Talladega Pas de Deux: why two is the magic number at 'Dega

The official Talladega mascot should be:


Pas de Deux (pronounced as "pah-day-due")

Merriam Webster dictionary defines "pas de deux" as


1. a dance or figure for two performers

2. an intricate relationship or activity involving two parties or things

A funny thing happened in Alabama on Sunday. Suddenly for the first time in memory two cars in a pas de deux outran an entire string of cars at "the big track." Until now a long string of cars-- 5, 10, 15 or more cars-- always had the advantage,…a huge advantage because a string of cars always had less overall drag than one or two alone. But on Sunday suddenly we saw two cars outrunning the freight train; how is that possible when it never worked before?

As many TV commentators remarked repeatedly, "the closing rate of the two cars over the rest of the field is incredible," as much as 15 mph or 22 ft per second, a car length per second. When you're only 3 feet away from another car, they're going 180 mph and you're doing 195, closing on them at 22 ft per second makes the slower car appear as if it is sitting still.

Several factors explain the two car run away: Talladega was repaved in 2006 and the surface is unusually smooth, allowing cars to get very close to each, nose to tail, and stay that way for long periods of time. The geometry of the CoT has the nose and tail of the car at essentially the same height so the trailing car can literally push up against the lead car and shove it. Previously with the car dubbed the Twisted Sister if the trailing car pushed this hard on the lead car they'd lift the rear wheels of the lead car off the ground and they'd both wreck.

Also the CoT with a spoiler on it has a very different wake than with the wing (red is highest speed air flow down to blue which is the lowest speed air flow).

There's a very distinctly larger area of low speed wake behind the race car with the spoiler compared to the race car with the wing. The result is that the two cars can actually touch and stay in contact which reduces the overall drag of the two car duet, considerably, by perhaps as much as 30%.

Power consumption increases with the cube of speed (speed x speed x speed) so the observed difference of two cars together at 195 mph vs one car or a string of cars at 180 mph should have required (7.415/5.832) 27% more power to go that much faster, but actually what happens is that the two cars linked together in a pas de deux have 27% less drag as shown in these studies.

While the two cars have a huge speed advantage there is very little air flow reaching the front of the trailing car, which means that the engine of the trailing car will quickly overheat because cool fresh air is not getting into the radiator. This limits how long the two cars can continue their pas de deux, and from watching the race one would deduce that a couple of minutes is about as long as two cars can stay in contact (NASCAR Cup cars can run 2.2 laps at Talladega in two minutes).


Harvick played the final lap pas de deux perfectly, and then at the last possible moment swung around his dance partner (McMurray) to win the race by a mere 0.011 seconds.

After the race Jamie McMurray was quoted, saying, "it's hard to explain to you guys that aren't in cars, but when there's someone directly behind you and they pull their car out of line really fast, it's like you pull a parachute in your car. It literally feels like you lose 3 or 5 mph immediately, and when that happens, the car that's doing the passing just has the momentum."

It doesn't just feel like the car slows down, it actually does slow down. The aerodynamic drag on a car is the difference in pressure on the front of the car, minus the pressure on the back of the car, and that difference of pressure applied over the frontal area of the car is the drag force (pressure multiplied by area equals force), perhaps 700 lbs or so on a car going 190 mph.

When the cars are nose to tail the low pressure area behind the lead car is filled in by the high pressure area on the front of the second car.

But when the trailing car gets out of line to go around the lead car, suddenly there's a low pressure area behind the lead car and the drag force on the front car suddenly increases by as much as 400 lbs. This has the same effect as throwing an anchor out, it slows the lead car by as much as 5 mph almost instantly.

These CFD studies in SolidWorks by FastTrack Racing Challenges for participating junior high and high school teams are possible due to the generous support of SolidWorks (visit their web site and look at the full software package at SolidWorks dot com) and in particular thanks to Marie Planchard, their director of worldwide education markets.