ESPN.com's NASCAR Icons took some readers' questions and went to Hendrick Motorsports' Sprint Cup series crew chief Alan Gustafson for the answers.
After some experience as a crew chief in the Craftsman truck series and Late Model Stock Car series and chief engineer in the Nationwide series, Gustafson joined Hendrick in 1999. He worked in the chassis shop before becoming the shock specialist for the No. 5 car in 2000 and the lead engineer for the No. 5 in 2002.
In 2005 Gustafson became the crew chief for the No. 5 car driven then by Kyle Busch. That's where Gustafson remains today, although Casey Mears took over as driver for the 2008 season.
Here are your questions and Gustafson's answers:
There were some tire issues at Indy. I was wondering: How much the lack of downforce plays into tire wear with skate and wheelpin? With the higher roll centers on the new car, how much more weight is placed on the tire this year vs. last year if you can get enough rebound from the shocks to control the springs and if teams are running coil bind setups with the new bump stops? what issues do bump stops present?
Gustafson: Downforce is a major contributing factor to how much grip our tires can generate. Downforce will add a vertical load [which the tires like] without the penalty of the lateral load [which tires don't like]. The higher roll center really taxes the right side tires.
The higher roll center of the Impala SS will transfer a lot of weight to the right side tire and, in some extreme situations, the right side tires will handle almost all of the load. That's why you saw only right side tire issues in Indianapolis. That also allowed two tires stops there because the left side tires were so lightly used.
As far as the bump stops are concerned, they are an advantage over coil bind where grip and tuning are concerned. They allow you more adjustability and are easier to adjust.
The issue with the Impala SS is more so the lack of available front travel. Our old Monte Carlos would have the ability to get 3.5 inches to 4 inches of right front shock travel, where our Impalas are only capable of getting 2 inches. That is more the issue than bump stops or coil binding.
What is your favorite or least favorite part of the pre-race spectacle as you get ready for the green flag?
Gustafson: My favorite part of the pre-race routine is the prayer. It is a great time to reflect and focus on the day and the opportunities it presents. The quiet and calm during this time is very important to me.
I really don't have a least favorite time. The only thing I could say that really bothers me is when someone does not know the words to our national anthem. That is tough to deal with.
How much vacuum are the Cup guys pulling in the crankcase now and how much would they be pulling if NASCAR had not put a limit on the length of the dry sump pump? What is the actual reason for the increased horsepower? Is the vacuum acting like a reverse supercharger and actually pulling a bigger charge into the cylinder on the intake stroke?
Gustafson: A typical Sprint Cup engine will produce approximately 18-24 inches of mercury depression in the crankcase. Much of the reason for increasing power with lower crank depression [remember this will be a higher number, because we are talking depression, not pressure] is due to the lower air density in the crankcase, thereby reducing the power required to rotate the crank assembly, much like a car pulling up in the draft.
You do get to a point where the power required to spin the oil pump becomes greater than the power increase found inside the crankcase. With proper ring seal the impact inside the combustion chamber would not be impacted by crankcase depression.
My question is concerning wheelbase. Do cup teams usually run a longer wheelbase on the right or left side, and why?
Gustafson: Front end setups and rear end alignment are the two biggest factors that determine our wheelbase. Caster is the biggest factor in the front end that will affect our wheelbase. Positive caster is how much we lean the top of our spindle back. When we do this it creates an aligning torque in our tire much like the wheels on a shopping cart at your local grocery store or the front tire on a motorcycle.
The rear axle is a solid rear axle. So as you adjust the fore-aft alignment of the housing it affects the wheelbase. The reason for the misalignment is to adjust how the car tracks, which is evident in the straightaway shots of the cars on TV.