Rear Suspension

[Longboarder]

Takes some thinking through. The relative height of diff to wheel hubs sets the camber. Without any change in springs/damper lengths if you raise the diff by say 3" the hubs will also rise 3", camber stays the same, the wheels disappear up into the wheel arches and the back end of the car body will drop 3" and drag on the ground. You have lowered the car body without changing the hub to diff relationship.

If you now fit 3" longer but the same rate springs and shockers i.e. raise the suspension, the wheels will come back out of the arches and the car body will rise so you will effectively have raised the car body and thus the diff relative to the hubs by 3" and the car body will be back where it started from. The hubs however will be 3" lower relative to the diff. We've all seen sierra cossies with lowered suspension at the back and massive negative camber. The opposite is true, raising the sierra suspension increases positive camber.

The negative camber problem seems to come about due to the mounting position of the diff in a Hood and the lower weight of the Hood, as the hubs if sprung to give level drive shafts would leave the wheels about 7" below the arches. So we all effectively lower the suspension to get the wheels up into the arches giving the right look but lots of negative camber. To get back to the same relationship of car body to wheels to ground as in the sierra means a higher fitted diff, which means also raised suspension and normal camber.

So yes, raising the diff mounting and some changes to the rear springs and shockers should avoid the negative camber problem and also put suspension movement on bounce and rebound back into an arc that reduces the rate of camber change. (I think the reasoning is right but do shoot holes in it if you see any.) OK Dan? (Too late and too tired for pics)

 

Nigel

[Grim]

Nigel explains it correctly. It's nothing to do with cv joints!

No Nigelagrams available. Think to yourself about how the camber changes with suspension movement, because the pivot is not perpendicular to the car.

Whether you are moving teh diff up, or the whole car up, makes little difference in terms of geometry compared to the change in ride height.

 

As for whether it'll make a differance... well, i think it will make a significant and worthwhile difference. There's little chance of removing all of the excessive camber, but i think it can come into tolerable levels.

 

I had my car laser aligned, and they measured the rear camber as bob on -2 degrees. I do run my car at about 6 inches to the chassis rail in front fo teh rear wheel.

[Guest salty_monk]

So in effect, you can only really take advantage of this if you have got moveable spring platforms on your rear suspension or you lengthen the chassis (or leave it longer if building) where the cup for the spring mount bolts.

 

Having said that I guess you can offset some of the effect of trying to get the wheels at a good position in the arches without moving anything other than the diff...

 

Interesting

[Joel]

I understood none of the technical jargon above, possibly because I've been drinking beer to celebrate fitting my new camber wedges today!

 

£25 well spent. Thanks Peter

[Grim]

So in effect, you can only really take advantage of this if you have got moveable spring platforms on your rear suspension

 

On the contrary! It makes no difference whatsoever. You are not moving the vertical position of the wheels, just their relative position to the diff.