Torsion bar selection with lightened car

drl911 · drl911's Garage

I have done a lot of reading this weekend, but still need some things confirmed.

Removing weight from a car effectively makes the suspension "stiffer".... right? I know the Tbars didn't change rate, but the feel would be a "stiffer" car (?). So for conversation my '86 Carrera with 25mm rear stock Tbars and ~200lbs removed from the rear end (bumper, whale tail, ac stuff, sound deadening, rear seats, etc...) would translate to the "feel" of what size stiffer Tbar in an otherwise stock weighted car.

The reason I ask is all of the conversations and recommendations I read never seem to ask "how much does the car weigh?" Wouldn't it influence the final choice of Tbar's if the car was a 1900lb gutted car or 2800lb stock Carrera?

Thanks,
Dan

porschenut · 10-31-2010, 08:51 AM

When I decided on TB's for my lightened (backdated) 86 Carrera, the lighter weight was a definite factor. My car now weighs around 2350 lbs, and I went with 22/29 TB's and I think the street/track ride compromise is just right. I'd say about 200 lbs. was removed from the rear and the rest from the front. I also upgraded the shocks to Bilstein HD's at all corners and left the stock sway bars in there. I might go with larger sway bars if I decide to do more track time.

GaryR · GaryR's Garage

I think even more important is what is the intended use of the car? Street only, Street/DE, DE only/Full Race? For a 2500LB 911 (IMO) a fairly stiff general use upgrade combo is 28/22, stiff would be 31/23, full race 34/24. Shocks should be re-valved to match whatever combo you choose.

drl911 · drl911's Garage

Thanks for the replies. I did my first 2 DE's this Fall and am definitely heading towards the 50/50 street/DE car. I am also currently at 2350 total weight so your real life testimony is most valued. I have ER polybronze rear bushings ready to be installed this winter so just trying to make a wise choice on the Tbars and shocks.

GaryR · GaryR's Garage

Do the fronts with PB while your in there! They are much easier than the rears, just be sure to place the grease nipples so you can get to them with any skid plates in place.. With a 50/50 car I would go 28/22 to retain a fairly good ride. Shocks/Seats/Tire type and profile all play a part in that also.

Zeke · 10-31-2010, 09:48 AM

Another train of thought is to use heavier sway bars in conjunction with the lighter car and the "new" spring rate. Just be sure you don't over dampen the car. Many suggest Bilstein HD's front and Sports for the rear. Might be a good way to go with the stock bars in back on the light weight car.

This set up will provide a good enough ride for street, performance driving and tracks that are not super high speed (or should I say with super high speed corners).

IROC · IROC's Garage

Quote:

Originally Posted by drl911

Thanks for the replies. I did my first 2 DE's this Fall and am definitely heading towards the 50/50 street/DE car. I am also currently at 2350 total weight so your real life testimony is most valued. I have ER polybronze rear bushings ready to be installed this winter so just trying to make a wise choice on the Tbars and shocks.

My '76 with a 3.2 weighs around 2350 and I have 22/29 torsion bars. Not "overdamping" the car is good advice. IMHO, shock selection can influence ride quality more so than torsion bar diameter (to an extent).

Personally, I would not go smaller than 22/29 if you're leaning towards more track use. Mine is fine on the street, but I could use some more stiffness on the track. Always a compromise...

RWebb · RWebb's Garage

other side of the coin is how easy it will be to sell a set of XX/YY bars if you don't like them and want to change

I usually figure bigger is easier to sell as there are fewer ones out there as opposed to something close to stock

Trackrash · Trackrash's Garage

To answer the question about weight and torsion bar size, lets do the math.
If you remove 280lbs from a 2800lb car that is ~10% reduction.
There is approxamatley 15-20% difference between two torsion bars one size apart (rear bars). So not that much difference in torsion bar choice.
There is much debate on torsion bar sizes. Either 22 and 28, 22 and 29, or 22 and 30 all seem like good starting points in a dual purpose car.