Suspension upgrade sanity check - torsion bars

widebody911 · widebody911's Garage

Ok, I managed to find a screaming deal on a set of hollow rear 31mm torsion bars, and a set of hollow 23mm front torsion bars.

My car (currently) weighs 2190 with a full tank of gas sans my ass. I intend to do some more lightening by switching to fiberglass/carbon fiber fenders and quarters, fuel cell, and removing the interior sound deadening.

Wheels & tires are 11x17 & 9x16, 315/35-17 & 245-45/16

I have Elephant Racing monoballs, control arm thingies, and Polybronze bushings. I also picked up a set of offset balljoints from Chuck at the PartsHeaven swap a couple weeks ago.

This is a track car that's driven to and from the track. Rarely driven on the street other than that.

Seeing as I might have some free time this weekend, I wanted to run this past the suspension gurus to see if this config makes sense. My primary concern is that the 31mm bars may be too stiff. In a previous thread, someone suggested 31's, but with my weight goal, I'm still not 100% sure.

Also, any suggestions for alignment settings?

fastpat · 06-17-2005, 10:02 AM

What's in the car now, and how do you like them?

Most folks that know recommend T-bars that are firm enough to handle the car in a straight line; controlling squat on accelleration and dive on braking (with the suspension set up well of course); and stiffer stabilizer (anti-roll) bars to handle increased spring needed for turns. Are your stabilizer bars stock or enhanced?

89911 · 06-17-2005, 10:16 AM

For cars that are heavily tracked, I've been often told that you can't go too stiff with torsion bars. I have 22/30 and my brother 23/31 and there isn't that much difference.

fastpat · 06-17-2005, 10:19 AM

I notice that he's considering hollow T-bars, but didn't say if the stated diameter is an equivalent number corresponding to a solid bar, or the actual diameter.

widebody911 · widebody911's Garage

I have Trg sway bars, can't recall the sizes. TRG doesn't use sized in mm, but rather firmnesses of "A", "B" and "C"

I have 22/29 now, and it's not enough. For example, I bottom out on 5A and 8 @ Thunderhill, which are turns that really compress the suspension.

widebody911 · widebody911's Garage

The values given for hollow bars are the effective diameter, not the physical diameter.

fastpat · 06-17-2005, 10:23 AM

Bottoming out could be a lack of compression dampening too, a call to Bilstein (hopefully that's what you have) could provide an answer.

MuffinMan · 10:48 AM

I have 23/33 bars (hollow Sanders...effective rates listed), and I don't think it's too much bar. I also have 22mm front & rear sway bars, and adjusting them one way or the other has a very notable effect on understeer or oversteer. When I researched this awhile ago, most shops suggested either 23/31 or 23/33, depending on the shop, so I don't think you'd find too much rear spring with the 23/31 combo.

MuffinMan · 06-17-2005, 10:35 AM

Also, what do you have for shock valving?

widebody911 · widebody911's Garage

Quote:

Originally posted by MuffinMan
Also, what do you have for shock valving?

That's next on the list; I have an extra set of shocks I was going to have re-valved to match the rest of the setup.

widebody911 · widebody911's Garage

All in favor? All opposed? Motion carried.

Now I just have to figure out how to set the rear spring plate angle...

patkeefe · 06-17-2005, 05:41 PM

http://www.rennlight.com/cgi-bin/spring.cgi

fastpat · 06-17-2005, 05:57 PM

Quote:

Originally posted by widebody911
All in favor? All opposed? Motion carried.

Now I just have to figure out how to set the rear spring plate angle...

Yeah, since I was quoted $600.00 to do this by a reputable shop in my area, I'm planning on doing this myself.

One of the things I haven't found in my archive searches is what is the preferred setting for the torque arm adjustment eccentric bolt. According to Bentley, it's set to enable raising the car to compensate for sag. Should I leave it in that position, or change it to enable fine tuning, i.e. in the middle of it's range to raise or lower?

patkeefe · 06-17-2005, 06:08 PM

Pat
Do the spring plates yourself, get them close as possible, leave the eccentrics in the middle. When you go for CB, the middle setting allows some finer adjustment of height, and maximizes the ability to tweak.
Pat

randywebb · 06-17-2005, 06:08 PM

middle or a bit off to compensate for any sag you expect -- or settlement...

widebody911 · widebody911's Garage

Actually guys, that was a tongue-in-cheek remark; that's my website with the spring plate angle calculator.

Although I just realised that I forgot to get a ball-joint nut tool...

fastpat · 06:33 PM

Quote:

Originally posted by widebody911
Actually guys, that was a tongue-in-cheek remark; that's my website with the spring plate angle calculator.

You dog, woof, woof.

I like to look at every angle before I tackle a task.

Mebbe I should buy the T-bars you take out for my '88? Will they fit a narrow body?

patkeefe · 06-17-2005, 06:32 PM

Thom:
I'm a nerd. I was trying to help.
That spring plate calculator is a wonderful tool...I have it bookmarked!
So, thanks!
Pat

Dixie · Dixie's Garage

I don't think 31s would be too stiff for a track car. I have 23/30 solid torsion bars on my '88 Carrera (2800 lb car). On the track, I could use a touch more spring. As far as the street, even my wife thinks it rides very nicely.