Suspension setup question

[joetiii]

So I'm not sure if this post should be in this forum or AutoX/Racing forum, But I need help setting up my old 911.

When I got my 69 three years ago, the first thing I did was upgrade the suspension. Did it right at Musante Motorsport in Ct. Upgraded the torsion bars to 21 frt/27 rear. ER polybronze bushings & monoballs, adjustable springplates, Bilstein HDs, turbo tierods, lowered balanced and aligned. It has a 20 mm sway bar on the front w/ nothing on the rear. We kept it that way cuz Chris wanted a bit of understeer built into it.

Now I'm starting to autoX and getting to know the car quite well. In Hartford, we have a very tight course and the car pushes around pretty good on this tight course. Everyone always marvels how I get so much inside wheel lift on my car. From what I know so far, the torque of the 3.0 SC has a bit to do with that body twist as well as a having no rear sway bar. From what I've been sensing, the wheel lift really hasn't affected traction since these lifts happen at less that 30 mph and the front tire seems to hold well at that speed.


I attended a higher speed event last week at Ft Devens in Mass. & was looking forward to a more open course with less hairpins. Boy what a difference. The car was much more tail happy at speed and I found myself correcting the wheel and back on the throttle to stay pointed in the right direction. (OK, there was one run that I couldn't correct quick enough and a spin resulted). My thought was that my tail happiness at higher speeds could be settled a bit with a rear sway bar. It would also help, I Think, to keep my front wheels a bit more planted on tighter slaloms.

But then I've read that many guys will disconnect the rear sway bar during a tight autocross & I'm not sure why?

My question simply is do I need to install a rear bar?
or...Can I just run front adjustable sway bar links to dial out oversteer?

If I'm at that point where a rear bar is needed, what size?

[2.7RACER]

Joe,
Adding a sway bar to the rear will help the front tire lift in the corners. Unfortunately it will also tend to make the rear a bit stiffer and more tail happy.

Reducing rear tire pressure, softening rear shocks, or a smaller rear torsion bar will help the rear looseness.

Conversely stiffening up the front can help to balance the car as well.

Too much added front stiffness will result in understeer. Not what you want at either AX or track.

You indicated the front sway is adjustable.
For the track, I would stiffen the front sways some, stiffen the front shocks, reduce rear tire pressure, or soften the rear shocks. Leave it as is for AX work.
Obviously you don't want understeer. You want balance and predictability.

I would try each of these, at the track, individually first and test. Any one of these might achieve what you are looking for. It may take a little bit of all of them. Test, test, test.

Personally I like a tail happy car for AX work. I tighten my REAR sway for AX's and soften it for the track. Since your FRONT is adjustable, I'd tighten it for track work and leave it as is for AX.

You'll find the answer.

[Chuck Moreland]

Originally Posted by joetiii

The car was much more tail happy at speed and I found myself correcting the wheel and back on the throttle to stay pointed in the right direction.

Sounds to me like a technique problem. You said you were "correcting the wheel and back on the throtte".

You never should have been off the throttle.

no throttle in a turn = oversteer

In general, once you get off the brake, you need to be feeding controlled throttle through the turn. At about the apex you should be reaching full throttle.

[Chuck Moreland]

And yes you should add a rear sway bar.

[joetiii]

Originally Posted by Chuck Moreland

Sounds to me like a technique problem. You said you were "correcting the wheel and back on the throtte".

You never should have been off the throttle.

no throttle in a turn = oversteer

In general, once you get off the brake, you need to be feeding controlled throttle through the turn. At about the apex you should be reaching full throttle.

Bingo!



Yes Chuck, the oversteer was primarily a technique issue. Actually, last sunday was the first time where I've really pushed the car to its limits at a higher speed in a controlled course. On the road, I'm always on the throttle in turns. Here, I was trying to get the rear out around corners. You know, experience what everyone says, "the old 911s are a tail happy car" Yada yada yada. Brake, turn in, then throttle got the rear loose. (Not the fastest way around the track I know). I was fairly happy to be able to control all but one turn. Next time I will feed throttle sooner. Tire pressures are set equal between front and rear.

Anyway, I have a through body front bar and see there are some turnbuckle style drop links I could use to adjust the front.

What type of bars would you recommend for the rear?

[Chuck Moreland]

I would suggest seat time with good instruction. Learn how to steer with the throttle. That doesn't mean breaking the tires loose ala drifter style.

Steering with the throttle is done with the tires firmly gripping the track, zero loss of adheshion. The throttle is used to modulate weight transfer between front and rear wheels, that is all. When the car is approaching the limit, the throttle is as effective, maybe more effective, than steering with the wheel. But again, the tires never slide or lose grip.

More throttle increases your turn radius. Less throttle makes you turn sharper. No throttle (or brake) makes you spin.

If you can get on a skid pad with an experienced instructor you can practice that and you'll see that it works. And how!

[joetiii]

Originally Posted by Chuck Moreland

If you can get on a skid pad with an experienced instructor you can practice that and you'll see that it works. And how!

Oh yeah..... I got to attend NorthEast Regions autox clinic back in April so I know what you're talking about. The skid pad was an aHa moment for me. After several times around the skid pad, throttle Steer took on a new meaning. Very nice way to direct the car. Slip angles were also something I worked on modulating.

All makes sense. More seat time is most important right now! Thanx


BTW, did those new fab crossover pipes for 911 trans get out yet? I've been away on vaca for a week and havn't been to the parts dept.

[burgermeister]

If you have same size front / rear tires (or even if you don't), in general I'd suggest higher pressure in the rears and lower in the fronts to increase stability. And +1 on the throttle comments above.

[911st]

60% of the weight of a 911 is in the rear.

Also, the rear has a higher center of gravity than the front with the driver in the car.

If you do not have a rear sway bar or have compensated significanty in some way like increasing the rear spring rates a bunch, you can not effectivly control body roll and weight transfer dynamics.

I am not an expert, just my two cents worth.

[joetiii]

Originally Posted by 2.7RACER

Joe,
Since your FRONT is adjustable, I'd tighten it for track work and leave it as is for AX.

Is this an adjustable front link?
I shot it tonite. If so, which way is tighter and which way to loosen?

[Flieger]

Your front sway bar is full stiff.

I would start at full soft and see how you like the feeling on a few laps after warm-up. Then you can move a notch and try it again until you find the best seting. Your adjustment range is limited to those holes, though.

[911st]

If you are still not running an rear sway bar and a 20mm front, get a 18mm rear sway bar to go with your 21/27mm torsion bars.

Your set up is very unusual.

Good luck.

[joetiii]

Well I did loosen the front sway bar one notch about a month ago and the difference was pretty noticeable on the street. Less push in tight turns at speeds 5-20mph. I am actually getting a bit of wheel spin if I'm on the gas too much, too quick. Turn in seems more crisp and overall, the car feels more neutral in 25-40 mph sweepers.

I did pickup a 19mm adjustable rear bar that installed pretty easy yesterday. I also got the welty turnbuckle style front adjustable drop links. I installed them and have them taking up zero slack right now. The directions suggest I drive a few miles to let the front and rear settle in a bit, then take up more slack with the turnbuckles.

I suppose an empty parking lot can help me dial in the proper balance. We've gotten rained out of last two autox so I've got another few weeks till the next. any other thoughts on dialing things in?

[RWebb]

Originally Posted by Flieger

Your front sway bar is full stiff.

I would start at full soft and see how you like the feeling on a few laps after warm-up. Then you can move a notch and try it again until you find the best seting. Your adjustment range is limited to those holes, though.

yeh - that is a old timey bar - i have one like it

[joetiii]

Well I have the front turnbuckles installed with a tad of tension. The rear is full loose as well and after 500 miles of street and country road driving, all I can say is WOW.
The car drives completely different. When I ran with front only set at its tightest, my car pushed in all corners up to 50 mph, and I could rarely get the rear end loose under hard acceleration. Only my exaggerated motions at the Ft Devon AutoX would make the car unsettled. As I loosened the front bar some, the understeer was minimal while the the rear would come loose under hard acceleration.

With both bars set loose, the car is more balanced. turn in is so crisp with vitually no push. I can feel the slip in the front as well as the rear and throttle controls the drift much more easier and gradual. I can't wait to get to the autocross. It'll be like learning on a entirely new car.

[ChkbookMechanic]

That is excellent that your car is driving much better.. now you get to think about stickier tires

[berettafan]

Originally Posted by Chuck Moreland

I would suggest seat time with good instruction. Learn how to steer with the throttle. That doesn't mean breaking the tires loose ala drifter style.

Steering with the throttle is done with the tires firmly gripping the track, zero loss of adheshion. The throttle is used to modulate weight transfer between front and rear wheels, that is all. When the car is approaching the limit, the throttle is as effective, maybe more effective, than steering with the wheel. But again, the tires never slide or lose grip.

More throttle increases your turn radius. Less throttle makes you turn sharper. No throttle (or brake) makes you spin.

If you can get on a skid pad with an experienced instructor you can practice that and you'll see that it works. And how!

Just reading up on suspension options and came across this again. Several months ago i read this and thought 'wtf does he mean steering with the throttle without breaking the tires loose?'

now, after two auto-x events, the most recent with a skidpad portion, i totally get this! been talking to everyone (coworkers, family, neighbors---they all think i'm nuts) who will listen about how cool it is to tighten up your turn by lifting a bit yet there is no sliding!!! the skidpad part was a big circle with a double gate right on it so you HAD to tighten up when you came back around. the only way to do it without killing an innocent cone was to lift just a touch as you came around to the gate the second time. just amazing how the car responds to that.

just too effing cool. wish i had started this sooner!

[kwikt 911]

Congrats for getting it figured out BTW, been autoxing my 72 911 for years and what works best for me is 21mm front and 26mm rear torsion bars. 15mm front and rear sway, 2* negative camber front and 2.8* negative rear. Also slight toe out front and slight toe in for the rear. 205/50/15 Hoosier A6's on 7x15 Cookies with the ride height set at 23.75"front and 23.5". Been thinking about trying 28mm rear torsion bars rear. Good luck

Kevin

[911st]

Not an expert but if you can get it try more neg camber in the front and maybe 225's for autoX.

I know of a racer that used to disconect his rear sway bar on the track then hooked it back up for autoX. He has many track reconds. Ran 225's ft and rear w 22/28's on a narrow body. He was crazy fast.

Seems, stiffer front for track work to make the rear hold best.

Soft front, stiff back to make the front stick for AutoX.