Rear squat

[zenithblue71T]

Hi all,



I think I have way too much rear squat when I accelerate.
Specs:
I have newish Billsteins in the front and rear.
I have stock rubber bushings.
My upper bushings on the original trailing arms seem old and original.
I believe I have stock torsion bars which I think on a 71T are 19mm front and 23mm rear.
I have a 70s after market H&H rear sway bar with that’s about 16mm thick.
I have stock non-adjustable swing blades and new swing blade bushings.

What would you do to get rid of that rear end travel?

[NorthernThrux]

It doesn't look that bad. Judging by the lean and where your eyes are pointed you are accelerating in a fast right hand sweeper?

Assuming your ride height is set correctly (or at least evenly, front to rear?).

Stock motor? Or hot rodded?

If so, then you need to look at the rear shocks, torsion bars and sway bar. Bushings aren't going to be the main cause of this as they simply don't have that much compliance to produce that much squat.

Torsion bars can lose their springiness due to corrosion, nicks and micro fractures over time. You'll be able to compensate to set the ride height properly, but their spring coefficient will be lower. Same can happen with sway bars. There is such a thing as a torsion bar tester, but without knowing what the actual spring constant is, you won't know if it is defective, unless you have access to a new one as well.

If you go to stiffer sway bars, it won't do much for squat (they twist to prevent roll and when going up and down together, they do nothing really)), but if they are too stiff in comparison to your torsion bars, you will notice that the ride is very harsh and jarring over sharp bumps in the road because the one wheel transfers the bump to the other. You will also still have lots of squat, so this isn't the first place to look. They are more for fine tuning.

Weak rebound damping on the front shocks can also cause this. So you need to evaluate those as well. I don't know how the Bilsteins work, but I assume if rebound damping is poor, compression damping will be poor too, so the rear and front can conspire against you doubly. However if they are newish, seems unlikely. Shocks last a long time on these light cars.

Ravi

[Rick Cabell]

Here is a old pic of my car in rear squat.

[xpensivewino]

The unique rear squat of a 911 under acceleration is the key to its traction and quick 0-100kph times. The early 911 is a relatively low horsepower car by sports car standards, but achieves quick acceleration. I wouldn’t try too hard to get rid of that squat, it looks quite proper in my opinion. Watch a late 70’s 930 under full acceleration it will scrape its tailpipe! And it still has a 0-100kph time that is relevant by today’s standards.

[zenithblue71T]

Thank you Ravi, Rick and Wino, very helpful. I will enjoy this as it’s a characteristic of the car. Next winter I will upgrade to 21mm torsions in front and 27mm torsions in the back plus add OEM adjustable spring plates.

To answer some questions from Ravi:
I just did a u-turn and was heading straight. Exiting cars and coffee.
See pic for ride height. I have I think 195/65 tires.
Motor is fire breathing 2.2S with solex profile cams.

[NorthernThrux]

You are already pretty low in the back, so as I said, doesn't look like you have that much squat (i.e. weight transfer) at all. Just enjoy it!
Stock at the rear would be about two fingers of space between the tire and the fender lip. 3 fingers at the front wheel.

Ravi

[Haasman]

James- to me your car looks low in the rear. Ideally, I set up my cars to be slightly nose down. I would start with checking ride height. Attached is what some call "European Ride Height". Use the images to help determine where your static Porsche 911 European Ride height.pdfride height is.

[zenithblue71T]

Thank you Haasman, I will raise to euro once I upgrade my torsion bars and swing plates to adjustable.

[Richy]

12 mm is the original specified ride hieght , there is no Euro ride hieght for '70 , '71 . Your car is lower than this , but you do not need adjustable spring plates to raise the ride height , adjust the spring plate angle as in the technical spec book or maybe a degree or 2 less . Your spring plate angle is in the low 30 degrees now .

[NorthernThrux]

As a reference, I set my car to 8 mm. Well, I thought I set it to 12, but 8 is what I got. Good enough for government work!
Front set 4 mm lower than spec as well to keep the F/R balance.

You can see how much lower you are than these settings. And also the 2/3 finger guidance I mentioned earlier.

Ravi