6 rear suspension travel Options

[nditiz1]

So I have posted on this before and am still confused.

How much rear suspension travel should there be on a 6?

74 chassis
2.4L engine
Springs appear to be 100 lb ones
Shocks are Bilstein C clip at lowest setting
No rear sway bar

With this setup the car sat low - cool, but there was no rear suspension travel. It was stiff back there. I push down and there is no give. Now, maybe that is how it is supposed to be?? I remember my 4 having a little bit of rebound, but that was with 200lb less back there.

So I am in the process of clicking up two spots on the Bilsteins to get some rebound back. Seems counter intuitive though. If I compress the spring more it will be more stiff. My thinking here is that there is now travel with two clicks up since before when down on the ground the spring and shock were already compressed so no suspension travel was left on the console and or the shock. Thoughts?

[Superhawk996]

For simplicity sake, let's say the motion ratio between wheel travel and shock travel are 1:1.

So for 1" of movement of the wheel you get 1" of spring compression and of course, 1" of damper rod travel.

Assume; added 200 lbs for /6 engine, lines, oil, oil tank etc. (assume it was all added the rear corners - won't be true but let's assume for simplicity)

So with 100 lbs/in springs that extra weight would result in the car sitting 1 inch lower than it would due to the 200 extra lbs has to be supported. Each spring will compress 1" adding 100 lbs of vertical force x 2 springs = 200 lbs. This means the car will be sitting 1" lower at rear.

But, you also LOST 1" of compression travel.

By pushing the lower rear spring perch up 1" you get your compression travel back and you're back to the original ride height. There is still an extra 1" of compression in each spring that is there - it was needed to support the "extra" 200 lbs of weight added to the vehicle. You've just moved the whole compressed spring upward (and the body with it).

Now let's look at 140 lb/in springs:

The added 200 lbs from the /6 engine would result in 0.71" lower ride height since you're now using stiffer springs to hold the rear of the car up.

The Bilstein rear ride height adjustment notches are about 0.5" apart.

So now, you would probably only have to push the rear spring perch up 1 notch (instead of 2) to offset the lowering caused by the extra 200 lbs. Overall, you would lose 0.21" of compression travel, the car would be at 0.21" LOWER than the /4 position and you would have less rake vs. the /4 starting position.

This is overly simplistic because the assumptions I've laid out ARE NOT true. But it gives you a general idea of why you might want to move up to 140 lb springs if you can't get the rake of the vehicle where you want it with the 100 lbs springs.

I should state the obvious. In order to prevent high speed, front end lift, you NEVER want the front of the vehicle higher than the rear.