Apr 172015

Sounds like an energy drink, right?

Listening to Kyle Busch’s press conference Wednesday was alternately fascinating and cringe-worthy. The fact that he remembers so much about the crash is amazing – it will be a great boon to the safety people who probably will use this as a case study in the future. And best wishes to Kyle to get well soon.

Kyle said he left the track at 176 mph, hit at 90 mph and sustained 90 Gs.  My twitter was flooded with people asking “90Gs? No one could survive that kind of a hit.”

That’s actually not true. Trying to quantify a crash via one number is a nice attempt at simplifying things, but totally wrong.

Warning – I wrote and researched this while flying halfway across the country, so we’re likely to need a re-write when I get back home Monday and have a little more time to make this prettier. But let’s start by clarifying terms.


The ‘G’ is quite possibly the most misunderstood unit in racing.  A ‘G’ measures acceleration, not force.   One ‘G’  is equal to the acceleration of any object due to Earth’s gravity. You are experiencing one ‘G’ right now. The product of your mass times the acceleration due to gravity is your weight.

Acceleration is how fast you change speed. If you go from 0 to 62 mph in 2.8 seconds (like the Lykan HyperSport in the Furious 7 Movie), you’ve got an acceleration of 22.4 mph each second. Every second, your speed increases by 22.4 mph. It’s an acceleration of a little more than 1G. (which, by the way does may the Etihad towers jump possible. I did the math, just thought I’d throw that in.)

Let’s set the scale. The Space Shuttle pulled 3G on launch, Apollo 16 pulled 7G on re-entry. A Formula 1 car pulls about 5-6 G laterally during sharp turns and 4-5G during linear acceleration. I’ve got a story in the Physics of NASCAR book about Texas Motor Speedway having to cancel an open-wheel race at the last moment because the drivers were pulling so many Gs that they were having mini blackouts. A good rollercoaster will give you 2-3G.

Electronics spec’ed for the military for use in shells have to survive 15,000 G.

Weight is the force resulting from the acceleration. Remember F-ma? When you experience ’3Gs’ of acceleration, the force you experience is the number of G’s times your weight.

We use the unit ‘G’ just like a unit like ‘dozen’.  I can express anything in terms of dozens:  a dozen eggs, a dozen jellybeans or a dozen beers.  Likewise, we can use the unit ‘G’ to express the acceleration of anything.  I can measure the acceleration when you step on the gas after stopping at a red light in ‘G’s.   I can measure the acceleration you feel on a rollercoaster in Gs.

Important: Although Earth’s gravity pulls down (toward the center of the Earth), we use ‘G’ to measure acceleration in any direction:  up or down, back or forth, or sideways.

How Many G’s Can a Person Withstand?

Again, this is by no means meant to minimize Kyle’s experience. He had a really hard crash and broke bones in both legs. So don’t interpret what I’m going to say as trying to say he’s lying or wrong or is trying to exaggerate his injury. It was serious.

But it wasn’t as simple as “90 Gs”

I’m pretty sure the numbers Kyle had were the numbers from the car’s transponder. As far as I know, NASCAR hasn’t instituted in-ear accelerometers like IndyCar.

An accelerometer is exactly what is sounds like: a meter for acceleration. Most iPads and iPhones today have one. Especially given the increasing concern about concussion, IndyCar and F1 have both provided drivers with a tiny accelerometer that fits into the ear and thus gives a much more accurate measurement of the actual acceleration of the head. (Remember that the problem with concussion is that the brain actually hits the inside of the skull.)

NASCAR relies on a transponder located near the frame rails (low) in the car. That means it measures what happens to the car, not the driver. A number of safety measures make the driver slow down less quickly than the car. I’ll come back to that.

There are three primary factors in a crash: The change in speed, the time over which the change in speed happens and the direction of the force.

So it’s not only how fast you’re going when you crash, it’s how fast you stop. When the people who study these things talk about crashes, they talk about the “crash pulse”, which incorporates the first two of these factors. Here’s one I drew for illustration.


When someone talks about 90G, they mean that was the peak value of the acceleration vs time curve was 90G. In my plot above, both curves show a crash from the same starting speed. The difference is that the red curve was a case in which the force/acceleration was spread out over a longer time. That’s why the peak value is lower.

How many Gs you experience depends on your starting and ending speeds and how long it takes you to stop. In the case of a crash where you go from 90 mph to stopped over 1 second, you experience about 4 Gs. If it happens in a tenth of a second, you experience 4o Gs.

Now let’s look at a real crash pulse.


Here, you see the crash and you see the backlash – that’s the negative acceleration on the right side of the graph. The details of these graph give you a much fuller picture of a crash because you learn how the force was distributed in time.

Although the peak force was 90G, that 90G was applied for a short time. Lesser accelerations were experienced during the rest of the crash. A peak force is like a snapshot of a dance. You get one impression, but it’s not the whole picture.

Let’s get back to measuring the car vs. measuring the driver. The driver is belted in by 2 to 3-inch-wide belts over the shoulders, around the lap and around the legs. Those belts are designed to stretch when they’re stressed, which means that the driver doesn’t stop as quickly as the car stops.

Same thing with the HANS device. The tethers on the helmet allow the driver’s head to move forward, but they slow the rate at which the head moves. So even if the car experiences 90G, the driver experiences less. How much less would require a lot of assumptions, but if the various safety devices double the time it takes for a driver to stop, it halves the force.

I mentioned direction is important. That’s because any force on your body also is a force on your blood. Pilots who make sharp accelerations up or down (parallel to the spine) have issues because the heart has to work extra hard to pump the blood. The human body can withstand higher accelerations perpendicular to the spine than parallel to it.

No, Really. How Many G’s Before It’s Really Bad.

StappSledYeah. That’s what you’re really asking, isn’t it? What are the limits of the human body? These are difficult questions to answer because you can’t really do the experiment. People don’t volunteer to be accelerated really fast so scientists can see if they survive.

With one exception.

Col John Stapp (Air Force, shown at left) was active in the late 40s and early 50s. We didn’t know how far or how fast airplanes (and rockets) would allow us to go. And even if we could build the machinery, would a pilot or passengers survive?

The military didn’t want to hand over soldiers for him to run experiments on.

So he experimented on himself.

Today, that would never happen because there’d be so much paperwork that he’d die of old age before he got approval. But back in the 50s, people got away with a lot more.

The picture shows a test in 1954 where Stapp accelerated at 15g for 0.6 seconds and reached a peak acceleration of 22 second. His record was 46 g, and he sustained more than 25 g for 1.1 seconds.

This was no 90 G, but whereas a driver might experience that acceleration for a couple hundredths of a second, Stapp did it for tenths or full seconds.

These experiments had consequences. There is one really big problem with acceleration perpendicular to your spine. Your eyes bug out (or in).

No, seriously. Your eyes are held into your skull by a couple muscles and optic nerves. High accelerations (and decelerations) is like putting your peepers on a bungee cord. What finally stopped Stapp’s experiments was that he sustained major damage to his vision. I highly recommend http://www.ejectionsite.com/stapp.htm if you’d like to learn more.

C’Mon. How Many G’s Has a Human Being Sustained Before…

O.K. A paper (Society of Automotive Engineers. Indy racecar crash analysis. Automotive Engineering International, June 1999, pages 87-90) says that IndyCar drivers have survived 100G+ crashes. I don’t know yet whether those are crashes measured with the in-ear accelerometer, so it’s difficult to make a direct comparison with NASCAR.

But remember that even smaller accelerations – if applied in just the wrong way — can have equally catastrophic results for the driver.

Closing note: You know what they use in doing crash research? Yes, Crash Test Dummies, but the human body is so complex and intricate that a dummy can’t tell you everything.

They use cadavers.






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.


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 202015

When winning means a few hundredths of a second, nothing is too small to be ignored.

I’ve talked a lot about energy and the importance of using it as efficiently as possible in racing. Gasoline provides a certain amount of stored (a.k.a. potential) energy. Everyone gets the same amount of energy. Winning lies in part in how efficiently you can transform the potential energy of the gasoline into kinetic energy (also known as speed).

We’ve talked about friction – anywhere two moving parts touch, you have to use some of the energy from the gasoline to overcome their resistance to rubbing past each other. Friction robs a car of speed.

There’s another way energy is used up: Deformation. Also known colloquially as “Squishing”.  Take a gander at the video below.

This is a common example we use in physics classes to illustrate the conversion of energy from gravitational potential energy (energy of position) to kinetic energy (energy of motion). The ball starts out still, but raised to some height. Its energy it entirely potential. As it falls, it loses potential energy and gains kinetic energy.

If the world were perfect (a phrase that should raise a red flag), the ball would return to it’s original height. All of the kinetic energy would be converted back into potential energy. Hopefully, you noticed that it didn’t. Run the video one more time and look at the overlay (the yellow circle) as the ball hits the floor. I wanted to emphasize what happens when the ball hits the floor.

It squishes. Deforms. Whatever. It changes shape.

Changing shape requires energy. That energy can’t be converted back into potential energy, which is why the ball doesn’t bounce back to its original height.  (Note that there are other places where we lose energy. For example, the ‘plonk’ sound when the ball hits the floor takes energy to create, too.)

In some cases, the fact that it takes energy to deform something is good. For example, some areas of a car are designed to crumple more easily than others so that the energy of the moving car is used to smush the car and not transferred to the people inside.  These are cleverly called “crumple zones”.

In other cases, deformation is not such a good thing. And one place where deformation happens a lot is in the tires of a car. Look at a tire lying on the ground. It’s round. When you put that tire on the car, the weight of the car deforms the tire, creating a flat spot – a deformation. I’ve embedded a video below from Goodyear – it’s part of their modeling package for simulations and it shows how the tires continuously deform as the car moves.

Every time the tire deforms upon hitting the ground, then springs back, you lose energy.

This is called rolling resistance. The United States Department of Energy estimates that 5% to 15% of the energy contained in the gasoline goes to overcoming rolling resistance in passenger cars. In big trucks, that number can be as high as 15% – 30% because the tires are wider and there are a lot more of them.

To put this in perspective: If you lose 20% of your energy to rolling resistance, that means that one out of every five fill-ups is used entirely to overcome the rolling resistance of the tires. (Side note: Once you consider all the friction, all the rolling resistance, the energy used by cooling units, only 12%-20% of the energy contained in the fuel is used to actually make a passenger car move.

GY_FuelSavinTiresIf you go to a tire store (as I did recently, thank you potholes), you’ll find advertising displays that talk about low rolling resistance tires. The grab in these ads is that low rolling resistance tires save you money by decreasing the amount of energy lost to the tires.

This is actually a thing. They run tests and studies to prove that it is true. Now, of course, this only works if you keep your tires properly inflated. Underinflated tires on a car deform a lot more than properly inflated tires.  You can verify this for yourself. As you let the air out of a ball and measure how far it bounces back after dropping it, the more underinflated it is, the lower that bounce-back will be.

Ideally, Goodyear would provide tires with exceptionally low rolling resistance; however, rolling resistance is linked to other parameters. A harder tire doesn’t deform as easily, so it will have lower rolling resistance; however, we also know that harder tires don’t wear much and don’t offer a lot of grip. Softer squishy tires give good grip – but have have higher rolling resistance.

Goodyear (and every other tire manufacturer) does research to find ways to decrease rolling resistance without sacrificing grip. A lot of their work is on the tread compounds. Tread compounds are super top-secret recipes with a huge number of ingredients that include everything from rubber to carbon and/or silica nanoparticles.

Now in NASCAR, all teams get the same tires – and teams are not allowed to make any changes to the tires – at all. So although the tires do affect the fuel mileage, every team gets the same equipment. If Goodyear comes up with a way to make a lower rolling resistance tire, everyone on track benefits.

Small Effects Add Up

You may be thinking that we’re talking pretty small numbers. We are, but they accumulate. If there’s something you can do that save you a penny every mile and you drive 50,000 miles a year, that’s $500.  On a larger scale, research indicates that reducing the rolling resistance by 10% would increase fuel mileage by 1%. That’s tiny, right? Well, in 2014, the U.S. used 136.78 billion gallons of gasoline. Decreasing that by 1% saves over a billion gallons of gas. Little things add up – as I keep telling my husband when he doesn’t turn off the light when he leaves the room.




Mar 062015

Jeff Gordon’s decision to step away from full-time NASCAR Sprint Cup racing has resulted in a lot of discussion about aging drivers. We’re on the verge of a turnover as a number of drivers (Johnson, Stewart, Junior, Harvick among others) reach their forties. And what an appropriate topic for this week as I hit one of those milestone birthdays next week myself.

Slowing down is a part of aging. The print on menus shrinks, you wake up with aches and pains you can’t figure out where they came from, and you find that it takes you longer to recover from colds and injuries. Sprint Cup drivers are no different. In fact, it’s probably exacerbated because they subject their bodies to more physical punishment than your average human being.

But there are some advantages to aging. You’ve got more experience.  And… well, I’m sure there are others.

So how does age affect a driver’s career? Let’s look at the numbers. (And while you’re at it, check out Eric Chemi’s blog – he took a different approach, but came up with mostly the same conclusions.)

What Do We Measure?

The challenge in questions like this is what to graph that actually makes some sense.

DriverAges_Stewart The first obvious thing to try is wins (or top 5s or top 10s) vs. age, right? I did this (at right) to look for obvious trends. (Note – you can click on any of these graphs and they should like to a full-size version so you can see details.)

This is pretty useless. Stewart won championships at ages 31, 34 and 40. All years where he won a respectable number of races; however, there are years where he won a lot of races and didn’t win the championship.

I also plotted Top 5s and Top 10s this way and it wasn’t any more enlightening.

So I had to re-think a little. What we’re interested in is whether a driver becomes a worse driver as he or she ages. This got me thinking about cumulative stats.

If you’re staying at the same level, you ought to add the same number of wins each year (on average, of course). So what if I plot the cumulative wins as a function of age. That turned out to yield some interesting information.

Cumulative Statistics

It’s always rewarding when you plot something and you realize you finally found the right thing to measure and graph. As a note, I did not include years at the end of a driver’s career where he (and they’ll all men here) didn’t run all the races that year. A number of drivers ran part-time at the ends of their careers, some for lower-tier teams and I didn’t think that would be a fair representation of their career to include those later years.

Let’s start by looking at stats for someone with a long career that spans a wide age range: Darrell Waltrip.

From top to bottom are cumulative wins, cumulative top 5s and cumulative top 10s. There are some subtle differences between the three graphs, but let’s talka bout what they have in common.

If you look at the later years, the graphs become essentially flat – which means there were no more wins, top 5s or top 10s. But the point at which they plateau changes. The wins flatten out first (no new wins after age 45), then the top 5s (only two more after age 50)  and then top 10s (8 after age 50).

The areas where the slope of the graph is constant over a period of time I would characterize as consistent. They are adding to their record at the same rate. All three of Waltrip’s championships (shown in the highlighted regions) came during that period of time.


DriverAges_Portrait_waltripByOwner2This would seem to suggest that this is a driver who reached a certain age and just couldn’t hack it after that – but there are some extenuating circumstances, namely a crash at age 43 and his transition from Hendrick to becoming a driver-owner shortly after.  I’ve put a thumbnail of the graph to right – click to see it larger.

Just a warning that you have to be careful about the rationale.

A number of drivers have very similar looking graphs: Both Labonte brothers, Dale Jarrett, and Mark Martin. But in those cases, there were also extenuating circumstances in terms of changing to lower-tier teams (Bobby Labonte went from Gibbs to Petty, for example). So let’s look at the drivers who don’t follow this pattern.



Wow. You want to talk consistent? Here’s a man who (until the nightmares of the last two years) is almost one straight line from start to finish. The top 5s and top 10s are almost perfectly straight lines. The wins have a little more scatter – but that’s typical because the overall numbers are smaller. Jimmie Johnson’s graphs look very similar.

When we analyze graphs we like to talk about curvature. There’s no curvature here. If the graph curved up (i.e. looked like a saucer), that means the person was getting better. If the graph curves down (as it does when it plateaus), then the person is getting worse.

And now for one of the the interesting ones. It’s interesting in part because Jeff Gordon has driven for the same company his entire career, which eliminates the question of equipment from the analysis. Here’s the raw data for wins.


Again, it’s small to save space – click to get a larger version. This is really interesting. You can divide his career into specific segments – see how the slope changes in different ranges of years? My first attempt to explain this was to look at personal events like marriages and children. There might have been a correlation there, but them I looked at his crew chiefs.


That’s sort of interesting, huh? I didn’t make a line during Steve Letarte’s (I know, I spelled it wrong in the graph) tenure. There was a jump there, then it was pretty flat. But that’s a pretty convincing correlation, I think.

Gordon’s still very consistent when it come to the top 5s and top 10s.


Okay, But Can Older Drivers Compete Against Younger Ones?

I know. I got carried away with the data. I do that.

I made a lot of other plots, but here’s the one I think is the most interesting.DriverAges_Champions

There’s been an influx of younger drivers – they start earlier and one might think that would lead the average age of the Sprint Cup Champion to be going down. Overall, though, it’s not. It’s going up. The most recent “Young” winner is Brad Keselowski – and he was 28 years old.


Don’t count the old folks out yet. Even at the advanced age of (gasp) 40-something, drivers like Tony Stewart (pre the last two years), Jimmie Johnson, and Matt Kenseth are remaining consistent with their performance when they started in the series.

Ever scarier, if you look at Kevin Harvick or Brad Keselowski’s graphs, they’re better than straight lines. These drivers are still improving (even as Harvick approaches 40 and Keselowski 30), which means we probably haven’t seen the best of them yet.


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.





Feb 062015

There’s a lot of talk about all the rules changes for 2015. The limiting of the horsepower has been a hot topic of discussion, with people suggesting that NASCAR is basically mandating spec engines.  Here’s a couple of things to think about in terms of engines as we get closer to Daytona.

“750 hp Engine” Doesn’t Tell the Whole Story

When someone says they have a 900-horsepower engine, the only thing that tells you is that the maximum power it outputs is 900 hp.  Importantly, power output changes with revolutions per minute (rpm), as shown graphically below.


The power curves for these two cars have the same maximum horsepower, but the range over which they have that horsepower is different.  Let’s say the gearing is such that you’re running most of the race in the 8000-rpm range. Car 1 would have an advantage because (in that rpm range), it has higher horsepower. Car 2′s curve, however, is broader, which means it has a higher horsepower over a broader range.

Tapered Spacers

The big impetus for engine rule changes is NASCAR’s desire to lower speeds (which, it is theorized, will improve racing by lessening the effect of aerodynamics making it hard to pass when cars get close to each other).

There are lots of ways to decrease engine horsepower, but remember that teams have put untold amounts of money into designing and refining the current engines. Designing entirely new engines is a major undertaking, and a risk to mandate without pretty high confidence that lower horsepower will indeed help the quality of racing.

For 2015 NASCAR has gone with the simplest solution: a 1.170 tapered spacer that they expect will reduce power by about 125 hp.

Combustion is the chemical reaction whereby fuel mixes with oxygen and releases energy. It’s very similar to another chemical process called respiration, which is how your body converts food to energy.  In this case, you mix two fuel molecules (C8H18 is octane, one of the hydrocarbons in fuel) and 25 oxygen molecules.



Remember your chemistry teaching talking about stoichiometry? Stoichiometry is the ratio of molecules, because they only combine in particular ways. If you’ve got four octane molecules, you need 50 oxygen molecules, etc. Combustion demands that exact ratio. The amount of fuel you put in a cylinder depends on how much air you can get in.

That’s how tapered spacers and restrictor plates work – they limit how much air gets into the cylinder, which limits how much fuel you can put into the cylinder, which in turn limits how much energy is produced.


A couple people have asked if this is going to have the the same effect as a restrictor plate. No! Fluids (and air is a fluid) travels differently through an orifice (the technical word for a hole) and through a nozzle (which is what the tapered space is).  Don’t believe me?  Here’s proof:

The tapered spacer does change how the air goes into the cylinder and that is something the teams are studying using Computational Fluid Dynamics — and figuring out how to use to their advantage.


The Rules Don’t Say “Your Engine Must Be 770 hp”

NASCAR engine rules address the physical properties of the engine – things like cylinder height and bore, compression ratio, and which materials can be used.  This has always been the case. They control things like rpms and horsepower indirectly via things like gear rules.

So teams actually have a fair number of variables with which to experiment.  The big emphasis is energy efficiency. There are two major energy transformations in the engines: combustion, which converts the potential energy in the fuel to the linear motion of the pistons, and then the linear motion of the pistons is converted to rotational motion.

The conversion processes aren’t perfect. If the air-fuel mixture isn’t right, you don’t get all the energy out of the fuel. This is addressed by specific geometry issues (which controls how the air gets into the cylinder), and EFI mapping.

The other main culprit in energy losses is friction.  In a conventional road car, only about 14% of the energy you put into it actually gets to the wheels. The rest is lost (or used by the air conditioning, power windows, radio, etc.).  Most of the energy losses are in the engine. In a conventional car, 60-70% of the energy loss is in the engine.

Surprisingly, NASCAR (and most race car) engines are more efficient than passenger car engines, due in large part to the use of advanced coatings on engine parts. A typical valve has at least three different coatings – A hard coating on the tip to protect against valve lash wear, low-friction coatings on the stem, and hard coatings on the dome to protect against valve seat recession.

MetTech_ValveFailureThese coatings are often very thin – a hair’s width or two or three. Materials used include Titanium Nitride (that’s what those gold-colored drill bits are coated with) and diamond-like carbon (DLC). DLC has a much smaller coefficient of friction against steel than steel (0.7) or titanium nitride (0.3). DLC has a coefficient of friction on steel of 0.2.

There are companies in the Charlotte area that offer detailed failure analysis of engine parts, like the valve below. They use scanning electron microscopy to examine the parts. The culprit is often the coatings coming off.

Remember back in 2008, when Hendrick Motorsports had a baffling sweep of engine failures? The culprit was the coatings on the cam and/or lifters. They delaminated (i.e. came off) and the small flakes got into other parts of the engine. The clearances between moving parts in a race engine are much smaller and the tiny flakes of coating jammed up the engines, leading to failure.

Teams keep such detailed records of which parts go in which cars that Hendrik was able to track down the batch of parts that failed and ensure they weren’t being used in any other cars.

So if these coatings make engines more efficient, why aren’t they in all our cars?  The usual answer – cost. Coated parts are more expensive and people don’t want to pay extra money for a small improvement in performance/duration. Race teams, on the other hand will spend whatever they can to shave a few more seconds off their time.

So there it is. We’re still nowhere near spec engines, even with the new rules.  I suspect at some point, there will be an engine design initiative, but NASCAR has been fairly respectful for not throwing a zillion changes at the teams at one time.

And don’t forget, we won’t even see the tapered spacer until after Daytona because Daytona and Talladega are still using restrictor plates.

Jan 232015

I was at a panel discussion some years ago at a motorsports engineering meeting about materials allowed on the car by different racing series. They had the tech people for IMSA, F1, Indy and NASCAR up there answering questions from the audience.

NASCAR gets a lot of ribbing because compared to, say, F1, we are sort of in the dark ages. See, NASCAR (in attempts to keep cost reasonable) frowns on “exotic materials”. Tubes in the chassis are steel, not titanium or titanium alloys. Exotic is usually a code word for “expensive”.

Someone asked the panel what exactly was meant by “exotic materials”. Robin Pemberton replied

“If you have to ask, it’s exotic.”

Lots of people think that NASCAR requires that all engine blocks be made of cast iron.  That’s actually not written anywhere.  The engine blocks have to be from the manufacturer’s original castings. There is an explicit rule that the engine blocks can’t be aluminum.

Why would you want aluminum?  Aluminum is much lighter. Newton’s Law says that the force the engine provides is equal to the product of mass times acceleration (F=ma). Don’t let people tell you NASCAR is about speed. It’s really about acceleration.

Newton’s law says that if you want a big acceleration, you need a big force and/or a small mass. So anything you can do to lighten up the engine (which sits relatively high in the car) will help your acceleration and your handling.

Ford’s new F-150, for example, replaces steel with aluminum to save weight and thus improve gas mileage. Aluminum has it’s challenges, but since NASCAR doesn’t allow it to be used in the engine block, let’s look at what you might do.

Crystal Structure

Get yourself a pencil and a diamond.  I’ll wait.

The pencil lead is grey, opaque and soft. The diamond is clear, shiny and very hard. But they’re both nothing more than Carbon atoms, with the atoms arranged differently.


This is graphite (pencil lead). Ignore the colors, they’re just there to show you that graphite is sheets upon sheets of carbon atoms arranged in a hexagonal pattern.  Every ball there represents a carbon atom.

Diamond is a little more complicated. Exact same atoms, but different arrangement (below).



Two big differences here to notice. First, each carbon atom in graphite is connected to three other carbon atoms, but in diamond, each carbon atom is connected to four other carbon atoms. This is the reason for the second thing to notice:  Graphite is made of planes of atoms with no connection between those planes. That means that it’s easy to shear (slide off) entire planes of atoms. That’s what happens when you write. The diamond planes are interconnected, which makes it much harder to remove one layer.

Yeah, But What’s That Got to Do with Engines?

NASCAR engine blocks are indeed made from cast iron, but not the cast iron you’re probably used to. A brief lesson on how you make cast iron. You start with iron, which is a very malleable (meaning easily deformed) material. Through millions of years of experimentation, people realized that you could change the properties of cast iron depending on what you added.

In face, if you put small amounts of Carbon in with the iron and heat treat it in a very specific way, the Carbon freezes in graphite flakes, like the picture on the left below. The flakes give the iron a lot of strength, but they also make it brittle. The sharp points on those graphite flakes are very high-stress points, which means it’s easier to start a crack there. If you’ve ever cracked an engine block or a frying pan, you know how that works. Once the crack starts, it keeps cracking. So gray iron, which is what this type is called, is strong, but brittle.

Then some enterprising soul figured out that if you add some magnesium, the Carbon doesn’t form flakes, it forms globs. (Yes, globs is the technical term.) Since there are no sharp points, there’s less stress and less cracking, which is why this type of cast iron is called ductile iron. Ductile being the opposite of brittle. This solves the problem of cracking, but ductile iron is nowhere near as strong as gray iron.


Sometime in the 1960′s, someone Baby Bear’ed cast iron. They found that if you added Mg anywhere from 0.007% to 0.015%, you get something spectacular, which is shown in the bottom-most picture. (Credit for the pictures: http://www.atlasfdry.com/graphite-iron.htm)

To set the scale, the bar shown is 50 micrometers. Micro just means millionth. Most human hairs are between 50 and 100 micrometers in diameter. The picture you’re looking at is three or four hair-widths wide.

If I had found this, I would have called it “micro-coral”. You get some of the flat flakes of gray iron, which provides the strength, but the edges of the flakes are round (like ductile iron). This cast iron is just right. It’s not as strong as gray iron, but it also doesn’t crack as easily as ductile iron.

This is called Compacted Graphitic Iron or, if you’re German, Gusseisen mit Vermiculargraphit.  I’ll abbreviate it CGI.

And CGI is the “exotic material” NASCAR teams use for engine blocks. You can have a comparable strength with less weight. CGI engine blocks are especially useful in V-shaped engines because that area between the two cylinder banks (the two edges of the ‘V’) has to take a lot of stress.

You may wonder why, if we knew about this material in the 1960′s, it’s taken so long to use it for engines. The reason is because of the very fine control over the amount of Magnesium added. It has to be controlled to within a few thousandths of a percent. A change of just one one-hundredth of a percent can drop the tensile strength by 25%. A person in a lab can exert this much control, but if you’re going to make this in a production facility, you need computers and computerized manufacturing.

This Week’s Semi-Gratuitous Colorful Picture for Moody

The pictures I’m showing you are Scanning Electron Micrographs. Instead of using light waves, we use electrons to make the image. Light can be thought of as a particle or a wave. So can things like electrons, protons, neutrons, etc.

Electrons have a much smaller wavelength than visible light, which means electrons can “see” things our eyes have no chance of seeing. Color doesn’t really mean anything when you’re talking electrons because color refers to a range of wavelengths that our eyes are capable of seeing.

But, of course, that doesn’t stop scientists from artificially coloring their images to make them clearer to explain or, sometimes, just because you can. So here, from The Telegraph, is an artificially colored scanning electron micrograph of a flea done by a gentleman named Steve Gschmeissner. He’s got everything from cells to bugs to plants.


And yes, there are a lot of scientists who buy images like this to frame and put on their walls. I have x-ray images of calla lilies and eucalyptus in my living room.

But no bugs.



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