Stock Car Science

After getting in late from Columbus, I made the mistake of listening to the radio as I attempted to sleep. Listening to the comments about the Red Bull Racing penalties got me slightly riled. NASCAR came down hard on Red Bull, including 150 driver/owner points, a $100 kilobuck fine and indefinite suspensions for the car chief and the crew chief. My preliminary thoughts about what might have happened and why turned out to be pretty close to what I’ve been hearing through the grapevine. But there are a couple big misconceptions running around from the sound of it. Let’s take a look at a few of them.

The penalties were so high because this is a safety issue. This is not a safety issue. We’re talking about twenty-five mils of steel versus twenty mils. (A mil is a thousandth of an inch.) The body is for aerodynamics, not strength. The strength of a race car comes from its roll cage. NASCAR does have a rule that you cannot race without a doorskin; however, that rule is probably outdated. In the new car, there is a 90 mil thick piece of steel in the passenger side door and a sheet of Tegris (the splitter material)in the driver’s side door. Those two components are there to prevent anything sharp from coming in between the door bars and hitting the driver. A twenty-five mil sheet of steel isn’t going to protect you from much and losing five mil from that isn’t going to make a noticeable difference.

The reason for the stiff penalty is that NASCAR is escalating penalties each time they catch someone messing with the chassis or the body. If you look at the penalties this year, they’ve steadily gotten worse. The exception is a 25-point penalty for the 12 car; however that was a height violation, not a chassis/body violation.

How could the driver not know that this was going on? Easy. With a very few exceptions, what the driver knows about the car is what the crew chief tells him. Some drivers ask a lot of questions about what springs and shocks and steering box are in the car. Few drivers spend a lot of time at the shop. They are usually so busy with appearances and such that they come from their motor home, spend a little while talking with the crew chief and get in the car.

There have to have been a lot of people who knew about this because acid dipping pieces of sheet metal isn’t easy to do. Acid etching has legitimate uses, some of which are applied to rather large parts. For example, if you want to weld or braze something, or coat a piece of metal with a decorative coating, an acid etch gives you a clean smooth surface. The words “acid dipping” conjure up a vision of a mad scientist with the vat of boiling green liquid. Solder flux is a type of acid etch. Stainless steel etch is usually a mixture of hydrofluoric and nitric acid. You could brush it on, leave sit for a little while and rinse it off pretty easily. It is, of course, possible that a lot of people knew, but the process is not a complicated enough thing to require that a lot of people be involved. We used a similar etch to clean stainless parts for a sputtering system. I remember as a graduate student leaving a couple shims in the etch for too long and coming back to find that they were totally gone - etched entirely away.

In my first post, I just used the side of the car as an example. Remember that you’re not just trying to make the car lighter - you’re trying to make it bottom heavy. The most obvious place to thin the metal would be the roof panel. If you were clever, you would thin only the center section of the roof because if you thin the edges, you might have problems in welding, and if you mess with the edges that can be seen (the bottom of the doorskin, for example), it would be easier to detect. If you estimate the roof at 4 foot by 4 foot (again, round numbers just as an easy estimate), and uniformly decrease the thickness to 20 mils, you’re saving maybe three pounds. But it is much more significant saving three pounds at the very top of the car compared to saving three pounds at the bottom of the car. The total numbers I’ve heard say that the car was somewhere around 12-16 lbs lighter. Where that 12-16 lbs was missing is very important.

How could the crew chief not know? This originally bothered me as well, but remember that the overall weight of the car is 3450 lbs. You’re talking about 0.4% of the total weight. Given everything else that can change on the car (and everything that has to be done before going to the track and at the track), I’m convinced it could be overlooked pretty easily.

Red Bull management must have known since they aren’t contesting the penalty. When something like this happens, teams usually find out pretty fast who was responsible for the infraction. You have two choices then: fire someone publicly, or do as Joe Gibbs Racing did when they were caught in the Nationwide Series. JGR simple said that they know how it happened, and that they believed the people involved deserved a second chance. It’s just not a NASCAR thing to identify some guy who works in the shop and throw out his name to the press. What the RBR statement says is that they know they were guilty.

I will write a little more about center of gravity in the future to explain why the location of the missing weight is so important.

The stock car science blog has been a little quiet lately, mostly because I’ve been working on a really exciting project I hope to be able to tell you all about in the very near future, but also because I’ve been traveling all over the country giving talks and because there hasn’t been a whole lot of science-related news in NASCAR lately. I was just joking in my talk yesterrday that I was sort of hoping someone would try something clever just so that I’d have something to write about. And voila…

Fox Sports reporter Lee Spencer is reporting that the No. 83 Red Bull Toyota, which was selected for random testing after Martinsville, was found to have not met the minimum thickness requirements for the body panels. Spencer anticipates that NASCAR will be levying “record-breaking” fines.

mum thickness of the body panels is 24 gauge, which translates to 0.025 inches or 1/40th of an inch thick. Let’s model the side of a car as shown below, as three rectangles with dimensions as shown. Yes, I’m using rectangles to make my calculations easier. I’m considering only one side of the car and I’m ignoring windows.

The area of the sheet metal on the side of my model car is 4771 square inches. Multiply that by the thickness of the metal and you get a volume of about 119 cubic inches of sheet metal.

The density of 1018 steel is 0.283 lbs/in³, so the weight of this much metal is roughly 33.75 lbs.

If you want to thin a material, you have options. You can mechanically polish the metal, for example, grinding away a thin layer. This tends to be difficult to do with any uniformity unless you’re really set up for it.

In the lab, I often need really clean surfaces, so instead of rubbing and sanding them, I etch them. Etching is dipping a material in something that eats away at the material. In the case of steel and other metals, the etchant is usually an acid and this is the “acid dipping or chemical milling” to which Spencer refers. You put the metal piece into a bath of acid and how much material is removed depends on how long you let the metal sit in the acid bath. The metal comes out looking like new. In fact, if you take a wedding ring to a jeweler to be cleaned, what they usually do is to dip it in a mild etchant. You lose a miniscule amount of metal from the ring, but it comes out looking shiny and new.

It would be hard to tell whether a piece of metal had been etched by looking at it by eye; however, a metallurgist can examine the metal (with the paint stripped away, of course) and can analyze the etch patterns. Certain directions in a crystal etch faster than others (see Figure 3 in this paper for example), so determining whether a piece of metal has been etched isn’t too difficult if you have the right tools.

How much weight could you actually save by etching away some of the sheet metal? Let’s say that the side of the car we calculated above was etched from 24 ga to 26 ga (which takes it from 0.025 to 0.01875 inches). The weight just on that side would be reduced by about 8.4 lbs and, making a lot of approximations, maybe by 20 lbs across the car. If the thickness were reduced to 28 ga (0.015625″), you’d save 12.6 lbs. But even someone casually familiar with sheet goods would likely notice that much of a decrease in thickness.

Why would you reduce the weight of the body? The answer is back to our old friend The Center of Gravity or CG. The new car has a higher center of gravity, and the higher center of gravity means more load transfer when the car turns. One reason the new car has a higher CG is because it is taller. More weight up higher in the car increases the CG. More load transfer makes the car harder to turn.

You can lower the center of gravity by adding weight (ballast) in the framerails of the car; however, you don’t want to make the car any heavier than the minimum 3450 lbs. Spencer suggests that the RBR team made the panels thinner so that they could save weight (she claims up to 75 pounds) and then use ballast to make up for the decreased body weight. That would lower the CG. The NASCAR R and D Center ought to be able to determine intent because they no doubt know how much ballast would be appropriate for a regulation car. If there is another 20 lbs or so of ballast in the RBR car, that would suggest that someone knew that there was a significant weight savings somewhere else.

Is this a safety issue? Probably not so much. The strength of the car is in the tube chassis, not the body. You can dent the sheet metal in the body pretty easily. Ask Carl Edwards and Kevin Harvick.

There is a potential complication in what I’ve presented you with here, which is that stock cars have curves. I don’t have an accurate estimate of the surface area of a stock car, so it’s difficult for me to calculate exactly how much weight could be saved in this manner mand whether the 75 lbs Spencer suggests is realistic. My intuition is that 75 lbs would be really difficult to shave off the car without it being somewhat obvious to knowing eyes. I am in Columbus Ohio today at Ohio State University, but I will update this post when I get back to Dallas Thursday and hopefully wheedle some more accurate numbers about the surface area.

UPDATE: Well, that didn’t take long. From what I’ve been told if you figure losing about 5 mil from the thickness, that leaves you with about 6.75 lbs for the side I showed above, so maybe 13 lbs or so is about the weight saving you might expect to see. I can’t see any way you could get 75 lbs.

Juan Pablo Montoya’s pole run last Friday at Kansas was disqualified when his shock absorbers failed tech inspection. The shocks and springs are important components of the supension. A car without a suspension would bounce all over the track. When you hit a bump, the springs compress. When you go over the bump the springs extend back, which keeps the wheels in contact with the track.

The problem is that springs are, well, springy. When you compress a spring and let it go, it extends, then compresses, and just keeps bouncing up and down. Hence the need for shock absorbers.

The shock absorber (like the spring) connects the wheel to the chassis. When a spring compresses, it stores energy. That energy is what is dissipated by friction when the car bounces up and down. You’d like to damp out the spring’s oscillations more quickly than friction allows.

A monotube shock absorber (the type used in NASCAR) has a piston (a disc with holes in it, shown below) moving up and down in oil. The holes in the piston are very small, which means it requires quite a bit of force to move the piston. Punch tiny holes in a piece of plastic and then try moving it through pancake syrup. This movement of an object through oil introduces an interesting way to control force.

The force exerted by a spring is proportional to how far you compress or extend it. (That’s Hooke’s law). In a shock, the force exerted by the shock is proportional to the speed at which the piston moves through the oil. So the force depends on how fast you move, not how far you move. You pick the shock to match the spring and the two work together.

A spring can compress and extend. So can a shock. When the shaft is pushed into the shock, it’s called compression. When the shaft is pulled out of the shock, it’s called rebound. You’d like to be able to adjust the rebound and the compression independently. One way you do this is that the two sides of the piston have different hole geometries. A hole may be large on one side and small on the other, which affects how the oil flows through the piston.

Another way you can tailor the compression and rebound response is by changing the shims (very thin washers) that bend when the piston moves up and down. The shims bend more when the piston moves faster, uncovering more of the holes and allowing more oil to move from one side of the piston to the other. (At very low speeds, a valve in the shaft allows direct flow.)

The key to how a shock works is the resistance to the piston’s motion. The resistance is provided by the oil. Most shock oils are between 2-5 wt. More viscous oil provides more resistance to motion.

Look back to the first picture of the shock. There’s an area there marked ‘gas’. Ignore that for a moment and assume you just screwed the two pieces of the shock together without doing anything special. If you want to try this experiment at home, get some cooking oil and put it in your blender. Turn the blender on - that will mimic what happens when the piston moves up and down. (If you have a French press coffee maker, that would be a more accurate analogy, but a blender has the same effect and is less likely to engender spousal irritation.)

Whirl the oil in the blender for a few seconds and you’ll notice that you have foam. Foam is gas bubbles trapped in a liquid or solid. Stryfoam, for example, is air bubbles in a polymer. The foamy mess you have in your blender was created when the whirling motion incorporated air bubbles into the oil. (When you have bubbles of one liquid trapped in another, that’s called an emulsion, but it’s the same idea.)

There’s a problem when shock oil foams. The principle on which a shock works is that the oil provides resistance to the piston’s motion. Air trapped in the oil makes it much easier for the piston to move. You use oil in a shock because it is incompressible, which means that when you press on it, it doesn’t change volume. When the oil foams, you push on it and the air that’s dissolved in the oil doesn’t provide much resistance. A marshmallow (which is a foam) is a combination of sugar and air pockets. When you press on a marshmallow, the first thing that happens is you press all of the air out of the air pockets and it’s pretty easy to do that. Only after you’ve squished the air out do you start to compress the sugar that forms the rest of the marshmallow. A shock has to be filled with an incompressible fluid for it to work. Foam isn’t incompressible.

You have to pressurize a shock. One reason is because oil sloshing around the inside of the shock won’t provide much resistance for the piston. If we fill the top part of the shock with an overpressure of air, the pressure above the oil will prevent the oil from sloshing. Air is about 21% oxygen, with the rest primarily nitrogen. Oxygen is more soluble in oil than nitrogen, meaning that it is easier to dissove oxygen in the oil than it is nitrogen. Depending on the type of oil, the difference can be a factor of two. This is why nitrogen is used to pressurize shocks. Nitrogen gas is less likely to create foam than air. In fact, if you press down hard enough on the oil, you can actually decrease how much gas is dissolved in the oil. You literally press the dissolved gas out of the oil.

NASCAR allows the rear shocks to have nitrogen pressures between 25 psi and 75 psi. Apparently, the rear shocks on Montoya’s car had a pressure of 85 psi. There was an interesting discussion on NASCAR Now with John Darby in which he pointed out that after the initial overpressure was discovered, they allowed the shocks to cool to ambient temperature before re-measuring the pressure. Why? The ideal gas law in action. When gas gets warm, the gas molecules in the tires move more rapidly, and that increases the volume and the pressure. The same thing happens in your tires.

NASCAR wanted to give the team the benefit of the doubt: perhaps the shocks had gotten so warm that the pressure had increased beyond the allowed value. I made a quick calculation (remembering that the 75 psi/85 psi are gauge pressures, so you have to add 15 psi of atmosphere to those numbers, converting degrees Fahrenheit into kelvin, and making the assuming that the change in volume is negligible) and I estimate that the temperature of the shock would have to rise about 60 degrees Fahrenheit to create a 10 psi change in pressure. It’s not at all unreasonable for the shocks to reach that temperature during two laps of qualifying, which is why NASCAR waited until the temperature of the shocks had come down before making the measurement.

What difference would an overpressure make? When teams realized the importance of the car’s attitude in terms of aerodynamics, the primary job of the shocks became keeping the rear end of the car up in the air to get maximum downforce. Higher pressure in the rear shocks could be used to keep the tail end of the car in the air longer. The upper pressure limit used to be 175 psi. That was changed after the 2005 fall Dover race, where two Hendrick cars finished 1-2. The Hendrick cars were set up so that the rear of the car didn’t come back down very quickly after a bump. Both the cars failed the post-race max height inspection after half an hour of waiting. The language in the rule book now requires the shocks to return to their normal position after compression within "a reasonable time", and a maximum value for the nitrogen pressure. A really high nitrogen pressure prevents the shaft from returning quickly.

There’s another reason for a maximum pressure limit. A closed container with a very high interior pressure is also commonly known as a bomb. If there were a failure in the threads or (more likely), the seals on the ends of the shocks, you could have shock parts flying out without warning.

Congrats! If you’re reading this, it means that they turned on the Large Hadron Collider without creating any black holes…yet.

If there’s one question I get when I speak it is: “If they were going to design a car from scratch, is the new car really the best they could do?” My favorite phrasing of this question is “If we can put a man on the moon, why can’t NASCAR build a car that can race? (Uh, how much money did that cost, how long did it take and how many people lost their lives in that endeavor?)

At this point in the season, I think everyone recognizes the big problems with the new car:

• The center of gravity of the new car is a couple of inches higher than in the old car. That exacerbates load transfer, which means that the car has overall less grip.
• NASCAR instituted a minimum and maximum height for the splitter. The old valence only had a minimum height. The new restriction reduces the front-end travel on the car, making it harder to get the car in the aerodynamically favorable “hound dog” (nose down tail up) position. The end result: less grip.
• The total aerodynamic downforce of the new car is less than the aerodynamic downforce of the old car–again, the end result being less grip.
• NASCAR tightly legislates body shape, precluding the teams from making the body asymmetric. An asymmetric body can help the car turn better. This removed one of the main tools teams had to get ahead, as very small changes to the body can produce big changes in aerogrip.
• The new car is much more ‘finicky’ (as Chad Knaus puts it) than the old car. We’ve seen a couple of examples where teams that are usually really good got to the track and "missed the setup". Even with three practices worth of tweaking, they could never get the car handling correctly.

These points have been well documented, so let’s put a moratorium on the cranky articles that do nothing more than complain about the car, or even complain that the right people aren’t complaining about the car. My father had a policy: If you can’t suggest something better, you don’t have the right to complain.

‘Better’ implies realistic, so all the calls to go back to the old car are banned under my moratorium as well. It just ain’t gonna happen. Can you imagine the teams scrapping two years of work–and inventory–and trying to buy back all those chassis from the ARCA teams?

Besides, most of the teams will tell you that they’ve learned a lot about the new car since the beginning of the year. Few teams bring back the same car to a track because they’ve made so many changes that the car from the first race–even a car that wonthe first race–wouldn’t be competitive.

There are two big components to my solutions. The first time. Teams used to have twenty races worth of data from which to determine set ups. This year, they have at most three races worth of data. It’s not entirely surprising that teams miss the setup sometimes. Every time I talk with engineers, they tell me how much more they understand about the car. That aspect is just going to work itself out with time; however, the narrowing of the ‘grey area’ is another matter. The primary ‘grey area’ teams used to have was manipulating the body shape. They don’t have that any more, so they have to focus on other (often less familiar) areas. Some crew chiefs complain that NASCAR is getting to be too much like a spec series, where everyone gets the exact same equipment. We’re pretty far from a spec series, but the series is definitely headed more toward that direction than I think most of us would like.

For what it’s worth, here are my suggestions for what NASCAR ought to be considering as they start to write the 2009 rule book. All of my suggestions end tied with one common thread,which is purposely making the box in which teams can work bigger.

• The CG has to be lowered. Teams are searching for even small changes in the weight distribution. Some teams are replacing metal dashboard panels with carbon fiber panels to save 6-9 lbs of weight that is located fairly high on the body. (This sort of defeats the idea of decreasing cost because carbon fiber is expensive.) A smart team would contact the Tegris people (the material from which the splitter is made). Milliken (the folks who make the splitter) recently launched a molded kayak made from Tegris that is strong and lightweight. The primary use of Tegris now is as sheet goods (cutting the splitter out of a flat piece), but Milliken has some really nice molding technology. Tegris will save weight without costing as much as carbon fiber. But these are small changes. Why not just make the car another 100 lbs heavier and let the teams put all of that extra weight on the left side of the car if they want. Yes, the cars would be a little less peppy (Not even NASCAR can outlaw F=ma), but if the handling improves, you’re going to get better racing and happier drivers.
• Give everyone the same basic engine block and cylinder head, but allow them a wider range of variation in how they can modify the components. Wait, you say–isn’t that moving into a spec series? I’m arguing it’s not because, although they’ll have the same basic components, I would give them a much larger box within which to work. For example, allow variation in bore dimensions (not volume, but aspect ratio) and a wider range of intake manifold geometries. I’m tired of the whining about how one manufacturer has an advantage because of their basic engine design. You shouldn’t be at a disadvantage because your manufacturer hasn’t gotten a new engine approved yet. Give all the teams the same basic components, enlarge the box and then let the engine guys do what they can to get as much horsepower as they can. There is nothing sacred about these engines: It’s not like the manufacturers pull a few off the production line and ship them off to Charlotte.
• Instead of mandating two or three rear-end gears, give the teams a continuous (and wider) range of gears to use. That will further broaden the box for the engine while keeping a limit on the rpm range.
• The car needs more downforce, so the aerodynamic issues have to be addressed. The NASCAR R and D center has a handful of engineers. Asking this small group of people to design a brand new race car and have it work perfectly is utterly unrealistic. On a major team, about 10% of the employees are engineers, which means over the last two years, there have been probably 350-450 engineers thinking really hard about how to make the car go fast. Some of those people are very smart aerodynamicists. NASCAR needs allow each team one participant, lock them in a room with the NASCAR R and D staff, sit them down around a table and let them propose how to change the car’s aerodynamics. They’ll bring a wealth of ideas and information. Give them as their goal coming up with an aerodynamic ‘box’. It would be a fun meeting to be at because different teams have been focusing on different aspects of aerodynamics. No one will want to reveal their closest-held secrets, but I bet a consensus of common issues would emerge that would improve the aerodynamic issues such as downforce and, most importantly, the effect of sideforce on turning and passing.
• A lot of people are calling for a return of the spoiler. The problem is that the higher greenhouse doesn’t let the air hit the old spoiler as well as it did in the old car. Don’t think NASCAR isn’t concerned about the wing. Notice that the Nationwide COT (NCOT) is keeping the spoiler, but the spoiler has a different shape. Since the NCOT uses the same chassis and presumably has the same height issues, here’s a chance for NASCAR to do some experimenting with spoiler shape. My rental car in Richmond had a wing in the back and I must say that not being able to see out the rear window is really annoying.
• If they’re going to reserve a room for the aero think tank, they might as well get suspension experts together as well and ask for ideas on how much they can increase the front travel without totally obviating all the work the teams have done with bump stops and chassis stops. Again, put reps from the different teams in the same room and let them say as much as they are willing to say in front of each other. If someone bright takes all of those ideas and puts them together to find the overlaps, they should end up with a box within which the engineers have plenty of room to experiment.

I’d like to close this week by thanking all the folks at Richmond: My hosts at VCU were terrific, especially Wanda, the administrative assistant in the History department who took care of all the logistics. I had a couple good meals and enjoyed myself greatly, even if my shoes still are a little damp. The people in Richmond–as in most places in the South–are very friendly, but especially so at the track. That’s a big difference from some places, where track security seems to enjoy telling people "no". The folks at RIR kept smiles on their faces, even as the rain moved in Friday afternoon and they realized they’d have to postpone the race. As fan-friendly as the larger tracks are, I really like the smaller tracks like Bristol, Richmond and Martinsville, where getting a dent in your fender doesn’t end your day. I look forward to returning to Richmond and getting to see a race there in the future.

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 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.