Another Sway Bar question
 

After reading this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/554650-size-smart-racing-sway-bars.html

I had my own questions...

The new setup:
I'm in the process of upgrading the susp. in the SC to 22/29 t bars. Larger 23/31 was considered, but it was recommended not to go that big by some local track friends due to Sebring's rough surfaces. The full Elephant poly-bronze and mono-ball setup will go in with no bushings left untouched. I will also be going to Bilstein struts and shocks all around. I Picked up a set of 22/22 adjustable sway bars to add to the mix.

The quandary:
I was going to just add the front sway bar and leave the rear stock to avoid ripping off the rear mounts and recoup some $$. However, reading the above thread made me think that I bought too small? Also I should go ahead and put the rear bar on?

Additional info:
I'll be running either 15/7x8 or 16/8x9 with z or r rated rubber and I have about stripped everything out of the car possible w/ no cage yet. This is a DE car w/ occasional street duty and I don't mind sacrificing the street ride so lets call it all DE.

Thanks in advance for your comments!

-Michael

As an anecdotal data point: I installed some larger sway bars on my car years ago and not too long after tore one of the rear mounts at Road Atlanta. This was 15 years ago and - not knowing any better - I just had a guy re-weld the mount.

Right after that, I installed larger torsion bars (replacing stock ones) and even bigger sways than I had previously. 15 years later, that repaired sway bar mount is just fine (along with the other one). My theory is that large sway bars, in combination with small torsion bars, lead to a situation where the sway bar is asked to do more than it's fair share of the work and that is what leads to the sway bar mounts tearing. The small torsion bars allow much more wheel travel which leads to lots of load going into the sway bar/mount and next thing you know, you're torn a mount.

I might be way off (not unlikely), but that's my story and I'm sticking to it.

That makes a lot of sense. Still the question remains... is 22 big enough for just the front? I think I have 20/18 now (stock SC stuff) I don't know... I was looking forward to the extra $ selling the rear off, but I may just put it on now anyway. I guess the real question is what matches 22/29 t-bars well?

Best regards,

Michael

Another factor is the stock sway bars do not have adjustable links so when you balance the car you may end up fighting the sway bar.

Being able to disconnect the sway, nail the balance and then reconnect without imparting any load is a big benefit.

As a data point. I have 22/27 torsion bars and 22mm Welties front and rear. I tore the passenger side sway bar mount but had it repaired and reinforced, 911ST style, not Wevo. The oversteer balance feels fine to me but there is a lot of dive/squat. The stiff front end does make for quick initial rotation on turn-in so it needs a good bit of attention in tight twisty turns and transitions, as one would find in autocross. I would be interested in 23/30 or thereabouts. Car weighs 2000 pounds, all monoballs, etc. "Sporty" alignment.

I agree that anti-sway bars should just be used to tune the front/rear roll stiffness distribution, and leave the roll control to the primary torsion springs.

I have the 22/29 T-bar set up. I used stock Carrera sway bars (22/21).

This is actually what I have also. It works fine for a compromise street/track car that weighs about 2400 lbs...

I went this route. I did 22/28 t-bars and a year or so later changed to 23/31's. In my opinion, go to the biggest now, you will eventually and you'll spend more money in the long run if you don't. I run Sebring all the time and turn 1:27's with 23/31 set-up. I agree Sebring needs a somewhat softer set-up, but t-bars only give you an effective rate of 300 to 400 lb/in. That is quite soft when you consider GT3 Cup cars are shipped with 1500+ springs.

I agree with Jerry. The effective rate of even the bigger torsion bars is rather low in terms of spring stiffness, so the larger bars like 23/31 still don't gain you a ton of spring rate over stock. On the track where you're heavily loading the suspension, even the 23/31 setup is well put to the test by a 2500 lb. car. Body roll still exists and sway bars are going to have to "flatten" the car's attitude in cornering. That's not to say the bigger torsion bars aren't worthwhile. I agree that if you go 22/28, your gains are minimal- still leans good like a stock car. See this topic with some pictures I shared for comparison

http://forums.pelicanparts.com/porsche-911-technical-forum/489401-best-tt-de-investment.html

I too had 22/29 on my '87 and it was a nice change from stock. Firmed up the ride nicely, but not over the top harsh. The more I tracked it, the more stiffness I wanted so I re-upgraded to 23/31. So i'm of the opinion you need to go big the first if you want to do it for serious dedicated track use. Otherwise you may end up doing it twice. Been there done that.

With respect to the sway bar (it was asked if he should install the new front and leave the rear alone), i'd say do the vice versa. Leave the front alone and install the rear. The stiffer main torsions will help with avoiding mount breakage (but is still a possibility), so don't let the breakage be your deciding factor. I've seen a number of stock cars that scoot around the track really good and have yet to break their rear mounts. More importantly IMO, the rear is easier to adjust. You simply reach under the car and loosen or tighten to your desire. Front requires you pull the both wheels off to adjust. Rear is easier to install too- doing the front means you have to get out the hole saw and cut a hole in the tub..... :D Plus I think for DE track use that the rear gives you the amount of adjustability you need. Stiffening or loosening the rear helps fine tune the car quite well IMO. I had a lot of success tweaking my car's corner exit behavior by tweaking the rear bar accordingly. Too much oversteer, soften the rear sway. Too much understeer, stiffen it up a bit.