Setting up a 1G AWD suspension for drag

[GSX_Dan]

There are many writeups on setting up FWD suspensions but I have only found bits and pieces on setting up the optimal AWD suspension. I am guessing we're going to adapt both concepts from the FWD world and the RWD world as our cars have traction on all four wheels.

First I would like to address the issue of weight transfer. They say for the front wheels to get optimal traction during a launch there must be the least amount of weight transfer. Now this conflicts with the RWD ideology of having a lot of weight transfer to the rear axle. Here is where everything gets confusing. Am I to setup the car as both a FWD and RWD independently? The front with a low stance, stiff shock/spring combo and the rear high up, soft shock/spring combo? The way I figure it is this way the nose will have a hard time lifting and the rear can squat due to the high CG. Another option would be to set everything up in between the FWD&RWD world. Such as F&R suspension stiffness not quite hard but not quite soft and a leveled body stance but this would be probably be difficult to achieve as I'm sure there is a very sensitive sweet spot where you can have too much or too little or any of adjustments. One more setup I can think of is to set everything on stiff with the lowest stance possible to minimize drag(yes also a factor when going 100+mph) and let the differentials do their magic but this is probably the least likely to work on a high powered vehicle where wheel spin is a big issue.

Secondly, I would like to know what works best for people as far as camber goes. On 1G's I believe the macpherson strut design up front maintains constant camber through it's travel so it would be logical to set the camber to 0* to maximize tire patch to road contact would it not? Should be noted this is bad for handling through, however good for braking also. Now the rear camber goes in the negative as the body lowers so what should the initial setting be? I know it's crazy to have positive camber for a street car, but again for strictly a drag application would a little positive camber benefit any in hopes of bringing it as close to 0* as possible once the rear squats ?

Thirdly, bump steer or toe allignment is also to be taken into consideration as the wheels while in forward motion want to move away from each other causing resistance if this happens. Based on that principle should the toe be set at 0* or slightly inward(negative toe) or will a nice new set of tie rods keep the wheels from separating even under extreme speeds and/or body lift?

Nevertheless, I am going to experiment with these methods on my AGX/GC setup but I don't want to waste my time especially with the toe/camber settings in case some of the ideas I tossed around are just off the wall

 

[pneumo]

A hard launch in an AWD car will transfer enough weight off the front wheels to let them spin first. Since the front diff is open, it's common to see the right front wheel spin at launch until the VC on the center diff catches it and sends power to the rear. An LSD front diff helps, just like FWD.

Ideally both ends should be set up with short stiff springs to limit weight transfer, use softer shock settings to help both ends keep traction, but not so soft that the car wallows at high speeds. The car should not bounce/oscillate during launch, once it squats it should stay down until you shift gears.

Front alignment is easy since there are no changes in camber or toe as the suspension moves. Set it up with zero toe and camber. Poly bushings will help eliminate alignment changes under high power. BTW the front end of a stock 1G AWD car has about 1/8 degree of positive camber.

Rear alignment is tricky, like you said. There is plenty of negative camber gained when the back end squats. I don't feel comfortable setting it up with positive camber just because of high speed safety issues. On my car, which is driven on the street, I use 1 degree negative camber and rely on stiffer springs to limit excess negative camber. I also have tires with soft sidewalls (Kumho MX) so camber changes have less effect on the contact patch.

Rear toe is more complicated. Did you weld the rear toe control link? If it's still stock it'll gain some toe out at launch. If it's welded and you have poly bushings, set it at zero. I still have a rubber toe control link, although it's filled with silicone caulking, and I've had good luck with just one millimeter of toe in. Stock setting is 3mm toe in.

Just for reference, my car has 300# front springs, 250# rear springs and it's street driven. IIRC the DSS drag kit (not the standard street kit) uses either 400 or 450# springs front and rear.