Suspension gurus: need help diagnosing rear-end squatting

[dd74]

I've lately noticed the rear of my car squatting on take off. Last year, I installed 26mm torsions in the rear suspension (up from stock 24mm), and heavy duty Bilstein shocks, with the idea of making my '74 more responsive, plus offsetting the additional weight of my 3.0 as opposed to when I had a 2.7. This helped, though the rear still squats as well as seems a bit mushy when either rear fender is pushed on.

I would like to get rid of the mushiness and eliminate the squatting, but don't know where to start. Should I get thicker torsion bars, maybe 28mm or even 30mm, or should I upgrade to sport shocks? I also don't want a rock-hard ride or too much bounciness, yet fairly firm is okay with me. The car will be mostly street driven. I have 60-series tires on the car now, but might put on 50 series at some point.

Any help would be appreciated.

Thanks.

[Wil Ferch]

There is a considerable difference of opinion on this subject. IMHO..all 911's are severely underdamped in the rear...just follow another 911 on the highway and see for yourself how the rear of almost *any* 911 bobs...same with some BMW's and M-B's. Must be a German thing.
That said...note that you would likely want *some* squat in order to hook-up the rear tires without being too skittish. The original fabled RUF CTR Yellowbird with 469 hp and 211 MPH top end.. uses 18.8 front and 25 rear ! The opposite camp will say that going as big as 29 or even 30 mm in the rear, in conjunction with proper shocks and tire construction, does not degrade ride as much as is expected.
--Tough call..but if you think you're squatting too much...the rear 26 upgrade may not have gone far enough. Maybe 28's , which would mean a spread of 9-10 between front and rear, which may be a bit much unless you go with 21 front's.
---Wil Ferch

[masraum]

I just recently put Bilstein Sports on my '88. It squatted a ton before (worn out original boges), but squats very little now. I used the Sport/Rallye rears B46-0975. It seems to hook up better than before when turning and goosing it, but the behavior is altogether different, so it is hard to say for sure.

As Wil said you need some movement to help with weight transfer.

[widebody911]

You wanna see some squat? Try putting a 3.6L in a '77 with stock t-bars and bilstein greens (HD). I could use the throttle and move the tail up and down when driving. When we dyno'd the car, the engine was hitting the dyno. I upgraded to 29mm t-bars, but for some reason I've resisted going to sport shocks.

[jluetjen]

What's wrong with the rear end squatting under acceleration? Are you bottoming? Squatting is just the weight transitioning slowly to the back of the car during acceleration. If the car didn't squat, then as soon as you picked up the throttle the weight would immediately transition to the rear end. It may sound like a good thing, but try balancing the car with the throttle through a turn set up like that and you'll most likely find that the rear of the car lacks feeling and handles on a knife's edge (unless you're Michael Schumacher). It will be even worse on a wet or slippery road.

If you HAVE TO reduce the squat - if your shocks are adjustable - you can try stiffening up the front shocks in (slow speed) rebound. This will help to slow the transition of weight to the back without making the rear end stiffer.

[dd74]

...no, the car is not bottoming. And I imagine my question was more along the lines of is this a common occurence, and what can be done to correct/offset the squatting. But jluetjen explained it well.

Thanks all.

[Jack Olsen]

Here's mine squatting with 31mm rear t-bars and custom revalved Bilsteins.

0-60 clip

[APKhaos]

I always thought that 30mm torsion bars were going to be too extreme, until a local guy showed me a track car that happened to have 31mm TBs and no shocks connected. The rear was surprisingly soft - not stiff at all. Shocks are a very important part of the equasion.

As others have said, the stiffest TBs adn shocks will still allow some squat. To get past that takes coil overs with 400 - 600 pound springs, which are way too harsh for street use.

[Eric Mckenna]

Here is some MORE SQUAT!!! this is Jockes BAD ASS! 930 dragging it's ass!




GREAT PIC Jocke!!!!

Eric Mckenna
78SC

[marcesq]

David:

FWIW I installed 26mm tb from a 930 when I first bought my car. Since installing the 3.2 I have a little more squat and in fact, when I take a hard right hander, I get a puff of smoke off the top of the right rear tire (rubbing the wheel well).

I bought a set of 28s after riding in and driving a friends Carrera who has 29s and 22s. His car was not too harsh and had alot of bite (He also has 9" fuchs on the rear). My car, like yours is about 2500 lbs while the Carrera is 2760 lbs so I'm guessing that the 28s will be just right.