Front t-bar sizing questions (after reading tons of threads)
 

I've obtained some 29mm rear t-bars (legally) and need to get a set of front t-bars to go with them. The prevailing logic seems to be 22mm for the front, maybe 21mm. My question is: since this seems to be on the borderline and could go either way, would it not make sense to go a little lighter (21mm) in front, and dial out any oversteer with an adjustable front sway bar?

The basis of my logic is that I'm looking at taking Tyson's advice, and keeping stock sway bar on the rear, and only putting on an adjustable sway bar at the front.

This is on an '84, with sport Bilsteins and Elephant monoballs and bushings all around. I run 225/245 MPSC's currently.

Until recently I used 22/29 mm torsion bars with Bilstein sports all around. I started off with no adjustable sway bar, then added both front and rear adjustable sway bars. This was a GREAT combo for a street/track car and I highly recommend it for that use. If I were to do it again and wanted to stay with 22 in the front I'd go to 30 mm in the rear.

My car is now a dedicated race and I upgraded to 23/33 with new shocks.

Cheers,

Jeff

Hmmm, that kind of lends credence to going with 21's in the front to go with the 29's I have for the back. If I can save $500+ by not putting adjustable sway bar on the rear, I'm all for that. If the car's t-bars would lend themselves to a bit of oversteer, an adjustable sway in front would be ideal for dialing a neutral feel in. Again, this is somewhat based on some posts I've read from Tyson stating he preferred keeping stock sway on the rear, and only going adjustable in front.

I probably need to clarify that I'm more concerned in track setup, as I probably do 50/50 mileage per year.

In my opinion 21 mm in the front is too small for a Carrera that will be seeing track duty.

The 22/29 with no adjustable sway bars has a definite bias toward oversteer, but this is compared to the factory setup which is WAY biased toward understeer. I think even more oversteer (again compared to the factory setup) is needed, so that is why I suggested even bigger in the rear i.e, 22/30.

If this is not a street car you should not even be considering 21s in the front. I think the most common setups are:

22/29
22/30
---- here is the point where you say "don't care how it feels on the street" ----
23/31
23/33

Cheers,

Jeff

Ed, 22/29 should be very close to the same tendencies the car has with stock torsion bars. 22/29 shares the same f/r spring rate ratio that the car came with from the factory (well, very close), and is set up for understeer. I have set up a few cars with 21/29 and 22/30 and even 22/31 which I thought were set ups that suited my driving style.

I would run the 21 in the front and then later, if needed, get some adjustable sway bars.

Here is some spring rate info that I stole from Wil (I think)

21mm front has a spring rate of 173lbs
22mm front has a spring rate of 210lbs
29mm rear has a spring rate of 254lbs.

Your car came stock with 18.8 and 24.1 bars. They yeild a rear spring rate that is 1.27(ish) times stiffer than the front. If you go 22/29 you have a rear spring rate that is 1.21 times that of the rear. Still favours understeer like the original set up. If you go with the 21 front you have rear rate that is 1.46 stiffer than the front. Now we are getting somewhere!! In my car I run coils 350/525 which is a 1.5 ratio and the car is very neutral. Don't forget how much more weight is on the rear of a 911.

If I can help with anything else, let me know.

Just run 22/29 and put the adjustable sway bar on the REAR.

Thanks Jeff, that follows the logic I was trying to validate. If I go a little softer in the front, adding adjustable sway there also will be where it would be best to have the adjustment, in my train of thought. I'd really like to stay away from adjustable sway front and rear to keep the cost down, and the simplicity up!

That, and I'd like to experience what having a little more oversteer would be like. :D

Search Tyson's comments on this board. He's 180 degrees from that statement. I'm not trying to negate your thoughts, but I've long respected his opinion here, as have many others. If you're going to only have adjustment on one end, the front is the way to go. It's easy to remove preload for corner balance, and the rears get in the way of messing with camber and such at the rear, and tend to be associated with more damage back at the rear.

But, all opinions are welcome, and this is the responses I'm looking for to help me in my decision.

How will you be using the car?

The rear swaybar will allow you to dial in any additional stiffness that you may need back there, but more importantly it will give you the ability to tune the car to your liking. I don't understand your comment about difficulty adjusting camber in the rear with an adjustable sway bar, and frankly I can't imagine any argument related to car handling that would make an adjustable front sway bar a better option than an adjustable rear sway bar, assuming you have a choice of spring rates.

The best setup is obviously adjustable sway bars on both ends.

If you go with 22/29 and feel the need to upgrade in the future, you can move to 30 mm in the rear and sell the 29s. But I don't think you will. I was very happy with the 22/29 setup for over 6 years on the track.

If you go with 21 in front your car is going to be too soft up front. You'll be riding the bump stops through the corners.

Cheers,

Jeff

As stated above, the split will be 50/50 track & street mileage. DE's, but I'm working my way up the food chain to the yellow group here, next being white, and then instructors (red), and we run at a pretty good clip.

It was toe adjustment, not caster. Here's the thread....

http://forums.pelicanparts.com/showthread.php?s=&threadid=259835&highlight=adjust able+mm+front+swaybar

I would go 22/29. I find this to be a good balance on a DE'd Carrera.

I prefer adjustable sways at both ends, but of course you can start with one - then add the second when you are ready.

Well I read that thread. I've never had any trouble with toe adjustment with my rear adjustable sway bar. Of course there is the issue of the rear mounts potentially failing with a bigger sway bar - my rear mounts are still stock and have held up fine for many years now. In your case I think that is counter-balanced by the relative ease of a rear swaybar install versus a front swaybar install.

Again there is no reason to prefer a front adjustable versus a rear from a car handling standpoint. As stated in that thread:

Cheers,

Jeff

Ok the toe adjustment thing just came to me.

I think the Smart Racing adjustable rear sway bars attach to one of the bolts on the spring plate. Mine attach to the factory mounting points on the banana arms so there is no interference with the adjusting bolts on the spring plates.

Not sure how the other adjustable rear bars attach (Tarett, Racer's Group).

Cheers,

Jeff