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.



Jan 092015

Welcome back from the holiday shut down. December in the U.S. is like August in Europe. Everyone you need something from is gone. I’m happy to be back to the regular grind.

Forty-three days till the Daytona 500. The shops are buzzing with activity as everyone adjusts to another new rules package. The engine folks are working overtime dealing with the changes there. The only thing that’s slowed down is planning for on-track independent testing, since that’s been eliminated this year. But more time in the wind tunnel, on the seven-post machine, at the computers.

Pit crews have a number of new issues to deal with this year and they stem from NASCAR’s decision to eliminate the tradition of having one official in each pit box during pit stops. Starting this year, they’ll rely on cameras to provide information about any infractions and calls will be made from a central location where all the camera feeds are monitored.

This change necessitates some compromises. Some rules will be easier to enforce via the cameras, while others will be more difficult. As the NASCAR Insiders point out, one of the less-enforced rules is that teams can’t be on the ground in their own pit stall until their enters the pit box immediately behind theirs.   The Insiders note that when NASCAR tested the system in 2014, they found that this rule was routinely violated, but called by officials only when the violation was blatant.

funny gifs

The gif above come from:  http://www.gifbin.com/988955 and it’s there to illustrate that one of the violations that will be more difficult to enforce with the video system is whether all the lugnuts are on tightly or not. Here’s the verbiage from the 2014 rule book.

Where tire(s)/wheel(s) are replaced, all lug nuts must be installed before the car leaves the assigned pit box area. When a NASCAR Official detects a violation, the car must return to its assigned pit box for inspection.

200610Lowes_TireCloseUpIf a lugnut ends up on the ground instead of on a wheel, that’s pretty obvious and officials would require the team to bring the car back in. (No one ever ‘inspected’ the tire – they just put a lug nut on the lug.)

NASCAR uses a five-stud configuration for their tires. Some sports cars and open-wheel cars using a single, central stud, but NASCAR likes to stick with things that look more like what we have on our cars.

As a side note, one of the disadvantages of the five-lug system is that when a lug nut gets away from the pneumatic air wrench (which spins it pretty quickly), it behaves very much like a bullet when it goes flying. Most people who have spent time on Pit Road have been hit by a flying lug nut. It hurts. Without proper head and eye protection, a flying lug nut could do some real damage.

Teams do everything they can to make getting tires on and off the car as fast and fail-proof as possible.


Notice that you see hardly any thread once the lugs are on. The rules require that the first thread must be visible when the lug nut is installed. The remainder of the lugs are smooth and the outmost portion rounded to enable the wheels to slide on quickly and the lugs to tighten fast. Teams are experimenting with different types of air guns to try to speed up their pit stops.

The lugs are mandated to be solid, one-piece heavy duty 5/8 inch diameter with 18 threads per inch. The lugnut itself is required to be one inch (OD) and a minimum of 0.650 inches thick.  So, if there’s 18 threads per inch and the width of the lug nut is 0.650 inches, then there are (18 x 0.65 = 11.7) just about 12 threads in play.

Yes, teams have been caught boring our the lug nuts so that there are fewer threads that have to catch, which means they go on faster.

The obvious question is: “How many lug nuts do you actually need to hold the wheel on?”  I asked a former tire changer. He gave me a big grin. His answer?

Two. But they have to be the right two.

The two next to each other won’t work very well. Two approximately across from each other would be better. Three would be even better. Two lug nuts aren’t ideal, but five is probably overkill.

Which brings us to the people questioning whether this is a really bad idea on NASCAR’s part because it encourages the teams to do something unsafe – possibly to skimp on making sure that every last lug nut is one-hundred-percent, absolutely positively tight as it can be. Teams will cheat a little now that they’re not being watched, which means we’re likely to have safety issues with wheels coming off.

It’s true that teams may not be as paranoid about making sure they don’t do something they could get called for. But the penalties have been called primarily for missing lugnuts, not those that aren’t completely tightened because that’s very difficult to see – camera or in person.

Plus, it’s in the team’s interest not to leave the lugs loose. If one is noticeably loose, you’re likely to develop a vibration in the wheel and that causes not only a potential problem with the wheel, it can totally freak out a driver into thinking he’s about to have a flat.

We’ve seen tire changers signals to the crew chief that they are afraid they missed a lug — even when the official didn’t see it or call it. A crew chief may call a driver back to check, just because a crash could knock you completely out of a race while checking will only set you back a lap or maybe two.

The rule I’m far more concerned about in terms of safety is that NASCAR will not allow one team to help the team in the next box from over the wall. The origin of the rule is to prevent one team (say a team in the Chase) from getting essentially an extra pit crew member, or allowing their pit crew to go faster because they’re got a safety net in the form of someone else corralling their stray tires.

But, the danger of a tire rolling out of a pit box and being punted by a car is significant. Tire plus wheel is seventy plus pounds. A flying tire can literally kill someone one. NASCAR is going to be more rigorous about ensuring that pit crew members  stay in control of the tires until they are more than half way back to the wall (where, in theory, they wouldn’t roll out into the path of an oncoming car), but I would really hate to see a case in which someone hesitated to stop a tire that ended up posing a threat to the people on Pit Road.

The NASCAR Insiders suggest that there are likely to be a plague of penalties in the first couple of races as the teams adjust to the new enforcement criteria. As usual, they’ll adapt quickly, but keep an eye on Pit Road for the first couple races of 2015.

In only 43 days!

And since I know Moody will be disappointed at the lack of colorful graphics, I’ll leave you with a New Year’s present. When you were toasting in the start of 2015, you probably weren’t paying a lot of attention to the bubbles in your bubbly. Well, a couple fluid dynamicists in France have made a career of studying bubbles and they provided some neat diagrams showing how fluid dynamics works in champagne.


I, of course, will have to procure a couple bottles of champagne so I can check this out myself…

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 202014

One of the biggest changes NASCAR has instituted for the 2015 season is eliminating individual team testing at any tracks. In 2014, teams were limited to four tests and were not allowed to test at tracks that were included in the schedule.  NASCAR may run some limited tests, but they won’t be having the week-long marathon that was Daytona Speedweeks.

Given the intensive schedule in February, most teams are happy to be losing the Daytona tests. A lot of focus for one race – and a race in which the probability that the car comes home in one piece is vanishingly tiny.

Will It Save Teams Money?

Even though some teams will amp up other types of testing, eliminating sending a dozen people and a car out to a track will most likely result in a net savings of money.  NASCAR’s done a good job lately talking with the teams and most teams were in favor of the new rule.

Perhaps more important than the dollars saved is the time and energy of the team members. The season is already 36 points-paying races, plus the week before Daytona and All-Star week. That’s a lot of time to be away from home.  Even when they are  in Charlotte, the team members are at the track enough that they don’t really have time to be “at home”. They get to sleep in their own beds, which is nice, but it’s still pretty intense work.

A lot of NASCAR crew members simply burn out. It’s fun being part of a traveling circus – for a little while.  But eating out all the time, getting irregular sleep and dealing with the stress of the race weekend takes its toll. Once you start having kids, or a crisis at home, being on the road becomes a huge barrier to living the rest of your life. There are a lot of former crew chiefs who are very happy working out of the shop.

The few at-track tests that will be allowed will be run by NASCAR, and one assumes that they will schedule those immediately before or after race weekends, which again will minimize transportation costs, although it’s another day away from the shop for the participating crew and the driver.

Types of Testing

You can divide “testing” into two broad categories:  testing with the driver and testing without the driver.  NASCAR has historically come at it from both sides, hoping they’ll meet in the middle.  The testing rule has effectively taken away a lot of the tools on one side with the intent that tools from the other will compensate.

Remember that NASCAR’s goal isn’t so much keeping the status quo. It’s ensuring that whatever the rules are, they don’t give one company a huge advantage over the others.

So here’s my breakdown:


You’ll notice the driving simulators are in a different color – that’s because that’s the only type of ‘testing’ that really involves only the driver. Teams are trying to use this tool in a more scientific way (see my blog on the Ford tech center, for example), but it still doesn’t address the communication between the team and the driver – which I happen to think is one of the most critical aspects of driver-involved testing.


With Driver vs. Without Driver

Some properties of a car are driver independent.  Drag is never a good thing, so any testing that shows you how to lower the car’s drag is useful and requires absolutely no input from the driver.  Similarly, downforce is almost always good, so changes that increase downforce are also good and will be the same, regardless of who’s inside.

But a lot of the magic in setting up a car is finding out what your specific driver prefers for specific conditions at specific tracks. Someone who comes from a dirt-track background has very different preferences than someone who grew up racing open-wheel cars on asphalt.

All drivers want more grip, but different drivers can make do with different levels of grip in different places along the corner. The really successful long-running crew chief/driver combinations (Chad/Jimmie, notably) work because the driver and crew chief have learned how to communicate. The driver can express what the car is doing and the crew chief knows how to change it so that it favor his driver.

What They’re Losing

This will be one of the few seasons where teams have no say in where and when they test. This eliminates their opportunity to strategize. When there were no rules regarding numbers of tests, you did as many tests as you could afford. You might test at places you were historically good at to optimize your changes of winning, or you might test at places you normally didn’t run well at so that you could get better.

When numbers of tests were limited, teams had to strategize. For example, some teams decided to make sure they were really good at one of the three races in a each segment of the chase eliminations. If you won one of those races, you were automatically in. And just about everyone who was in the Chase wanted to test at Homestead. Now those choices are out of the teams’ hands entirely.

Goodyear will run tire tests – but they aren’t promising they’ll include everyone. Tire tests exist for Goodyear to get the information they need to produce a good tire. That goal is often at odds with the information the teams would like to get from testing. Goodyear prefers 3-5 cars in a test.  You need one from each manufacturer at a minimum to ensure fairness, but you don’t want too many voices providing feedback because it becomes impossible to get detail.

Goodyear also has drivers and teams they like testing with. Some drivers are better at providing the kind of feedback Goodyear would like. And, frankly, some teams are just easier to work with than others. If you mandate that every car running the full season get to participate, that disadvantages Goodyear – which means disadvantaging the rest of us.  That kind of scheme means more Chevrolets test than the other brands, simply because there are more Chevrolet cars.  But if you limit the test to one or two teams per manufacturer, then some Chevy teams will be disadvantaged because there won’t be enough slots for everyone.

NASCAR-run tests are the best shot most teams will have to get real testing with the driver in the car.  The tests will be open, so everyone has a shot at participating. The disadvantage is that NASCAR decides the tracks. Given history, NASCAR is likely to hold tests at tracks that have been repaved, or for which there are new tires. Helping teams perform in the Chase is not part of their strategy.

Although both tire tests and NASCAR-run tests will allow the driver and crew chief additional practice at communicating, drivers who are changing companies and/or crew chiefs are the ones who will suffer most from this testing ban. The crew chief-driver relationship is critical. I maintain that one of the reasons Tony Stewart struggled the first part of this year (I’m talking before the accident in New York) is that his time out of the car with the broken leg the year before interrupted his developing the routine week in-week out relationship you need with your crew chief.

If I were Rick Hendrick, for example, I might put Keith Rodden (Kasey Kahne’s new crew chief) and Kasey in an XFINITY Car (that still sounds weird) just to give them some quality one-on-one time during an actual race. Because the cars are different, not a lot of specifics will transfer; however, the practice in driver giving feedback and crew chief adjusting is absolutely critical. Those lower-level series may be the only opportunity some drivers get to forge a bond with a new crew chief.

Without the Driver

I’m going to cover each of these techniques in a little more detail over the break, but for now, suffice it to say that the type of information you get from a technique like a seven-post rig or a wind tunnel is much more general. Yes, the particular car being tested will have the setup (springs, shocks, etc.) that the driver favors, but you’re missing the crucial component of the driver telling you how it feels.  All the charts and graphs in the world do not compensate for having a driver’s butt in the seat.

Below is what the underside of a seven-post rig looks like.  The four large pillars make the tires go up and down. You program the movements of those pillars based on sensor data you collected from on-track testing. The quality of the results go up the better input data you have. If you have data from a couple years ago, or data from the car with a different driver, you’ve lost some fidelity, some precision.


And the unfortunate fact is that we just don’t know enough about reality to be able to replicate it in our theories. A wind tunnel has a huge advantage over a computation fluid dynamics simulation because one of the hardest things to simulate in a computer is turbulence (shown below, in red just because turbulence looks way cooler in red.)


Will The New Rule Level the Playing Field?

One of the claims I’ve heard people make is that banning on-track testing will help the smaller teams. Let’s start by saying that there are very few teams that are single-car operations anymore. Not because a given company has more than one car, but because manufacturers are doing a better job sharing information between their teams. So the question of one-car vs. multi-car really isn’t a relevant as it used to me.

The question of smaller vs. larger teams, however, is very relevant. Anyone can book time at a wind tunnel, but with time running $1200-$1700 an hour, smaller teams will spend much less time in the wind tunnel than teams with higher budgets. Larger teams have their own seven-post rigs, so they can run 24/7 if they are so inclined.

But even if NASCAR limited wind tunnel time and even the amount of computational fluid dynamics calculations you can make, it still wouldn’t be even. Smaller teams pay less. They generally have less-experienced crew and smaller R&D divisions. If you gave everyone exactly the same amount of data for their cars, the smaller teams would not gain as much as the more experienced teams.

RCR has (at last count) five Ph.D.-level people on staff.  The whole point of getting a Ph.D. is that you are being trained not to implement things that are already known, but to figure out things no one else knows. That is the level at which teams are analyzing this data. If I want to work at SpaceX or Orbital Sciences developing the next alternative to the Space Shuttle, there is a very well-defined path I take.  I train for eight to twelve years, learning as much as I can about what we already know. Then I strike out and try to learn things we don’t know.

There isn’t a Ph.D. level program in race car engineering in this country. The folks who are working in the industry have created their own set of knowledge and boy, is it proprietary. Their experience isn’t in books. So even if a team suddenly got a windfall and can hire smart people, they have to find a way to pull them away from the existing teams. I’ve got a Ph.D., but I couldn’t walk into a race team and help them. It would take me months, maybe years, to understand what they’re doing and what they know before I’d be able to make a contribution.

I think the upshot is that the new rule will keep things pretty much the way they are already, with the exception that teams with new driver/crew chief combinations are going to be at a disadvantage because of the lack of on-track testing.



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.

Sep 292014

Last time, I explained what the center of gravity (CG) is. This time, let’s look at why we care.

A fast reminder – the grip you have on each tire depends on the force pressing down on that tire. The force pressing down depends on the weight on that wheel, plus the aerodynamic downforce. Today, I’m ignoring aerodynamic downforce for the sake of argument.

Let’s start by trying to get the car so that the weight is distributed equally on all four tires.  (Yes, I know that’s actually not what you want for ovals, but I’m trying to make things a little simpler here, okay?)  Let’s assume a 3600 lb car+driver, so that would be 900 lbs on each wheel.

Here’s the problem. That weight changes when you brake, accelerate or turn.  You can divide a car into two pieces:  the sprung mass is that part of the car that is supported above the suspension.  (You often include part of the suspension mass in there as well). The unsprung mass is the wheels, tires, and lower half of the suspension.

The unsprung mass is more or less tied to the ground. It responds directly to any bumps or wiggles. The sprung mass, however, is attached via mushy, springy things like springs and shocks, which means that it doesn’t respond directly to changes at the wheels. This is good in the sense that a suspension isolates the passengers from a rough road; however, we know that in racing, the goal is speed, not comfort. The moving around of the sprung mass complicates things because it changes how much weight pushes down on each tire. In other words, the sprung mass changes how much grip you have.

TippyTruckSignThe tippy truck sign (at left) is a good general breakdown of sprung and unsprung. The top half of the truck (the rectangle) is the sprung weight and the unsprung is the axle and wheels.

It’s not a perfect analogy, though. I hate to break it to you, but the sign is wrong. The truck doesn’t just rigidly rotate. The wheels stay on the ground (unless you’re taking that curve really fast), but the sprung mass does shift.  When you break, weight shifts from the rear wheels to the front. When you accelerate, it’s the reverse. Weight shifts from the front to the rear. When you turn left (as the truck in the picture is doing), the sprung weight shifts to the right.

That means that the grip on each tire also changes every time you speed up, slow down or turn. That’s why a car can be loose coming out of a corner and tight going in. The set up is the same – but the top part of the car is shifting constantly.

And here’s why the center of gravity is important. The amount of the shift – is proportional to how far off the ground the CG is .


The car in the left picture has a lower CG than the car in the right. That means that when the right car goes around a corner, it will experience a bigger shift in grip from the inner wheels to the outer compared to the car with the lower CG.

This is why SUVs and semis are much more likely to tip over than sports cars. When the CG shifts outside the box formed by the wheels, the vehicle will tip over. Stability means that your CG is firmly over your base.  Football players use the three-point stance (crouched low) because it does two things: it forms a wide base (the triangle formed by the two feet and the one hand) and it lower your CG. This is one you can try at home. Especially if you have little brothers because, face it, that’s what they’re there for, right?  Try to knock one over when they’re standing up with their feet together. Then have them move their feet apart. Finally, let them crouch down like a football player on the line and try to knock them over now.

In addition to tuckering yourself out, you’ve managed to show that a lower CG is more stable. For a race car, that translates into less weight shifting on acceleration, braking or cornering. This was a big issue with the COT (Gen-5) car because the CG was much higher (a few inches if I remember right) than in the previous versions of the car. Just raising the CG messed up everything the engineers had figured out in the old car, never mind all the other changes.

This is why the ballast for the race car is placed in the (left) frame rails. You don’t want to raise the CG. More weight lower in the car brings the CG closer to the ground and helps improve the grip on all four wheels around the corner.  Teams are even using carbon fiber composite (a very expensive material) in dashboards and seats to try to save weight and keep that CG as low as possible.

So that’s why keeping the CG low in the car is so important. The weight of the car doesn’t change – but the distribution over each wheel does and weight translates directly to grip. You can only go as fast as your least grippy tire, so the less change in weight transfer as you turn, the faster you’re going to be able to go.


Sep 192014

You hear engineers and crew chiefs talking a lot about the racecar’s “center of gravity”. There’s a reason for all the talk. The center of gravity really is the point around which everything else on the car rotates.

Terminology: CG vs CM

You will hear people in racing use the terms “center of gravity” and “center of mass” interchangeably.  It drives physics professors and people who work at NASA crazy. No one else really minds.

The reason for the two terms is that things weigh differently depending on the gravitational field they are subject to. If you are on the Moon, for example, your weight would be one sixth what it is on the Earth. Your mass – the amounts of ‘stuff’ that makes you you – doesn’t change, but the pull of the planet (or satellite) on which you’re standing makes you feel heavier or lighter.

The location of an object’s Center of Gravity is the same whether it’s sitting on Earth, the Moon, or Pluto. Each has a pretty constant gravitational field at their surface. If you work for NASA, you have to make calculations of things like galaxies, where the gravitational field changes throughout the object. That matters, and it means that the center of the mass and the center of gravity aren’t always the same thing.


CGIconHowever, if you’re driving a race car — unless something goes terribly, terribly, wrong — you will always be in a uniform gravitational field and the center of gravity will be the exact same thing as the center of mass. So we tend to use the two terms interchangeably.

We abbreviate them CM for Center of Mass and CG for Center of Gravity.  The abbreviations are much short and it makes us look like we really know what we’re doing.  Also, we use the cool icon at right to denote the CG.  You may have seen this icon on crash test dummies (the real thing, not the band) before.

What is it?

The simplest explanation is that the CG/CM is the balance point of an object. Finding the CG/CM ob a uniform object is simple. Take a ruler, for example. If I asked you to balance the ruler on one finger, where would you put your finger?

CG_Ruler_FingerYep. Right in the exact middle. If I gave you a yardstick, the CG would be at the 1-inch mark. The CG of a meter stick is at the 0.50 meter mark. For anything uniform, it’s pretty easy – it’s at the geometrical center.


And you’ll notice from the donut in the lower right-hand corner that the CG/CM doesn’t have to be on the object. It could be out there in space. It’s an imaginary point.

Finding the CG for a racecar is a little more challenging because racecars are not uniform objects. There are heavy parts, light parts, and they’re all weirdly shaped. For most race cars that turn left, the CG/CM is located somwhere near the driver’s seat.   (I mean literally the driver’s seat.  His or her butt.) The diagram below is from an excellent book by Bob Emmons called the Racer’s Math Handbook.


You want the CG as low and as left as possible in the car (for oval tracks) because that’s the position that’s going to help you turn faster and circle track racing is won and lost in the turns. The location of the CG is often limited by your sanctioning body’s rules, either explicitly (specifying front/rear and left/right weight distributions) or implicitly (limiting how much ballast can go in the left frame rail).

Finding the CG height of a racecar is usually done experimentally by measuring how the weight is distributed between the front and the rear of the car, then raising the car and re-measuring. Longacre has a nice online calculator that not only tells you how to do the measurement, but explains why it works. Note that the CG of the car will be different with and without the driver in the car, especially if you have a heavier driver.

In Part II, I’m going to examine the relationship between CG and stability.

Related Posts:

Sep 152014

In the last blog entry, I explained what brake bias was and how it could be used to improve the car’s handling during green-flag runs. This time, let’s look under the hood (or I guess, more accurately, under the dash) and see how this is accomplished.

Let’s start with the schematic from last time:




WilwodBrakeBiasKnobNow we’re going to look at what happens at that little dial icon in the graphic. We start with a knob in the cockpit. It’s a simple knob, with two directions: front and rear. Turn to the right and more brake force goes toward your rear brakes. Turn to the left and the brakes are biased in favor of the front. The cable runs down to the brake bias bar, which I show below in a schematic drawing first, then a picture of the real thing.

On the left side of the drawing is a threaded rod – the bias bar (running up and down) with a center pivot point and two rods (one at either end) that are used to apply force to the two master cylinders.



The next picture shows the entire pedal box assembly for a Rally Car.



When you press on the brake pedal, the bias bar moves to the right, which increases the pressure on the master cylinders. When the bias bar is perfectly centered, meaning that the distance from the center to the left rod and the distance from the center to the right rod are equal, then the force is applied equally to the two cylinders.

Now consider moving the center pivot to the left or the right. This changes the distances from the center to the left and right rods and tilts the bias bar (like is shown in the diagram at top).  Now when you press on the brakes, the force is split between the two master cylinders differently. The side that the pivot is closer to will get a larger fraction of the force.  Instead of a 50:50 split, you can get a 60:40 split, for example.

You can see in the photo immediately above  that the center pivot is already adjusted slightly to the right of the picture, so the right master cylinder is going to get more of the braking force than the left one. Often, because of the inherent weight distribution of the car, the ‘neutral position’ of the brakes is biased a little toward the front or the rear.

And that’s pretty much how it’s done.