Treading Lightly: Tires at Indy

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.


  1. At issue here is that the Indy track is cut/grooved to provide better grip for the lightweight and substantially aero aided open wheel cars. Put 3400 pound stock cars with comparatively little downforce on that surface and what happened is what we saw on Sunday. It does not take a brain surgeon to figure this out. For how many years did we suffer with Darlington eating tires on the old car which was significantly aero bbetter than the COT. There at least they would not crumble as the did at Indy this week, but the grip would go away quickly.

    Sealing the track is no solution because I seem to recall they used to do that at Darlington and the surface would come up and if I am not mistaken they did it a year or two ago at New Hampshire and the same rule applied. What needs to be done is to repave the place as they did at Talladega and watch the racing improve.

  2. Hi Paul: I guess what I’m still confused about is why the tires were producing powder and not coating the track. The issue of cording has always been a problem, but the rubbering of the track always seemed to take care of itself. DLP

  3. One interesting side bar noted from the comments yesterday.

    That Goodyear brings the same compound combination to Pocono and Bristol. It would be interesting to hear the theory of the tire loads on such different tracks.

  4. as you suggest, maybe one reason we saw the wear move front right front to right rear is b/c the drivers began to brake differently. and that may have happened b/c of their feeling that they carried grenades beneath the fenders and needed to become more cautious entering the corners.
    in addition, teams knew (w/i a few laps) when those endless competition cautions were coming and it certainly looked as if they were “racing” to those yellow flags.

    i have never seen tires go to dust versus marbles — that was certainly strange and to me speaks of the wrong compound for that track. i kept waiting for the track to rubber up and it never did. DW suggested on wind tunnel that they should have dragged tires prior to the race to help but if that track was still so green at the end of the race that tires were still showing wear, i don’t know how much that could have helped. that track just looked green all day: no racing grooves ever appeared.

    wonder how that dust effected the engines and if any team will bring that engine to another track or if the engines have been compromised beyond repair?

    scary moment when the #17 lost not only the right rear fender but the whole right side, including the C-post. matt’s a lucky camper.

  5. Race cars are a complex, inter-related system of chassis design, aerodynamics, tires, and track surface. NASCAR has attempted to reduce the engineering aspect of racing with their COT which greatly restricts the chassis options a team has by dictating springs, limiting camber, caster, toe, and chassis geometry, i.e., all the things that determine roll center. Many of the problems seen with the COT could be mitigated if the teams could do more to move the roll center, but they can’t due to NASCAR rules about chassis configuration.
    While NASCAR doesn’t allow teams to grind or shave tires, the Legends series, which I drove for several years, does. Tire shaving and/or grinding is an interesting and little understood process. I had more than a little help from a couple of tire designers at the Greenville, SC, tire research facility of Michelin.
    Goodyear delivers tires with stagger already built in, that is the right side tires have a larger circumference than the left sides. In the Legends cars we started with 4 identical tires and would not only shave or grind them to add stagger but also make the tires cone shapped. The temperature and loading conditions on the tire when the grinding is being done are all important in determining whether the result is little chips, dust or gummy glue. NASCAR was hoping for gummy glue which would have stuck to the track and reduced tire wear, instead they got dust.
    NASCAR simply does not understand the vehicle dynamics of what they’ve created with the COT. NASCAR may be great at marketing, but it’s becoming more blatantly obvious every week that vehicle dynamics engineers they ain’t.

  6. Having spent a few years in a business that made powders for commercial use, it seemed to me that the tires may have had more mold release (i.e. talc,mica?)to help the compound pop from the mold. As this would be blended into the “rubber” itself, it would act as a mold release at the track interface as the tire wore.Your thoughts?

  7. Hi Rich: It’s entirely possible. I cannot tell you how many times we’ve a small change in something in the lab that shouldn’t have made any difference in the process and then spent months trying to figure out why things weren’t working any more. It is so hard to tell when you’re dealing with something as complex as a tire. And yes (you no doubt know already) tires are complex things. Sometimes a very minor change can make a big difference.
    Wouldn’t it have been interesting to try dragging some tires sideways and seeing if they behaved differenly? Or dragging a couple Pocono tires to see if they laid down any rubber? I’m sure the Goodyear engineers are just as upset as the race fans and they are doing everything they can to resolve the problem. They get all the tires back and the tires are tagged with a RFID chip, so they can work with the teams and know which sets of tires were run on the track and for how long. Perhaps they will find some clues from that type of analysis.

  8. Hi PittCaleb! Thanks for the comment. Yep, I’ve been referring to it as a “race”. You can’t blame fans for being disappointed, but we should point out that this was a major disappointment for the team members as well. Poor Mark Martin was so happy with his car and his engine that he predicted he might win — and he never says things like that. Who knows whether he might have if the tires hadn’t been an issue.
    Every car has thirty (or more) people who invested their time and hopes during the week making it run good. Then something like this happens. The crew guys aren’t the ones taking home the megabucks either. I am very curious as to what the industry will learn from this debacle. DLP

  9. The ESPN commentators kept talking about the track being “grooved,” but I don’t remember it being grooved when I took the track tour last year. The only part of the track that is grooved is the yard of bricks.
    The pavement there is very flat due to the grinding. The agregate appears to be small rocks and sand. It looks very different from the pavement you might see on the street. It was very unusual looking.

  10. Diandra,
    As far as the differing wear on the right front vs the right rear, all I can go on is what I was hearing on the scanner of my driver. He said that it seemed the restarts were causing the right front to wear, but the rear wear came in later. And he also said that if the car was on the loose side, the right rear wore more than if the car was snugged up. A race chat room I was in had other reports of other drivers saying similar things. Many of the drivers were learning how to drive the car, but taking extreme care in the corners. I believe my driver’s observations were born out as valid when his crew chief reported the tire status and appearance after every pit stop.

  11. Hi Snafam: As far as the tires tearing themselves up: Have you ever had a snag in a pair of nylons that all of a sudden pulled into a giant hole? It’s sort of the same thing. (Now there’s an analogy you’re not going to find on too many NASCAR sites, huh?)
    The tires were wearing across the width, but not evenly. The belts help hold the tire together. As soon as one point in the tire wears through, it creates a weak spot and the whole thing falls apart. It looks like an explosion, but it’s not exactly a pressure-induced failure: It’s primarily mechanical.
    I don’t think I understand why the restarts would cause right front tire wear. The right front is loaded on breaking and turning. Accelerating ought to load the rear tires, so maybe someone else out there can fill me in on what I might be missing.
    Thanks for the info about the drivers’ feedback!

  12. Hi Susie: I was sloppy in my answer. There IS pressure involved because the tire is the only thing keeping the 40-50 psi of nitrogen gas inside the tire. A couple drivers had tires go down – they had a small hole that created a leak and they started losing air. The tires that ‘exploded’ probably didn’t have any greater pressure inside than the tires that just went down. The ‘exploding’ tires just had the outer layer of the tire pull apart (that’s the mechanical failure). So snafam is right that pressure is involved, but the ‘exploding tires’ most likely didn’t have any greater pressure from inside than the ones that just went down.
    The sheet metal on a stock car is minimum 24 gauge. That’s about 0.027 inches. An average sheet of 20-lb copier paper is 0.0038 inches thick, so the sheet metal on a stock car is about (0.027/0.0038=7.1) seven sheets of copier paper! The strength of the car is in the steel tubing chassis, not the sheet metal.
    When you see that much sheet metal ripped away (like the No. 17), it’s from tire parts hitting the body. The wheel is rotating about 2180 times per minute at 180 mph. The pieces of tire that are loose on one side and attached to the tire on the other side whip around like those things you put on the end of a drill to remove paint. The tire pieces (which are still pretty strong) hit the sheet metal and rip it to pieces. That’s why drivers are so careful getting back to pit road when the have a tire they know is going down. Even if the car doesn’t hit anything, the tire coming apart can tear the car body right off. Thanks for making me be more clear!

  13. Solve all their prolems easy. Get rid of the splitter and wing. Raise the valence to 10 inches. That will get rid of most of the aero issues, running bump stops and put the car back in the hands of the racers. Of course the speeds will be down, but how many fns have you seen with stop watches. Probably too simple for NASCAR. Maybe we would see some passing.

  14. Bob Emmons comment brought a chuckle. He may not have a grasp on the physics needed to turn cars. His comment took away all ability to turn a car and get it to pass other cars. Yes, Bob, too simple for NASCAR, indeed.

  15. It is interesting you say the front tire wear improved but not the rear. I would then think that the track did rubber in. The rears were most likely wearing out on the straights due to the 1 degree of toe out?
    If you looked at the outside wall just before entering the corners you would see a pile of tire dust that was desposited there at the turn in point and the air from the cars dropped the dust there. The only way they could get there is if the tires were wearing out on the straight.

    Normally the marbles are at the middle to exit of the corners where the wearing takes place.

  16. I was talking to a polymer scientist yesterday (about something totally other than tires!), but the tire issue came up. He reminded me that heat cycling is very important. When the tires heat up, they basically break and form molecular bonds in the rubber. It is possible, we decided, that higher-than-expected loading in the initial laps of a run made significant enough changes in the molecular structure that the tires powdered instead of wore as usual. DLP

  17. Hi Alan: A couple interesting issues you bring up. I was just looking at some problems in expectation of the fall semester in a physics book. Remember the one about what happens to a package if you drop it from a plane? Everyone intuitively expects the package to drop straight down, but it has the same forward velocity as the plane, so it actually continues moving forward as it falls. I would think that there is some similar effect with marbles because the rubber has to have some initial velocity coming off the car. The thing I can’t decide is whether it is forward or backward. But I’m not sure that you can make a one-to-one correspondence between the location of the marbles and the location of the wear. Sounds like a great experiment to try!
    The rear slant of the tires may very well have played a part; however, the tirs are made to withstand turning and the lateral forces (force across the width of the tire) on cornering are much larger than I would expect them to be down the straights. The fact that the edges of the tires were wearing first suggests that camber might need to be scaled back. DLP

  18. Perhaps since what was coming off the tires was bsically dust, wouldn’t the amount of air generated by the cars blow the rubber around?
    By the way RAEckart, the tire patch is what makes a car change direction. If my physics is false than no car would be able to turn.

  19. Diandra,

    Thank you for the tire lesson. I learn so much from you.

    I’m curious to know why NASCAR didn’t run the Pocono tires on Kevin Harvick’s car (or someone else laps down) just to see what would happen. Tire testing during a race, it doesn’t get any better than that.

  20. thanks for searching out that answer about the engines and all that tire dust! i’ve often wondered about it when we see red flag stops and all that speedi-dry that clouds up the track during the subsequent racing.

    i watched a bit of the replay of the race today –painful as it was! — and what struck me again was that tires were wearing out along the edges (which would implicate a camber issue) but also across the tire as well as around the tire in the middle of the tire in a large band. essentially, it was all over the place. since we never got to see tires from one driver thru the entire race, no way to know if, say, the tires on the 88 wore down consistently across all sets that were pulled. was the driving style and/or set-up being reflected in the tires wearing in a consistent way? or were the tires wearing differently each time?

    that, and the dust in the corners question are two that i’m still puzzling with the limited access to information we have.

    thanks again for the engine answer, tho’: good to know!

  21. I admit, I have not been on this webpage in a long time… however it was another joy to see It is such an important topic and ignored by so many, even professionals. I thank you to help making people more aware of possible issues.
    Great stuff as usual….

  22. Thanks as always for your technical and scientific analysis of what we say on Sunday. Regardless to the reason, the race was bogus for race fans. 10-lap shoot outs with “your” driver basically not having a chance to race and win is just stupid.

    Reminds me of the complaints about the Steeler game a couple years back when the field was a wreck and people begged for it to be post-poned. They would have been better to cancel the race and come back in the fall IMHO.

    Waste of a weekend for the fans in attendance and the teams that spent money to travel there. Guess the top few finishers got a good weekend, not not worthy of the nearly $10 million purse they were awarded.


  23. Thanks for this explanation, Diandra. Thankfully, I didn’t watch the race live so I didn’t catch all the nuances with the dust, etc.

    I have to wonder, though — what the heck happened to the 17’s tire??? It downright exploded and ripped the entire right rear quarter panel off the car. It’s one thing for a tire to wear, blister, etc. and go down – but to explode so violently? That’s some pretty impressive P in the whole PV=nRT scheme of things. What the heck happened there???

  24. So from your recent reply, it sounds like Matt Kenseth’s tire exploded from mechanical failure and not a “pressure-induced” failure? That seems odd to me, but hey, I’ve never seen a tire pop rip open the rear end of a driver’s car before (neither has Matt, by the way). Perhaps the rubber dust particles ignited and added to the explosion? The mechanical failure thing just doesn’t make sense…sorry.

  25. Ah ha, I get it now! Thanks for taking the time to explain. It was just that everyone keeps referring to the tires as “exploding” but now I understand the damage was due more to the gross mechanical failure of the tire – which in turn ripped apart the car. There’s been a lot of discussion on Matt’s website about “the tire explosion” so I will let my fellow 17 fans know. Thanks again, Diandra.

  26. Bob – “By the way RAEckart, the tire patch is what makes a car change direction. If my physics is false than no car would be able to turn.”

    And so does the wing, splitter and valance panel that you are claiming would improve the car if they were removed.

1 Trackback / Pingback

  1. The Dirt on Radials vs. Bias-Ply Tires : Building Speed

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.