Turning at Bristol: A Weighty Matter

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

The Digital Dashboard

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.

Infographic: Fuel Mileage Races

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