Jul 112014
 

Doug Yates was  guest on Dave Moody’s SiriusXM Speedway last week. He brought up a conversion you hear a lot in the week before Daytona and Talladega.  Every 25 horsepower in the engine translates to about a 1 second decrease in lap times. Dave did the math: Removing the plates would increase the engine by 450 horsepower. Four hundred and fifty more horsepower equates to 18 seconds off the lap time, assuming all other things equal.  That last part was a very important qualification. It will come back to haunt us in a moment.

David Gilliland got the pole at Daytona with a lap speed of 45.153 seconds, translating to a speed of 199.322 miles per hour. Using the above argument, his lap time would decrease to 27.153 seconds.  That translates to a speed of 331.456 mph.In 2004, Rusty Wallace ran 228 mph at Talladega in an unrestricted engine. That’s almost 100 mph slower than our theoretical max speed. Let’s ignore the concerns that NASCAR racecars tend to get aerodynamically unstable if they turn around at high speeds and think only about straight line speed.

So let’s look at what limits how fast a car can go.  We’re considering two major forces: the force the engine makes, which propels the car forward, and the drag force, which pushes the car backward.

 

DragandForceActingonCars

It’s exactly like a tug of war. Which ever is pulling harder, that’s the direct the car is going to go. (That’s because force is, as your physical teacher no doubt repeated over and over, a vector.DragandForceVectorSumsAt most tracks, if you want to pass someone, you step on the gas, the engine produces more force and you accelerate.  Daytona and Talladega are unique in that engine power is limited to about 450 hp. The pedals on the floor the whole way around. You’re perennially in the last situation, in which the car moves at a constant (a terminal) speed, which is the fastest speed you can get. The engine is doing all it can.

So here’s the catch – the reason why the phrase “all other things equal” causes problems.  All other things are not equal. Specifically, drag. Drag is simply the force of the air molecules pushing on the car, but that force increases quadratically, just like downforce. If the car goes twice as fast, you get four time (two squared) the drag.  It’s not fair: you have to work four times harder to get twice as fast. But that’s physics for you.

The argument above relied on the assumption that the drag remained constant – and it definitely doesn’t. It gets worse, because power depends on velocity cubed. So to go twice as fast, you have to overcome four times as much drag and you need eight times (2x2x2) the power.

You can estimate the terminal velocity of a racecar using some simple physics. The terminal velocity is the ratio of the power (P) to the drag (D):

EQ_TerminalVelocityPowerDrag

The maximum drag you can have is proportional to the terminal velocity squared:

EQ_terminalvelocityvsPower

Which means that the terminal velocity ends up depending on the cube root of the power!

EQ_TerminalVelocityPowerCubeRoot

If the power of an engine doubles, the terminal velocity only increases by the cube root of two, which is 1.26. If we take 200 mph as a nice round terminal velocity for a restricted engine, removing the plates and doubling the engine power to 900 hp would only increase the terminal velocity for the unrestricted engine to 252 mph.  That’s pretty surprising – you double the engine power and you only get 50 mph more.  Such is the power of cube roots.

If nature were linear, it would be a whole lot less interesting.

Many thanks to my friends Josh Browne and Andy Randolph, both excellent engineers and always willing to let me bounce ideas off them and verify that I’m not crazy.  Not, at least, when it comes to physics.

Jul 082014
 

Given all the rain at Daytona this weekend, there was plenty of time to think about auxiliary NASCAR issues.  Regular readers know that I’m a huge fan of the racing-reference.info website because they have a trove of data just waiting to be analyzed.  The spouse asked about payouts and whether it really made much of a difference for a team to get back on the track, so I plotted up some data.

I’m showing below for the Nationwide and Sprint Cup Series, the winnings as a function of position. The line is not monotonic (decreasing with each point) because of all the contingency plans, sponsor deals, etc, but the data work pretty well in terms of overall trends. I’ve plotted both races in 2014 – July (red) and February (green).

BSPEED_DaytonaWinningsNWide

Two things surprised me here:  first,  how quickly the prize money goes down and second, how small the money is in the first place, especially relative to the Sprint Cup.  You’re talking about $20,000 for finishing in the upper 30s in the July race and $40,000 in the February race. If you consider how expensive it is to just build a racecar, much less hire a driver and people for the track, that’s not a whole lot of money.

If you look at the drop off, it’s huge for the first five places. From 1st to 2nd in February, we’re talking a drop of almost $30,000. When you get out to 21st compared to 22nd, it’s less than a thousand dollars.

I thought the difference in prize money between February and July was interesting as well.  It’s even more pronounced in the Sprint Cup, as shown below.BSPEED_DaytonaWinningsThe first thing to notice is the huge difference in purse from the 500 to the 400.  The money for first place is four times as much for winning in February versus July. From first to second for the Daytona 500, you’re talking $357,000, but for the July race, it’s “only” $134,000.  If you come in dead last in February, you take home $292k, whereas last weekend, poor A.J. Allmendinger went home with a little under $70k for finishing 43rd.

That outlier at position 32 for the 500 is Paul Menard. I double checked the data at my other favorite source of racing information, jayski.com, and they have the same information. (UPDATE: as @nuggie99 points out in the comments, there was that $200,000 bonus for leading at halfway.) I have no explanation for why he’d make $200,000 more than the guys who finished immediately in front of and behind him.

For both series, though, you can see why it makes sense for teams that aren’t running all the races, or teams with limited resources, to disproportionately focus attention on the restrictor plate races. With the wild card nature of the races, getting a top five can make a huge difference in the money you take home – and thus your ability to build a more competitive team.

 

 

Jun 242014
 

This weekend, we learned that the real weather challenge for the NASCAR Nationwide Series isn’t rain. It’s not enough rain. It wasn’t raining hard enough to put on rain tires, but it wasn’t quite dry enough to safely race on slicks. (I’ve written before about why racing in the rain is hard.) But they managed to pull it off, put on a great show and @Brendan62 finally got that long-sought-after win.

When the teams switched to rain tires, the crew chiefs had to remind the drivers that their tach readings for maintaining pit road speed would be different .  I’ve written quite a bit about tach readings and speed limits:

If you know the  gear ratios in the transmission and the rear end, you can convert the engine speed (in revolutions per minute) to the rotation rate at the wheels.  How far the car moves each revolution of the axle depends on the distance around: the bigger the tire, the further the car moves. This is why your odometer and speedometer get screwed up if you don’t use the right size tire on your car.  You can check this out yourself using two tumblers with different sizes.  If you lie them on their sides and start at the same place, they roll them each one revolution, the larger tumbler will have gone further.

Rain tires have thicker tread and a larger circumference. The car moves further along with each rotation of the tires. If you don’t compensate for this in your tach readings for pit road speed, you’ll end up with a speeding penalty, even though you would have been fine at the same tach readings with the slicks on.

I couldn’t find the difference in the circumferences, but remember that teams are always pushing to get as close to the pit road speed limit as possible, so even a relatively small change in the relationship between speed and circumference can put you at the tail end of the longest line.

Jun 202014
 

 

Brad Keselowski, that never ending source of material on slow news days, had a few words about the state of American Motorsports Engineering. These quotes are from an article by Mike Pryson in Autoweek.com.

“It’s probably a larger story in itself that the American engineering pool is very shallow right now,” said Keselowski after he qualified sixth at Michigan International Speedway on Friday for Sunday’s Quicken Loans 400 NASCAR Sprint Cup Series race. “Penske is moving to any other country [to find them]. We’ve hired multiple engineers from Europe over the last three or four years and we’re pilfering everyone we can in the great country of Canada, so if you know any of them, send them our way.

“It’s just very hard to get engineers with the educational background and commitment that we need to be successful at this level from the United States. There’s certainly a shortage, not just at Penske, but throughout the garage.”

His comments (here and in the last few days) have to be interpreted in the context of their being responses to questions about why Ford (and Penske) were struggling compared to Chevy (and Hendrick in particular).  The mainstream motorsports media (try saying that fast five times) tend to want a simple answer, like “They have more horsepower”. As we know, racing is a holistic enterprise and often it’s the interplay of things and not just the things that is most critical.  And people want to reduce answers to more provocative things like “Keselowski hates American Engineers”.

I know a lot of racing engineers who found his comments derogatory. It reminded me of being in grad school and always hearing the professors complain that they needed “More and better graduate students”. When I finally called on on this and told him it bothered us, he looked at me blankly. “We don’t mean you guys. You guys are great. It’s our applicant pool…”

Sometimes a little clarification makes a huge difference to the people involved. The big thing I got out of it after reading all the media reports I could find about Keselowski’s comments was that he said that Penske got a very small number of applications from highly qualified American engineers.

Let’s look at the numbers. In 2012, according to the American Society for Engineering Education, 88,176 bachelor’s level and 49,372 masters level engineering degrees were handed out.  There were 1.7 million bachelor’s degrees in all fields, which means that engineering degrees make up only 5% of all bachelor’s level degrees. Compare that with Japan and Chine where engineering degrees are 50% of the degrees granted.  That’s for all fields of engineering. Most people working in motorsports have degrees in mechanical engineering (few schools offer a dedicated motorsports engineering degree), which is somewhere around 20,000 degrees at the bachelor’s level and 6,o00 master’s level degrees. (85- 90% of mechanical engineering degrees are earned by men, incidentally).

The schools that offer motorsports engineering degrees are schools like Indiana University – Purdue University at Indiana (IUPUI), UNC-Charlotte and the University of Northern Ohio.  In fact, UNC-Charlotte boasts that 10% of NASCAR engineers come from UNC-Charlotte.  Other schools, like the University of Colorado – Denver offer motorsports specializations within mechanical engineering. Nothing against these schools. But if I look at the engineers I know who are successful in NASCAR, they’ve got degrees from places like Northwestern, Duke, Penn State, Stanford, Carnegie Mellon.  Newman went to Purdue. Those universities attract a different level of student. Nothing against folks who went to a small state school. I did. But if you want the best and the brightest, you’ve got a higher likelihood of finding them at the elite engineering schools.

Europe, in particular, has a well-established stream of motorsports engineering because of the high technical level of F1. I was at Oxford On Brookes in England a few years ago and their facilities and program are amazing. Well ahead of most of what we have in the States.

The numbers are small to start with, and I think three factors narrow the pool:  Money, work environment, and personal goals.

The mean annual wage for mechanical engineers, according to the U.S. Bureau of Labor is $85,930 – and it’s much higher (over $100,ooo) in select field like energy.  I started off thinking salary wasn’t an issue because teams like Hendrick and Gibbs have very deep pockets and understand how important it is to have strong engineering. On second though, few people get to start with the big teams. So salaries may  be a contributing factor to there being a smaller application pool. If someone’s faced with a starting salary from an auto manufacturer or a  Nationwide-only team, the production car job might look a lot better.

Even if the salary is high, you have to consider the job responsibilities relative to the salary. NASCAR engineers work in an extremely high-stress, rapid output environment. They have to work with a broad range of people, from mechanics to public relations people (to drivers, some of whom are not shy about throwing their teams under the bus when they don’t finish well). Failure in motorsports is extremely visible. If you are slow, the whole world sees it. Many engineers spend a significant amount of time on the road, away from family. Even those that don’t travel as part of the raceday team are involved in testing.  A lot of people don’t want an eighty-hour-a-week, high stress job.

Finally, there’s the question of what you want out of your career. People I know who have worked in motorsports and left are working in everything from production car development to trying to make the country less dependent on foreign energy sources. A number of them enjoyed motorsports, but there are bigger and more significant problems in the world than making cars go fast. People want different things out of life. You have to really like racing to make a career of it.

Keselowski pointed out as much in a tweet.

kestweet

 

 

But that didn’t make it into any of the stories, of course.

Jun 162014
 

Equilibrium. It’s more than just a neat word. It’s the holy grail for a racecar driver.

Brian Vickers lost his car on the first lap of yesterday’s Michigan Sprint Cup Race. Vickers said (quote from an article by Jay Pennell of Fox Sports).

“I was going into Turn 3 and expecting to follow the 48 in there and the 22 jumped inside of us and it just came around,” Vickers said. “I mean I just lost it. I have no idea what happened or why. The car just got really loose into three and I chased it all the way up to the wall. I thought I had it saved and it just came all the way around.”

A racecar driver’s goal is to keep the car exactly at equilibrium. Equilibrium means that all the forces acting on a object equal out.  For example, I’m sitting in a chair at my desk. Gravity pulls me down with a force equal to my weight. The chair pushes up with a force equal to my weight. If you add them up, they equal out. If the chair were to break, it would exert less force on me than gravity and I would accelerate downward.

The chair is actually capable of exerting a much larger force than my weight (which I know because people heavier than me have sat in this chair and it didn’t break.) Most things we use have a safety factor – they’re much stronger, or capable of exerting a greater force, than we will ever need.  We’re not even close to having to worry about equilibrium.

Racing is the act of keeping the car exactly at equilibrium. I like to think of equilibrium as applied to racecars like this:

EquilbriumWhen the forces are exactly balanced, you’re living up to car’s potential and getting it to go as fast as it’s capable of going.  If you’re not pushing the car to the limits of the tire’s traction, you’re giving up speed.  If you push the car beyond the tire’s limits, you crash. Look at the in-car cameras during a race and see how tenuous the connection is between the car and the track.

With the car perched on the top of an unstable equilibrium like the one diagrammed above, all it takes is a little perturbation and the car moves off the peak position. If the perturbation is small, the driver may be able to recover. But it doesn’t have to be very large – a good wind is more than enough – and the driver is caught in a spin. The side of a racecar presents a huge area for the wind to push on. It’s not surprising that a good wind, hitting at exactly the wrong angle, could spin out even a 3,480 lb racecar – because the racecar is already on the edge of crashing.

 

Jun 132014
 

You are hurtling down the frontstretch at Michigan, your speed approaching 215 mph.  Your seat moves up and down as you hit the seams, but your focus is squarely on getting into Turn 1 losing as little speed as possible.  You squeeze the brakes and feel yourself moving forward, only to realize that you’re still moving too quickly. As the car starts to head toward the wall, you panic and squeeze the brake even harder.

The car snaps loose and the next thing you feel… is an engineer’s hand on your shoulder.  You turn around to see her barely suppressing a smile.

“Let’s try that again. Maybe you want to brake earlier this time, huh?”

The latest racing simulators are far more involved than your steering-wheel-feedback-enabled video game. When you hear drivers talk about using simulators to familiarize themselves with new tracks, you are only hearing about the surface layer.

Ford opened a new Racing Technology Center in Concord NC just about a month ago.  The old Ford facility used to be called “The Shack” because of it’s size. The new facility, which is across the street from Roush Fenway Racing, is 33,000 square feet. One of the main features is a driving simulator similar to the ones that F1 uses.  Five screens provide a 180-degree view for the driver. The cockpit is the front half of a NASCAR Sprint Cup car that is set on a full-motion platform.  The platform duplicates the exact motions you would feel in the car – bumps, slips, sways, yaw.

Let’s move away from the driver for a moment, because he (or she) is a relatively recent addition. All race teams use vehicle dynamics simulations: computer programs that predict lap times for specific setups. A crew chief changes the setup on the computer – camber, cross weight, track bar, etc. – and can see in advance whether the changes make the lap time better or worse.

DriverintheLoop2

Simulation programs have to be validated, meaning you have to make sure they correspond with reality. Every team also has (or rents time on)  K&C and seven-post rigs.  (K&C stands for Kinematics and Compliance – I’ll be getting into those in upcoming posts.) These machines attempt to quantify how the car responds to external changes, like turning, bumps, etc.

Engineers thus went back and forth between theory (the simulations) and experiment, developing a model of the car, testing it against how the car behaved, and then refining their model.  (Unsurprisingly, this is exactly how scientific research on things like alternative energy sources and cancer works.)

This is a great model for the Google driverless car. But that’s not how racing works. Racing requires a living, breathing, thinking (hopefully) human being in the seat who has to constantly take in information, process that information and act on it.

And that’s where racing simulators are moving. The buzzword is “Driver in the Loop”, which means that you’re creating a model that includes the driver.  This is not an easy step. Drivers are very different in terms of their preferences for set-up, what they’re comfortable driving, how loose they’re willing to be early in a run to make the car faster later, etc.

The simulator in the new Ford Tech Center is a sled-type simulator. Less advanced models have hydraulic pistons that raise and lower the cockpit to simulate bumps and change attitude.  The sled can actually duplicate all six types of motion: three linear motions (up/down, left/right, front/back) and three rotational degrees of freedom (yaw, roll and pitch).  This motion platform was developed by a British company called Ansible Motion and the picture below is from their website. You can see the sled rails at the back, and the 180+degree surround on which the images of the track are displayed. The steering wheel provides feedback to the driver and even the seatbelts are cued in so that when you brake, the seatbelt tightens just as it would in a real car. Ansible is the same vendor that worked on McLaren’s F1 simulator. The Ford folks claim that this design has a much faster response time, meaning that the time between when you turn the steering wheel and when you feel the result, is shorter and more like real life.

AnsibleMotionPlatform

 

 

At present, they’ve got ten tracks in the library for the new simulator – eventually they will have all the NASCAR tracks and, since the Tech Center is meant to support all of Ford’s motorsport activities, they will be able to change out the cockpit to, say, a Daytona Prototype, and including tracks like Sebring.

So far, I’ve made it sound like they’re just one-upping iRacing, but a prime feature of the center is that there is a whole room associated with the simulator that is filled with engineers who are watching both the driver and the racecar input/output data.  The driver is being assimilated into the simulations. This is why it’s called “Driver-in-the-Loop” simulation.
DriverintheLoop

 

On the one hand, the driver will help validate all the models.  If there’s a bump on Pit Road at a track that gives a driver trouble, he or she will recognize when it’s not in the model of the track used by the simulator. (And since tracks change significantly, the models have to change to keep up with reality.)

While we’re talking tracks, let’s point out that the track models aren’t made by someone sent out with a tape measure. Tracks are laser scanned to a resolution of a few millimeters. Every dip and bump is recorded and used in modeling the tracks. Laser scanning not only collects three-dimensional location information, it looks at the quality of the reflection.  Laser scanning can differentiate between a white painted line and a yellow painted line, between two different lanes of asphalt, or even skid marks. When you’re traveling at top speed, any surface irregularity becomes important because all it takes is for the car to be throw a little out of equilibrium and you’re in the wall.

In addition to the track, the driver can also provide feedback about whether the “car” responds the way it does in real life. But at the same time the driver is evaluating the simulator elements, the engineers are evaluating the driver. They can start to look at things like how a particular driver’s comfort level may dictate a different line for them relative to another driver. They can run repeated tests to find out how constant a driver is. Do they brake the same way going into Turn 1 at Charlotte every time? Or are they hyper aware of something like tire fall off and able to tailor their braking to the condition of the car?  This type of research has great potential to improve communication between the team and the driver.

Skeptics will worry that we’re getting uncomfortably close to a situation in which we have a bunch of engineers sitting around driving the racecar via remote control and the driver is no more than a warm body executing commands as he’s told. The beautiful thing about human beings is that you can’t model a human being. Having done research in both physics and science education, there’s a huge difference between measuring electrons and measuring people. You kick an electron twenty times and it will pretty much do the same thing each time. You kick a person twenty times and (aside from the danger of being kicked back), you’ll get at least ten responses depending on the person’s mood.

It’ll be interesting to see whether tools like this can help the Ford teams (especially Roush Fenway Racing) catch up to Chevy.

Jun 032014
 

We lost a lot of racing people this week. Although I never knew him personally, Speedy Bill Smith was a big part of my racing education.  Bill passed away on May 30th at the age of 84.

When I first got interested in motorsports, I was living in Lincoln, Nebraska. Not only did I not know anything about NASCAR prior to writing my book, I actually didn’t know much about cars.  One of the best resources I had was catalogs – and Speedway Motors, a huge shop filled with race gear, race parts and racers.  Bill Smith was the owner and set the tone for the shop. He also founded the Museum of American Speed, a non-profit enterprise with more than 135,000 square feet of cars, engines, parts and (my favorite) toys.

Smith was involved in many different types of racing and most of the obituaries focus on his being in numerous racing hall of fames, having been owner for drivers like Tiny Lund, Bob Burdick and Lloyd Beckman, having won the Knoxville Nationals as an owner.

The thing I like best about racing, however, is the people involved.  Smith was a great member of the Lincoln Community. He was a distinguished alumni of Lincoln High School and Nebraska Wesleyan University, and not only was he in the Nebraska Auto Racing Hall of Fame, he was in the Nebraska Business Hall of Fame.  He was married to his wife, Joyce (who predeceased him), for 61 years.

Speedway Motors was always a place I could walk in and ask a question, no matter how ignorant, and I always got a respectful, clear and helpful answer. The folks there love racing and racers.  They didn’t mind if I came in and looked at suspension parts for an hour. I bought my first firesuit there.

A “Celebration of Life” will be held on June 14th at the Museum of American Speed, 599 Oak Creek Drive, Lincoln NE.  The museum is always looking for donations, as well as volunteers to help research the provenance of various artifacts, so if you’d like to recognize Bill’s contributions to motorsports, either would be a great way.

 

May 282014
 

Everyone’s favorite “planet” killer had a spare hour because COSMOS was pre-empted Sunday by the Coca Cola 600.  Astrophysicist Neil deGrasse Tyson edified us with some “NASCAR physics”.

NDGTweet1

NDG2

There were 43 drivers who had no problem taking the corners at more than 165 mph without skidding into the “embankment” and a couple million viewers who knew instinctively that these were not correct statements.

CarTurning

Some basic physics. A car going around a racetrack in a circle is no different from a ball on a string being swung in a circle. In both cases, the reason the object makes a circle is because there is a force that point toward the center of the circle at all times. For the ball, it’s the string. For the car, the tires generate that force through friction between the tires and the track. The car tries to slide away from the center and the tires keep it from doing that.

The amount of force the tires generate is proportional to the force pushing down on the car. If you slide a tire across a parking lot, it takes you a certain amount of force.  If someone sits on the tire, you need more force to pull it. The force the tires generate is given by:

FismuN There are two forces pushing down on a racecar: the weight of the car (which provides mechanical grip) and the aerodynamic downforce (which provides aero-grip). Let’s ignore the downforce for a moment because it gives car more turning power and lets it reach higher speeds, so it only helps the argument.

If you look at a flat track, all of the frictional force is in the direction you want it to go – toward the center of the turn.

CaronFlatTrack

 

I’m showing three forces: The track exerts a force on the car equal to the car’s weight. The frictional force is toward the center of the turn, as required.

In most situations, the coefficient of static friction (the μs) is less than one, which means that you get less frictional force than the weight of the car. For regular tires on asphalt, for example, you only get 70-80% of the force pushing down.  On ice, you get maybe 10-20% of the force. Racing tires are different. They take advantage of some really interesting physics, which is that of adhesive friction (versus abrasive friction, which is what we all learn about in school).  Rubber is a truly amazing material. While the actual coefficients of friction for specific race tires are closely guarded, you can use 1.2-1.3 as a good approximation.  The 165 mph number Tyson came up with is a result, I believe, of having used the coefficient of friction for regular tires, not race tires.

Now throw in banking.

BankedTrack

The directions of the forces change. Except gravity, which (on Earth) always points straight down.

The track always pushes perpendicular to its surface, so now part of the force from the track is pushing up and part is pushing toward the center – the banking helps the car turn.  The higher the banking, the more help you get turning.  If the track had a banking angle of 45 degrees, half the track force would be pushing up and half would be helping the car turn.

If you’re paying attention, you’ll notice that the frictional force (which always acts parallel to the track surface) also changes direction. In fact, the amount of frictional force in the direction you need to turn actually decreases a little; however, you get such an advantage from the banking that it compensates for the loss due to the frictional force.  (Of course – otherwise, no one would bank tracks.)

The calculations (without aero) are pretty straightforward and standard in many intro physics courses.  Hyperphysics is my go-to reference for basic physics when I don’t have a textbook handy.  You can follow them through the whole calculation to get the equation that shows the maximum velocity is determined by the radius of the track (r), the static coefficient of friction between the track and the tires (μs), and the banking angle of the track, θ and the acceleration due to gravity (g).

vmax

The parameters are easy to look up. g has a value of 32.2 feet per second per second (ft/s2), the turn radii at Charlotte vary (

At Charlotte, the turn radii are 685 feet (turns 1/2) and 625 feet (turns 3/4)  and the banking angle is 24 °.  Hyperphysics even gives you boxes and lets you plug numbers in on their site, so you can play around to see how the maximum velocity changes with the parameters.

The important thing here is the difference in friction between race car tires and regular tires. Race car tires are made of a different composition of rubber. They get much hotter than passenger car tires and the surface layer of the tire actually melts a little bit. Rubber gives additional grip in a way I like to describe as what happens if you step on a piece of chewing gum on a hot day. The chewing gum sticks to your foot and prevents you from moving – a slightly different type of friction.

Physics classes rarely teach students about materials that aren’t pretty well-behaved solids. Stretchy, squishy materials like rubber or any type of liquid introduces a lot of complications. I had been teaching physics for 15 years before I learned  you could have a coefficient of friction greater than one.  So it’s not too surprising Tyson didn’t know it either.

However, as my friend James Riordan points out, theory always has to be checked against experiment. And that’s part of what’s so annoying about this. All you had to do was watch the race to know this upper limit was incorrect.  A huge number of media outlets re-tweeted these ‘facts’, or featured the tweets as they exclaimed how wonderful it was that an astrophysicist was explaining NASCAR to its fans.  Sorry folks – NASCAR fans are smarter than they are given credit for.  There’s a level of complication and sophistication to the sport that people who have never paid attention to it simply don’t appreciate.  Sure, NASCAR isn’t F1 – but there aren’t many of the high-level teams that don’t have at least a few Ph.D. level aerodynamicists and mechnical or chemial engineers on the payroll. It’s a must if you want to be competitive.

 

May 272014
 

Okay. COSMOS was pre-empted Sunday in favor of the Coca Cola 600 and COSMOS host, astrophysicist Neil deGrasse Tyson, decided to edify us with some NASCAR physics.

NDGTweet1

NDG2

 

I bet 90% of NASCAR fans immediately know there’s something wrong here. In fact, all you had to do was watch the broadcast.  I’ll write a longer post, but here it is in brief.

The calculation for a car rounding a banked track with friction is pretty straightforward. There are a lot of angles in it, but if you work through it, it does make sense.  Check out hyperphysics for the details. The important thing here is that the maximum velocity is determined by the radius of the track, the coefficient of friction between the track and the tires, and the banking of the track.

banked

 

where r is the radius of the track, θ is the banking angle and μs is the coefficient of static friction. I know, it looks complicated, but stay with me.  The next paragraph is just the important stuff.

At Charlotte, the turn radii are 685/625 feet (the two turns are different, depending on whether you’re going into the dogleg or the backstretch) and the banking angle is 24 °.  Hyperphysics even lets you plug in numbers on their site, so I could very quickly determine that 165 mph is what you would get if you assumed a normal coefficient of friction between a regular tire and an asphalt track (around 0.75).  The reality is that NASCAR tires have a much higher coefficient of friction, which is why they easily exceed 165 mph and have no problem staying away from the “embankment” – whatever the heck that is.

Details to follow, but I wanted to get this up because I’m getting flooded with questions.

 

 

May 092014
 

OK, so ‘monozone’ is just a fancy way of saying it’s the old tire.  It’s all in the branding, isn’t it?

Goodyear has been experimenting with multi-zone tires since last year.  Multizone tires attempt to get the best of both worlds by combining a harder compound on the inner 2-3 inches of the tire (for wear resistance) and a softer compound across the rest of the tire (for grip).  I went over the reasons for the need for a tougher inner shoulder to the tire and why the new camber rules in a good amount of detail previously.

Multizone tires were a hit last year in Atlanta, but not as praised much in Kansas.  Likewise, this year the tires made for great racing in Texas, but the Richmond race featured a lot of tire wear and some unhappy drivers.

Goodyear tested a multizone tire at Kansas Speedway on April 14th this year. They weren’t happy with the results and have opted to go with a monozone tire at the race.  They used a combination of information in the historical record regarding previous compounds used at Kansas, along with lab testing to develop a new monozone right-side tire.  The compound is slightly different than the grip-centric compound that had been used on the multizone tires.  The same left-side tire will be used as has been used previously.

Given that Goodyear starts making tires for Daytona back in October, it’s pretty impressive that they were able to generate the tires for the race in a little under a month.

The problem seems to be excessive wear on the inside edges of the tires. I covered the reasons for this previously, but those reasons are exacerbated when you’re at a track with a lot of grip.  This means that the problems are more likely to rear their heads at grippy tracks (i.e. newly paved tracks) and during night races because the cooler temperatures result in more grip.  The other factor is high loads on tires, especially transient (i.e. short-time) loads.

Larry MacReynolds pointed out this morning on SiriusXM NASCAR radio that the teams have the car suspensions set up to be be rather stiff.  In the corners, there isn’t much springy in the car except the tire – the tire becomes the only point with any give. That puts a lot of stress on the tire.  Corner speeds have also been much higher this year – and that’s were much of the load comes about.

The one common thread I’ve heard is that there is a very small window between ‘fine’ and ‘oops’ – the tires are good for a long time and then they just go.  This is a problem because you don’t get much predictability – there’s no way they can run enough testing during practice to know that they can go 54, but not 55 laps before the time starts wearing enough to get into the danger zone.

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