Originally Posted by Kraig
So lets take this one step further in our discussion as I think it will help a lot of people.
Chassis, to the best of our knowledge is not tweaked but how would you verify?
The first thing I do is check chassis tweek. If the chassis is twisted, and you can't get it out, and it's the middle of a race day, it's not the end of the world. But the car is never going to be as "right" (which means it's easier to work on) than it will if you got it square to begin with.
You can check chassis tweek by setting the car on setup blocks, on the screws where the front and rear suspension mounts pass through, and then see if the car lies dead flat or "rocks". If it rocks, it's not square and you need to try and get it straight before you move further forward.
In order to untweek it, you are going to need some tools. You can buy something to untweek the car that's really fancy like this:
Or, you can home brew something. My "home" rig is a piece of 1" x 2 1/2" x by 13" billet aluminum remnant stock I got from a local industrial stainless and aluminum company and the biggest anodized aluminum knitting needle you can find at Hobby Lobby.
(This space reserved for a picture of my $7 setup when photobucket stops being a grump)
At the track, I just use my setup board and the knitting needle because I don't want to haul around this block and my Marc Reinhart setup board is already pretty robust.
At the track, I check it on setup blocks between rounds.
My standard setup regimine is:
- Check/fix chassis tweek
- Set droop (I usually use 20mm blocks and an off-road 20-30mm ride height block, but can use a steel rule and my eyes)
- Put race tires back on in their appropriate wheel positions (I mark my tires in sets, never seperate them and never rotate them) and set the ride height.
- Check cambers and toe, recheck/set ride height.
- Put the car on the scales and see what the L/R, F/R, and split weights look like. There is a way to get the car unwedged/us tweeked without scales using an exacto knife. If you KNOW the car is 50/50 left and right, you can pick up one end with the exacto knife and see which tire comes up first.
- The way you adjustment you make to fix it is remove a small amount of preload the shock DIAGONAL on the chassis to the heavy tire, and add the same amount to the DIAGONAL tire that is light. That way, the ride height isn't disturbed, but you fix the split on the other axle.
Real life MBA case study problem:
The RF and LF tires weight the same. The RR is 30 grams heavier than the LR.
Add 1/8 of a turn to the RF (taking weight off the LF and RR, moving it to the LR), remove 1/8 of a turn from the LF (adding weight off the RF and LR, reducing weight on the RR). Recheck and do it again till you are happy.
If I get the car within a couple of grams, I usually quit. If you bump a curb, a board, or another car, it's going to be wrong, especially if you use a plastic chassis car.
The above mentioned car is not exactly 50/50 left to right, the math indicates it's 30 grams heavier on the right side. Assuming the car isn't 30 grams underweight or have 30 grams to be relocated, it's probably never going to be. The best you can do in a situation like this is get the cross weights equal (LR+RF = RR+LF) and hope all the high speed sweeper corners are right hand.
IMO the f/r bias is more important than the l/r bias. Moving the weight forward and backward on the chassis has a far greater effect on the car having appropriate handling characteristics getting in the corner and making grip off the corner (slow corners) than having the car be exactly perfect left and right.