Europe, in particular, has a well-established stream of motorsports engineering because of the high technical level of F1. I was at Oxford On Brookes in England a few years ago and their facilities and program are amazing. Well ahead of most of what we have in the States.

The numbers are small to start with, and I think three factors narrow the pool:  Money, work environment, and personal goals.

The mean annual wage for mechanical engineers, according to the U.S. Bureau of Labor is $85,930 – and it’s much higher (over $100,ooo) in select field like energy.  I started off thinking salary wasn’t an issue because teams like Hendrick and Gibbs have very deep pockets and understand how important it is to have strong engineering. On second though, few people get to start with the big teams. So salaries may  be a contributing factor to there being a smaller application pool. If someone’s faced with a starting salary from an auto manufacturer or a  Nationwide-only team, the production car job might look a lot better.

Even if the salary is high, you have to consider the job responsibilities relative to the salary. NASCAR engineers work in an extremely high-stress, rapid output environment. They have to work with a broad range of people, from mechanics to public relations people (to drivers, some of whom are not shy about throwing their teams under the bus when they don’t finish well). Failure in motorsports is extremely visible. If you are slow, the whole world sees it. Many engineers spend a significant amount of time on the road, away from family. Even those that don’t travel as part of the raceday team are involved in testing.  A lot of people don’t want an eighty-hour-a-week, high stress job.

Finally, there’s the question of what you want out of your career. People I know who have worked in motorsports and left are working in everything from production car development to trying to make the country less dependent on foreign energy sources. A number of them enjoyed motorsports, but there are bigger and more significant problems in the world than making cars go fast. People want different things out of life. You have to really like racing to make a career of it.

Keselowski pointed out as much in a tweet.

kestweet

 

 

But that didn’t make it into any of the stories, of course.