I just got the BMR track pack and it says to adjust the pinion angle for a manual tranny to -2 to -3 degrees. How does this affect traction. I don't understand how the angle of the rear end is affected by that. Thanks for any help.

 

BMR's method is a little misleading. Make sure to measure the angles from the driver's side.

http://www.go-fast.org/z28/pinionangle.html

 

Thanks for the info. What I'm wondering is what does the angle of the rear end have to do with traction?

 

I really doesn't effect traction that I know of, it's more of keeping your driveshaft and u-joints in the correct orientation during suspension movement to prevent damage and vibration.

 

I've been doing some research on BMR's site and here is what I found. Thought this might help others with my same question.

Why is the correct pinion angle important?

When a car launches, the rear suspension twists and the pinion angle moves upward. With a stock suspension, there is no way to adjust for this and the pinion angle will enter a positive angle(pointing upward). Ideally you want to adjust the pinion angle down(negative) when the car is unloaded. Then on vehicle launch that angle should never exceed zero degrees if set properly. If the angle exceeds zero and becomes positive, there are chances of driveline bind and maximum torque is not applied.

 

Okay so how do you determine if your angle is exceeding zero degrees on your launches??

 

I would assume that you would have to guess and use the rule that autos require -1 to -2 and for a manual tranny to -2 to -3 degrees.

 

Depends also on how much power the engine is putting out.... the more power, the larger the required negative angle. And, it also depends on what the front of the torque arm looks like.... a rubber mount deflects the most, poly next, and the spherical rod end deflects the least. I've seen numbers recommended as high as -4deg for high power (500+HP) cars running a poly front bushing. And, you can't "street" drive with that much negative pinion angle, you have to readjust to -2deg or less when you leave the track.

I think most setups will be OK with -2deg.

 

I've got my turbo car set of -3. I'll see how it hooks (and how much the front lifts) and I'll readjust if need be. Lots of test & tune to get the suspension done right.