Need advice on selecting torsion bar size...

[speedracer]

Hi All,

A broken rear torsion bar has provided me the opportunity to go with something a little thicker. To my understanding my car has 19mm up front, and 24.1mm at the rear (85 carrera). At this point I will only be changing out the rears and was wondering what a good width might be, keeping in mind I will probably keep the fronts stock for a few years until more suspension work is required.

Would upgrading to 26mm at the rear for know be an ok setup with 19's at the front? This is for weekend driving and very little track time...

Any thoughts?

[RonDent]

Jim, I changer mine over the winter. I run AX events with mine so I went with 21's up front and 29's in the rear. Pretty stiff for day to day but drives like hell. Maybe, 21's and 27's would be much better for street use with an improvement for track use.

Ron

[speedracer]

Thanks Ron. I bet she handles well!

[ttweed]

Originally posted by speedracer
Would upgrading to 26mm at the rear for know be an ok setup with 19's at the front? This is for weekend driving and very little track time...

How much is "very little" track time? If you upgrade the rears and do nothing to the fronts, you're going to find the car oversteering more at the limit. If you never approach the limit, you will not notice this, but if you do track the car that way, it could be very loose. Disconnect your rear sway bar if you have one and run bigger tires in the rear if you can. Or just bite the bullet and do both front and rear now "while you're in there." You will need to have an alignment anyway, why do it twice?

TT

[speedracer]

Good advice Tom. Very little time is: I have never tracked or done a de and this is something I might do in the future. But not high on my priorities. Maybe I will do all while I am in there....

[88-diamondblue]

The 89 turbo ran 27 rears and 19 fronts prior to that the turbo's were 19 & 26. My 88 is 19 and 25 and will be upgraded to 21 & 28 next winter.

[Wil Ferch]

Cribbed this from my answer in another post...
- Wil
===========

Here's a breakdown of front and rear TB sizes and their spring rates ( EDIT..effective wheel rates), after my exhaustive investigation on sizes, bar lengths, pivot arm lengths, etc:

Front:
18.8= 110 lb/in
21= 173
22=210
23=250

Rear:
24=120 lb/in
25=140
26=165
27=191
28=221
29=254
30=294
31=332
33=427

Notice some interesting trends.... many people say to upgrade to 21/27...or 22/28. The 21/27 combo equates to 173/191...and the 22/28 combo equates to 210/221. In both cases...fairly equal. This maintains the front/rear balance Porsche designed into these cars, but some say (me included) that we can go proportionately stiffer in the rear to dial-out some unwanted low speed understeer. So...maybe 21/28 ( 173/221)....or 22/29 ( 210/254).

[Bobboloo]

Originally posted by speedracer

Would upgrading to 26mm at the rear for know be an ok setup with 19's at the front?

Absolutely, Good choice for a street car.

[dad911]

Originally posted by 88-diamondblue
The 89 turbo ran 27 rears and 19 fronts prior to that the turbo's were 19 & 26. My 88 is 19 and 25 and will be upgraded to 21 & 28 next winter.

Turbo engines are heavier, I don't think you would want the same torsions in a NA car????

Speedracer - the fronts are simple to change compared to the rears. So if you try a bigger bar, the fronts can be changed to balance the car if necessary.

Have you done any other suspension work? Are the struts, bushings, sways original?

[Wil Ferch]

Even though Turbo's might be heavier...their "stock" set up can be readily used as a mild street upgrade for a NA car....19 fr / 26 rear is not a bad thing..

Wil

[speedracer]

Originally posted by dad911
Turbo engines are heavier, I don't think you would want the same torsions in a NA car????

Speedracer - the fronts are simple to change compared to the rears. So if you try a bigger bar, the fronts can be changed to balance the car if necessary.

Have you done any other suspension work? Are the struts, bushings, sways original?

Thanks for all the input guys. I am not sure if the rest of the suspension is original I am going to take a closer look at it. Thanks again.

[nostatic]

I would say do both and all associated bushings. Odds are they are very tired...

I went 23/31, but that's for a primarily track (though still street legal and regularly driven) car. The change in handling was significant on the street, and downright terrifying at the track. Took the the whole weekend just to get back to having a handle on what the car could/would do...

I have to wonder how much of this was due to the worn/sloppy bushings and other bits on the old setup...