We installed the new Goodyear...
We installed the new Goodyear tires on the 12-inch wide Aero steel rims. At the front, after making adjustments to the caster split to help the car turn left, we found the toe had changed. Once we reset the toe, the car turned much better. Only 1/8-inch of toe-out is needed on asphalt versus a half inch on dirt.
The lowering of the rear lowered the right side of the Panhard bar by one inch, which is a ton. A lower bar resulted in a lower rear moment center and that would increase the rear roll and tighten the car. We did a toe check and found that the car was toed out 5/8-inch, another ton by asphalt standards. So, we retoed the front wheels to 3/16-inch out, raised the right side of the Panhard bar one inch, and went back out.
This time the car looked great. Bobby was getting faster and putting down very consistent lap times. In fact, on the final run of the day under threatening skies, he put down about thirty laps, and the last five were the fastest of the day by far on tires that had close to a hundred laps on them by now.
Along the way we had fine tuned the front cambers after reading the tire temperatures and slightly adjusted the air in the tires, but other than the above, we never touched a spring or shock. We feel that with the way Bobby adjusted to the asphalt driving style and the way the car looked and handled, we should do well come race day. Above are the spring rates we ran with the equivalent rear rates as if the springs were mounted on clamps.
In selecting our spring rates,...
In selecting our spring rates, we needed to balance the roll tendencies front to rear. We did this by using a stiffer right rear spring rate and a Panhard bar height combination. Once we fixed some mechanical problems, the car exhibited the tendencies that relate to a balanced setup, being even front to rear tire temperatures, a good rotation in the middle of the turns and good bite off the corner.
When preparing a dirt car for a run on asphalt, there are several things to make sure you address. The toe setting must be reduced to between 1/8- and 3/16-inch out. Change the caster settings, which are normally more even right to left on a dirt car, to a split with the left being around 2 degrees and the right to between 4 and 5 degrees positive. Eliminate any Ackermann that might be in the steering system.
Move your lead around to achieve a more fifty-fifty front to rear percent. Move it left, too, and down to get more left side weight and a lower CG, all necessary for asphalt racing. Eliminate rear steer in the car. On a four-bar car, drop those upper links and do whatever you need to do in order to decrease the movement of the wheels fore and aft when the chassis rolls.
Run spring rates that will equal out the roll tendencies of the front and rear, i.e. keep the left front tire on the tarmac. Try to relocate the Panhard bar to a right side chassis mount. We had already done this on our car, and it worked out well. Have the driver run a straight line and arc the turns to keep the momentum up. The driver will learn that he can use much more throttle than could be used on most dirt tracks, but don't get carried away. You still must use throttle control on asphalt. If you dirt track the corners, the rear tires will only last a few laps.
Rob Fisher will be at the race with Bobby and crew. I will be far away on Kachemak Bay in Alaska in a float plane, but that is a whole other story. We will document our run and any changes we might need to make. Who knows, more dirt series just might start including asphalt tracks in their schedules much like the ARCA RE/Max Series has the two dirt tracks (DuQuion and Springfield) on its schedule. It make's for a very interesting deviation.