Ryan Pemberton - Ask The Pro

Each month, Stock Car Racing asks a set of readers' questions to a different professional in the racing industry.

Q: Do Winston Cup cars have speedometers, tachometers, or both? Does NASCAR allow speedometers?
Jim Eastlack
Pitman, NJ

A: NASCAR doesn't allow speedometers. We have a pit road speed we have to abide by, and drivers use a tachometer to gauge their speed. Typically, a 45 mph pit road speed would be, depending on the gear ratio and everything, somewhere around 3,800 to 4,000 rpm, in second gear, at most of our oval tracks. At the start of the race, NASCAR will run pace laps at pit road speed. That's why they break the field up into two parts at the beginning of the race, behind two caution cars, so everybody has a better chance to get an accurate rpm reading on the two pace laps before every race.

Q: What are truck arms and track bars? Do Winston Cup cars use both of these?
William Dickerson
Hershey, PA

A: Truck arms are what the rearend housing is bolted to, and they're attached to the rearend housing and middle crossmember on the chassis, just behind the transmission crossmember. A track bar is hooked to the truck arm and it stabilizes the car from left to right. It's bolted to the chassis on the right-hand side, and to the truck arm on the left-hand side, on oval tracks. In most cases, it's mounted the reverse of that for a road course. The track bar is adjustable on the chassis side with a jackscrew. You can raise it up and down three to four inches during a race, and it's a great tool for us to use on Sundays.

Q: If NASCAR decides to legislate bigger greenhouses, won't that make entire fleets of cars obsolete?
Cecil Pridgen
Santa Barbara, CA

A: It could potentially make obsolete just about everything we have. It will be dictated on whether we have to change the rollcage and halo bars. If those two are changed, then the chassis and everything attached to it will be obsolete. Basically, we're waiting to see what the greenhouse is going to be like and what it's going to allow us to do with the halo bar. If we can make it wider, bigger, and safer for the drivers, then we'll probably build all new race cars.

Q: Why are Cup cars so low to the ground in front and high in the back?
Pete Triplett
Plano, Texas

A: That's just something we've been working on over the last few years. We're trying to take advantage of the aerodynamics as teams learn more and more about what's better for these race cars. The nose being lower to the ground makes more front downforce; the back of the car being stood up makes more rear downforce. If you can get them to work in conjunction with each other, you can make a lot more downforce and get the cars to run a lot faster through the corners.

Q: Bill Elliott said he used the same car to win at Pocono one week and Indy the next. How common is it to run one car in consecutive races? What gets replaced?
Bob Row
Northumberland, PA

A: Pocono and Indy are very similar racetracks. They're both 2 1/2 miles long, with flat corners, and very fast. Those are tracks where you try to use the same car back-to-back, if it survives. Obviously, when you win the race, you haven't torn the car up too much, and that's a nice luxury to have, to be able to bring a car back the next week. For the most part, the car is stripped down after the first race. One hundred percent of the suspension will be taken off; it will all be Magnafluxed and inspected; it will get new brakes, tie-rod ends, ball joints; wheel bearings will be repacked; everything will be put back one hundred percent. When it gets to the racetrack the next week, it's basically a brand new car.

Q: Why do race engines perform better in cool temperatures?
Wanda Goodman
Athens, Georgia

A: Race engines run better in cooler temperatures because the air quality is better. The correction factor is usually better, the air is cooler, it's denser, and there's more oxygen in the air. Race engines love nice, cool, clean, dry air, and they make the most horsepower when they have it. If you go to a track where the altitude is real high, or if it's hot and humid, some of these engines could be off as much as 75 or 80 hp.