krazykarl

I'm trying to get a better understanding on the mechanics of the 944 rear suspension. I bought an S2 back in September and the PO mentioned the rear struts could stand to be replaced because he could feel the rear end squat under acceleration. I know in mcpherson suspensions the struts main purpose is to dampen the oscillation of the springs, but does it work the same way with a torsion bar? Can warn struts cause squatting?

Here's a picture of my car on acceleration coming out of the start of an auto-x course


Is it bad? Or is it fairly normal? This is my first RWD car so I'm still learning all its characteristics compared to FWD. Thanks.

Spidey944

Well, the rear suspension on these cars has shocks, not struts. A worn set of shocks can cause some squat under accel and at other times.

krazykarl

ah right, somehow I still get those two words mixed up. shock absorbers are what I'm inquiring about.

Van

It is likely that the rear shocks are original and could stand to be replaced. Although, in your picture, that weight transfer to the rear is quite typical of a rear wheel drive car...

Due to momentum, really Newton's law about an object at rest wanting to stay at rest unless an outside force acts upon it, when the engine tires to push the car forward from the rear, it is fighting the desire of the body to stay at rest. Because the tires are pushing against the ground at "ground level" and the center of mass of the car is "above" the ground, there is a "twisting moment" that causes the front of the car to "lift" and the rear of the car to "squat".

The "weight transfer" happens regardless of how much the body "moves" - the body movement is dictated primarily by the springs (the stiffer the springs - or torsion bars - the more force it will take to "compress" them) and by the shocks (the function of a shock, or damper, is to reduce the "suddenness" of movement that acts on the suspension).

So, with new shocks, the amount of rear squat may diminish because the shocks prevent the rear suspension from compressing so fast - but, your weight transfer will be the same - that is dictated by the amount of power you have and the CG (center of gravity) of the car (e.g. if you lower the car, the squat will be less).

Regardless of whether or not you feel like replacing the shocks (which, unless they're quite new, I'd do it in a heartbeat - new shocks make the car feel fantastic), if you pay attention to this weight transfer, and how it affects your available traction, you will greatly improve your autocross times.

So, think about what I've just gone over... Under acceleration, the weight transfers to the rear - there is less weight on the front... there is now less traction in the front - which means less traction available for steering. Did you ever try to accelerate out of a tight corner and find that the car was "understeering" (not turning as tightly as you wanted it to)? That's because you have less front traction when you accelerate.

xsboost90

my car squats under hard excelleration and i have 525lb springs back there. A good set of Koni sport shocks should tighten it up but wont keep it from squatting. Bigger torsions or coilovers would help but you have to make the front match.

Makis

I found that also soft front shocks can make the car squat under acceleration. Good shocks at the front will resist the front lifting easily under acceleration thus keeping chassy movement under control and reduce squat.

Van

Ummm... according to your sig, you're putting down 360 HP!

krazykarl

As far as I know the car still has the original suspension with 114k miles of use, so I know it could stand to be replaced. I haven't decided how far I'm going to go though, I'd like to keep it fairly stock to start with while I learn how to properly drive the car.

whalebird

the primary thing I would look at is the shocks. Another thing that dynamically reduces dive and squat are rigid sway bar links. Make sure all sway bar bushings and drop linls are up to par-front and rear.

krazykarl

Rear sway parts are in decent shape, but the front needs some work. The infamous power steering leak has destroyed one of the sway bar bushings, and the end bushing is distorted because one of the small metal washers is missing. I have replacements bushings for the front, just haven't put them in yet.

FRporscheman

The cause of rear-end squat is horsepower. You need to take away some of those horsepowers. I will take them for $1 each.

Shocks are obviously important, but if we're only talking about squat, then the effect can be reduced by using thicker torsion bars or adding springs (coilovers).

Catfood

more weight to the rear to keep the power down, dont worry about it.

krazykarl

Bumping my old thread because I'm looking to replace my rear shocks. The decision I'm trying to make is whether to go with Bilstein HDs or konis. The car is a summer driver that's going to see some autocross and DE duty, but nothing extreme. Fronts are going to stay the same for now, but will probably end up being replaced with Koni inserts and some stiffer springs in the future. Any possible issues mixing koni fronts with bilstein rears?

Also, here's what 20 years and a power steering fluid leak does to a sway bar bushing...

Mike C.

Yea that's pretty typical on the sway bar bushing. I think oil filter changes also have an effect here since it's difficult to clean all of the spilled oil above the PS pump. As for squatting under acceleration, I read somewhere that certain suspension geometries/configurations are better than others at resisting squat (and that the 944 suspension is somewhat antiquated in this respect). I'll see if I can dig it up.

FRporscheman

Bah, that's nothing. My first 944 had no bushing left - it just decided to jump out and leave. It made a clunk sound only when turning left... I think it was left anyway...