Oct 022015

Last week at New Hampshire, Kevin Harvick easily had the most dominant car, but failed to win the race. They ran out of fuel with three laps to go and finished 21st. The #4 team wasn’t the only team that gambled on gas, but they were probably the team that lost the most. Now they’re in a must-win situation this week at Dover.

Team owner Gene Haas said that the team made a “simple miscalculation” about how far they could go on the final tank of gas. As reported by Jared Turner on FoxSports.com. Haas said,

“Somewhere we were off in our calculations. That’s something we’ll be talking about tomorrow and the next couple days real hard.”

A lot of people wrote this week that Childers and Harvick have been their own worst enemies during this year’s Chase. Can a wrong calculation cost them a shot at a second title.

https://www.wylio.com/credits/flickr/3288067069How Much Fuel Gets in the Car?

NASCAR race cars have approximately an 18-gallon fuel cell. Each fuel can (at right) holds about 12 gallons.

Before a pit stop, team members carefully weigh each fuel can and record the weight. After the pit stop, the fuel cans are weighed again.

The weight of fuel that went into the car is the difference between the two weights.

To get from weight to volume, you have to use the fuel’s density.


On their website, Sunoco gives the density of the E-15 fuel that NASCAR specifies for all cars and all races as 6.2 lbs per gallon. That’s accurate enough that we can suss out that the weight of the fuel inside a 12-gallon fuel can is (12 gallons x 6.2 lbs per gallon =) 74.4 lbs.  The fuel plus can weighs about 94 lbs total, which is why the gas man is usually right up there with the jackman in terms of pit crew member muscles. It takes about 10 seconds to fully empty a can of fuel into the car.

So let’s say that we put 105 pounds of fuel in the car on the last pitstop. Then we can back calculate how many gallons that is:


This seems like a pretty coarse calculation, but Sunoco actually provides a much more specific value for the density to the teams each day. Why would it change? Temperature and humidity can affect the density of any gasoline – which we talked about the last time we were in Dover when Kurt Busch’s team was told they weren’t allowed to try to cool down the fuel during an unseasonably hot race.

This is how regular gasoline changes density as a function of temperature. When the temperature rises, the molecules in the gasoline like to have slightly more space between them, which means that there are fewer molecules in a given volume. If you had a row of seats that normally sat six and you insisted on having an empty seat on either side of a person, you’d end up with only three people in the row instead of six.


The E15 fuel that NASCAR uses has a similar change in density with temperature. Humidity can also impact the density because ethanol likes to absorb water. So each morning, Sunoco distributes a very precise (measured) number to the teams and that is the number they use. It’s an incredibly precise (and simple) calculation to make.

Theoretically, you’d have to make a pretty massive mistake to screw up that number.

But the big uncertainty in fuel mileage calculation is not in the calculation – it’s in the assumptions that go into the calculation.  There’s really two levels of assumptions, too:

  1. How much fuel got into the car and
  2. How fast is it being used?

And, as the diagram below shows… there are a lot of places to screw things up.

Gas In

Spillage and Leakage: We used to have an outlet on the gas tank so that any overflow would go into a catch can. That amount was put back into the gas can and weighed. The new models of gas cans are supposed to prevent spilling, but if you don’t get the can coupled to the gas inlet correctly, or if there’s a malfunction with the gas can, you can spill gasoline on the ground or on yourself. That’s gas that doesn’t get accounted for when the cans are weighed. And since everything happens quickly, it’s possible no one can tell how much was spilled well enough to make a good estimate. It’s also possible that there’s a leak in the fuel line or the fuel cell, although that’s a rather more serious issue because that goes to safety.

Miscalculation: It is surprisingly easy to screw up a calculation when you’re in the rush and crazyness of a race weekend, especially if you’re short-handed, new or a lot of things are changing – or even if you have a new baby and you’re not sleeping much. Someone reads the scale wrong and reports the wrong weight. Someone messes up the excel spreadsheet where the calculation is done, or you’re using the wrong density for some reason. These are the most irritating possibilities because, frankly, they are preventable.

Hold that last thought because I’m coming back to it later.

Gas Out

Here’s where things get really tricky. You’ll hear commentators throw about a number like 4.6 miles per gallon under green and half that under caution. In reality, the teams try to make much better estimates of these two numbers because they are absolutely critical.

Measuring Gas Mileage: Most drivers don’t get the same mileage at all tracks. Gasoline usage is tracked carefully during practices. Gas mileage changes with the condition of your tires, so every time the tires are changed, the gas mileage calculation is done anew. Over the course of a couple hours of practice, the crew chief gets a snapshot of how his or her particular driver’s style at that track with that particular set up uses fuel.

But when you’re racing, some of that goes out of your hands. If there’s someone on your tail and you don’t want to give up a position, the driver may be more aggressive, which means he or she is using gas at a faster rate.  The teams get scads (a techincal term) of data from the Electronic Fuel Injection system that they can mine for more information about how their driver and car use fuel at different tracks.

Cautions: Is it me, or has there been a lot more talk in recent years about drivers’ abilities to save fuel under caution? They’ve always played games like flipping off the ignition and coasting during cautions, or driving on the apron to decrease the distance traveled. Now we’re hearing more about getting off the gas a little earlier, getting on a little later. I think a lot of that focus on finesse is due to the EFI date. After a race, you can go back and show your driver how good he or she was at saving gas.

So What Happened to Harvick?

You have to understand that, for an engineer, being accused of screwing up a calculation is like being stabbed through the heart. It’s a simple calculation and you’d have to be pretty far off your game to screw it up.

So I wasn’t all that surprised when Rodney Childers tweeted an explanation of what went wrong and used some choice words in reference to the people calling for his head for costing Harvick a chance at winning the race.

BSPEED_2015_NHMS_ChildersFuelMileageRaceChilders was able to look at the EFI (Electronic Fuel Injection) data and determine that Kevin had saved enough fuel that they should have had six laps worth of fuel left. They should have been able to finish the race with fuel to spare.

But they were short by three laps.

This can only mean that they overestimated the amount of fuel that went into the car.  Childers suggested the crew hadn’t gotten all the gas from the can into the car or that possibly a fuel cell bladder might have “come apart”. It’s also possible someone misread the scale or mis-recorded the weight.

As he points out, these kinds of mistakes are pretty rare (and I add, especially with top-level people like Childers and his crew) – but it couldn’t have come at a worse time.

Ultimately the crew chief takes responsible for everything except driver decisions, so it does fall on Childers’ shoulders – but all the commentaries attacking him for using bad judgement at New Hampshire are just wrong. He made the right decision based on the data he had in front of him. That data was incorrect. The problem isn’t the judgement – it’s the data.

And you can bet they are going over every step of every process this week at the shop because Dover is their last chance to keep their hopes alive for a repeat championship.

Fuel mileage concerns never go away. Just for kicks, I wanted to see how much fuel you needed for each of the tracks in The Chase.


Remember that there are 128 ounces of fuel in a gallon, so even at the longest track in the Chase, you’re talking about a little more than a half-gallon of fuel for that last lap. If you think about the times someone’s run out of fuel coming around turn 4, divide those numbers by four and in some cases (looking at you, Martinsville), as little as a quarter of a cup of fuel could lose you a race. This is a sport not only of tenths and hundredths of seconds, but also of quarter and half-cups of fuel.

Disclaimer: Back in 2008, Rodney Childers was one of the crew chiefs for Elliott Sadler and I spent a weekend with the team at Daytona while writing the update for the paperback version of my book. His desire to win coupled with a measured calm and can-do attitude makes him a person you really can’t help but like and admire. So I’m probably biased toward him, but I think my analysis still holds up!

Sep 182015

Every year about this time, someone grumbles that The Chase needs a road course. The frequently-cited rationale is that the regular NASCAR season has two, so a champion should prove he or she can perform on the same racetracks that make up the regular season.

This seemed like one of those things you can solve with data. Is the Chase really reflective of the overall NASCAR season? Let’s start by classifying the tracks. I broke them down as follows:

Track Type Tracks Included
Short Tracks (less than a mile) Bristol, Martinsville, Richmond
1 to less than 1.5 miles Darlington, Dover, New Hampshire, Phoenix,
Intermediate (1.5 mile) Chicago, Kentucky, Atlanta, Texas, Charlotte, Homestead
2-2.5 mile Indy, Pocono, Michigan, California
Superspeedways Daytona, Talladega
Road courses Watkins Glen, Sonoma

Then I went through and counted.


Because I have counting issues.

Track Type Regular Season Chase Total
Short Tracks (less than a mile) 4 15.4 2 20.0 6 16.7%
1 to less than 1.5 miles 5 19.2 2 20.0 72 19.4%
Intermediate (1.5 mile) 6 23.1 5 50.0 11 30.6%
2-2.5 mile 6 23.1 0 0 6 16.7%
Superspeedways 3 11.6 1 10.0 4 11.1%
Road courses 2 7.7 0 0 2 5.6%

I know we usually break things into small, intermediate and big, but let’s take a little more detailed look, okay?

Of course, it’s not science without colorful graphs, right? Let’s start by looking at the distribution of races throughout the whole season. As you can see from the pie chart….


… a NASCAR season is pretty well balanced. You’ve got a little more 1.5 mile tracks, but there are more 1.5 mile tracks out of the tracks NASCAR runs than anything else, so that makes sense in terms of supply and demand. Now let’s compare that to the regular (first 26) and chase (last 10) races.



So I thought this was pretty interesting. We knew that 1.5 mile tracks make up half the chase, but in addition to there being no road courses, there are also no 2-2.5 mile tracks. There are about the same proportion of superspeedways, short and 1-1.5 mile tracks, but the places that would have been taken by a road course and a 2-2.5 mile track is replaced by 1.5 mile track.

The husband said that trying to compare pie charts was too confusing, so I also put this together in terms of a bar chart. The legend turned out a little small, so I’ll note that the light green is the regular season, the blue is the chase and the purple is overall (a weighted average, since there are 26 races in the regular season and only 10 in the chase.)



Let’s Fix This!

Okay, let’s go on the assumption that The Chase, in order to crown a real champion, should reflect the regular season. What do you change out?

Here’s the problem. The Chase happens in September, October and November. Where are all the 2-2.5 mile tracks? In the Northeast or Midwest. Pocono in November would take a huge chance in terms of weather. There’s California and you could pair that up with Phoenix to make a mini West-coast trip. Given that the racing’s been so much better there lately, that might be an option. But I’ll tell you, come the last couple races of the season, everyone is exhausted. The logistics of getting two cars out to the west coast are complicated and everyone is just bushed.

There’s the same problem with the road courses. Watkin’s Glen in the fall is iffy and Sonoma brings up the whole West Coast argument again.   Road Atlanta would work… but then we into the question of taking a race away from another track.


I got curious about the geographic distribution of races, so I tallied that up as well. Not surprisingly, the majority of the races are run in the Southeast, as befits a sport that originated in the Southeast. I did do the pie charts for Regular Season vs. Chase – but the distribution really doesn’t change, so I decided not to include those. (It takes time to make these things!)




I also looked at the distribution of the Nationwide series compared to the Sprint Cup Series. Since they run together at a lot of tracks, I expected it to be pretty close. It was.


Sep 042015

I get this question a lot: If NASCAR decreases horsepower for everyone, how does that make it easier to pass? You’re basically taking everyone down by the same amount, right?

To explain this, we have to touch on a couple concepts.  Moody asked me this a couple weeks ago and I gave him a really crappy answer. I’ve been feeling guilty ever since.

Horsepower vs. Torque

We usually talk about horsepower when we talk about engines, but the important quantity here is actually torque. As a friend likes to say, horsepower lets you go fast, but torque makes you feel good.

Horsepower is how fast the engine delivers energy. (Power is energy divided by time.) Horsepower is actually a unit. It was proposed by James Watt (the 18th Century Scottish inventor, not the Secretary of the Interior under President Reagan). The Scottish Watt invented a viable steam engine by understanding some very complicated thermodynamics, most of which wouldn’t be formalized by scientists for another 100 years. His Watt Steam Engine was a critical driver of the Industrial Revolution.

Watt was successful at convincing a lot of people who ran factories to switch from the current Newcomen steam engine, which was extremely inefficient and used a lot of coal to make a little bit of power. Watt’s engine needed much less coal and he actually licensed the engine to people for royalties – he got 1/3 of the money they saved on coal relative to the Newcomen engine they had been using.

But there are only so many industries. Watt saw his engine as being useful to much smaller enterprises, like mills. But this was a different PR task. You weren’t convincing people to trade out one machine for another – you were convincing them to trade out their trusty horses — which work steadily and require only a little hay and water — for a machine.  It’s a real paradigm shift. How do you even compare two things that are so dissimilar?

Watt estimated – and I use the word ‘estimated’ loosely – the power of an average horse. He sort of measured it on what I’d describe as a horse dyno. That gave him a way to parameterize the power of his steam engine in terms of what he hoped to replace: the horse.

Nowadays, most of the world uses the metric unit for power – the Watt. One horsepower is 746 Watts. So that 60-Watt lightbulb in your lamp is actually a 0.08 horsepower lightbulb. A 1000-W hairdryer is about 1.3 hp. A 750-hp engine is the equivalent of 932 60-W lightbulbs.

Object Power
hp Watt
60-W lightbulb 0.08 60
100-W lightbulb 0.13 100
hairdryer 1.3 1000
lawnmower 5.0 3,730
2016 Ford Mustang V-6 300 22,380
race engine 750 55,950

Torque vs. Horsepower

Torque and horsepower are both properties of an engine. As we’ve discussed before, we usually talk about peak values (like the Mustang engine above is 300 hp at 6500 rpm), but the actual values depend on the engine speed (in rpm). A friend who designs engines likes to tell me…

Horsepower lets you go fast. Torque makes you feel good

Power is how fast you can supply energy – and determines your ultimate speed. But when you step on the gas, what you really want is acceleration.

A minivan and a Mustang both reach 60 mph. But there’s a big difference between punching the gas and hitting 60 mph at the end of the on-ramp and standing on the gas and it taking fifteen seconds to get to 60 mph. Speed is good, but acceleration is actually much more important. And acceleration requires torque.

Torque and horsepower are related, as shown in the graph below.


Every torque and hp curve you see will have the torque and the horsepower curves cross at the engine speed of 5252 rpm. That’s because the horsepower and the torque are related to each other by a pretty simple equation.



So when NASCAR limited horsepower, they also effectively limited torque. That, in turn, limits how much acceleration you get.

Kinematics and Quadratics

This is a perfect time of year to discuss this because every high school student starting a physics class is probably learning about distance, velocity and acceleration right now.

Velocity is how much distance you travel in a particular amount of time. If you’re going 60 mph, it literally means that you go 60 miles every hour.

Acceleration is how fast you change your speed. A Bugatti Veyron goes from 0 to 60 mph in 2.4 seconds, which means that it goes (on average) 25 mph more every second,.

When you’re coming out of turn 2 or turn 4, onto the straightaway, what you want is acceleration. You’ve had to slow down to take the corner, so the goal is to be going as fast as possible coming out of the turn, accelerate as quickly as possible, and put as much distance between you and the guy behind you as possible.

No Acceleration

The distance you travel at a constant speed is proportional to the time.  If you go 60 mph, after one hour, you’ve gone 60 miles. After two hours, you’ve gone 120 miles. After three hours, you’ve gone 180 miles. It’s linear.

This seems obvious, but if I am behind you by half a second, there’s no way I can pass you unless I go faster. But just look at how much faster I have to be going.


Car 1 is the blue line, going at 180 mph. Assume car 2 is a half second behind. If car 2 goes 190 mph, then it will take just about 9 seconds for car 2 to pass car 1and that’s the red line.

If Car 2 goes 200 mph, it takes only about 3 seconds for car 2 to pass car 1.

Of course, if we’re talking about cars directly battling for position, we’re probably talking about one being a tenth of a second behind. In that case, if car 1 goes 180 mph, car 2 going 182 mph would take almost six seconds to pass and car 2 going 184 mph would take about 2 seconds.

The Magic of Quadratic Dependence

Here’s the big deal for acceleration. The distance you travel is proportional to the SQUARE of the time.

Let’s do this first with simple math. Let’s say you accelerate such that you travel 100 feet in one second. After two second, you haven’t gone 200 feet – you’ve gone 400 feet. And the longer you go, the bigger the difference gets.

Time  Distance
Linear Quadratic
1 100 100
2 200 400
3 300 900
4 400 1600
5 500 2500
6 600 3600

I think graphs are easier to see this, so here’s a representative graph. Both cars have the same acceleration; however, Car 2 doesn’t start accelerating until half a second AFTER Car 1.

BSPEED_KinematicsofPassing3The interesting thing here is that the distance between the two cars doesn’t stay the same. Car 1 gets further and further ahead just because how far it goes depends on the square of the time. Car 2 never catches Car 1.

Another words, the long Car 1 accelerates, the more distance it puts between it and the car behind it.

What if Car 2 can accelerate faster?


After some time, Car 2 will pass Car 1. How long that takes depends on both car’s accelerations.

But there’s one more important thing we have to consider.  How long the cars accelerate.

Terminal Speed

An engine can’t accelerate indefinitely. At some point, it reaches its top (or terminal) speed. Then the distance it travels goes back to depending linearly on time. The graph below shows a car that accelerates for four seconds, then reaches its terminal speed. Notice how the graph changes from being quadratic to being linear at the crossover?



Compare that graph with how far the car would’ve gone if it kept accelerating. I’ve shown the quadratic in blue below and the same behavior as in the graph above in red. You can see how much further the accelerating car goes and that distance just keeps growing bigger the longer you go out in time.


When you reduce engine power, you have a lower terminal speed and you reach it faster. That means you don’t get to put as much distance between you and the next guy. And that was the big complaint in a lot of places. One guy gets out front coming out of turn 2 or 4, gets a big lead coming down the straightaway, and the guys behind don’t have a chance of catching him.

At the big places like Indy and Michigan, that was one of the big problems. A car got going down the straightaway and it was gone. There was no catching up to it. The theory behind the lower horsepower there is that the cars reach terminal speed faster, which limits how much of a lead a car can get. The same idea applies pretty much anywhere.

So why doesn’t NASCAR just do the calculation and figure out the sweet spot for each track? Too many variables. A driver will get on the gas at a different point coming out of a turn, or brake later going in. There’s no way to precisely figure it out.

But the general principle applies. If you limit acceleration and top speed for everyone, you limit how much of a lead a car can get. That means that the cars behind have a chance at passing for the lead.


Aug 212015

A lot of drivers cite Bristol as one of their favorite tracks. It’s a great exhibit for the argument that racing is more than just pure speed. High banks (which we know mean speed!) and a short track, which means tight racing. But a lot of drivers will tell you that Bristol is one of the most exhausting, physically demanding tracks on the circuit. Add to that the inherent stress of short-track racing, where 43 cars are operating in a limited (half-mile) track.

Regular readers know that the force it takes to turn a race car is given by:


So it is harder to turn (i.e. you need more force)

  • when you have a heavy car
  • when you’re going fast
  • when you’re trying to make a tight turn

So when you compare a thousand foot turn radius like at a superspeedway with the 250-foot turn radius of Bristol, it’s four times easier to turn at Daytona  — if you’re turning at the same speed.

Turning Force

Using a typical weight for a Gen-6 car (3300 lbs of car and 180 lbs of driver), we can figure out how much force it takes to make a car turn.  (Disclaimer: Parts of this table are from a previous blog.)

Track Turn radius
Turning Force
Talladega 1000 33 180 6,848 1.97
200 8,456 2.43
Daytona 1000 31 180 7,532 2.16
Bristol 242 24-28 130 16,235 4.67
100 9,606 2.76

Newton’s First Law says that a car going straight down the frontstretch at Bristol will keep going straight (and into the wall) unless a force acts on it and causes it to turn.

Consider a soccer ball rolling past you. You want to change its direction, so you kick it at a right angle to the direction it’s headed. The faster it’s moving, the harder you have to kick it to change its direction. The direction it goes is a combination (a physicist would say “a vector sum”) of the direction it had been heading and the direction of the force (the kick) you applied to it.

Putting Turning Force in Perspective…

Just to put these numbers in perspective, let’s look at one of the largest land animals, the elephant. My father always made a big deal of knowing the difference between an African and an Asian elephant. The African elephant is larger (up to 13 feet tall) than the Asian (“only” 12 feet). You tell them apart because the African elephant has much larger ears, has two ‘fingers’ on its trunk, and has much more wrinkly skin. The Asian elephant has smaller ears, only one ‘finger’ on its trunk, and smoother skin on the head and face.


What does this have to do with anything? An adult male African Elephant weighs, on average, 15,400 pounds.

Turning a NASCAR race car at Bristol at 130 mph requires a force slightly greater than the weight of an African Elephant.

I’ve graphed the force needed to turn as a function of speed below. (Note that the turn radii at Bristol are different for turns 1/2 and 3/4. Turns 1/2 have a turn radius of 242 ft, while 3/4 have a turn radius of 256 ft.)



Compare this to Daytona, which has higher speeds, but also larger turns.


So it’s actually easier to turn at Daytona, even though the speeds are a higher, you’ve got four times more turn radius.


We can also look at this in terms of the g’s the drivers pull while traveling around Bristol.


Just for reference, most amusement park rides top out at about 3G; however, some roller coasters go up to 4G (SheiKra Rollercoaster at Tampa) or 4.5G (e.g. the Titan Rollercoaster in Texas).

Although the “G” is the acceleration due to the Earth’s gravity (which always points to the center of the Earth), we use G to measure acceleration in any direction: up or down, back or forth, or sideways.  Drag racers experience accelerations of about 5G backward at take off.  When you’re turning at constant speed, the acceleration is sideways (which engineers call ‘lateral’).

The green line is on there because around 5-6 G’s, drivers start to be impaired because the forces actually change the ability of the blood to circulate through the body. Drivers may experience greyout, which is a loss of color vision, tunnel vision (loss of peripheral vision), blackout (complete loss of vision, but still conscious) and finally G-LOC (which is loss of consciousness because of gravitational forces) .

Now, if you’re paying close attention, you will notice that the graph of ‘G’s and the graph of forces look very similar. In fact, they are the same trend because you get the g’s by dividing the turning force by the mass of the car and the acceleration due to gravity (32.2 ft/sec/sec).

The Effect of Banking: Inside Line or Outside Line

One of the most interesting things about Bristol is that it now has graduated banking – from 24 degrees to 28 degrees. As we’ve discussed before, the higher the banking, the more the track helps the car turn. But here’s the twist: If you go up high to take advantage of the higher banking, you actually have to travel a longer distance.  The racing surface width is 40 feet. Now, one of the problems with the way track measurements are specified is that you don’t actually know where they measured the track length.

BSPEED_Bristol_TrackConfigLet’s assume for the purposes of argument that the 0.533 width was measured at the apron – which means that the end of the track at the outside wall is 40 feet further out. The distance down the front and back stretches are the same, so all we’re worried about is the difference in the turns.

If you take the outside line rather than the inside line, you’re going about 125 feet more distance than your competitor who takes the inside line. So you have to find out, given your car’s setup, whether the additional banking helps you turn faster.

If you take the outer line then at 130 mph, you need 13,910 lbs of force, compared to the 16, 235 lbs you need at the inside. You pull 4.00 gs instead of 4.67 gs on the inside. At 130 mph, you’re covering 190 feet per second, so the time it takes you to traverse the extra 125 feet is a little more than half a second. Not much, right?

Except lap times run around 15 seconds.

At the April race, final practice times ranged from 15.043 seconds (Kurt Busch, in first place) to 15.818 seconds (Alex Kennedy in 43rd place).  Half a second takes you from first to 40th place. So you darned well better be faster if you’re traversing the outside.

Now, I don’t know where the 242.45 feet for the turn 1/2 radius was measured. If it was measured at the midpoint of the track, then the differential is smaller, but I figure I’d take the most extreme case to make the point.

Related Posts:

Racing Without Friction

Why Turning is Hard

Aug 072015

Analog vs. Digital

VinylRecordAlbumThe big difference between analog and digital is continuous vs. discrete. An analog signal is a continuous signal in which something like a pointer moves the same way as something else. For example, an analog multimeter has a dial that moves in proportion to the voltage it is measuring.

Those of you of a certain age may remember these odd looking flat black vinyl things called ‘records’. Records are analog devices. A groove is cut into the vinyl. A stylus rides along the groove and translates the wiggles in the groove into an electrical signal, which is then transmitted to a speaker, which turns it into a vibration (which, when pleasant, we call “music”.)

Digital files (your mp3s, for example; everything on your iPod) encode music in 0s and 1s. Instead of a continuous, physical groove, it’s a bunch of data. There are a lot of advantages to digital. It doesn’t degrade with repeated playings, it’s much less fragile, and you can include a lot more information compared to a record player.

On the other hand, digital music can loose some of the ‘character’ of analog music and you cannot substitute a mp3 file for a frisbee.

Like music, the gauges on a car may also be analog or digital. Up until now, NASCAR hasn’t allowed digital gauges. Here’s examples of all three:


On the left is an analog gauge. This is the usual dial gauge that many cars still have. Like the record and the needle, physical components move in response to the car’s speed. (How Stuff Works has a nice explanation of how speedometers work.)

In the middle is an analog gauge that’s been supplemented with LED lights. This was the big deal change a few years ago. The driver didn’t have to squint and try to read the divisions of the gauge. The mechanics would pre-set the gauge so that a few lights would display when the car reaches a particular rpm. The really fancy gauges even had different colored LEDs so that the driver not only had the lights turning on, but the colors to warn them.

A Brief Digression about LEDs

The LED-modified gauge didn’t work its way into racing until the last five to seven years. There’s a good reason why. LEDs are a pretty new innovation. Yes, now you can buy LED lights that change colors and change their colors using your phone.

The principle behind Light Emitting Diodes (LEDs) was discovered in the 1920s, but the first practical LEDs didn’t show up until the 1960s. The first LEDs (circa 1962) were red and so low brightness they were difficult to see. Remember the first calculators?


They had to add plastic, prismatic lenses to make them easier to read because they were hard to read by themselves. They just weren’t bright enough. It wasn’t until the 1970s that high-brightness, affordable LEDs were being made and the spectrum of colors ranged from red to… orange-yellow.

As you move through the rainbow, the wavelength of the light changes. Red is somewhere around 700 nanometers and violet around 400 nanometers. We figured out how to make longer-wavelength LEDs first from a semiconductor material called Gallium Arsenide Phosphide. High-brightness blue LEDs were not invented until 1994 and utilized a different semiconductor called Indium Gallium Nitride. This led to the development of white-light LEDs (you use phosphors to convert blue to red. yellow and green). White light is the combination of all colors and that’s why you can now go and buy a LED lightbulb. The reason we didn’t have LED gauges until recently is that the LEDs needed to be bright and robust enough to survive being a racecar. But those gauges are about to become history. NASCAR will allow digital gauges.

Back to the Digital Tachometer

A digital tachometer gives you numbers directly.  No more trying to read the tiny little divisions on an analog gauge to see how close you can get to your pit road cut off without going over. Whereas an analog tach may tell you you’re somewhere between 4000 rpm and 4100 rpm, the digital tach will tell you you’re at 4036 rpm. Most of the time, that type of precision isn’t good for anything — but when you’re on pit road and trying to stick below the pit road speed limit, you want to know EXACTLY how fast the engine is going.

Actually, you want to know how fast the car is going. Any gauge can be digital – oil pressure, speed, fuel pressure… pretty much any gauge can be made digital.

A digital gauge MAY include a graphical display of some type – sometimes, even ones that look like the familiar analog dials.

The Glass Cockpit

Brian France mentioned the idea of the “glass cockpit” back in July 2012. There’s a continuing fight within NASCAR about how much information drivers and crews should have – and how much of that information ought to be accessible to fans. It seems sort of silly that people are losing races because they got a pit road penalty for speeding. It’s frustrating for everyone involved.

Moving to fuel injection necessitated adding a number of sensors to the cars and integrating them into a single . Digital dashboards were tested back in April at Kentucky, but we’ve heard very little about them since them.

The term “glass cockpit” comes to us from aviation. By the 1970s, the average plane had over 100 gauges and dials. If you need a piece of information – the status of a wing flap, or your fuel level – you don’t want to have to search for it. It needs to be right there, at hand. A racecar isn’t as complicated as an airplane, but the amount of information the driver has access to is getting larger and larger.

Here’s an example of an early-2000’s era dashboard.


Recently, we’ve added a trackbar adjustment knob, too. It’s a lot to look at when you’re going 180 mph.

Here’s a helmet-cam picture from Kevin Harvick’s car. I included it because you’ll notice that the driver is looking through the steering wheel. If you go to the original video (https://www.youtube.com/watch?v=8Pp4PFGeDxk), you can see that the gauges on the sides disappear from view when turning.


Not only can you not see all the information that’s there…  there’s a lot of information that’s not there. There’s no speedometer (I’ve explained that a tachometer is actually more accurate than a speedometer, but when you go to digital, that’s out the window.) There’s no lap time displayed, or cockpit temperature or fuel gauge or tire pressure or…

As NASCAR moves more and more toward technology, the drivers (and crews) will have more and more information available. This is good… up to a point.

How many times have you fumbled around all the menus on a piece of software looking for that command you know is there, but you never remember where it is?

When I’m coming down Pit Road for a pit stop, I don’t care about my lap time or my oil pressure or my fuel pressure. I care about one thing: Don’t speed. And this is one of the big reasons for the digital dash.

Information can be grouped into pages, displaying only the information that is relevant to the driver at that time.

Jamie McMurray tweeted a couple pictures of the digital dashboard during a tire test in Kentucky.

NASCAR_DigitalDash_McMurray2 NASCAR_DigitalDash_McMurray

Important note – it’s the same display in both pictures, just different pages.

A couple interesting things to note:

You can display information in different formats. Your driver is used to gauges? Sure. Note that in the upper picture, there is a red line, a green line and a yellow line right on the tach. A visual indicator for the driver when he or she is getting close to pit road speed or the engine speed at which the engine designers start to get nervous.

The lower display shows lap times! Right now, the driver depends on the spotter or crew chief for that information. And, of course, if you have a driver who doesn’t want to know, you just don’t put that piece of information on the screen.

It looks like the McLaren PCU-500N Digital Dash Display will be the only one allowed for competition. McLaren already makes a display unit (the PCU-8D) for F1. You can get an idea of the types of information they display in the video below.


Optional Now… Mandatory for 2016

ChadKnausAccording to the NASCAR Sprint Cup Series rule book, digital dashboard display

“may be used at all Events after August 5, 2015. Digital dash display use will not be permitted before August 5, 2015. Effective January 1, 2016, a digital dash display must be used at all Events.”

Why August 5th?  Some of the conspiracy theorists over on Reddit suggest that the significance of the date is that it’s Chad Knaus’ birthday.

It’s also Alan Gustafson’s birthday, but Gustafson won’t be using the dashboard in Jeff Gordon’s car this weekend. Why?

As Gustafson said on SiriusXM Radio’s The Morning Drive, the digital dash is about 5 pounds heavier than the analog dash they’re using now. The advantages of the digital dash don’t outweigh (literally) its weight penalty. Five pounds located up high in the car, is a pretty stout competitive disadvantage – until 2016, when everyone is required to run the new dashes.

Aug 052015

Well, it finally happened.

They made it so easy to make an infographic, even I — the least design-savvy person in the entire world — can do it.

It’s not perfect – the tool I used doesn’t seem to like fractions, so I couldn’t get it to give me any lines between 0 and 1 on the chart of how much fuel you need to complete a lap at different tracks – but hopefully the bars give you an idea.

Fuel Mileage Races Infographic

Jul 242015

Aerodynamics is complicated. Let’s just get that out of the way. But it’s not so complicated that we can’t understand what’s going on with just a little patience.

Why 3D?

Every wonder why they call it three dimensions? The reason it’s three is because I (or you) can denote any point in space with only three numbers. For example: a latitude, a longitude and an altitude. Since we’re dealing with much more limited spaces, a simple Cartesian Coordinate system, like this one, usually suffices.


The line that goes out to the point P is a three-dimensional vector. It’s got parts going in the x, y and z directions. By specifying that there is so much in the x-direction, so much in the y-direction and so much in the z-direction, I’ve told you everything you need to reconstruct that vector.

Forces in 3D

A force (a push or a pull) can act in any direction, but in order to understand the effect of that force, it’s easier if we break it down into its components – how much of the force acts in the x-direction, how much acts in the y-direction, etc.

When we do this on a race car, we give the different directions their own fancy names – just to make us seem extra clever. Basically, any force that acts in the opposite direction the car is going is called drag. Any force that pushes the car into the track is called downforce.

When the force acts up instead of down, it’s called lift. Yes, I know it should be called ‘upforce’, but the people who study aeroplanes named it.

Not shown in the picture below is side force, which would be in or out of the page.


Spoiler Alert!

Let’s think about the air acting on the spoiler. Because the spoiler is at an angle, the force on the spoiler is at the same angle (it’s perpendicular to the surface). So some of the force on the spoiler points down and some of the force points horizontally.

Which means some of the air hitting the spoiler creates downforce, and some of the air hitting the spoiler creates drag.


The more area there is for the air molecules to hit, the larger the force. A tall spoiler creates  more force than a short spoiler – but because of what I said up above, the angle of the spoiler is absolutely critical.

The more upright the spoiler, the more of the force is drag and the less of the force is downforce.  If the spoiler were horizontal, you’d get all downforce. If the spoiler were perfectly upright (vertical), all the force would be drag.

Why a Different Package for Indy vs. Kentucky?

In Kentucky, NASCAR went with a shorter spoiler to reduce the downforce. Passing has been a persistent problem at 1.5 mile tracks and the idea was that if the cars weren’t quite so dependent on aerodynamic forces, then the loss of those forces when you get close to another car wouldn’t have such a great impact.

And that strategy seems to have paid off well.

But Indianapolis and Michigan are very different kinds of tracks. At 2.5 miles and 2 miles respectively, they  are closer to superspeedways than they are to 1.5 mile tracks. At Indy and Michigan, the cars get going very fast down the straightaways, which lets the leading car get away from its pursuers. And it’s pretty tough to pass a car if you’re two lengths behind it going into the corner.

So the goal at these almost-superspeedway tracks is to slow down the maximum speeds along the straightaways so that a car can’t get away so easily. This is a little different than the goal at the intermediate tracks.

There’s a couple of ways to slow down a car: the two most obvious are

  • Decreasing horsepower
  • Increasing drag.

Decreasing horsepower introduces its own challenges, as we know from restrictor plate racing, so NASCAR is using the increased drag approach at Indy. And they’re doing that by setting the spoiler height at a pretty astounding 9 inches tall. At Kentucky, the spoiler had been reduced to 3.25 inches.

The best way to understand how much of a difference this is comes from a tweet from JGR Racing, which actually shows you the difference. Extra points for having gotten the product placement in there!


That’s a pretty big honking spoiler, eh?

But, you’re thinking (at least I hope you’re thinking) wait a moment… If they increase the spoiler height to increase the drag, aren’t they also increasing the downforce?

Yep. They are. It would be lovely to have a knob that you could turn and independently change the amount of front and rear downforce, and the amount of drag. But real life isn’t that simple.

Those Poor Engineers… NOT

The spoiler isn’t the only thing that’s changed. The changes in toto are…

  • 9″ spoiler
  • 1″ wickerbill (aka Gurney flap)
  • 2″ splitter
  • 43″ radiator pan width
  • speedway extension on the quarterpanels and rear bumper – the same ones run at the superspeedways.

So you’re thinking – my goodness, pity the engineers. All these changes.

Lemme tell you – the engineers are not upset. They love the opportunity to get ahead of the other teams by being smarter and figuring stuff out before someone else does. This is a chance for a team to get a win simply by understanding the set ups better than anyone else.

And something else to think about. In my column about Kentucky, I showed the changes in the spoiler and radiator pan sizes as a function of time. Well, I’ve updated those.

BSPEED_2015RulesChangesbyTrack_Spoiler BSPEED_2015RulesChangesbyTrack_RadiatorPan

The radiator pan is the exact same size at Indy as it was in 2014. The spoiler is only one inch taller than it was in 2014. And the teams have plenty of experience with the rear aerodynamic extensions from years of racing at Talladega and Daytona.

Yes, it does mean that they have to put those disparate elements together – which they haven’t done before – but the teams with the strongest technical staffs will be in the best position to take advantage of these just-in-time adjustments.

Personally, I’m psyched about track-specific packages. It gives the teams much more of a box to work in, which means they have that much more room to be creative. Looking forward to Indy!


Jul 132015

Someone asked in the comments how much kinetic energy Austin Dillon had when he hit the catchfence at Daytona. I don’t know exactly how fast he was going  (probably was somewhere around 180 to 200 mph), so I figured I’d just make a graph and include a couple reference points in terms of kinetic energy scales.

The left axis is labeled in MegaJoules (MJ), which are millions of Joules. To give you an idea

  • 0.009 MJ = energy contained in a AA alkaline battery
  • 0.038 MJ = energy contained in one gram of fat
  • 0.04-0.05 MJ = energy contained in one gram of gasoline
  • 8.4 MJ =  daily recommended energy intake for a typical active woman  (2000 calories)
  • 110 MJ = energy expended by a typical rider in the Tour de France
  • 122 MJ = energy contained in a gallon of gasoline
  • 1000 MJ = energy of a typical lightening bolt

So without further comment, here’s the kinetic energy of Austin Dillon, where I used his NASCAR official weight of 185 lb and minimum car weight of 3300 lbs. Black cowboy hat not included.


Jul 072015

As some of you know, I was in New York for the weekend celebrating my anniversary, so I’m just now catching up on the weekend’s accident at Daytona. Note: Some basic information about catchfences is modified (and updated) from a blog originally posted on 11/14/11.

And I bet there are some typos, still.

A Brief History of Barriers

Track barriers originally were erected to keep cars separated from spectators.  In addition to concrete walls to prevent the cars from driving off track, debris-spewing accidents necessitated fencing to contain airborne objects.

ChainlinkFenceCatchfences should have the same properties as walls, but they can’t block the view.  Chain link fence is a good compromise: It’s cheap, plentiful, easy to put up and surprisingly strong given its high visibility.

Chain-link fabric is an elastic metal mesh. It can give in two ways: gentle forces cause the mesh to deform.  The diamonds stretch out of shape, but when the force is removed, the fabric springs back to its original shape. The fence can also deform by stretching the wires that make up the mesh. A large-enough force will break the wire entirely.

The mesh must must supported, usually by poles and cables. How much the mesh can stretch depends on how it is supported.  If the frame is too big – meaning that there’s a very large area of mesh between supports — the mesh can stretch too much. How the poles are attached to the mesh is critical, because the attachments allow the load to be shared between the fabric and the poles.  The larger the forces, the more robust the links between the poles and the mesh must be.
Catchfence_Daytona2Race track fencing is stouter in just about every way.  The mesh is made of larger-diameter wire with higher tensile strength.  The links between the poles and the fabric are stronger:  In the picture at right (Daytona), steel cables run horizontally through the mesh and are fixed to the vertical poles using some massive turnbuckle-like fixtures.

Different tracks have different installations.  Some have metal tubing running horizontally as reinforcement. Catchfence improvements have primarily been via stronger mesh, stronger or a greater number of poles, or better links between the poles and the mesh.  But it’s basically the same fundamental design.

The chain-link fence is a motorsports institution, with different sanctioning bodies requiring different standards for debris fencing.  In the FIA test, a 760-kg  (1675 lb) test mass is shot into a fence at a speed of 65 km/h (40 mph) at heights of 1.6 m and 2.5 m (5.25 and 8.2 feet respectively).  While 40 mph seems very slow, they’re taking just about the entire mass of an Indy car and concentrating it in a relatively small sphere.  A real car would impact over a much larger area and spread out the force.


The photo at left shows a Geobrugg fence being tested:  The mesh deforms (a lot!) – but it does not break. Load is transferred to the poles, with the poles nearest the impact bending, but not breaking.  The emphasis, however, is pretty strictly on containment.

Geobrugg, one of the primary catchfence providers for motorsports (and many other things) made the video below that shows a car going into a standard vs. going into one of their fences.

The advances in catchfencing that have been made are huge; however, you are always going to have issues. As long as the fence is permeable, small pieces (and fluids) are going to get through the fence. Some of the people injured in the Carl Edwards crash in Talladega were burned by oil. Unless you use a solid fence, this is a hazard you will never eliminate.

Is Speed a Factor?

We’ve been hearing calls for slowing things down at Daytona. Is speed the issue? It is certainly true that speeds have been increasing.


Here’s the pole speeds at Daytona over its entire history. You have to be a little careful. The idea of group qualifying is very recent, and we know single car speeds are lower than those of cars in a pack, so it’s not quite fair to compare these one one one. But the pack qualifying pole speeds are a good 4mph below the peak single-car pole speed, which means we’re still probably 8-10 mph slower than the highest speeds that have been raced at Daytona.

So maybe it would be helpful to compare speeds at different tracks this year, since single-car speeds aren’t really all that different than race speeds at non-plate tracks.


I put triangles above the plate tracks. You’ll notice that speeds there aren’t that much higher than many of the other tracks – and Michigan was faster than either Talladega or Daytona.

Which led me to wonder about whether this year was just an anomaly. So here’s this year and last year.


Michigan is consistently faster than either Daytona or Talladega. I also wanted to look at the speeds for the Sprint Cup versus the XFINITY series, because the last big accident we had at Daytona was Kyle Larson running in the then-Nationwide series.


You can see that the lower-level series runs at significantly lower speeds (10-15 mph) – and still they’re getting in the air.

So I have a hard time believing that simple reducing speed is going to have a lot of effect on these types of crashes.

Pack Racing

So what’s the big different between Michigan – the fastest track – and Daytona/Talladega? It’s the restrictor plates. Restrictor plates produce a very different type of racing. If you watch the throttle/brake indicators during non-restrictor plate races, you’ll see the drivers easing off the throttle going into the turns, or even braking. The pole speed is an average speed, which means they’re generally traveling faster down the straightaways and slower in the turns.

Not at a plate track. The throttle is full open at all times. The cars are maxed out in terms of their engines.

Remember that, at 204 mph, a car goes a football field a second. Think about that. You’ve seen cars scatter to avoid accidents on other tracks. You can’t do that on a plate track because there is nowhere to go. You’re blocked in on all side.

An accident on a plate track is more likely to involve multiple cars. The last line here is the total number of cars involved in accidents

Michigan 2014 Daytona 2015 July Daytona 2015 Feb Las Vegas 2015 Atlanta 2015
6 1-car accidents
1 9-car accident
5 1-car accidents
1 7-car accident
1 9-car accident
1 11-car accident
2 1-car accidents
2 2-car accidents
2 7-car accidents
3 1-car accidents 2 1-car accidents
1 4-car accidents
1 6-car accidents
15 32* 20 3 12

*Racing-reference.info didn’t mention how many were involved in the end-of-race crash because it wasn’t technically a caution, so the number is much larger.

The numbers are small, so it’s hard to prove this, but my intuition, based on observations and the data we do have, is that more cars involved in an accident at close quarters mean

  • more likelihood of a car spinning (and cars are more likely to become airborne if they are not going straight)
  • more likelihood of a car launching off another car and getting airborne

When all this happens in conjunction with high speeds, you have all the elements for a catastrophic accident.

I am not suggesting we remove restrictor plates – that would be just plain stupid for both the drivers and the fans.

So Let’s Just Make Pack Racing Safer!

Everyone seems to assume that NASCAR will come up with a solution that will allow pack racing to continue the way we’re used to it happening. They’ve done an admirable job of dealing with past issues…


There are limits. I mean, if we could do anything, we’d have cured cancer and found a way to make sure everyone in the world has access to clean drinking water.


If there were an obvious solution to make pack racing safer, NASCAR would have already done it. It is possible that there isn’t a solution and that pack racing will always be inherently more dangerous than other types of racing.

Cars travel just as fast at other tracks and they don’t leave the ground nearly as often as they do at Talladega and Daytona.  Putting on a smaller restrictor plate to decrease speeds will not help. It’s not the speed. It’s the combination of the speed and the pack racing.

Perhaps the best that can be done is to protect spectators and let drivers take their chances. (If you’re wondering whether a Lexan ‘hockey-type wall’ would work, I addressed that elsewhere. (TL;DR: expensive and difficult, especially since you not only have to stop the car and parts from getting into the stands, you have to make sure that you don’t make it more dangerous for the drivers.)

Perhaps you have to make a radical change to the engine so that the drivers have to brake and accelerate around the track and you don’t get pack racing. This would make a lot of fans upset. There is nothing as breathtaking as standing in the infield watching the entire field take the turn.

There is also nothing as breathtaking as that gasp of fear, your heart skipping a beat and the feeling in the pit of your stomach as you whisper a prayer that the driver in the crunched up shell of a car just coming to a stop will climb out and wave and live to race another day.

Jul 032015

Daytona is an enormous, sweeping track. Two-and-a-half miles, 31-degree banking and corner radii of a thousand feet. The infield by itself is 180 acres. If you’ve ever been there (or Talladega), it really does take your breath away when you first enter. Now, bigger tracks (or rather, tracks with bigger turns) automatically mean higher speeds.

There’s a formula for this that tells you how much force you need to make a car turn under specific conditions.


The way to think about this is that it is harder to turn (i.e. you need more force)

  • when you have a heavy car
  • when you’re going fast
  • when you’re trying to make a tight turn

So when you compare a thousand foot turn radius like at a superspeedway with the 250-foot turn radius of Bristol, it’s four times easier to turn at Daytona if all other things are held equal.

The equation above is the equation for centripetal force, which is the force that makes a car turn. The centripetal force tends to confuse people because of its direction. The centripetal force points toward the center if the car is moving in a circle. The way I think of it is if you swing a tennis ball around on a string in a horizontal circle over your head, the thing that keeps it going in a circle is the string – producing a force toward the center.

Well, it’s the exact same thing for a car, except instead of a string, you have tires. The force needed to turn a NASCAR stock car at 130 mph at Bristol is about six tons. Yep, tons.


Because Daytona is so much larger, you need about four times less force to turn at the same speed.

But why stop at 130 mph?

When Daytona was being planned in the fifties, Bill France knew he wanted high banks. Why?


That’s right, banking equals speed, too. Here’s why. Look at the car on a flat track first. I’ve drawn it so the car is moving away from you and it’s turning left (of course).



The force the track exerts on the car is always perpendicular to the track surface. So none of the force of the track on the car is in the direction that helps the car turn. All of the turning force has to come from the interaction between the tires and the track. If you don’t have enough friction, then you’re going to slide out toward the wall.

Banking helps us turn. Let’s give our track a little banking and see why.



Two things change. First, the friction between the tires and the track have also tilted. That means you’re not getting the full force from the tires that you did before; however, the force of the track on the car has also shifted direction.

Now the track is helping the car turn. The higher the banking, the more help the car gets from the track.

If you’ve never been on a track, it’s almost hard to appreciate banking. Here’s me filming for our Science of Speed webvideo series at Texas Motor Speedway. I had this great pair of boots I had planned to wear for this shoot, but it turns out you really can’t wear heels on 24 degrees of banking.

And no, the car is not moving. I am adventurous, but I am not (usually) stupid.



Turning on Ice

So one of the questions I sometimes get asks how important friction is in turning corners. So let’s play Einstein here…

Einstein thought up all kinds of very strange and mathematically intense ideas about how the universe – space and time, specifically, work. He couldn’t actually do experiments to test all of his ideas. (Plus, he was a theorist and it’s usually best not to trust them with anything more potentially dangerous than a sharp pencil.)

So he did what are called gedanken experiments. Gedanken is the German verb for ‘to think’. These are thought experiments – but they sound much more impressive if you call them gedanken experiments.

We’re going to imagine that a highly localized ice storm hits Daytona. So localized, in fact, that it just hits turns 3 and 4 of the Daytona International Speedway. It covers them with ice. What happens to the car hurtling in there?

There’s an equation – and if you’re the kind of person who breaks into a cold sweat at the sight of a radical (that’s a square root), then just grab your chair tight for a moment. (If you want to see the details, I suggest the wonderful Hyperphysics site.)



All this says is that it is possible to bank a track highly enough that you can take the turn without ANY FRICTION AT ALL.

So if we plug in the numbers for Daytona… we find that, in the absence of friction, you could go 139 mph around the turn.This shouldn’t be all that surprising – after all, Daytona could be viewed as an overgrown luge or bobsled track, right? Those tracks have very high banks because there’s a minimal amount of steering going on.

Being the mathematically OCD person I am, I graphed the maximum speed as a function of banking degree.


Remember that we not only have friction, we have lots of it from the tires interacting with the track – that’s why the cars go much faster than in our frictionless case here.

Interestingly, if a car doesn’t go fast enough around a banked turn, it will actually slide down the track.

This presents a major problem when you’re repaving a very banked track because, as a rule, heavy machinery doesn’t move very quickly. The video below shows the 2010 Daytona repaving (pictures, but mostly video).

You’ll see that the paving trucks are actually being held in place by other equipment because otherwise, they would slide (or worse, tumble), right down the track. And that would make for some pretty sloppy surfaces to race on.

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