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 132014
 

You are hurtling down the frontstretch at Michigan, your speed approaching 215 mph.  Your seat moves up and down as you hit the seams, but your focus is squarely on getting into Turn 1 losing as little speed as possible.  You squeeze the brakes and feel yourself moving forward, only to realize that you’re still moving too quickly. As the car starts to head toward the wall, you panic and squeeze the brake even harder.

The car snaps loose and the next thing you feel… is an engineer’s hand on your shoulder.  You turn around to see her barely suppressing a smile.

“Let’s try that again. Maybe you want to brake earlier this time, huh?”

The latest racing simulators are far more involved than your steering-wheel-feedback-enabled video game. When you hear drivers talk about using simulators to familiarize themselves with new tracks, you are only hearing about the surface layer.

Ford opened a new Racing Technology Center in Concord NC just about a month ago.  The old Ford facility used to be called “The Shack” because of it’s size. The new facility, which is across the street from Roush Fenway Racing, is 33,000 square feet. One of the main features is a driving simulator similar to the ones that F1 uses.  Five screens provide a 180-degree view for the driver. The cockpit is the front half of a NASCAR Sprint Cup car that is set on a full-motion platform.  The platform duplicates the exact motions you would feel in the car – bumps, slips, sways, yaw.

Let’s move away from the driver for a moment, because he (or she) is a relatively recent addition. All race teams use vehicle dynamics simulations: computer programs that predict lap times for specific setups. A crew chief changes the setup on the computer – camber, cross weight, track bar, etc. – and can see in advance whether the changes make the lap time better or worse.

DriverintheLoop2

Simulation programs have to be validated, meaning you have to make sure they correspond with reality. Every team also has (or rents time on)  K&C and seven-post rigs.  (K&C stands for Kinematics and Compliance – I’ll be getting into those in upcoming posts.) These machines attempt to quantify how the car responds to external changes, like turning, bumps, etc.

Engineers thus went back and forth between theory (the simulations) and experiment, developing a model of the car, testing it against how the car behaved, and then refining their model.  (Unsurprisingly, this is exactly how scientific research on things like alternative energy sources and cancer works.)

This is a great model for the Google driverless car. But that’s not how racing works. Racing requires a living, breathing, thinking (hopefully) human being in the seat who has to constantly take in information, process that information and act on it.

And that’s where racing simulators are moving. The buzzword is “Driver in the Loop”, which means that you’re creating a model that includes the driver.  This is not an easy step. Drivers are very different in terms of their preferences for set-up, what they’re comfortable driving, how loose they’re willing to be early in a run to make the car faster later, etc.

The simulator in the new Ford Tech Center is a sled-type simulator. Less advanced models have hydraulic pistons that raise and lower the cockpit to simulate bumps and change attitude.  The sled can actually duplicate all six types of motion: three linear motions (up/down, left/right, front/back) and three rotational degrees of freedom (yaw, roll and pitch).  This motion platform was developed by a British company called Ansible Motion and the picture below is from their website. You can see the sled rails at the back, and the 180+degree surround on which the images of the track are displayed. The steering wheel provides feedback to the driver and even the seatbelts are cued in so that when you brake, the seatbelt tightens just as it would in a real car. Ansible is the same vendor that worked on McLaren’s F1 simulator. The Ford folks claim that this design has a much faster response time, meaning that the time between when you turn the steering wheel and when you feel the result, is shorter and more like real life.

AnsibleMotionPlatform

 

 

At present, they’ve got ten tracks in the library for the new simulator – eventually they will have all the NASCAR tracks and, since the Tech Center is meant to support all of Ford’s motorsport activities, they will be able to change out the cockpit to, say, a Daytona Prototype, and including tracks like Sebring.

So far, I’ve made it sound like they’re just one-upping iRacing, but a prime feature of the center is that there is a whole room associated with the simulator that is filled with engineers who are watching both the driver and the racecar input/output data.  The driver is being assimilated into the simulations. This is why it’s called “Driver-in-the-Loop” simulation.
DriverintheLoop

 

On the one hand, the driver will help validate all the models.  If there’s a bump on Pit Road at a track that gives a driver trouble, he or she will recognize when it’s not in the model of the track used by the simulator. (And since tracks change significantly, the models have to change to keep up with reality.)

While we’re talking tracks, let’s point out that the track models aren’t made by someone sent out with a tape measure. Tracks are laser scanned to a resolution of a few millimeters. Every dip and bump is recorded and used in modeling the tracks. Laser scanning not only collects three-dimensional location information, it looks at the quality of the reflection.  Laser scanning can differentiate between a white painted line and a yellow painted line, between two different lanes of asphalt, or even skid marks. When you’re traveling at top speed, any surface irregularity becomes important because all it takes is for the car to be throw a little out of equilibrium and you’re in the wall.

In addition to the track, the driver can also provide feedback about whether the “car” responds the way it does in real life. But at the same time the driver is evaluating the simulator elements, the engineers are evaluating the driver. They can start to look at things like how a particular driver’s comfort level may dictate a different line for them relative to another driver. They can run repeated tests to find out how constant a driver is. Do they brake the same way going into Turn 1 at Charlotte every time? Or are they hyper aware of something like tire fall off and able to tailor their braking to the condition of the car?  This type of research has great potential to improve communication between the team and the driver.

Skeptics will worry that we’re getting uncomfortably close to a situation in which we have a bunch of engineers sitting around driving the racecar via remote control and the driver is no more than a warm body executing commands as he’s told. The beautiful thing about human beings is that you can’t model a human being. Having done research in both physics and science education, there’s a huge difference between measuring electrons and measuring people. You kick an electron twenty times and it will pretty much do the same thing each time. You kick a person twenty times and (aside from the danger of being kicked back), you’ll get at least ten responses depending on the person’s mood.

It’ll be interesting to see whether tools like this can help the Ford teams (especially Roush Fenway Racing) catch up to Chevy.

May 282014
 

Everyone’s favorite “planet” killer had a spare hour because COSMOS was pre-empted Sunday by the Coca Cola 600.  Astrophysicist Neil deGrasse Tyson edified us with some “NASCAR physics”.

NDGTweet1

NDG2

There were 43 drivers who had no problem taking the corners at more than 165 mph without skidding into the “embankment” and a couple million viewers who knew instinctively that these were not correct statements.

CarTurning

Some basic physics. A car going around a racetrack in a circle is no different from a ball on a string being swung in a circle. In both cases, the reason the object makes a circle is because there is a force that point toward the center of the circle at all times. For the ball, it’s the string. For the car, the tires generate that force through friction between the tires and the track. The car tries to slide away from the center and the tires keep it from doing that.

The amount of force the tires generate is proportional to the force pushing down on the car. If you slide a tire across a parking lot, it takes you a certain amount of force.  If someone sits on the tire, you need more force to pull it. The force the tires generate is given by:

FismuN There are two forces pushing down on a racecar: the weight of the car (which provides mechanical grip) and the aerodynamic downforce (which provides aero-grip). Let’s ignore the downforce for a moment because it gives car more turning power and lets it reach higher speeds, so it only helps the argument.

If you look at a flat track, all of the frictional force is in the direction you want it to go – toward the center of the turn.

CaronFlatTrack

 

I’m showing three forces: The track exerts a force on the car equal to the car’s weight. The frictional force is toward the center of the turn, as required.

In most situations, the coefficient of static friction (the μs) is less than one, which means that you get less frictional force than the weight of the car. For regular tires on asphalt, for example, you only get 70-80% of the force pushing down.  On ice, you get maybe 10-20% of the force. Racing tires are different. They take advantage of some really interesting physics, which is that of adhesive friction (versus abrasive friction, which is what we all learn about in school).  Rubber is a truly amazing material. While the actual coefficients of friction for specific race tires are closely guarded, you can use 1.2-1.3 as a good approximation.  The 165 mph number Tyson came up with is a result, I believe, of having used the coefficient of friction for regular tires, not race tires.

Now throw in banking.

BankedTrack

The directions of the forces change. Except gravity, which (on Earth) always points straight down.

The track always pushes perpendicular to its surface, so now part of the force from the track is pushing up and part is pushing toward the center – the banking helps the car turn.  The higher the banking, the more help you get turning.  If the track had a banking angle of 45 degrees, half the track force would be pushing up and half would be helping the car turn.

If you’re paying attention, you’ll notice that the frictional force (which always acts parallel to the track surface) also changes direction. In fact, the amount of frictional force in the direction you need to turn actually decreases a little; however, you get such an advantage from the banking that it compensates for the loss due to the frictional force.  (Of course – otherwise, no one would bank tracks.)

The calculations (without aero) are pretty straightforward and standard in many intro physics courses.  Hyperphysics is my go-to reference for basic physics when I don’t have a textbook handy.  You can follow them through the whole calculation to get the equation that shows the maximum velocity is determined by the radius of the track (r), the static coefficient of friction between the track and the tires (μs), and the banking angle of the track, θ and the acceleration due to gravity (g).

vmax

The parameters are easy to look up. g has a value of 32.2 feet per second per second (ft/s2), the turn radii at Charlotte vary (

At Charlotte, the turn radii are 685 feet (turns 1/2) and 625 feet (turns 3/4)  and the banking angle is 24 °.  Hyperphysics even gives you boxes and lets you plug numbers in on their site, so you can play around to see how the maximum velocity changes with the parameters.

The important thing here is the difference in friction between race car tires and regular tires. Race car tires are made of a different composition of rubber. They get much hotter than passenger car tires and the surface layer of the tire actually melts a little bit. Rubber gives additional grip in a way I like to describe as what happens if you step on a piece of chewing gum on a hot day. The chewing gum sticks to your foot and prevents you from moving – a slightly different type of friction.

Physics classes rarely teach students about materials that aren’t pretty well-behaved solids. Stretchy, squishy materials like rubber or any type of liquid introduces a lot of complications. I had been teaching physics for 15 years before I learned  you could have a coefficient of friction greater than one.  So it’s not too surprising Tyson didn’t know it either.

However, as my friend James Riordan points out, theory always has to be checked against experiment. And that’s part of what’s so annoying about this. All you had to do was watch the race to know this upper limit was incorrect.  A huge number of media outlets re-tweeted these ‘facts’, or featured the tweets as they exclaimed how wonderful it was that an astrophysicist was explaining NASCAR to its fans.  Sorry folks – NASCAR fans are smarter than they are given credit for.  There’s a level of complication and sophistication to the sport that people who have never paid attention to it simply don’t appreciate.  Sure, NASCAR isn’t F1 – but there aren’t many of the high-level teams that don’t have at least a few Ph.D. level aerodynamicists and mechnical or chemial engineers on the payroll. It’s a must if you want to be competitive.

 

May 272014
 

Okay. COSMOS was pre-empted Sunday in favor of the Coca Cola 600 and COSMOS host, astrophysicist Neil deGrasse Tyson, decided to edify us with some NASCAR physics.

NDGTweet1

NDG2

 

I bet 90% of NASCAR fans immediately know there’s something wrong here. In fact, all you had to do was watch the broadcast.  I’ll write a longer post, but here it is in brief.

The calculation for a car rounding a banked track with friction is pretty straightforward. There are a lot of angles in it, but if you work through it, it does make sense.  Check out hyperphysics for the details. The important thing here is that the maximum velocity is determined by the radius of the track, the coefficient of friction between the track and the tires, and the banking of the track.

banked

 

where r is the radius of the track, θ is the banking angle and μs is the coefficient of static friction. I know, it looks complicated, but stay with me.  The next paragraph is just the important stuff.

At Charlotte, the turn radii are 685/625 feet (the two turns are different, depending on whether you’re going into the dogleg or the backstretch) and the banking angle is 24 °.  Hyperphysics even lets you plug in numbers on their site, so I could very quickly determine that 165 mph is what you would get if you assumed a normal coefficient of friction between a regular tire and an asphalt track (around 0.75).  The reality is that NASCAR tires have a much higher coefficient of friction, which is why they easily exceed 165 mph and have no problem staying away from the “embankment” – whatever the heck that is.

Details to follow, but I wanted to get this up because I’m getting flooded with questions.

 

 

May 092014
 

OK, so ‘monozone’ is just a fancy way of saying it’s the old tire.  It’s all in the branding, isn’t it?

Goodyear has been experimenting with multi-zone tires since last year.  Multizone tires attempt to get the best of both worlds by combining a harder compound on the inner 2-3 inches of the tire (for wear resistance) and a softer compound across the rest of the tire (for grip).  I went over the reasons for the need for a tougher inner shoulder to the tire and why the new camber rules in a good amount of detail previously.

Multizone tires were a hit last year in Atlanta, but not as praised much in Kansas.  Likewise, this year the tires made for great racing in Texas, but the Richmond race featured a lot of tire wear and some unhappy drivers.

Goodyear tested a multizone tire at Kansas Speedway on April 14th this year. They weren’t happy with the results and have opted to go with a monozone tire at the race.  They used a combination of information in the historical record regarding previous compounds used at Kansas, along with lab testing to develop a new monozone right-side tire.  The compound is slightly different than the grip-centric compound that had been used on the multizone tires.  The same left-side tire will be used as has been used previously.

Given that Goodyear starts making tires for Daytona back in October, it’s pretty impressive that they were able to generate the tires for the race in a little under a month.

The problem seems to be excessive wear on the inside edges of the tires. I covered the reasons for this previously, but those reasons are exacerbated when you’re at a track with a lot of grip.  This means that the problems are more likely to rear their heads at grippy tracks (i.e. newly paved tracks) and during night races because the cooler temperatures result in more grip.  The other factor is high loads on tires, especially transient (i.e. short-time) loads.

Larry MacReynolds pointed out this morning on SiriusXM NASCAR radio that the teams have the car suspensions set up to be be rather stiff.  In the corners, there isn’t much springy in the car except the tire – the tire becomes the only point with any give. That puts a lot of stress on the tire.  Corner speeds have also been much higher this year – and that’s were much of the load comes about.

The one common thread I’ve heard is that there is a very small window between ‘fine’ and ‘oops’ – the tires are good for a long time and then they just go.  This is a problem because you don’t get much predictability – there’s no way they can run enough testing during practice to know that they can go 54, but not 55 laps before the time starts wearing enough to get into the danger zone.

Related Posts:

 

May 012014
 

We’ve heard a lot, especially this week at Richmond, about tire wear.  A lot of right front tires were wearing excessively.  As seems to be usual at this point, teams would like Goodyear to use a stronger tire and Goodyear would like teams to dial back their setups, especially their camber.

What’s Camber?

Camber is the tilt of the wheels relative to the vertical.  If the top of the wheel is father out (away from the car’s centerline) then the bottom, it’s called positive camber.  If the top of the wheel is closer than the bottom, it’s negative camber.

CamberIllustrated

Turning Left

On oval tracks where all the turns are left, they use negative camber on the right wheel and positive camber on the left.

CamberIllustrated_TurningLeft

NASCAR opened up the range of allowed cambers on the Gen-6 car.  In 2013, the front wheels could have up to 9 degrees camber and the rear wheels 3.5 degrees.  Clint Bowyer even tweeted about having blown the setup by being over agressive.

Although this makes turning easier, it means that the cars are riding on the edges of their tires when they’re not turning.  See how the inside of the right tire is the lower part?

The camber isn’t the only issue.  When you change direction, brake or accelerate, the car shifts (called load transfer).  When you turn left, the load shifts right.  When you brake, it shifts forward.  So if you brake hard while turning left, or if you have a suspension setup that allows a lot of shifting, you’re going to put a big load on the right-front tire and that also stresses the tire.

Goodyear used their dual-tread tire on the right-side tires at Richmond, where the rightmost ten inches are softer rubber and the innermost two inches are harder – but they were still having problems with cording on those inner edges of the right front tires.

Stu Grant, Goodyear’s General Manager of Global Race Tires, noted that “the operating window between acceptable wear on the right front and unacceptable wear is pretty small.”  Tires seemed to do fine up to a point, and then went catastrophically.

While Goodyear’s decided they’re going to look at the tire wear before this Fall’s Richmond Race (which will have a lot on the line), the teams are also going to have to do some set-up searching and decide how much of a risk they want to take with high levels of camber.

 

 

Mar 272014
 

LasVegas

I know this isn’t a picture of California.  But it’s a picture out my window, which is why this is a sort of short post.

There seems to be a clear division between the people who are upset about the tires Goodyear brought to California and the people who aren’t upset about the tires Goodyear brought to California.

The people who had problems are upset.  The people who didn’t have problems aren’t upset.

Here are the facts:

  • Goodyear brought the same tire they brought in 2013 – the first year of the Gen-6 car, which featured weight reductions, higher speeds, and higher loads.  The same tires (D4522 on the left/D4408 on the right) were used in 2012.  There weren’t a lot of complaints after that race – in fact, those two races have been cited as some of the most exciting races at California ever.
  • NASCAR tweaked the aero package and the suspension setup rules between 2013 and 2014.  The biggest suspension change was the removal of the minimum front ride height. These were relatively small changes compared to the changeover to the Gen-6 car.
  • California continues to change as a track.  The seams between lanes are getting more pronounced.  The bumps down the backstretch are getting bigger.
  • The teams continue to improve their setups as they learn more and more about the Gen-6 car. They are moving closer and closer to the edge of stability in an effort to make their cars faster.

Goodyear looked at the changes and considered how they would affect the current tire. In the end, they opted not to change the tire.  I have no way of knowing how much notice Goodyear had of the suspensions/aero changes for 2014.  They start making Daytona tires in October of the previous year, so they need a minimum of 3-4 months advance notice.

The teams knew about all these changes, and knew that Goodyear was bringing the same tire.  Most teams likely started off with something close to their fastest setup from last year.  A number of the drivers mentioned they had to back off their setups from practice because they weren’t happy with tire wear. That’s part of setting up a car – taking into account changes from the last time you were at the track.

NASCAR is still looking into the issue, but their initial impression was that the teams were too aggressive with their set ups.  They cited very low tire pressures as one reason for the failures, many of which appeared to be sidewall related.  Goodyear recommends 20-22 psi in the left-side tires and apparently some teams were starting off at 11-14 psi.  (Most of the failures were on the left side.)

Teams have always started out with low pressure in the tires because tire pressure increases as the tires heat up.  If you put the pressure you’d like to have in the tires at the start, it would quickly get higher than you want it to.  So you start with a low pressure and let it build up.

The problem with very low pressures is that instead of the air in the tire supporting the car, the tire sidewall is supporting the car.  This puts a lot of stress on the tire and, given how punishing a full fuel run is on tires, the stress can, over time, lead to early tire failure.

This is a very common pattern with race car setups.  NASCAR makes changes, Goodyear tries to anticipate how the tires will behave under the likely setups.  Teams try setups, make changes and Goodyear tries to keep up with the changes.  I suspect the reason we’re seeing the problems this year and not last is that the teams have become more bold with their setups.

It’s a never-ending iterative process, with Goodyear trying to anticipate the effects of new setups, rules changes and track changes, and teams constantly pushing the envelope.

That’s the challenge, though.  How much are you willing to risk to get just a little more speed out of your car?

Feb 282014
 

Repaving is the last possible remedy a track wants to use, but when potholes (see: Daytona) show up, there is no choice but to tear up the old asphalt and replace it with new, fresh blacktop.  In the last few years, Daytona, Phoenix, Michigan, Pocono and Kansas have all been repaved.

We hear a lot from race teams about their ‘notebooks’ – the collected wisdom and experience from prior experiences at a track.  When that track is repaved — or reconfigured — the notebook pretty much goes out the window .  They have to start over.

They’re not the only ones.  I had a chance to talk with Greg Stucker, Manager of Race Tire Sales for Goodyear as part of an article I was working on for a British publication called Race Cup Technology about the many challenges inherent to ensuring that the tires provided to the teams are safe and fast.

Goodyear doesn’t categorize tracks the way most of us do, with the superspeedways, mile-and-a-halfs, short tracks and road courses. They have to take into account not only length, but the track surface and the loads the tires experience.

Venue Groupings

Grouping Tracks
Group 1 Daytona, Talladega
Group 2 Charlotte, Chicago, Darlington, Homestead, Kansas, Las Vegas, Michigan, Texas
Group 3 Atlanta, California, Dover, Kentucky
Group 4 Bristol, Indy, Iowa, Phoenix, Pocono
Group 5 New Hampshire, Richmond, Gateway
Group 6 Martinsville
Group 7 Sonoma, Road America, Mid-Ohio, Ontario, Watkins Glen

This results in seven “venue groupings”, with superspeedways and road courses in their  own categories.  Martinsville, that unique concrete corner/asphalt straightaway hybrid also stands in a class by itself.  The remaining tracks are categorized into four groups.

Although Atlanta and Kansas have similar length and shape, they are in different groups. Atlanta’s surface is much older and rougher.  Speeds are higher.  That places different demands on the tire than a smooth, newly paved surface like Kansas.   Goodyear’s categories change almost yearly as tracks age and are repaved.  Kansas used to be in the same group as Atlanta prior to the former’s summer 2012 repave.

You wouldn’t think that Bristol, Iowa, Indy, Phoenix and Pocono had much in common, but as far as tires are concerned, they are all in the same group because of the combination of track surfaces and loads.

There’s another dimension to consider here:  time.  Michigan and Kansas  - two tracks in the same venue grouping – were paved within six months of each other.  Stucker points out that the surfaces aren’t aging the same way.  This is a combination of on-track activity, and the vagaries of weather – how extreme the temperature changes have been, how much moisture the tracks have sustained, etc.

Goodyear is starting a new program to record representative three-dimensional images of track surfaces as a function of time so that they can develop a better understanding of how track surfaces age.

The track-mapping project uses a technique called fringe projection.  Imagine that I create a pattern of alternating light and dark stripes, similar to the one in the upper right hand side of the graphic below.

FringProjection1

I’m going to project that pattern onto a surface and use a camera to capture the reflection.  A perfectly smooth, regular surface will not distort the pattern; however, if there are any irregularities – bumps or voids for example, then the stripe pattern will be distorted.

By varying the pattern and the angle at which the pattern is projected and recorded, you can use some very fancy mathematics to work backward and determine the shape of the surface that’s responsible for the distorted reflection.

The picture below shows you an example of a stripe pattern and the effect of shining the stripe pattern onto a toy fish.

FringeProjection2]

Goodyear’s project will produce a series of 1.5 by 2-inch samples that can display details as small as three micrometers  (about one ten-thousandth of an inch).   This is smaller than the diameter of a red blood cell and about a tenth to a thirtieth the diameter of a human hair.

This surface-mapping project will help clarify both the smaller year-to-year changes of track surfaces due to weather and use, but also will provide information on how major changes like whole-track resurfacing or reconfigurations affects the racing.

Stucker points out that track technology constantly changes.  You can’t compare the most recent repave of Daytona with the repave more than a decade ago.  One big difference is that the binder – the black sticky stuff that sticks the rocks together –  tends to be much denser than it used to be.  The denser binder prevents water penetration and is more durable, which should decrease how frequently the tracks have to be resurfaced; however, that increased density means that it takes a lot longer for the track to start showing signs of wear.

It’s a cool application of a new technology that is being applied to a large number of possible uses.  The “light” used for these measurements can be any type of light, including lasers, visible light and/or infrared or radio waves, depending on the particular data desired.  This technology is used in Microsoft’s Kinect camera, which is used on the XBox to translate a user’s motions onto a computer display.  That system uses infrared light. Other applications include 3D imaging of the mouth (for dental work), of vascular walls, for facial reconstruction, corrosion analysis and failure evaluation.

 

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