Posted by Mike Bales on September 3, 2009, 4:25 pm
Board Administrator
Monthly Tech Tips Part 2
Posted by Mike Bales on September 2, 2009, 8:05 pm
Board Administrator
Vol. 2 of the Set-up Series.
The set-up of the rear end.
Part 1of 2
With our race car still on the jack stands and the suspension tubes holding the suspension at our ride height. The front and rear end squared; you can put that lead into the rear end if you want. If the rear tires are turned to the outside of the race track the car will be loose on entry and loose off. If the rear end is turned to the inside (infield) it will be tight in the middle and off. It is important that the frame of the race car and the rear end are square and working in the same direction.
Alignment of the right side tires. It is also probably the most important part of setting up a chassis. If your line on the floor is down the left side of the chassis from squaring the front and rear, use a large carpenter square at the right side hubs to which the wheel mounts and pull a tape measure over to the line on the floor down the left side of the car and get a measurement. Do this on the front and back to the right side hubs. If you came off the middle cross frame rail for squaring the front and rear, then using the carpenter square make a line down the right side of the race car and then take your measurements off the hubs. The right side tires are what the race car uses the most to get its grip. If the right front tire is in from the right rear tire, the car will seem to always be loose; the back end will not stay under you. If the right rear tire is in from the right front tire, the race car will never seem to want to turn. This is because the tire that is in will accept more weight transfer faster and get more grip. The right side wheels is where I always had spacers to work with, 1/8” to 1/4” in or out here or there could tighten or loosen a car for qualifying or racing rather then adjusting wedge or a turn in or out of a sway bar, but then again this is a fine tuning tool. A rear on a rear car should track about 1” to 1-1/2 narrower then the front. Rear end toe. A rear end housing is opposite of the front end. The rear end toe is 0” to 1/16” toed in. I always worked to get the left rear as straight as I could and worked the toe with the right rear. Use your toe in gauge with your tires on the rear end or use toe plates. The best way is to clamp two straight edges one on each side of the rear end 24” to 36” long by clamping to the hub itself or to the brake rotor. Use your plum bobbs on each end going to the floor and pull your tape measure for side to side front to rear housing. This is not an easy job but it is something that needs to be done. Wide five users, Joes Racing Products makes a gauge that bolt right where the drive plates do. The best is straight ahead and parallel to each other, having no toe at all. So to recap, the direction of the rear end of the race car is how it will behave. If the rear end is pointed to the right of the chassis line it will be loose in and throughout the turn. If it is pointed to the left it will be tight in the middle and off the corner. Next the lower trailing arms. They hold the rear in place, and control the amount of rear steer. Running angle up on the lower trailing arms will have an effect on the cornering and the acceleration of the chassis. The more angle running uphill toward the chassis you have, the more the traction you will get exiting the corner under acceleration, if there is angle split from the left to the right, there will be rear steer in the chassis. Remember that there is always rear steer in the rear end on a 3-link chassis. You need to have control over it by adjusting the arms to your desired setting. If the left arm is up, and the right arm is level, the rear end will pull the right side forward as the chassis rolls over. This can cause a push in the chassis. If the right arm is up, and the left is level, the rear end will trail backward on the right side making the chassis loose when the chassis rolls. This is a fine tuning tool. I would start at 3 degrees uphill to the chassis at ride height for both. Next month the rest of the rear end set-up.
Until next time
Mike
"The man who can drive himself further once the effort gets painful is the man who will win." Roger Bannister
