Mailbag: Tire Codes, Bristol Waves and the Science of Cheating

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–4146; Right-side– D–4150

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 science) 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.


  1. There’s a very fine line between creative engineering and cheating. A good cheat (and that may be an oxymoron) is one who does it so well you never find out that they were cheating. The Gibb’s case is just poor, because it was so obvious and easy to detect. There’s a real art to cheating, a good con is never detected.
    The Knaus case a couple of years ago with shock absorbers was brilliant creative engineering, not cheating. The shocks (which had a very slow rebound) met all of the rules when they were built. NASCAR said they didn’t conform to the “intended spirit” of the device. Which is the problem with a race series that wants a “parity” between the big teams. No real engineer or driver wants parity, they want to be the best and crush their competitors. If that isn’t your attitude then you should look into a different line of work.

  2. ESPN has a nice article on their website with Chad Knaus saying just about the same thing as Jeff and Bob. He sounds really frustrated. DLP

  3. The Gibb’s case is just poor, because it was so obvious and easy to detect. There’s a real art to cheating, a good con is never detected.Really i am impressed from this post….the person who create this post it was a great human..thanks for shared this with us.i found this informative and interesting blog so i think so its very useful and knowledge able.I would like to thank you for the efforts you have made in writing this article

  4. I’m with you Jeff. Gibb’s case is stupidity. To me that is outright cheating as opposed to someone who works within the grey of the rules.

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