Apr 032015

There are three things you don’t mess with in NASCAR: engines, fuel and tires.

Tuesday, NASCAR handed down a P5 penalty – the penultimate penalty on the books – to Ryan Newman’s 31 team. Crew Chief Luke Lambert was suspended six races, fined $125,000, and Newman and his owner Richard Childress were each docked 75 points. The tire specialist and team engineer were suspended for six races as well. RCR is appealing the penalty, but I wager they’ve got an uphill battle.

NASCAR’s made its stand loud and clear in the last few weeks. Tire bleeding will not be allowed. If you persist in trying, they’ll come down hard on you.


Why Would You Bleed Tires?

The hotter the gas inside a tire gets, the higher the tire pressure gets (says the ideal gas law).


The tire volume changes a little with temperature and pressure, but it’s not a huge change. If you were doing actual calculations to use in a race, you wouldn’t ignore it. For us, it’ll be good enough to approximate that the volume remains constant.  The equation tells us then that the ratio of pressure to temperature has to stay the same. If the temperature goes up, the pressure goes up, and vice-versa.

The video below (from the National Science Foundation) details how and why the tire pressure increases. Steve Letarte is a nice person and a very clear explainer of things. I look forward to seeing how he does when NBC takes over broadcasting NASCAR later this year.

The main problem with changing tire pressures is that grip depends on tire pressure – a lot.  If the tire pressure is too low, you lose energy to rolling resistance. If the tire pressure is too high, the sides of the tread pull away from the track, giving you a smaller contact patch and less grip.

Tire builds can be significant. At some tracks, you might see a 35 psi change in tire pressure. A large build means teams have to start a run with very low tire pressure – 8-10 psi at some tracks. If you look at a car at Martinsville waiting to go out on track, it’ll appear as thought it has flat tires.

Bleeding tires prevents the tire build (increase in pressure) from getting too large by releasing some of the pressure once the tire pressure reaches some value.

Wait… Like a Pop-Off Valve?

This is the same principle teams use in the radiator systems. Put water into a closed metal tube and heat it. We call that “a bomb”. As the liquid gets warm, it turns into gas, the gas pressure increases and eventually the gas inside pushes so hard it breaks the radiator or the tubing in the cooling system.

So we use a little valve called a pop-off valve on the radiator. When you see steam pouring out from near the bottom of the windshield, it means the pop-off valve has popped. The video below explains the pop-off valve in the cooling system.


That’s a great idea, right? They ought to make something like that for tires, so that the tires can’t get overinflated.

TireBleedValvesThey do. It’s called a tire bleed valve. Shown at left, you install it in the valve stem of the tire. Most are adjustable between some range of pressures.

An o-ring sits atop a spring. When the pressure is low enough (left), the spring is relaxed. The o-ring forms a seal on the valve seat,which holds in the air.

When the pressure inside the tire increases past a pre-set value, the spring compresses and unseats the o-ring. Notice how by where it says “no seal” the o-ring doesn’t touch the sides of the valve anymore . This gives air a path to escape. As soon as enough air has escaped so that the pressure returns to the maximum value, the spring relaxes and the valve closes. There’s less air in the tire, which allows the pressure to remain lower.


Seems Like the Perfect Solution. So…?

So bleed valves (or tire pressure relief valves) aren’t legal in NASCAR. However much nitrogen you put into the tire is how much you have and the driver is supposed to deal with the changes in the tire pressure. The harder you drive the tire, the hotter it gets, so having a way to relieve pressure gives the driver the option of pushing the car harder than a driver who is limited by the building tire pressure.

The scuttlebutt around the garage is that the tires on the 31 had small holes poked in the sidewalls. Rubber is stretchy enough that you can get a tiny, tiny puncture and it won’t open up a gaping hole that lets all the air out of your tire. The rubber on the sidewall is thinner than the rubber on the tread, so a pin prick or something similar would do the job.

The disadvantage of this method is that it’s totally random. With a bleeder valve, you can set it to go off at 35 psi and you know it won’t let any air out until 35 psi. With something like poking tiny holes in the tire, you have to guess at the number and placement of holes so that you don’t let out too much or too little. There’s also a safety issue, in that your well-intentioned “tiny” hole might actually do more damage than you intended – or noticed until the right front below out going 180 mph into a turn.

Plus, one of the fundamental tenets of NASCAR is that you do not mess with the tires. It’s bad from a sportsmanship angle and from a safety angle.

How would you tell?  The easiest way to find out if there are tiny holes in the tire is to over pressure the tire (maybe fill it up to 50 psi) and toss it in a bathtub or a swimming pool. If there are holes, you’ll see air bubbles coming out from the holes. (We actually used to use this technique to find big leaks in our vacuum chambers.) If you can’t submerge the tire, you can overpressure the tire and then squirt a little soapy water on the suspicious areas. You’ll see bubbles (from the soap) appearing near the holes.

If you want to be really pedantic about it, you can look at the material under a microscope once you’ve narrowed down where you suspect the holes might be located.

Can You Really Be Sure Someone Cheated?

There are a lot of things that could put a hole in a tire. But not the same size/shape hole multiple times in multiple tires. NASCAR is pretty cautious about not nailing people without solid evidence. I will be majorly surprised if RCR wins their appeal. That’s not to say upholding the penalty means there was a plan by the team to cheat the tires that way. It could have been one person thinking they were helping and the folks who got fined knew nothing about it. Science says nothing about intention or motive.


Apr 012015

The Scariest Part of Racing?

During the XFINITY series race at Richmond, a malfunctioning fuel can spilled a huge amount of gasoline in the pit stall. A spark ignited the fuel, engulfing gasman Josh Wittman and rear tire changer Anthony O’Brien. A crew member for a team pitting nearby (Clifford Turner, working on Eric McClure’s car) was also injured. Although all the men were conscious and moving around immediately after the incident, all three were taken to the hospital. O’Brien wasn’t released from the hospital until Monday following the Friday incident happened.

If you were to poll racecar drivers about safety, I bet the majority of them would say the scariest situation isn’t a crash.

Two fears you have as a race car driver: one is being on fire and two is being T-boned in the driver door – everything else you sort of accept.  –Elliott Sadler

That quote was from before the Gen-5 car brought additional reinforcement to the drivers side door in the form of additional tubing and IMPAXX energy-absorbing foam. But what can you do to minimize the risk due to fire?


You need three things for fire: BSPEED_FireTriangle Without any one of these three, you don’t get fire. Which is a good thing because we pretty much walk around surrounded by oxygen and fuel all the time. Pretty much any clothing, regardless of whether it’s made of natural or artificial fibers, is fuel. The air is about 21% oxygen, with 78% nitrogen and 1% preservatives and fillers. No, actually the 1% are other gasses, like hydrogen, krypton, neon, etc. and they’re present in such tiny quantities that we don’t care. At all.

Back in The Day…

Way back in the day, drivers and crew wore street clothes and hoped they wouldn’t catch on fire. Then fire-retardant chemicals became available and people would dip their clothing in the chemicals to make it fire-resistant. The problem is that you do tend to want to wash your clothes after driving in a hot car for a couple hours and the chemicals would wash off.

And believe me, after three or four hours in a hot car, you want to wash whatever’s been in there with you.

Polymers = Repeating Molecules

Then we learned how to design polymers. The prefix “poly” means many. Polygon means many sides. Polymer means many units. The unit in this case is a particular arrangement of atoms into a molecule.

For example,  below is a schematic of an ethylene molecule and the polymer polyethylene, which is nothing more than a bunch of ethylene molecules hooked up together.

polymerExamplePONYou can make the polymer long or short by varying how many times you repeat.

Kevlar and Nomex: First Cousin Polymers

Kevlar was discovered by DuPont chemist Stephanie Kwolek, who passed away last June at the age of 90. How Kevlar came to be is an interesting story. A looming expected gasoline shortage led DuPont in the early 1960s to look for strong, yet lightweight fibers for tire manufacturing. One of Kwolek’s attempts at making a liquid that would be spun into a fiber ended up looking rather yuck. It was cloudly and thin, totally unlike what she expected, yet she insisted that it be made into a fiber for testing anyway. 

Her invention was Kevlar, a polymer that is five times stronger than steel by weight. Below is a Kevlar molecule. Grey circles are carbon, Blue are nitrogen, red are oxygen and white are hydrogen. There are actually a bunch more hydrogen atoms in the single molecule that I don’t show because it just makes the picture messy and confusing .



You’ll notice something very interesting about the Kevlar polymer – it’s very straight. That linearity is a big contributor to its strength. Kevlar chains link with each other in a very orderly way and make a fiber that can be used in bulletproof vests, as well as serving as a reinforcement for tires and carbon fiber pieces.

But Kevlar isn’t a miracle material. It has its limitations. When you heat it up to 900 degrees F, Kevlar literally falls apart. The atoms start letting go of each other.

But check this out.



Compare the molecules left to right. Exact same atoms, just arranged differently. Kevlar is this nice straight molecule, but Nomex is… well… Nomex is a little kinky.

That difference in conformation – straight vs. kinked – makes all the difference. Nomex is nowhere near as strong as Kevlar; however, when you heat Nomex, it doesn’t melt and it doesn’t burn.

It chars. While that might seem like a bad thing, it’s actually good.



When the Nomex fiber chars, it forms a layer of carbon on the outside. That makes the fiber thicker, which does two things: First, the thicker fabric gives you a little more protection from heat transfer, but second, the thickening of the fibers  closes the air gaps and prevents oxygen from getting through to the skin and feeding the fire.

The video below is one of DuPont’s promoting Nomex. Reminder. Don’t try this at home.


Nomex used to have a monopoly on the market, but recently there’s been a new material making waves. CarbonX is a blend of oxidized polyacrylonitrile and other strengthening fibers and is inherently non-flammable. Polyacrylonitrile is the precursor for 90% of carbon fiber production. One issue is that oxidized PAN is pretty much available in your choice of black or black, so the fibers have to be blended with other fire-resistant fibers to get colors.

One of the things CarbonX has is a very high LOI (Limiting Oxygen Index). That’s the percentage of oxygen that has to be present before the material will combust. CarbonX won’t combust unless 55% of the air is oxygen. Remember oxygen makes up about 21% of normal air, so to some extent, that’s a moot point because anything with a LOI over 21% is going to work about the same as far as motorsports goes.  You can hold it at 2600 F for two minutes and it won’t ignite or burn.

Prices have come way down on CarbonX since I first investigated them. You can get a CarbonX sport bra for about $80 and a CarbonX balaclava for about $65 now. A good Nomex balaclava will cost you almost the same.

The choice of CarbonX vs Nomex comes down to comfort, since they both will protect you in a fire. Drivers worry about the weight of the suit, mobility and breathability. The people I know who have tried both feel like CarbonX suits are heavier, but more breathable and less scratchy.

Can We Fireproof Racing?

FuelingApronPeople are very careful with their terminology when talking about fire safety. Nomex is not fireproof. Nomex firesuits are fire-resistant. Firesuits are made in layers, with the air between the layers also providing insulation against heat. That works the same way the air gaps between double-pane windows works.

SFI, a non-profit foundation that writes specifications and tests motorsports safety equipment, rates firesuits in terms of how long you can be exposed to fire before you’d get a second degree burn. For example, a 3.2A/1 rated firesuit gives you three seconds of protection, while a 3.2A/5 rated suit gives you 10 seconds of protection. (For the curious 3.2A is the SFI specification that deals with fire resistant uniforms).

NASCAR mandates that drivers wear a 3.2A/5 rated firesuit, as well as cover the remaining parts of the body with accessories that meet SFI specifications, including shoes and gloves. Crew members who go over the wall are required to have 3.2A/1-rated suits, although the NASCAR rulebook recommends going to the 3.2A/5.  The exception is that anyone handling gas must have the the 3.2A/5 suit and must wear a fire-resistant apron.

Fire resistant underwear and socks aren’t mandated, but they are recommended. The danger here is that if you close enough to a fire, synthetic fibers like nylon and rayon melt. Then they stick to the skin and are very difficult (and painful) to remove. So for the weekend racers, if you can’t afford a full set of Nomex undies, at least make sure everything else you’re wearing is 100% cotton. And ladies – no metal hooks, clasps or underwires. Metal heats up faster than fabrics and you’ll get burned in particularly bad places.

As you might expect, the higher the level of protection, the more expensive the suits are – although you’d like to think that a couple hundred dollars per suit difference is worth a few days in the hospital – or worse. Used to be the pit crews didn’t wear firesuits or helmets. If a fire similar to the one in Richmond happened then, it would likely be fatal.

Let’s also note that the fire wouldn’t have happened if there hadn’t been a malfunction in the fuel can that allowed a couple gallons of gasoline to flood the pit lane and probably get on the gas man as well. I also want to note that the stuff they use in fire extinguishers is a pretty nasty brew of chemicals that aren’t exactly good for people to breathe – but they’re a lot better than burning to death.

Safety is about protecting people on all fronts. Even though the gas can failed, the safety equipment stepped up to the worst-case scenario. Thank heavens everyone is safe.




Mar 262015

Joel asks:

Can racetracks work together to make interchangeable/transportable SAFER barriers? To clarify – could SMI or ISC tracks (politics, blah) standardize wall heights, angles, etc. so that they could use barriers at Michigan to fill in the critical areas and then move the necessary walls to Darlington or Homestead? Or even simpler – could the existing walls be setup to install barriers that could be moved from track to track? In the long term I know this is probably not the most cost effective solution. But in the short-term if there are supply problems or significant cost barriers, I thought this could help?

Thanks for the question, Joel. (And apologies for taking so long to get to answering it.)

Installing SAFER barriers is a little more complex than installing a fence in your yard. SAFER barriers are custom manufactured for each section of the track taking into account the wall height, width and condition, the track banking and width. Even putting aside track politics, having a system of barriers versatile enough that they could move from Michigan to Darlington and be equally effective in both places would probably be cost and time prohibitive. You’d need a dedicated crew of people moving from track to track, trucks to transport the barriers and a procedure in place to inspect and qualify each piece after each race.

Standardizing wall heights could be more expensive and time consuming that it’s worth. Each track has its unique geometry and trying to make a one-size-fits-all barrier might be more trouble than it’s worth — and not as effective as just installing barriers.

Plus, if an area of the track is dangerous, it’s not just dangerous during NASCAR races. No track is going to claim they can’t afford to put more barriers in – especially after Kyle Busch’s accident. And although they do take time to manufacture, there are a growing number of companies certified to fabricate, install and maintain the barriers.

But you’d think there would be a better temporary alternative than a bunch of tires, right?

One of the things the SAFER group was thinking about last time I talked to them was a transportable version of the barrier that could be used for street courses. It’s a formidable challenge. The current barriers are fastened to the track wall, which is pretty firmly in place. How would you anchor something to a street in such a way that it would stay in place, but could be removed without significant damage to the road/sidewalk/parking lot?

Another problem that I haven’t really heard talked about is that it’s impossible to line a track with SAFER barriers inside and out. Emergency vehicles must have free and immediate access to the track (and a way out) when needed. The SAFER group also has investigated hinged barrier that could open and close, but developing a hinge that can take a direct hit from a 200-mph racecar and still open easily is a pretty stout challenge as well.

It all goes back to what I tell Moody (it seems) every week. If it were simple, they’d have already done it.

Thanks again for the question!

Mar 042015

A couple observations about history at Las Vegas…

Pole Speeds



Pole speeds hovered inthe 170-175 mph until 2007. After the 2006 race, LVMS changed over to progressive banking, which increased the banking overall and changed the amount of banking in different lanes of the track. This added about 10 mph to the pole speed and it’s been on an uphill trajectory ever since. With the lighter car, it will be interesting to see what type of speeds they reach this year.




The maximum number of cautions we’ve seen was in 2009, with 14, but recent years have averaged around four to six.

Best Drivers

It’s tempting to note who has the most wins – but the important thing is really how many times they won relative to how many times they’ve raced. In this case, Jimmie Johnson wins both categories – 4 wins, which means he wins approximately 30 percent of the time he races there. Keselowski, KyBu, Stewart and Gordon all have one win, but the percentage win rate ranges from about 15% (Keselowski) to 5% (Gordon).  Get well Kyle!


After last week’s embarrassment at Atlanta, there will be extra emphasis on qualifying. Like most 1.5-mile tracks, where you start does have some influence on where you finish, so a good qualifying spot is sort of important.


Here’s a graph of starting position vs. finishing position for last year’s race. I’ve highlighted the cars that finished 10 or more laps down. Those cars are usually in an accident or have a major parts failure, so they should be noted in case they skew the result.

You’ll notice there’s a general trend that suggests where you start influences where you finish, although the correlation seems stronger at the lower positions. The first 10-15 starting positions seem pretty random.  (Compare this to what you find at a plate track like Daytona, where staring position is pretty much entirely irrelevant. There’s also a more thorough discussion of how to analyze these types of plots in that blog). I made the graph for 2013, but it looks pretty much the same as for 2014, not I’m not posting it here.

Will be on SiriusXM NASCAR radio this Friday (March 6th) sometime between 3 and 7 East to talk about aging and the effect it has on drivers.


Feb 252015

TL;DR:  No.

As the extent of Kyle Busch’s injury Saturday evening at Daytona became evident, Twitter erupted in angry calls for SAFER barriers to be put up on every wall at every track. An interesting division of sides appeared. A small number of people cautioned that simply plastering every track with SAFER barriers was likely to not only not prevent driver injuries, but might actually introduce new problems. Other people accused this group of being insensitive and “stupid”.

Interestingly, the small number of cautionary voices were people like the folks who write Racecar Engineering magazine, people who have been involved with motorsports safety research and people with advanced engineering degrees.

So let’s be really clear here. While I appreciate the passion with which people responded to the accident, opinion has absolutely no place in science and engineering. We work with facts, realizing that oftentimes, we don’t have all the facts we need. In an ideal world, we would have data from collisions at every track in the world, from every angle, with every type of racecar. But we don’t.

It’s fine for fans (and especially for drivers and their teams) to raise their voices and demand more attention to safety, but the average fan (or the average driver) has zero business specifying what those safety measures ought to be. The average NASCAR executive or track administrator doesn’t, either.  Motorsports safety is a constantly evolving research field and luckily, NASCAR recognizes that and works with the top people in the field.


Let’s start with the obvious. A bare concrete wall at a track where speeds reach 200 mph is indefensible. To their credit, NASCAR and the Daytona folks promised to rectify that right away. Tire barriers – which are not ideal, but are definitely better than nothing – were up for the next day’s race.

Racetracks originally put up concrete walls to contain the cars and protect the fans. They weren’t there for driver safety. People don’t question the status quo.  It wasn’t until a number of serious accidents in both IndyCar and NASCAR prompted an effort to develop a better wall. I detail the origin and development of the SAFER barriers in my book, The Physics of NASCAR, based on my interviews with the barrier developers. The effort was initiated by IndyCar, but gained momentum when NASCAR threw their support (and money) behind it.

Once the technology was developed and proven, NASCAR mandated SAFER barriers on the outside walls of all tracks. It was a long road to development because it was a brand new (and frankly, counterintuitive) idea and everyone wanted to make sure it would work under as many conditions as possible.

How SAFER Barriers Work

For an overview of NASCAR safety, check out this video I made with the National Science Foundation. Here’s the brief version.


The SAFER barrier works by extending the time of impact. It’s much more comfortable to fall on a mattress than a floor because the mattress gives. The mattress absorbs and dissipates energy, so that the energy isn’t dissipated through you.

BSPEED_SAFERBarrier_HitA NASCAR stock car going 180 mph has approximately the same kinetic energy as stored in 2 pounds of T.N.T. When the car comes to a stop, all that energy has to go somewhere. Energy can be dissipated by skidding (friction between wheels and asphalt), light and sound (it takes energy to make that screeching noise and to produce sparks), spinning (energy is used to rotate the car) and deformation (energy is used to crunch or break things).  The key is that you want to dissipate energy any way except through your driver.

A mattress won’t make much difference to a speeding stock car. You need something much stiffer, and that’s the purpose of the SAFER barriers. They’re like mattresses for race cars. They use the energy of the car to deform the barriers and spread out the impact over a longer time. This directs energy away from the driver.

Why SAFER Barriers Aren’t the Only Answer

SAFER barriers save lives and this analysis is meant in no way to diminish their importance. But the inventors of the SAFER barriers would be the first folks to remind us that it takes multiple safety devices, working in unison, to protect the drivers (and the crowds). HANS or hybrid devices, helmets, restraints and the car itself are all part of the equation. You can’t address any one of those elements without considering the others. So here, briefly, are some things to think about.

Kinetic Energy Ranges

SAFER barriers work best in a specific kinetic energy range. I was surprised when interviewing drivers for my book to find that more than one mentioned that hitting a SAFER barrier at low speed actually hurt worse than hitting a concrete wall. But it’s true. The wall works by giving. If you don’t hit it hard enough, it doesn’t give and then it is just like hitting a concrete wall. This is relevant for a couple reasons.
1.  Most tracks host more than one kind of racing series. The kinetic energy scales of those series can vary widely. Any solution has to make the track safer for everyone who races there, not just stock cars.
2. Different tracks have different speeds, so even just within a single racing series, this means different kinetic energies. Compare Martinsville and Daytona, where the maximum speeds are a factor of 1.5-2 different. That means the kinetic energy scales differ by a factor of 2.25-4. That’s a big range. The response of the SAFER barriers can be tuned by using different strength foams and different types of steel tubing – but again, it has to work for all series racing there, not just NASCAR.

Get Off Your Grass

Get rid of the grass. Grass has no business being anywhere in a racetrack that cars could possible end up in.

a. Remember how I mentioned that you can dissipate energy by friction between the tires and the ground? The higher the coefficient of friction between the two materials, the more energy you dissipate. You know what the coefficient of friction is between grass and rubber? Very small. It’s even smaller when the grass is wet. This is why road courses have gravel traps. Huge friction that slows down the cars and hopefully stops them before they hit. (Gravel traps have their problems, notably that it’s near impossible to get out of one once you get in one, and that flying gravel is dangerous and difficult to clean up.)

b. Second, there is a drop off between the asphalt and the grass – a lip on which the car can catch, creating a torque. Check out Elliott Sadler’s crash at Talladega.

When he comes from the grass back onto the track, the roof of the car catches on that lip and starts the car rolling again. If I were a driver or an owner, I would be after every track to get rid of any grass near the track.

The Car Itself

NASCAR has done an amazing job engineering a much safer car than we had fifteen years ago. But the job isn’t done. There hasn’t been a career-ending injury (including death) during a race in any of NASCAR’s three major series since 2001. (Note added. It was pointed out to me that Jerry Nadeau‘s career ended after a very hard hit in 2003 during practice for a race at Richmond.) The injuries we have seen have all been below the knee. Dario Franchitti broke an ankle at Talladega. Brad Keselowski hit a wall testing at Road Atlanta and broke an ankle. Kyle Busch’s injuries from the Daytona crash were to his left foot and right lower leg.

The pedal box and the front of the car need some attention. Can the idea of collapsible steering columns be worked into the pedals? The front of the car is designed to crush (thus dissipating energy) in a crash, but maybe there is a way to refine how the crushing happens and reinforce the driver’s cockpit near the legs. I’m sure the folks at the NASCAR R&D Center are already thinking about this side of the problem.

Perhaps there are driver safety devices than could be developed as well, similar to the HANS device that prevents the head from slamming forward in  a wreck. Maybe there’s a carbon fiber leg brace or similar piece that could provide some extra protection for the driver’s legs in a crash. Of course, anything developed can’t interfere with the driver’s ability to control the car after a crash.

The Fallacy of Safe Racing

Motorsports is dangerous. People are killed participating in motorsports – especially at the lower levels, where the safety requirements are much lower than in the high-dollar, high-visibility series. But even in NASCAR, even in F1, even in Indy, there will be serious injuries and – I’m sorry to say – we haven’t lost our last driver to an on-track incident. All you need is that one in a thousand, one in ten-thousand confluence of events.

What Should Fans and Drivers Be Demanding?

Don’t tell NASCAR and the tracks that they should cover every conceivable wall with SAFER barriers and then sit back and congratulate yourself for a job well done.

Consider for a moment the ratio of people whose job it is to make cars fast to people whose job it is to make racing safer.

NASCAR has become so much more proactive about safety in the last years. If I were a driver, I would be lobbying NASCAR to hire more people at their R&D Center focused on safety, and to support more motorsports safety research at universities and industry.

The FIA has an Institute for Motorsports Safety.  It’s a non-profit foundation that centralizes safety initiatives and testing and works to get safety innovations on the track quickly.

Maybe it’s time for NASCAR to team up with IndyCar and the Tudor United Sports Car series and form something similar in the U.S. This isn’t an issue that should come up only after a serious wreck. It’s an issue that needs long-term, on-going commitment and attention. As a fan, I’d pay an extra buck or two on top of a race ticket if that ‘tax’ were earmarked for safety research.

For More:


Feb 202015

Okay, it obviously does if you’re one of the cars that fails to make the race. But beyond that- given the huge amount of attention that’s been given to the ’embarrassment’ that was this year’s qualifying – does where you start make any different as to where you finish?

To investigate, I plotted the starting positions against the finishing positions for each race at Daytona. I wanted to do both the July and the February race to see if there was any difference given the different formats of the qualifying (regular qualifying+ duels vs. regular qualifying).

If there were a trend, you would expect a pattern to emerge on the graph. For example, starting position tends to be very important at mile-and-a-half tracks. Although there’s some scatter in the data, there’s a pretty clear trend that the people who start toward the front tend to finish toward the front. Same for the folks who start in the back.


It’s always interesting to look at the points that don’t follow the trend. For example, the point in the upper right circled in red is a car that had engine problems and didn’t finish the race.

The point that is the furthest from the line (furthest defined as the perpendicular distance between the point and the line) is the one circled in crimson and labeled “Harvick”. Despite leading 23 laps, Harvick had axle/hub trouble and spent 30 laps in the garage. His 41st place finish didn’t reflect how good his car was – at least until it broke.

Similarly, the other crimson-circled data points represent cars that ran more than 3 laps down due to problems in the pits, mechanical difficulties, or accidents that didn’t result in the car leaving the race, but did enough damage to require time in the garage or pits fixing the car.

Here’s similar data for Phoenix – it shows the trend even more strongly. If you started well and your name wasn’t Kurt Busch (engine failure), you finished pretty well. If you started in the back, that’s pretty much where you stayed.


So if this post is about Daytona, why am I going on and on about Las Vegas and Phoenix?  Well…

I wanted to show you what you were looking for first. And the analogous plot for Daytona is a mess. You might not realize that it means there isn’t a trend if you hadn’t seen data where there was a trend first. So here’s last year’s Daytona 500.



Again, plotting starting spot on the horizontal axis and finishing position on the vertical axis. I got clever this time – the red shading represents finishing positions that were six laps or more down relative to the winner. The red circles represent DNFs, due either to engine problems or crashes. (Just for comparison – at Las Vegas in 2014, only the last nine positions were six or more laps down.

There’s no discernible trend in this plot. Now you see why I showed you the other one first, right?

But maybe it’s one of those anomalous years, right? Let’s look at the data for the last three Daytona 500s.


<sarcasm> Oh, yeah. Much clearer.</sarcasm>.

The trend (or rather, the lack of a trend) holds for the last three Daytona 500s and, in fact, for the July races as well.

Drivers and media types tend to talk about Daytona being a ‘crap shoot’. That’s reflected by the fact that where you finish has very little to do with where you start when you’re talking Daytona.

Why? Well, one big factor is that the close proximity of the racing means that you are much more affected by everyone else on the track. You can be the perfect driver, but it you happen to be behind Donny Dangerous and he spins, you have little chance of avoiding being caught up in it yourself. Remember at 190mph, you’re talking traveling a football field in the blink of an eye.





Dec 122014

The primary motivation for all the changes to the Chase format was to up the excitement factor – the “game seven moments” as NASCAR brass put it. While the fact of the matter is that you can’t guarantee excitement, all the machinations put in place definitely increased the stakes of the chase races.

I’ve heard a lot of people say that the increased stakes spurred the drivers to be more aggressive and that resulted in better racing.  To be sure, we had a couple notable off-track incidents. It’s pretty surprising when Matt Kenseth loses his cool. But what about on-track?

Lead Changes

I started thinking about how you would measure that.  My first inclination was to look at lead changes. If drivers are being more aggressive, there ought to be more lead changes in Chase races than in other races. Now, comparing this is a little tricky.  You can’t compare a Talladega (where the ever-shifting lanes of cars trade the lead, resulting in hundreds of lead changes) to a Martinsville or a Charlotte.

But there are eight tracks in the Chase that have races earlier in the season.  What about them? I looked at how many lead changes there were at each track in the Fall, then compared that to the Spring. Kudos, as always to racing-reference.info for putting all this data at my fingertips. I took the difference, so that a negative number means that there were more lead changes in the Spring and a positive number means there were more lead changes in the Fall.

For example, At Loudon, there were 18 lead changes in the Spring race, but only 10 lead changes in the Fall race, so you get a bar going down of magnitude (18-10=) 8. Surprisingly, For all races except Texas, there were the same or MORE lead changes in the Spring race.


This, of course, led me to wondering. Could it be that perhaps drivers were being less aggressive during the Chase? So I looked at tracks with two races but neither one of them in The Chase. I added them (and made the graph 3D because it looks cooler that way). The last five races (the ones on the right) are non-Chase races.



So regardless of the race being in or out of the Chase, the first race at a track routinely (with one exception) has an average of seven more lead changes than their latter-season counterpart races. The only difference (and it’s very minor) is that there are an average of 4.75 fewer lead changes Fall vs. Spring in Chase races and an average of 10.4 fewer lead changes in non-chase races.

Finally, I thought it might be helpful to look at the same data for the year before, where we didn’t have the playoff format.


And it’s pretty much the same story. There are fewer lead changes in fall races than spring races in 2013 as well.  Recall that the races where cuts were made were Dover, Talladega and Phoenix, and there’s no big standouts there either.

So if you want to quantify racing quality by lead changes, you can’t really make a case that the new format led to more aggressive or better quality racing to any great extent.

I looked at a couple of other parameters as well. I tallied up the number of accidents in each race, counting true accidents as well as spins, but not debris, competition or drunk-people-sitting-on-catchfence cautions. I then compared those Spring vs. Fall. In chase races, there was an average of one more accident in the Fall than the Spring and in non-chase races, there was an average of just about one more accident in the Spring than the Fall. Over the course of the season it average to just about zero, but remember that these are very small numbers of races, so you can’t read too much into the statistics. There would have to be some overwhelming difference in numbers to be convincing.

Next up – looking at Driver Finishes to see if they’re driving more or less aggressively.

Nov 072014

Flared side skirts became an issue when social media started noticing them somewhere around Kansas. The fact that the most obvious example of this was on the 2 car and Brad Keselowski is rapidly taking over from Kyle Busch as most-love-to-hate driver in NASCAR may have brought the issue to the fore faster.

The side skirts (or ‘vertical extension panels’) help seal the bottom of the car to the track. This picture, of the 2013 Toyota Camry, shows the clearest example of the side skirt because you can see the line where the side skirt joins onto the side of the body. The cutout is for the jack – if there were no pit stops, there’d be no reason for the cutout. The side skirts help funnel the air that does get under the car smoothly out, and they keep air from coming on on the sides.


Side skirts are made of a durable rigid plastic — except for one spot on the right side of the car near the tail pipe area. The rationale for this is that exhaust pipes get very hot. Although plastics are indeed the material of the future, plastics that are really, really heat resistant also tend to be expensive and harder to work with.

The plastic from which the side skirts are made is pretty rigid. You can cut it and bend it a little, but you really can’t monkey with it too much.  Except for that metal part, near the right rear wheel.  You know… this part:


Flaring out the right rear of the side skirt started out being done by a couple of teams and now you can find most all of the teams doing it.  So now for the burning questions.

Is it illegal?

Nope. NASCAR hasn’t fined or taken points from anyone for doing it.

Is it happening accidentally?

A lot of internet pundits initially claimed that this was the result of hard racing, no ride-height rule, and drivers racing on the apron, where the possibility of banging the car on the track is maximum. But not when it’s happening to so many cars and happening every week.

And then video appeared that showed jackmen pulling out the skirt during pit stops – right in front of the NASCAR officials overseeing the pitstop.  So no, it’s not happening by accident.

Is it really an advantage?

There have been a number of times in the garage where a team started doing something goofy just to see how many other teams would copy them. There are some cases I know about where teams made a modification they’d seen other teams make without understanding it — but they also had their engineers figuring out whether it was doing anything. If one of the backmarker teams had started doing this, I doubt anyone else would have noticed, unless that team all-of-a-sudden improved.

NASCAR does have a history of allowing something and then cracking down on it when it becomes too blatant, so the first teams doing this knew they might get their hand slapped.

The argument people have made is that it changes the balance of aerodynamic force. you’re providing a couple more square inches for air molecules to slam into. In this case, I doubt there’s much of an effect down the straightaway (especially with the rear-end skew), but it probably does help a little in the corners.

It certainly isn’t hurting the cars, or teams wouldn’t be doing it.

Why are they only doing it on the right? If it increases downforce, wouldn’t you do it on both sides?

They can’t do it on the left. The left-side skirt is entirely plastic and you can’t bend it. Plus, the issue here is really in helping the car turn, so you wouldn’t want to make the same change on both sides.

Should NASCAR prohibit it?


First, let’s note that this has been going on for much longer than most people realize.  Like most things in NASCAR, it starts with one team sticking their nose out a little (or their skirt out a little) and escalates until it’s a big enough effect that those of us sitting at home notice.

It’s not like NASCAR hasn’t been aware of what’s going on.

The main reason I can see for NASCAR stepping in is that a sharp piece of metal sticking out at wheel height has the potential to turn Phoenix and Homestead into the Roman Colosseum.

Not that anyone would purposely try to cut someone’s tire down, but it makes bumpin’ and bangin’ a very different proposition.

Here’s the problem. It’s going to be tough to police. And I don’t say that just because Jeff Burton said it and he’s almost always right. It is possible for the skirt to get bent and banged by (for example) a tire being pulled off at an angle, or contact on the track.

The NASCAR pit officials can’t see everything. Their primary job during pit stops is to make sure the wheels aren’t going to come off again. Do you want them to take their eyes off the tires so they can check what the jackman is doing? Maybe with the electronic pit officiating coming next year, that will be possible.  Not this year.

NASCAR’s Sprint Cup Series Director Richard Buck told popularspeed.com

“I will say the garage is comfortable with how we’re managing it right now.  It’s the same for everyone. That’s how we try to manage everything — that it’s the same for the big teams as it is for the little teams.”

NASCAR has done a really good job not knee-jerk reacting to things. They tend to wait and see how things evolve. When they threaten to get out of hand, NASCAR makes a rule. This happened with the skewed-out rear ends a few years ago. It got to a certain point and then it got silly.  The cars couldn’t even get up on the rails for tech. When NASCAR made the rule, it had all the details – how much they would allow, how it would be measured.

I wouldn’t be surprised if they do something next year, but don’t expect anything to happen in the next two races – unless there’s a catastrophic accident that can be linked back to the flared side skirts.

And on a chemical note…

I always tried, as a teacher, to find analogies to help my students understand scientific concepts.  For example, my mental picture of “potential energy” is of a cat about to pounce or a sprinter on the blocks the second before the gun starts the race. You can see the energy ready to go in the tensed up muscles and once they move, you can see the kinetic energy (energy of motion).

Last Sunday at Texas, I got another one.

A catalyst is a chemical that initiates or speeds up a chemical reaction, without taking part in said reaction itself. All I need is a good video from Texas to make my point now.

That, or chemists everywhere should start referring to catalysis as “Harvicking”.





Oct 172014

Every year at this time, we hear that Talladega is a wild card because “Anyone can win”.  Which, of course, made me wonder — can anyone win?

Who Wins Races?

Let’s start by looking at who wins races in general. I analyzed the last three years and everything we have so far for this year and put it in a table. Why a table? Because tables help you see your way through all the numbers.  What I was interested in was trying to find a correlation between who wins and how “good” a driver they are, as determined by how high they finish in the standings at the end of the year.

The number in each box is the percent of all wins run by drivers in the top 5, top 10, top 15, top 20 and the Chase.  Note that I discarded some situations, like Brian Vickers, who won a race in 2013, but sat out much of the season due to illness and finished 78th in points. Same thing for Hamlin and Stewart, neither of whom ran all the races that year, but won a race.

Note that the new rule – that anyone who wins is automatically in the top 16 is going to invalidate this type of an analysis in the future because someone who would’ve finished lower in points gets boosted up by the win.

Year T5 T10 T15 T20 Chase
2011 44.4 63.9 83.3 91.7 77.8
2012 48.6 88.6 94.3 100 88.6
2013 61.8 70.6 91.2 94.1 85.3
2014 35.5 71.0 96.8 100 100

Here’s a gratuitously colorful graph of the same data, just for Moody:


The take-away message:  It is very unusual for a driver who ends the season outside the top 15 to win a race. In fact, for the last three years, more than 70% of the races are won by the top ten drivers. (And I don’t know about the goofy perspective Excel uses in those graphs.  It makes it look like the numbers for 2013 and 2014 are less than 70% – but they’re not. I promise.)

But What About Talladega?

If Talladega really is an ‘equal opportunity racetrack’ in terms of winning, then the stats ought to look very different over the years. I analyzed Talladega races all the way back to 1990, which is almost 50 races. You know what? It’s not that different from the average.

Year T5 T10 T15 T20 Chase
2011 44.4 63.9 83.3 91.7 77.8
2012 48.6 88.6 94.3 100 88.6
2013 61.8 70.6 91.2 94.1 85.3
2014 35.5 71.0 96.8 100.0 100.0
Talladega 44.7 72.3 91.5 95.8

The stats are almost identical relative to every other race track out there. Out of the 47 races I included, only two were won by drivers outside the top twenty.

Jamie McMurray – 2009 Fall (22)

David Ragan – 2013 – Spring (28)

I omitted the Spring race in 2009 because the driver (some guy named Brad Keselowski (?)) only finished in 38th place – but only ran 15 out of the 36 races. So if you’re currently running below 20th place, you’ve got less than a 5% chance of winning.

Even the year Michael Waltrip – the patron saint of teams hoping for an upset at a plate track – won, he finished 15th.

Wait a Minute… That Can’t Be Right

We all remember David Ragan winning Talladega and Daytona and Trevor Bayne winning the Daytona 500.  Is it true that if you’re not in the top 15 and you’re going to win, it’s likely going to happen at a plate track?  Let’s look at the exceptions.

Year Driver Finishing Rank Track
2013 Martin Truex, Jr. 16 Sonoma
2013 David Ragan 28 Talladega
2012 Joey Logano 17 Pocono
2012 Marco Ambrose 18 Watkins Glen
2011 Trevor Bayne 53 Daytona
2010 Regan Smith 26 Darlington
2010 Paul Menard 17 Indy
2010 Marcos Ambrose 19 Watkins Glen

This year Aric Almirola won Daytona, and I’ve left that out because we don’t know where anyone is finishing yet. He could be 15th or better still.

But even if you counted him, not even half of the “upsets” take place at restrictor plate tracks.

But I swear I remember all these times…

I gotta tell you. I sweated this one out. I have looked at Dega Data for two straight days because I knew there had to be something interesting in there.

And I finally found it – but it runs counter to all my intuition. This is one of those things scientists have to be very, very careful about – not letting our expectations get in the way of reality. If you expect to see something, you’re more likely to see it.

So why does everyone think anyone can win Talladega?

It’s not at all surprising – it’s called the von Restorff or isolation effect. It’s named after a woman named Hedwig von Restorff (1906-1962), a psychiatrist and children’s doctor who conducted a set of memory experiments and found that an isolated dissimilar item surrounded by otherwise similar items would be better remembered.  In other words, it basically says that when something stands out as being very unusual, we tend to remember it.  For example, consider two lists

21 GTS
16 PDY
13 MTX
54 DVQ

The same three-letter sequence is in both lists. If I showed you the lists, then took them away and asked you what you remembered, you’d remember the letters better if I’d given you the A list than if I’d given you the B-list.  We tend to remember the unusual. And there’s a reverse effect, in that you may actually remember less about the things that don’t stand out.

Now if only I could wipe Michael Waltrip’s last dance (and 70’s mustache) out of my memory.

Oct 032014

@NASCARRealTime, @TheOrangeCone and @CircleTrackNerd had an interesting dialog when the 2015 rules were announced. They were debating whether the track records that are now standing are going to be essentially locked into history. The debate ended with an appeal to me and Goody’s Headache Powder. TwitterConvo_TrackRecords

When the Gen-6 car was introduced in 2013, new track speed records were established at 19 of 32 qualifying sessions. Yes, that’s more tracks than we run, but the record at Martinsville, for example, was broken in the spring and again in the fall. Another way to look at it is that out of 20 tracks where there was an opportunity to break a track record (meaning we exclude Dega and Daytona because their records are pre-restrictor plate, plus rainouts) – it happened at 16 places.

Why? The primary change was the much lighter car – they took 150 lbs off relative to the Gen-5 car while maintaining the same engine power and increasing downforce.

That changes in 2015, as one of the new rules NASCAR announced is a 1.170″ tapered spacer that will reduce power by about 125 hp. Gene Stefanyshyn (senior vice president of innovation and racing development for NASCAR) expects this is only going to decrease speeds by no more than 3-4 mph in most instances.

That seems like a weird trade off, right? 125 hp = 3-4 mph? Well, that’s because the engine isn’t the only place they’re making changes. They’re going to decrease the spoiler size to six inches, which will take away about 300 lbs of downforce, but will also reduce the drag on the car.

Here’s the theory: racing on ovals is won and lost in the corners. The primary impact of horsepower (all other things held equal) is determining maximum straightaway speed. In the corners, you’re not (except for plate tracks) using all the horsepower you have – you’re more limited by your lateral grip, which is determined by downforce.

Any driver can mash the gas coming down the frontstretch. What makes a difference is how soon they get off the gas/onto the brakes coming into the corner and how soon they get onto the throttle coming out of the corner. Let’s say you have to slow to 180mph to make a corner. It makes a difference when you start braking if you’re going 210 mph vs. going 200 mph.

You may actually be able to take the corner faster if you aren’t slowing the car down quite so much. A number of the drivers and NASCAR officials have stated that slowing down the cars a little (and remember, we’re talking 3-4 mph) should give drivers more options in the corners and thus make for more exciting racing.

But What About the Records?

Yes. A lot of records were broken in 2013. But a number of those records have been broken this year. The overall trend of pole qualifying times is up. Even when a rules change or a track change decreases the qualifying time, the next year, it starts creeping back up. I plotted qualifying times for a couple tracks to show this. Everyone’s been talking about these records being broken as if the speeds were stuck and then suddenly they jumped up. Not at all.


So here’s Charlotte.  There are year-to-year oscillations, but the overall qualifying times have ben nothing but increasing.  On average, over the last twenty years, they’ve increased by about 0.7 mph each year.  So let’s assume that speeds are down across the board by 3 mph. In four or five years, they will likely be right back where they were before. You see a big jump in the slope of the curve (how fast it’s getting larger) from Gen 1 to Gen 2, but after Gen 2, it’s been pretty consistent.

I put each of the car generations on the graph to see how much difference changing car models actually made, but the track condition also makes a huge difference. Let’s blow up the last twenty years.


So there was a big jump after the 1994 repave. Then remember 2005 when we all learned a new word: levigation? They diamond ground the track, which made it very rough. Pole speeds jumped and the fall race that year was an unmitigated disaster, with tires blowing left and right. They did a formal repave in 2006.

And if you really want to see what a different track surfaces make, take a look at Kansas.


After the re-pave, the pole speed jumped from 176 mph to 191 mph. There’s almost no history to rely on, but the following year, the fall speed was 4.3 mph slower than the spring speed.

In addition to major changes in the track, you get year-to-year oscillations due to things like weather and the tires Goodyear provides. One of the goals for the new set up is to allow Goodyear to make grippier tires that wear out faster, which could have a big impact on qualifying and (more importantly) racing.

So are the track records safe?  Probably for a couple of years.  But I’m not betting for much beyond that. The guys designing the race cars are just too clever to let little things like rules keep them down. The impressive thing is going to be if they figure out how to make the cars faster while also making the engines more reliable and longer lasting.

A final note. In the end, we judge drivers on race wins and championships. Poles may help you win a race, but I guarantee you if you give a driver a choice between a win and a pole, they’re going to choose the win.

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