From the Lab Notebook: Las Vegas and the Mysteriously Missing Oil Tank Cover

 Aerodynamics, Downforce, Drag, Edwards Carl, Jack Roush, Las Vegas Motor Speedway, Rules  No Responses »
Mar 062013
 

As we head for Las Vegas this weekend, I thought I’d repost on of my most popular posts from stockcarscience.com on 3/5/2008  since the redirects for the old stockcarscience.com site don’t work reliably.  The post is about Carl Edwards’ 2008 win at Las Vegas when the team was subsequently fined for having their oil tank cover lid askew at the end of the race.  I have edited the post extensively, adding some new information and better graphics.

Danny LaDue asks: Can you explain the location of a NASCAR oil tank reservoir and how the lack of one could improve aerodynamics?

Thanks for the question, Danny.

NPR got this one wrong.  Frank DeFord in his usual Wednesday commentary made a comment that was essentially — look, the lid was still in the car, it didn’t give him a weight advantage, so NASCAR was wrong to penalize the team.  Don’t these folks known anything?

That’s the problem with aerodynamics — you can’t see it happening.

Unlike your car, the oil in a NASCAR car isn’t stored in the engine (called a wet sump system).  NASCAR uses a dry sump system, in which oil is

stored in an oil  reservoir. The oil reservoir is located behind the driver’s seat and is surrounded on the sides and top by sheet metal, which forms the oil tank.   The sheet metal minimizes heat radiating into the car, traps fumes from the hot oil, and serves as an additional firewall.  This function is so important that NASCAR doesn’t allow the top of the tank to be attached using quick connect fasteners. Some teams duct tape the lid on. The picture to the right shows the location of the oil tank with respect to the chassis. It doesn’t show the cover, which would sit on top of the tank.  The oil reservoir itself is closed and pressurized.

So if the oil tank cover plays such an important role, why would you leave it loose, much less leave it off?   The answer is aerodynamics.  The air exerts forces on the car in different directions.   Drag is the force air creates along the length of the car.  Air creates drag when it hits the front of the car,  but it also creates drag when it gets inside the car because there is no way for it to get out.   Drag always acts opposite the direction the car is trying to move, so you want to eliminate as much drag as possible.

Downforce and lift are the names for the forces pushing straight down or up on the car. Downforce pushes the tires harder into the track and provide grip, while lift pulls up on the car.  These two forces are in direct opposition to each other.  The bigger force wins.  You want to maximize downforce and minimize lift.

Downforce_oilTank1The oil tank is open to the bottom of the car. Air under the car creates lift.  Even though you try to keep the splitter close to the ground, there is always some air that gets under the car.  If the oil tank lid isn’t firmly tightened down, it creates a path for air to get out of the car, which reduces lift.

When the amount of lift decreases because of the loose oil tank cover, then the net downforce is larger because there is less air pushing upward. More downforce translates directly into more speed, as shown in the figure below.  Remember learning about ‘net force’ in physics?  Yep – it is actually useful.  The loose oil tank cover likely provided a little extra downforce — in a sport where races are won by thousandths of seconds, even “a little” advantage is important.

Downforce_oilTank2

One of Rusty Wallace’s cars originally penalized in the Nationwide series won its appeal on the basis that all of the bolts on the oil tank cover were engaged fully and the design of the oil reservoir was such that it led to the apparent opening. I can imagine (especially having seen graduate students overtighten bolts) that if you screwed down really hard on the bolts and the oil tank lid were on the thin side, you might be able to warp the cover on the oil tank lid a little and get some air escape.  The problem with this argument is that you can only use a ‘bad design’ argument once because NASCAR will make you redesign it.

The case of the No. 99 car’s oil reservoir lid is a little different, though, because the reports have been that the lid was entirely missing. In fords, the oil tank cover is held on by a single bolt.  Carl Edwards said on NASCAR This Week that a “bolt backed out”.  Jack Roush made the argument that the vibrations in the car caused vibration harmonics that caused the bolt to unscrew itself.  Even if that’s true (and I have to admit I’m a little skeptical about it), should you really have a safety feature held in place by a single bolt?

NASCAR fined the driver and the owner 100 points (old points scheme!), fined crew chief Bob Osborne (B.S. in Mechanical Engineering from Penn State) $100,000, 100 points and suspended him for six weeks.

Will the Gen-6 Car Affect the Number of Cautions?

 Cautions, Edwards Carl, math, Racing, Tony Stewart  4 Responses »
Jan 252013
 

I love the Gen-6 car.  Not as much as I love the Nationwide cars (but that’s got more to do with what I drive than it does the cars).  The big question is whether the decrease in cautions is going to be changed because of the new car.Let’s start (as we usually do) with the new car.

Graph4Let’s start (as we usually do here) with the data.  I’ve tabulated the data for cautions for the last twelve seasons and found that cautions have been decreasing since 2005, as shown,  for both the Nationwide and the Sprint Cup series.

In order to compare the two series and to compare between seasons within a single series, I’ve plotted the number of cautions per 100 miles.

In 2012, the Sprint Cup series had 1.57377 cautions per 100 miles.  They drove 13725 miles total, so that was 216 cautions total.

In 2012, the Nationwide series had 2.23969 cautions per 100 miles.  They drove 8240 miles, with comes out to 189 cautions — essentially the same number of cautions per mile they had last year.

Conclusion #1.  If the Nationwide drivers had driven the same number of miles as the Sprint Cup drivers, they would have had 307 cautions.

You’ll notice that I’ve drawn lines through each set of data.  They aren’t just a best fit by eye – I actually did a non-linear least-squares fit that determines the line that goes closest to all the points.  The data are decidedly linear and, more importantly, there aren’t any bumps or jump in, say, 2008, when the COT (which I guess is now the Gen-5 car) was introduced, or in 2011 when the Nationwide car was changed.  The data remained pretty consistent.

Conclusion #2.  Cautions are not affected much by the car that’s being driven.  Sure, I expect there to be some driver errors when a car doesn’t handle the way the driver expects it to behave; however, these guys catch on really quickly, so that’s going to be maybe 5 cautions.  Five out of 216 is like 2.3 percent, which is well within the error in the fit parameters.

Why are the cautions decreasing?  I’ve gone into this before, but I believe it is essentially because the drivers have a lot more experience now than they did in previous years.  There are a lot of veteran drivers in the Cup series right now, and I calculated that if you add up all the races run by the current crop of drivers, they have run a total of about 1000 more races in 2011 than they did in 2005.  That’s a whole lot of experience, and it’s distributed amongst the drivers.   Compare just two drivers:  Tony Stewart had run 248 races in  2005 and at the end of 2012, had run 500.  Carl Edwards had only run 49 races in 2005 – compare that to the 301 races he’d run as of today.  (I am only counting points paying races.  If you could somehow quantify the number of practice laps, time testing, etc., I think that would only make my argument stronger.)

So, in short, I don’t expect there will be any significant change in cautions because of the new car — up or down.  What do you think?

 

Is There Really a Second-Place Curse?

 Clint Bowyer, Dale Earnhardt Jr., Denny Hamlin, Edwards Carl, Jeff Gordon, Jimmie Johnson, Kasey Kahne, Keselowski Brad, Kyle Busch, Mark Martin, Martin Truex Jr, math, Tony Stewart  No Responses »
Dec 072012
 

One of the commentators after the final race in Homestead mentioned that Jimmie Johnson should be happy he finished in third because it allows him to avoid the “dreaded second-place curse”.
Anytime someone says something like that, it makes me wonder whether there really is a curse, or whether that person had just been talking to Carl Edwards.  So I analyzed a little data and guess what… there really IS a second place curse.

I used data from the last twelve years — from racing-reference.info, bless them!  After trying a couple of different approaches to making the data easy to visualize, I ended up with something a little more complicated than I would have liked.

Bear with me – it’s not as yucky as it looks.  I have plotted on the horizontal axis the place in which a driver finished in the first year listed, which we’ll call “X”.  I then calculated the change in positions of the same driver the next year (X+1) and plotted that on the vertical scale.  So the first set of data has X = 2000 and X+1=2001.

  • A positive number on the vertical axis means that the driver finished better by that many places in the following year. For example, +5 means that the driver finished five places better the next year than they finished the year before.
  • A negative number on the vertical axis means they finished worse the next year. A -5 means they moved down five spots in the final standings.

I went through and removed any special cases — like Mark Martin running full time one year, but not the next, Busch brothers missing races (that’s a different kinds of curse), people retiring, etc.  The graph below summarizes the top 16 finishing places and the change in final standing over the last twelve years.

There’s an obvious statistical implication:  If you finish second, for example, you have only one place to move up and forty one places to move down.  You’re either going to win the championship next year, become second again, or move down.  The probability is that you’re going to finish worse than second.

To look at the data in a slightly different way, I plotted it the same way they plot the daily activity of the the stock market:  the symbol shows you the average.  One line extends up to the maximum increase in position and one line extends down to the largest drop in position.

 

The first-place curse

In fact, if we’re going to call dropping in the standings a “curse”, then there is clearly a first-place curse that affects everyone except Jimmie Johnson.  Mose drivers who win the championship one year inevitably finish worse the next year.  When I say ‘drop in points’, it’s not a huge drop:  nine places was the most anyone who finished first dropped.

The average first time finisher fell almost five positions.  That’s including four consecutive ’0′s due to Jimmie Johnson.  If we exclude Jimmie just because what he did was really unprecedented (and unlikely to be duplicated), the average first-place finisher falls almost seven positions the next year – about the the same as the second-place driver.

The second-place curse

Second place shows a very similar story, only worse.  There is only one case in twelve years in which the second place finisher one year won the championship the next year.  That was Jimmie Johnson.  Whoops – Rick pointed out my mistake.  It was 2001 -2o02 and the driver was Tony Stewart!  On average (including Jimmie), the second place finisher finishes about seven positions lower the next year.

The three biggest drops in point standings (-15, -13, -11, -9 and -7) are due to Martin, Edwards, Biffle, Edwards and Hamlin.  There are no extenuating circumstances like crew chief changes, owner changes, etc. on which to blame the drops.  Four out of five of those drivers were all driving for Roush at the time… maybe there’s a Roush curse?

The bad news for Jimmie Johnson… and everyone else who made the chase

Here’s the bad news for Jimmie:  Yes, he avoided the second-place curse; however, no third-place driver has gone on to finish first or second the next year.  The best they’ve done was to match their third-place finish.

Yep, perhaps there’s a third-place curse as well, as third-place drivers finish an average of three places lower the following year.

In fact, you don’t find a finishing position in which there is an average probability of bettering your finish until 7th place.  On the graph above, you can see that the majority of finishes were improvements, although without one -11 change, it would be a much more positive number.  After that, it’s an oscillation between slightly better and slightly worse.

A caveat of this data analysis is that the Chase sort of messed things up going out past 10 because a driver in the Chase can’t finish lower than 10th, even if he misses races or otherwise would have fallen much lower without the Chase format.

 

Aerodynamic Downforce: A Passing Fad?

 Aerodynamics, Downforce, Edwards Carl, NASCAR, Rules, Safety  4 Responses »
May 212012
 

The question of why it is so difficult for cars to pass each other at 1.5 mile and 2 mile tracks is getting more and more attention.  Carl Edwards put it succinctly:

“I firmly believe, and NASCAR hates it when I say this, that we should not be racing with downforce, sideforce and all these aerodynamic devices.  We do not need splitters on the race cars and giant spoilers.  I have not been around long enough to say something definitely, but it is pretty common sense: if all the cars are very similar and all the drivers are within a tenth of a second of each other but are relying on clean air and downforce, then by definition if the guy in front of you is disturbing the air then your car is not going to be able to go as fast as it could in clean air.”

Other drivers disagree — Jimmie Johnson, for example, believes that changes must be made to the track to enable passing.  But let’s look for a moment at the aero/mechanical force question.

Grip (aka static friction) is determined by two factors:  how well the tire grabs the track and how hard the tires are pushed into the track.  Goodyear is entirely responsible for the first factor given that everyone runs the same tires and teams are not allowed to modify those tires in any way.

There are two components to the second factor: mechanical grip and aerogrip.  Mechanical grip is easy:  that’s the weight of the car.  Given the minimum weight of 3450 lbs and a Jeff Gorden-sized driver, you’ve got a total of 3600 lbs of weight pushing the four tires into the ground.  How that weight is distributed between the tires is a topic all to itself, plus the weight distribution changes as the car accelerates, brakes and/or turns.  Regardless of where the weight pushes, there is never any more force that the total weight of the car.  (You can only go as fast as your least grippy tire, so getting that weight evenly distributed is something engineers spend a huge amount of time trying to do.)

The other factor is aerodynamic force.  When air molecules hit a surface, they push down on the surface.  Although each molecule is very tiny, the billions and billions of molecules hitting a car’s surface (especially at high speed) can create thousands of pounds of additional downforce on the car.

Aerodynamic downforce varies with speed squared.  If you double your speed, you quadruple the aerodynamic downforce.  A car that has 1000 lbs of aerodynamics downforce at 90 mph will have 4000 lbs of aerodynamic downforce at 180 mph.  This is why aerodynamics are less important at tracks like Martinsville where the speeds are lower, and incredibly important at tracks like Texas, Michigan, Atlanta, etc.

Mechanical grip doesn’t change much when you drive around other cars – but aerogrip does.  Aerodynamic downforce changes depending on how the air flows over the car.  A nice smooth laminar flow is like sheets of air tracing the car’s contour as they flow.  That’s “clean air”.  The opposite is “dirty air”, which means that the air is turbulent or being diverted in some undesirable way.

So imagine that you are running a couple car lengths behind the leader.  You both have comparable cars, with (say) half of your total grip due to aerodynamics and half being mechanical.  As you get closer to the car you’re trying to overtake, the air coming off the rear of that car disturbs the air flowing over your car.  You feel the front end grip decrease and you know the television commentators are telling the audience that you’re “aeroloose”.  You’ve got no choice but to back off and get the air flowing back over your car.  Or you could just keep going and spin yourself out.

Let’s look at an alternative:  say that aerodynamic force is only a very small fraction of the total force.  Getting close to another car decreases your aero downforce, but if you’ve got a better setup on your car, the improved mechanical grip might just be enough to compensate and you could then be able to pass.

The spoiler and the splitter create a pressure differential.  The splitter “splits” air by forcing it to go around the car.  The pressure on top of the splitter is higher than the pressure on the bottom and thus the net force is downward.  The spoiler provides a surface for the air coming over the top of the car to hit and thus provides rear downforce.  A shorter spoiler provides less area and thus less overall force.

So can we follow Carl Edwards’ advice and just get rid of the aerodynamic devices?  Sure – if you’re willing to have the cars be slower.  The fewer aerodynamic devices, the slower the cars are going to be.  It’s a question of scale.  You have to decrease the aerodynamics enough so that they don’t dominate, but not so much that we’re falling asleep during the six hours it takes to run 400 miles at a 1.5 mile track.

NASCAR’s recent change to skirt heights is an example of what I believe is an attempt to make minor changes to the aerodynamics of the car without requiring teams to make a major reboot on a car that is in its last year of  existence.  Robin Pemberton said that the recent changes were informed by the research being done on the 2013 car in terms of both competition and safety.

Keeping the skirts higher off the ground has two potential impacts:  one is that it can help air get out from under the car in case of a spin.  Air underneath a car pushes upward, which decreases downforce and – in extreme cases – can cause the car to leave the ground.  The higher skirts will give the air a plan to escape when the car spins.  Prior to the change, skirts had to be 3 – 4.5 inches off the ground (measured when the car is sitting still during tech).  The new rules require the right side skirts to be 4 to 4.5 inches off the ground and the left-side skirts to be 4.5 to 5 inches rm the ground.

The other consequence of this change is that it will be harder for teams to keep the car sealed to the ground.  Air flowing under the car will push upward, which decreases grip.  Even though the spoiler and splitter will not change, the net force pushing down will decrease.

Pocono: Slightly Shifty

 Denny Hamlin, Edwards Carl, Engines, rear-end gear, transmission  No Responses »
Jun 112011
 

The big news for Pocono is that drivers can shift…again.  Which brings up the obvious dual questions of: Why would you want to? and Why didn’t you before?

Compare how fast the wheels have to rotate with how fast the engine rotates.  Both are measured in revolutions (or rotations) per minute – rpms.  Assuming a tire circumference of 88.6 in, tires have to rotate from 417 rpm (at 35 mph), to 1490 rpm (125 mph) to 2146 rpm at 180 mph.  The graphic tachometer on television tells us that the engine runs between 7000 rpm and 9500 rpm most of the time.

Gearing for a Borg Warner MM6 manual transmission and a GU6 3.42 rear-end gear, as might be found in a Corvette.

You can’t connect the engine directly to the wheels because of the difference in rotation rates.  This is where the gears come in.  A car has two sets of gears:  The first I’ll talk about is the rear end gear, which I seem to remember is somewhere around 3.8 or 3.9 for Pocono.  The rear gear reduces the rotation rate coming from the driveshaft and sends that rotation to the wheels (as shown in the diagram).  A 4.0 gear would produce a rotation rate coming out of the gear that is 1/4th the rotation rate coming into the rear gear.  If the driveshaft is rotating at 5000 revolutions per minute (rpm), the wheels would be rotating at 1250 rpm. (A 4.0 gear would mean that for every four rotations coming in, one rotation goes out.)

With a 4.0 rear gear, your engine would have to change speed from 1600 rpm to about 8500 rpm going from 35 mph to 180 mph.  The problem is that an engine produces its maximum power over a narrow range of rpms.  (It also produces its maximum torque over a small range of rpms, although not the exact same range as the maximum power band.)  You’d like to have the engine operating in the target range all the time.

This is why you need a second set of gears, which are found in the transmission.  This series of gears (usually 4, 5, or 6 different gears) gives you different sizes so you can keep the engine running near its sweet spot — regardless of how fast you’re going.  Fourth gear on most transmissions is 1:1, meaning that there is no speed change through the transmission.  On a passenger car, like the one from the gearing figure, the higher gears (overdrive) reverse the ratio.  0.50:1 means that the rotational rate coming out is higher than the rotational rate going in.  NASCAR prohibits overdrive.

In trying to go faster and faster, teams were moving their engine’s target range to higher and higher rpms – which means higher and higher costs.  In 2005, NASCAR instituted a gear rule to keep engine speeds (and thus cost) down.  NASCAR gives you a limited choice of rear-end gears and dictates the transmission gears as well.  Those choices keep the maximum engine rotation rate below about 10,000 or 10,500 rpm without having to implement a difficult-to-enforce engine rule.

NASCAR changed the gear rule for Pocono this year.  First gear can be anything you want.  Second gear can be 1.70:1 or greater, and – this is the big change – the third gear limit changed from 1.28:1 to 1.14:1 or greater.  Fourth gear stays at 1.00:1.   (“or greater” means that the first number may be larger, but not smaller.)  NASCAR still doesn’t allow overdrive.  Normally, the rule book prohibits gears between 1.00:1 and 1.28:1 except for road course events.

Pocono - certainly one of the more unique tracks on the NASCAR circuit

Why Pocono?  Most oval tracks have four turns, with the frontstretch and backstretch close to the same length.  Pocono has three turns and three straightaways:  a frontstretch of 3740 feet, a backstretch (Long Pond) of 3,055 ft and a short straight of only 1,780 feet. You can imagine that the rpm the car reaches is very different coming down the two long straights (i.e. coming into turns 1 and 3) compared to coming down the shorter straight (i.e. into 2).  What you’d like is for the engine to be turning at about the same rpm into each turn.

It seems like NASCAR’s change is too small to be meangingful – from 1.28:1 to 1.14:1 is only 0.14, right?  Actually, it’s a factor of two.  What makes a difference is how much above 1.00 the gear is.  The important thing about moving from 1.14:1 to 1.28:1 is moving from 14 to 28.

For the sake of argument, let’s say the engine is ideally in 7200 rpm in fourth gear.  When you shift to third, a 1.28:1 gear (which used to be the lowest for third), requires the engine to run at 9216 rpm (=1.28*7200) to maintain the same speed.  That takes you far away from the best rpm range for your engine.  Changing from 1.28:1 to 1:14:1 means that third gear only requires your engine to run at 8208 rpm.  That may seem like it is still a big shift; however, given the way the power and torque curve vary with rpm, it’s small enough to mean that you’re close enough to your power band for it to work. It’s a shift of about 1000 rpm instead of 2000 rpm with the 1.28:1 gear.  That gives the engine shop – and the driver – some interesting options.

This type of a rules change is, in my opinion, exactly the direction NASCAR ought to be moving to open up areas for people to be innovative.  It’s a relatively minor change in terms of enforcement.  It keeps the teams from pushing into the higher rpm ranges (and thus steeply pushing up engine costs), but it allows the engineers and the drivers to pursue different strategies.  For example, most drivers will be shifting in turns 1 and 3, but others (like Denny Hamlin) plan to shift only in turn 1.  Another aspect is how shifting affects fuel mileage.  Overdrive gears are there because the more rotations an engine makes, the more friction it has to overcome.  And, as Carl Edwards points out, every time you shift, you run the chance of screwing up and damaging the transmission.  Most NASCAR drivers aren’t used to shifting this much during a race.  Do you try for what might be a small advantage and shift at the cost of possibly screwing up the transmission?  Do drivers like Marcos Ambrose, who have a lot more experience shifting, have an advantage?  Does the engine shop adapt different strategies for drivers who are comfortable shifting compared to those who are not?

Unfortunately, this rule really makes a difference only at Pocono due to it’s unique configuration.

Yaw Envy – Repost

 Aerodynamics, Edwards Carl, Jeff Gordon, Yaw  No Responses »
May 082008
 

This blog was originally published in May 2008 on the stockcarscience.com site.  I’m reposting it here as part of the migration of that site to buildingspeed.org.

Apparently, Jeff Gordon has a slight case of yaw envy. David Newton reports on ESPN.com that Gordon asked NASCAR to take a look at the No. 99 car of Carl Edwards because he thinks that yaw is the reason Carl’s been so competitive this season.

You may have learned that it takes three numbers to uniquely locate an object in space: For example, right now I’m in Los Angeles at the corner of Hope and 8th Streets and I’m on the 11th floor.

The limitation of this description is that it only identifies a point. I (like a car) have spatial extent. I could be lying down or standing up, and the three points I just specified don’t tell you anything about how I’m oriented, only where I’m located. We have to specify the angles the car makes with respect to three axes, which we call the x-axis, y-axis and z-axis. In vehicle dynamics, the x axis is along the length of the car, the y-azis is crosswise, pointing toward the driver’s right, and the z axis points downward, as I’ve drawn below. (Engineers take the z-axis to be positive in the downward direction.)

Yaw describes the rotation of the car about the z-axis. The yaw angle is the angle between a line pointing in the direction the car is moving and the car’s x-axis (which is the direction the car is pointed). In the simplest case (shown on the left side of the drawing below), the car is traveling straight and is pointed in exactly the same direction it is traveling, so it has no yaw. The car on the right is yawed, which means that the car is headed in a different direction than it is pointing.

A car by definition is yawed when it corners because it is pointing in a different direction than it is moving at every point along the turn. Yaw is important because air hits the car differently when the car is at an angle to the oncoming air compared to when it is hitting the air head on, as shown below. In effect, the car on the right has a head start on the turn because it is yawed before it enters the turn. Yaw puts the car in a position so that the air helps the car turn.

A number of people have noticed that some cars seem look yawed heading down the straightaway. They appear to have an inherent yaw built into them. Darlington has nice straightaways, which is why yaw has been in the news this week.

Let’s review some history. The old cars were asymmetric–literally kidney-bean shaped–as shown below. Compare how much of the left fender (on the right side of the picture) you can see relative to the right fender. Gary Nelson, the founding director of the NASCAR Research and Development Center said once that the cars were so misshaped that they looked like they had been in an accident before they even got on the track.

All of this body manipulation was for aerodynamic advantage; however, the research that goes into figuring out exactly how to optimize bodies, as well as the cost of cutting off and replacing bodies, was getting out of hand. This was one NASCAR’s major motivations in introducing the new car.

Compare the old car with the new car in the drawing showing yaw. There still is some built-in asymmetry in the new car: Note how the wing isn’t exactly centered between the two taillight decals, for example. The left rear quarter panel is much more tapered than the right rear quarter panel; however, the amount of asymmetry is pretty much fixed by the NASCAR body templates.

Of all the drivers, Jeff Gordon knows that you don’t mess with the new car’s body. He has complained that something is more amiss than it should be with the rear end gear on the No. 99, causing it to have yaw and thus giving it the same type of asymmetry the new car’s fixed body shape was meant to eliminate.

NASCAR cars have a solid rear axle. The rear end gear links the driveshaft to the rear wheels. There are three holes in the rear windshield: Two of those are for adjusting the springs on either side of the car. The third (the bottom one on the right) is for adjusting the trackbar. The trackbar shifts the rear end gear to the left or the right, as I’ve illustrated in the drawing below. I’ve exaggerated the shifts–if I drew them to scale, you wouldn’t be able to see them. The leftmost drawing is a car with no offset in the rear end gear. Note how the front and rear wheels are lined up. The rear wheels would follow right in the front wheels’ tracks. The middle drawing shows a car with the rear end gear shifted to the right and the rightmost picture shows that a car with such a shift will be yawed.

Kyle Busch referred to the way Edwards’ car moves as it looks “stupid going down the straightaway because it’s dog-tracking.” (ESPN). A running dog is usually a little sideways. The rear paws never follow in the front paw prints. It’s also sometimes called crabbing, and refers to the situation shown above: the rear wheels do not follow straight behind the front ones.

The situation with some cars is so extreme, that Gordon said:

“When cars can’t even get on the scales because they’re running sideways, it’s something they need to address.” (ESPN)

The scales used during inspection are four plates(two in front, two in the rear), that are in line with each other. Jeff is suggesting that the offset between the front and the rear wheels is so great that some cars have trouble getting onto the scales.

It’s ironic that Gordon is complaining about this, as Hendrick Motorsports was one of the first teams to experiment with introducing yaw using the suspension. One possible motivation for Gordon’s comments is that he is of the opinion that Roush Fenway Racing is headed down the same slippery slope as coil binding: The engineers are modifying the car in way that makes it much more difficult to drive.

Almost every team has tried to duplicate what Edwards has, but not every driver can handle it. “It makes the cars drive so terrible that it doesn’t really help us in any way that we really need it,” Gordon said. (ESPN)

There are rules about how much you can move the trackbar, so there are obviously other things being done to induce yaw in the car. One possibility: The wheelbase (the distance between the front and rear wheels) can be 110″ plus or minus 1/2″. If you make the wheelbase 109.5″ on the left side and 110.5″ on the right side, you’ve gained an inch of asymmetry. There are a number of other places where you can make little changes and, when all the little changes are considered, they add up to a significant effect.

I noted early on in the introduction of the new car that it was only a matter of time before the very clever people working at race shops would come up with ways to get around the new NASCAR-imposed limitations. One consequence of this type of offset is that the cars are drifting, much like they do on dirt tracks. It should be no surprise then, that someone like Edwards, who still does a lot of dirt track racing, is comfortable driving a car set up like this. That’s one rationale to account for why Edwards, who really struggled with the new car last year, is doing so well this year. As with coil binding, some teams have figured out how to get yaw and others are a little behind on the curve. Some drivers caught on to how to drive a coil-bound car a lot faster than others. The question that remains is whether there are other ways to get the car to turn better that would be more comfortable for the drivers who aren’t comfortable driving horizontally down the straightaways.