Stock Car Science

Just when you think things can’t get any busier, they do. It’s the end of the fiscal year at my university, which means getting buried in a mound of paperwork. We’re doing three workshops this fall for teachers on using NASCAR to get kids interested in math and science, plus I’m giving a number of talks around the country. The next talk is in Richmond VA on Thursday, September 4th at VCU. I’m really excited about a project we’ve just started with the Dallas Museum of Nature and Science that will culminate in a week of activities at the museum prior to the Texas race November 2nd. We’ve got lots of support from the track and Office Depot on that event, so I hope to see some locals there.

I am cleaning out my mailbag and realized I have a couple questions I haven’t answered, so here they are:

What are tire codes? What do they tell the driver about the tire?

They don’t actually tell the driver a whole lot, but they are very valuable to the tire specialist and the crew chief

You can find a lot of information about tires. I usually look on jayski’s race pages, but the information comes from Goodyear and is public domain, so you may find it in other places. If you look at last February’s California race, you’ll find:

Number of Tires: Left-side–1,525, Right-side–1,525

Tire Codes: Left-side– D&ndash4146; Right-side– D&ndash4150

Tire Circumference: Left-side–87.3 inches; Right-side–88.6 inches.

Technical Inspection Inflation: Left Front–30 psi; Left Rear–30 psi ; Right Front–48 psi; Right Rear–45 psi

Minimum Recommended Inflation: Left Front–22 psi; Left Rear–20 psi; Right Front–45 psi; Right Rear–42 psi

Estimated Pit Window: Every 40-44 laps, based on fuel mileage

Let’s see what we learn from that. First, there are a heck of a lot of tires. For comparison, they bring about 525 tires for the Nationwide Series when it runs at California. If you figure 44 teams, that’s 35 sets of tires per team. Normally, teams get six-seven sets of tires for practice and qualifying, and 10-16 sets of tires for the race. The exact number depends on the length of the race and number of practices. For example, Richmond in two weeks is an impound race and there is one practice. There will be three practices this weekend at the track I’m trying really hard not to keep calling Fontana.

The teams have their wheels delivered to Goodyear. Every wheel has the team name on it so Goodyear knows who gets the tires. Goodyear has to mount and balance all of the tires for all of the teams. In the lower left of the picture below (about 7-8 o’clock), you’ll see two silver things and lines drawn in silver Sharpie (the best thing for writing on tires with!). Those are weights that are added to balance the tires. The writing is there so that if the tire comes back without the weights, the team can tell that there was supposed to be a weight there. Some time the chatter in a tire is due to unbalanced tire.

The tire codes (D-4146 and D-4150) are Goodyear’s way of identifying specific tire recipes. Different code means different type of tire. With the exception of the road courses, you’ll always see different tire codes for the left and the right. The left-side tire is softer. Left-side tires don’t carry as much load as right side tires (because we always turn left). If you made the two sides wear equally, the lefts wouldn’t wear as much as the rights. You’ll also notice that the left and right-side tires have different circumferences, which I’ve explained elsewhere.

Tires with different tire codes can have different tire wall construction, different types of cords, and different types of rubber for the tread. Goodyear usually runs 20-30 different tires during the course of a season. Some are particular to particular tracks (i.e. Indianapolis is a special case), and others you’ll find run in a number of places (like 1.5 mile intermediate tracks).

In addition to the tire code, there is also a barcode (which you can see at about 7 o’clock in the picture). The tire code is like a zipcode. The barcode is like an address. The barcode tells the tire specialist (the full-time person at the track who does nothing but deal with tires) what mold number was used to make the tire, what day the tire was made, and what shift the tire was made on. Goodyear had experienced a strike toward the end of 2006/start of 2007 and I remember the tire specialists at Atlanta in 2007 identifying which tires were made during the strike

The tire specialist reads the barcodes and can download all of this information at the track from a Goodyear database. The tire specialist then groups the tires into like sets. He or she (and yes, there are some women tire specialists) tries to group tires according to date and time made, mold number and circumference. Making tires is an incredibly imprecise process. You’re putting something in a mold and then basically steaming it. Not all tires will shrink to exactly the same size, so they measure the circumference of each individual tire.

The crew chief then looks through the tire specialist’s group and sometimes will ask the tires to be regrouped if the crew chief thinks there is a more optimal pairing. They want each set of right-side and left-side tires to be as similar as possible. The tire sets are given numbers (1, 2, 3…) and the crew gives the tire specialist an idea of what order he’d like the tires to be on the car. If you are on pit road right before a race, look for long strips of masking tape with numbers on the back of the box. That’s the order of the tires the crew chief has dictated. You may see similar strips of tape on the front pants legs of the race engineer. I’ve seen a couple of them keep a copy of the order there for easy reference. The numbers are, of course, upside down so the engineer can read then when he’s sitting.

Two sets of pressures are given: one set is the set the tires are expected to be at during tech inspection. Note that the left sides have lower pressures because, again, the left-side tires carry less load than the right-side pressures. Goodyear mandates minimum tire pressures. The NASCAR official in each pit checks the pressure of one of the front tires to make sure it is above minimum. They don’t need to check all because you need the tires to be balanced. If you fill one tire to the right pressure and underfill the others, you’re going to have a squirrelly car. (Yes, Marc, “squirrelly” is a technical term. I know you were going to ask.)

Can drivers tell when there’s a mismatched set of tires? Some can. It usually depends how mismatched they are, or if there’s something else going on (like lug nuts not being tightened enough).

For those of you wondering, the tire in the picture is from Junior’s car in 2006 October at Lowe’s. The pink lines are meant to help the tire changer register the lugs faster. There’s an experiment waiting to be run–see if the pink on the lugs and/or the hubs actually makes a difference. I’ve seen studies about general visual accuity, but not about pit stops per se.

What kind of wave was the crowd doing at Bristol?

Physics teachers everywhere thank you for that question. That was a transverse wave. A transverse wave is when the things making up the wave (in this case, people), move in one direction, but the wave itself moves in a direction perpendicular to the direction the people move. The wave moved around the track, but the people moved up and down.

The other kind of wave is a longitudinal wave. A longitudinal wave moves along the same direction the things making up the wave move. To do a longitudinal wave, you’d stay seated and move to your left or right. Sound waves are longitudinal waves. Next spring at Bristol, I think they ought to go for the world record for the largest longitudinal wave. I think it would be easy to break because I’m not sure the Guiness people differentiate between them. But we’d know.

Why would a good team like Gibbs cheat?

I’ve been doing a series of interviews for ‘hero cards’ we’re making for the people who use math and science to make cars go fast, so I’ve gotten to ask a lot of people some very personal questions. I learned two things. First, people who work in NASCAR are competitive. I realize most people don’t associate ‘engineer’ with ‘competitive’, but the people who are are the top are definitely very competitive. Secondly, working in NASCAR, even if you have a job where you don’t go to the track, is extremely stressful. Things are very close and the stakes are large when you’re talking about holding on to sponsors, drivers, crew members, etc. I hadn’t appreciated how much pressure people who work for race teams feel. If you’re at the top, it’s the struggle to stay there, to avoid getting paranoid that other teams are starting to gain on you and that maybe you’re missing something that’s going to turn out to be really important in three or four races.

I’m not condoning cheating, especially if it’s the stupid kind (as opposed to the innovative kind where you sort of have to chuckle a bit and appreciate either the guts or the brain it took to try it). Even very honorable people sometimes do things they wouldn’t normally do if they weren’t under pressure. Either Joe or J.D. Gibbs made a comment that the folks involved were good employees. They’ve given up a lot for the team. (Ask how many people who are on the road for a race team have missed anniversaries, graduations and birthdays). Gibbs said that these employees made mistakes, but they had the confidence that they were one-time judgment lapses, not character flaws. If anything questionable happens with one of these people again, however, I wager that they are going to be out the door.

On the other hand, there is still a culture of glorification of cheating in NASCAR. We had our own scandal in physics a couple years ago, when a guy who worked at Bell Labs (The Hendrick Motorsports of NASCAR) was caught using the same graph in two different papers–with two different axes. He was no doubt a smart guy. But they ended up firing him and his university revoked his Ph.D. The community even had an interesting discussion about whether his supervisor ought to bear some of the blame for not keeping close enough track of his employee (or whether he even knew about it). It was not a shining moment for the field of condensed matter physics.

Hendrick Schon, the scientist in question, eventually got another job in science. The rumor is that the person who hired him said, “He must have something going for him because he fooled so many smart people for so long.

I keep telling my physics friends that there are lots of similarities between physics and NASCAR.

I have never seen Robin Pemberton looking so disgusted as he did during an interview replayed on NASCAR Now Monday evening. (Well, maybe not since Daytona 2007.) NASCAR did a chassis dyno test after the Michigan race on a number of NASCAR Nationwide cars. They found 1/4-inch-thick magnets underneath the accelerator pedals of the 18 and the 20 Joe Gibbs Racing cars. To their credit, JGR took responsibility, apologized and started an internal investigation to figure out who was responsible.

You may have heard some strong reactions from some of the other owners. One of the reasons for the animosity is that Toyota runs the same engine in Cup and Nationwide, whereas the other manufacturers have to maintain separate engine programs for the two series. I know that some of the companies that run both series have 90% of their engine shop dedicated to Cup engines, so there’s some resentment that Toyota only has to run one program.

The facts: The purpose of the magnetic shims was to prevent the accelerator pedal from being pushed all the way down. In a carbureted engine, pushing the accelerator pedal opens valves in the carb. The more you push the pedal, the more the valves are opened. The valves regulate how much of the air/fuel mixture enters the engine. The wider the valves are opened, the more air/fuel mixture goes into the cylinders and the more energy is produced. If you prevent the pedal from going all the way to the floor, the throttle doesn’t open all the way and you produce less horsepower.

As you probably remember, NASCAR gave Toyota a more tapered tapered spacer than the other manufacturers after engine dyno numbers showed that the Toyota engines had a 15 hp peak horsepower advantage. The cheat was an attempt to have the Gibbs Toyota engines show lower horsepower than the engine actually was capable of and (I guess) either make NASCAR feel guilty that they penalized Toyota too much, or prevent further reductions of the tapered spacer. Some thought must have gone into how thick a magnet they needed: If they had knocked the horsepower down too much, it would have looked suspicious.

Why magnetic shims? You could have accomplished the same thing with a non-magnetic shim; however, you would have had to have come up with a way to hold the shim in place, like glue or tape. NASCAR mandates the use of magnetic stainless steel in the car. A rare-earth permanent magnet will stick really really well to magnetic stainless steel. I have a couple neodymium-iron-boride magnets that you literally have to keep a piece of cardboard between becuase if they get stuck together, you’re going to have a very difficult time getting them unstuck. So all the folks who are wondering if those magnets they claim you can put around your gas line to save money actually work, forget it. They don’t. The only reason a magnet was used was because it could be put there quickly, would stay put, and could be removed quickly. They could have used plastic or non-magnetic metal and had the same effect on the throttle action; however, the high heat in the car might have softened any adhesive or tape used to stick it in place or the driver might have knocked it loose.

Every report I’ve heard says that the magnets were in place during the race. (correction) As the story has evolved, it appears now that the crew members derived a ploy about needing to retrieve a forgotten notebook to get into the car after the race, so it now appears as though the magnets were NOT in the car during the race. (correction) Given how closely the cars are watched (especially the 20, which finished 3rd), there wouldn’t be many possibilities to slip something in place (although doing so would only have taken a very few moments). At Milwaukee, where NASCAR did engine dyno tests, the cars pulled off the track and headed toward their haulers, but the NASCAR officials stopped all the cars just inside the garage gates. None of the teams seemed to know what was happening until they got the word that there were going to be engines selected for dyno testing. The only other possibility I can think of would be the driver moving the magnet into place after the race and I just can’t see Tony Stewart going for that.

What makes the decision to try this even more questionable is that this was to be a chassis dyno test, not an engine dyno test. In a chassis dyno test, the cars are rolled up onto a mobile chassis dyno, which is a platform that has a large massive drum on which the rear wheels are placed. The car is strapped onto the platform and when the throttle is pushed, the rear wheels turn the drum instead of moving the car. If I remember right, NASCAR uses a DYNO-mite dynamometer.

A chassis dyno test doesn’t test only the engine: it also reflects all the frictional losses in the drivetrain. So, for example, if your oil were thick for some reason, you might have the best engine, but you would see lower numbers on the dyno because some of your engine power was being used to overcome friction and that power wasn’t available to the rear wheels. An engine dynamometer measures only the engine. I can’t see that NASCAR would make decisions on engine policy based on a chassis dyno measurement since a chassis dyno measurement measures much more than the engine. It is tough to imagine that, based on a chassis dyno test, NASCAR would decide to make the holes in the Toyota tapered spacer larger again. Just for the record, NASCAR used an engine dyno when they tested NNS cars in Milwaukee and Chicagoland and a chassis dyno in Atlanta earlier in the season.

So what was really the point of this? You make yourself less competitive (unless there was some way that the magnets got put into the cars after the race) and you chance a huge fine. I’m working on a novel and this seems like a perfect revenge scheme for a disgruntled employee, doesn’t it? You compromise the performance of the car AND you create a scandal that could result in long-term suspensions for crew chiefs and car chiefs. Or it could just be someone doing something amazingly ignorant.

The penalties are likely to be major. I’m sure NASCAR has the same feeling I get when I catch a student cheating in a really stupid way. You’re incensed because they’re cheating and then you’re more incensed because they think you’re so stupid that you wouldn’t catch it. When there was a major cheating scandal in F1, they made the guilty company ineligible for the equivalent of the manufacturer’s championship. That’s a punishment for the offenders, but it also puts an asterisk next to the manufacturer that does win the championship.

The arguments that it was justified for JGR to cheat because NASCAR unfairly took away 15 hp from Toyota when they were within the engine rules is just plain bogus and I bet that most of the folks at JGR would tell you the same thing. The people who work there that I’ve met are simply too good to resort to doing something like this.

UPDATE 8/20/08 Dave Moody has a really good summary of the penalties, announced Wednesday, so I won’t type in my own attempt to explain because I think he covered just about everything. I personally was expecting car and crew chief suspensions for the rest of the season, so the indefinite suspension came as quite a surprise.

UPDATE 8/20/08 Lee Spencer has a nice article with a rational description of the incident, the penalties and why this is all such a big deal.

UPDATE 8/23/2008: Mike Mulhern has a great column in which he sheds a little more light on the deception. Apparently the crew members involved had thought enough about this that they had a cover story. Great, except the cover story was that (as one of the comments below suggested) they were arguing that the magnets were stops to prevent the throttle cable from being overextended. They used a magnet in the car because then the driver could kick it out of the way if they wanted to. Sounds perfectly reasonable. Except they forgot to let the drivers in on the story, so it was obvious to the Nationwide officials when they asked the drivers that the driver had no clue what was going on.

Goodyear has figured out (or at least thinks they have a good idea) what the problem was with the Indy tires. They confirmed that the tire compound was indeed the one they intended to use and identical to the one they’ve run there the last two years. They double checks for mistakes with the formulation or processing. They contacted every one of their suppliers to make sure that none of them had changed the raw materials they provided. I’ve had that happen to me when doing chemical synthesis: you buy the same chemical from the same company, but it’s a different lot and all of a sudden, the synthesis doesn’t work. Any of you who knit or crochet know that you can get subtle variations from dye lot to dye lot. Same thing goes for chemicals.

The conclusion they came to is that the drivers are driving differently. Because the new car is so hard to turn, the drivers drive into the corners differently than they used to. It’s not just that the higher center of gravity is shifting more weight to the right-side tires, which would make you think that both right sides would wear and not just the right rears. According to David Poole’s blog, recounting an interview he did with Goodyear’s Stu Grant:

"Grant said drivers were pitching the car into the corner and then sliding the right-rear tire as they tried to get the new car to turn."

The track at Indy has grooves cut in it to allow the lighter Indy cars to get enough grip to race. Remember that Indy is a very flat track. As David goes on to point out, the sliding means that means that instead of the right rear tire riding along parallel to the grooves in the track, it was riding perpendicular to the grooves.

Get out your box grater and a piece of Parmesan cheese (the closest edible thing in my house to tire rubber). Use the largest holes and compare what happens when you grate in one direction to what you get when you grate 90 degrees perpendicular to that direction. You get very different wear. That’s what Goodyear thinks caused the fine powder that wouldn’t stick to the track. It’s not so surprising that Goodyear didn’t get that from the tire test they did–the drivers might not have figured out that sliding is the best way to get the car to turn. Some drivers might have picked it up race weekend.

Why didn’t Goodyear coming up with a reason get as much coverage as the problems at the race? Trying searching for this story on Google. What you’ll get are all the columns with people complaining that Goodyear screwed up. Then Goodyear actually comes out with a reasonable explanation that makes sense and gives them a place to start for next year and you have to dig for it. It’s like printing retractions in legal-sized font in the back of the newspaper. I’m pretty religious about reading through the jayski.com headlines once a day (more when I’m trying to put off tasks I don’t want to do) and I didn’t see a whole lot about Grant’s quotes. Thanks very much to the reporters who take the time to post transcripts so fans can get the whole story and not just “breaking news” soundbites. For example, Claire B. Lang had an in-depth interview with Grant about the tire situation that really gets into the complexity of the problem and gives you a chance to hear about the strategy that Goodyear used to determine the problem. This is a great lesson in problem solving if nothing else.

Now that they have a candidate problem, they at least know what direction they should head in trying to come up with a really good tire for next year. I don’t envy the folks who work at Goodyear!

There’s a wonderful gadget called wordle that analyzes text and picks out the words that are used with greatest frequency. So I had it analyze the blog and this is what it came up with.

Maybe it’s because they counted tire and tires as two separate words, but I sure feel like we’ve been talking about nothing but tires lately. I guess wordle could be used as a kind of blogger Rorschach test. According to it, I clearly have an engine fixation.

We’re talking about tires anyway. It took them a week, but Goodyear outlined their plan for making sure that what happened at Indy won’t happen again. They expressed the plan in corpo-speak, that unique permutation of the English language spoken only by PR types, upper-level managers and university administrators. Personally, when I hear “stakeholder", I think vampire. I’ve included a bit of translation and exposition beneath each point. Goodyear says their plan includes:

• Completing the extensive post-race analysis in process that includes all internal aspects of tire design and manufacturing and discussions with key external stakeholders, including representatives from NASCAR, team owners, crew chiefs and drivers to gain insight to information that will provide clarity to the final analysis.

Translation: We didn’t create this problem and we can’t fix it by ourselves.

• Engaging research scientists and engineers, including available assets and modeling capabilities from the Sandia National Laboratories, to develop a range of potential short-term solutions.

Translation: We need to do something really quick and we’re calling in outside experts to make sure we’ve got something by next July.

Comment: Metals are usually pretty well behaved. Rubber is made of intertangled polymer chains with a lot of other stuff added in. The polymer chains stretch and squish and the other stuff in the mix affects how they stretch and squish. That’s what happens on an atomic level. Then you make the rubber part of a macroscopic item like a tire, into which you have to build belts, cords and other structures. This is not a simple problem.

The folks at Sandia National Laboratory have great expertise in computer modeling. ‘Modeling’ is producing something in the computer and then testing it in the computer. Modeling is to tire testing sort of like computational fluid dynamics is to taking a car to the wind tunnel. You can test a lot of ideas on the computer at fairly low cost and then take the most promising of those to try in the real world. The danger is that the output of computer models is only as good as what goes into the models. Sometimes you get surprised when you find that your model doesn’t agree with reality and you have to go back and tweak the model. Sandia scientists use computers to model things like surface water in Iraq, biobatteries that can be implated to power things like artifical retinas, and combustion. Sandia has expertise in non-linear responses, which is when a small change in an input can produce large changes in the output. Think of a really touchy volume knob that blares if you touch it just the wrong way. Tires exhibit bigtime nonlinearity, so if you’re going to pick minds, Sandia is a good group of minds to pick.

• Scheduling a fall track test at Indianapolis with multiple participants to test solutions to full fuel stop capabilities and test again in the spring of 2009 to fine-tune the specific race setup.

Translation: If we have problems again next year, no one is going to be able to complain that they didn’t get to have some input. We’re leaving the Spring test with everyone there saying that we’ve got a good tire, so if something does go wrong, we’re going to remind everyone that we brought what they were happy with.

"Full fuel stop capabilities" is a fancy way of saying that we need tires that will last as long as a tank of gas. Goodyear counted on the track rubbering up the same way it had in the past. They had how many years of coming to the track, having tire problems in the first practice, and then having the track rubber in. They need additional track time to see exactly what is happening. You can do all the computer modeling you want, but the ultimate test is on the track.

• Accelerating discussions with appropriate NASCAR representatives, team owners, drivers, crew chiefs and track management on any future tire. Among elements already being considered are larger overall diameters, wider section widths, and larger bead diameters.

Translation: We didn’t create this problem and we can’t solve it by ourselves. We’re tired of everyone blaming us. If we have another disaster, we’re not going down by ourselves. More about the possible changes below.

• Developing future tires as a long term solution, looking proactively at the vehicle, tire, setup and track combinations for a complete package to assure only the highest level of performance for NASCAR’s racing fans.

Translation: We know fans were unhappy. Don’t look for anything radical in the near term. Our first goal is to fix the problem for next year, but the long-term solution is probably not going to be making a minor change to the existing tire. NASCAR is going to have to give us the flexibility to do something very different in the long term because we’ve learned that adapting the old tire may not work everywhere. Teams are going to have to help us out by giving us set-ups so that if they’re going aggressive with the suspension, we’re testing aggressive.

I don’t mean to sound anti-Goodyear, (except for my general dislike of people who make up words when there are perfectly fine words that say the same thing.)

The big long-term changes are wholesale modifications to the tire size, construction, bead size, etc. What does a bigger tire do?

A wider tire will do a better job dissipating the heat induced in the tire by friction between the tire and the track. If the volume of the tire increases, there are more gas molecules inside the tire. The heat generated by friction is spread out over a larger number of molecules. The pressure won’t increase as much when the temperature increases (and you thought you’d never use the ideal gas law!) The larger number of rubber molecules will also help dissipate the heat better, which will also keep the tires cooler. But if there is a larger area of tire rubbing on the track won’t that create more heat? Remember back to high school physics: The size of the frictional force (which is what creates heat) is independent of the area of the two objects that are rubbing together.

If you have a wider time, there is more rubber, so more rubber should be available to rub off on the track (provided, of course, that the rubber sticks to the track.)

There are some stress issues as well. The wider the tire, the better force is distributed across the tire. If you have 1800 lbs of force on a tire, it makes a big difference if the force is being supported by 36 square inches or 42 square inches. Each square inch of the tire will support less force becuase there is more total area. If you don’t believe me, go put on a pair of stilletto heels and walk around for a half hour, then do the same thing in your flip flops.

A wider tire WILL provide more grip, but not because it creates more friction. (You can look in the book for the ‘why’ of that one.)

There are a lot of benefits to a wider tire; however, the teams are going to have to develop new suspension setups. Look for engineers scratching their heads during practice the first couple of races with the new tire when the setups that were working wonderfully last year are failing miserably with the wider tire.

The other tire issue this week was at the Montreal Nationwide race, where they raced (for the first time ever as ESPN reminded us again and again) in the rain. Rain tires have grooves instead of the entirely flat surface of the slicks they normally race. Why? Treads aren’t for grip: the recesses allow water to get out from under the tires, giving the tire a better shot at gripping the track. Slicks allow hydroplaning: Water gets between the tires and the track. The problem with water (as with any liquid) is that the molecules aren’t connected very well to each other, so when you push on water, it doesn’t push back. That makes it really hard to get any traction between the tires and the track.

One of the teams almost put the rain slicks on the wrong wheels. This is significant because the treads are directional: They are angled to channel the water away from the car. If you put them on backward, the water gets directed under the car, which is not so good.

The most important thing they learned from Saturday’s experiment is that you can race when the track is wet, but maybe not when it’s actually raining. The windshield wipers are not exactly state of the art, and I wonder if some teams didn’t believe NASCAR would make them go out in the rain since a couple cars opted not to use wipers, One of them was Carl Edwards (loved him trying to squeegee the outside of the window under caution). You know that money isn’t the reason they didn’t have windshield wipers. There were two major crashes under caution because it rained so hard the drivers couldn’t see. So maybe rain tires are a solution to very long track-drying times, but it remains a fact of motorsports that the driver has to be able to see where he’s going.

Tire problems again, but the issue here was different than the tire problems we saw in Atlanta earlier in the year. At Atlanta, the tire was too hard. The drivers complained that they didn’t have enough grip to race. That wasn’t the problem today.

Let’s look at the anatomy of a tire. The outermost layer is the tread. When you hear people talk about the ‘tire compound’, what they mean is the particular rubber recipe used for the tread. Immediately underneath the tread are belts, which are usually made from Kevlar or other strong fibers. The belts are laid on the tire at an angle. Underneath the belts are the cords, which are made from copper that may have metal reinforcements.

The harder the tire tread, the less the tire will wear, but the less grip the tire will have. Goodyear has to find that perfect compromise between safety and wear – the same challenge I discussed on my Atlanta blogs. At Atlanta, Goodyear erred on the side of hard tires for the sake of safety.

This weekend, if you saw the pictures of tires on the television after they were on the car later in the race, you saw a grayish area worn in the center of the tire and some copper color on one edge of the tires. (NOTE: Ryan McGee’s blog has a really good picture of this.) The grey material you saw was where the tread was worn away, exposing the belts. The copper was where both tread and belts had been worn away, exposing the cords. Early in the race, we were seeing cords across the tire. The edge of the tire is likely to wear faster when the tire has more camber.

Like Atlanta, Indianapolis is a very rough track. When practice starts, wearing down tires to the cords isn’t unusual. In the past, as practice goes on, rubber transfers from the tires to the track. Rubber builds up on the track and the rubber on the track decreases its roughness, so tire wear decreases.

This is the first time we’ve run the new car at Indy. The center of gravity of the new car is higher, which means that more weight is transferred from the inside to the outside of the car when turning. Since we turn left, this is why all the problems involved right-side tires.

Some commentators suggested that Goodyear misjudged the load that the new car would place on the tires; however, the problem appeared to be more that the track never rubbered up. The Nationwide and Truck series ran at O’Reilly park, across town, so they weren’t helping getting the race track prepared.

The track gets rubbered because friction between the tires and the track heat the tread. Small amounts of the tread melt. Some of the tread gets deposited on the track and some rolls up with other grit and dirt on the track and forms ‘marbles’.

What was unusual this year is that the tire debris at Indianapolis was extremely fine. The tire tread was coming off as very small pieces. During practice, some of this very fine rubber got under Robby Gordon’s car and caught on fire. Normally, rubber doesn’t catch on fire easily; however, if you make any material small enough, you make the surface area much larger, and surfaces are where chemical reactions like oxidation start. Another problem was that the small pieces of rubber were getting everywhere: radiators, into the car, into the driver’s mouths, etc.

As far as I’ve been able to discern, there haven’t been any major changes in the track in terms of levigation (i.e. diamond grinding). The track was last ground in 2002. The different manner in which the tread wore off the tires suggests that there was a problem with either the nature of the tread compound used, or with the tire processing. The tread compound is the same one that was used last year. If the wear rate was faster due to the additional loading caused by the new car, wouldn’t that cause the track to rubber up faster? Even after 370 miles, the tires were still showing significant wear and NASCAR felt that 10-11 laps of green-lap racing was appropriate before they mandated a tire change. There were six competition cautions, and 52 out of 160 were laps run under caution. That makes 108 green-flag laps. Assuming 10 sets of tires, that’s an average of 10.8 green-flap laps per tire.

To be fair to Goodyear, Indy is an anomaly. It isn’t like any other track: It is 2.5 miles and flat (9 degrees banking in the corners). They did a tire test with three teams, but there was not a mandatory test at Indy as there has been in the past. Indy is a one-off tire, one that Goodyear has to develop with a minimum of data.

One interesting thing I don’t have an answer for is that the radio commentators mentioned that, during the first competition caution, the right front tires looked really bad. After that, the majority of the problems were on the right rear tires. I don’t know if the drivers were able to change their braking style, since the right front is loaded going into a corner and the right rear is loaded accelerating out of the corner, or if perhaps that part of the track rubbered up a little more for some reason.

This is part of the frustration of trying to figure out answers from in front of the television. I had the choice of going to Indy or Daytona and I picked Daytona. Hindsight is 20/20: I wish I had picked Indy because I would have like to have seen the actual tire wear patterns myself. I think NASCAR did an admirable job under very difficult circumstances, but my heart aches for teams like the 29 that probably were differentially impacted by the tire issues. This race was decided more on the basis of chance than engineering skill and driver talent and that’s never the way I want to see a race go.

UPDATE for Red: Got an answer to your question about engines and small particulate matter from Tommy Wheeler, who is the Technical Director at Evernham Engine Technology. Tommy says that, because they tear down the entire engine after each race, they don’t really worry about particulate matter in the engine. The biggest problem regarding small particles and the engine on Sunday was clogging the fuel filters and causing problems with the fuel flow to the engine. Also, because the rubber wasn’t sticking to the track, it was getting all over the cars and Tommy says that teams were a little worried about under-car fires. Thanks for the question, Red and to Tommy for the answer.