News & Media

Fuel mileage involves more than just 'witchcraft'

June 03, 2011, Mark Aumann,

KANSAS CITY, Kan. -- Keeping on top of ever-changing calculations biggest challenge for crew chiefs

On its face, figuring fuel mileage would seem deceptively easy: miles divided by fuel used. But when Sprint Cup crew chiefs are scrambling to determine if their driver has enough fuel left in the tank to make it to the finish, there's a little fudge factor involved in the calculation.

Why one car makes it to the finish line when another doesn't isn't an exact science. And being able to guess the closest without running out is the hallmark of the sport's best pit box bosses.

"We've got a pretty good formula for figuring how much gas we spill, so it's become quite the art figuring it out, but it's pretty precise."


Adding to the complexity is fuel mileage doesn't occur at a constant rate. It improves or declines based on a variety of factors, including track conditions, weather, traffic, handling and whether the driver is doing anything inside the cockpit to help conserve. Even the miniscule amount of fuel that spills from the tank during the stop needs to be added into the equation.

"It's witchcraft, there's no doubt," said Mike Ford, crew chief for Denny Hamlin's No. 11 Toyota. "You try to understand the best you can where you are on mileage, but these cars without having a fuel level monitor, it's about impossible."

For Ford, it's all about taking into account everything that could be advantageous or adverse.

"The track conditions dictate what you get for mileage," Ford said. "If you're running in traffic, you're going to get better mileage. If the sun comes out, you're going to get better mileage. There's so many variables that come into play, you don't know. If the balance of the race car changes, how much fuel will it use?"

Engineers Jeremy Bullins and Matt Swiderski handle the fuel mileage calculations for Gil Martin, crew chief for Kevin Harvick's No. 29 Chevrolet. In addition, the team has a third crewman working on a second set of equations.

"I think a lot of it used to have a lot of guesswork going into it," Martin said. "But Jeremy and Matt do a tremendous job of keeping up with that now on the box. Our engine tuner, Cameron Brown, he does a backup system on the box and that way, if we have a big discrepancy, we can look at it. But as long as they're pretty well on line with each other, we pretty much know exactly where we are.

"We've got a pretty good formula for figuring how much gas we spill, so it's become quite the art figuring it out, but it's pretty precise."

For Martin, keeping a close eye on the stopwatch can raise red flags as to whether you're getting the right fuel mileage.

"To a certain extent, you've got to watch your lap times, if you've increased the speed a tremendous amount from one run to the next or from daylight to dark," Martin said. "As you watch that, and as you watch the times that go by, you have to have a driver like Kevin who's capable of telling you 'I conserved some fuel here because of letting off early in the corner' or a caution where he could shut the car off, whatever the case may be.

"He's pretty aware of how much he's done and how much he's been able to save. We've been working together long enough, we've got a pretty good idea if what he thinks he has, we've got an idea of how much it is."

Just like with Harvick, what Carl Edwards can do inside the No. 99 Ford can make crew chief Bob Osborne look like a genius in the closing laps, if he has the correct information at the start of the run.

"The hardest thing is knowing whether the car is full of gas," Osborne said. "We go off a baseline number that we've been getting through the race, and then with experience, we know how many laps we can save with 'x' number of laps to go."

Still, no matter what the data may be telling him, Ford admits an experienced crew chief has to make the final decision as much by feel and instinct.

"Basically, you want to know a ballpark [number]," Ford said. "You take an average from throughout the race, you try to understand the environment you're in and you have to know how much [fuel] you actually hold in the car. And a lot of it is a fair guess."