Is a little inner rear lift ok near (mine, at least) cornering limit

[sbrown.nw]

Ok, here is how the story goes. 1972 T Targa with 85 Carrera fenders and 16x6&7 Fuchs when I bought her. Put large (22mm front and rear If I remember correctly) adjustable sway bars on her, handled nicely but no autoX events to really push her (note, she has factory sized torsion bars in her but with new upgraded bushings). Then I went to 17x7.5&9 Rota Foxes with new and stickier tires (Kumho XS - love them) but I noticed immediately more understeer. Had the front sway bar tightened and the rear bar loosened. Much more balanced maybe to a touch of oversteer.

So, when I went autoXing in Packwood a few weekends ago with the Oregon and WA clubs (great 2 day event!), I got reports from multiple people that I was getting a little inner rear lift on a couple of quick and abrupt turns. Also, with some follow-up discussion, people said body sway was pretty minimal.

Is that ok or should I loosen up the rear bar some more, since it has a little more room to go in that direction? Also, my 915 trans does not have a LSD but I hope one day to get one in her.

Here are some picts of my car and the event:





http://www.oregonpca.org/events/autocross/ax-results/2009-ax5/ax5-media/

http://www.914world.com/bbs2/index.php?showtopic=98391

TIA a bunch!,

Scott

[javadog]

I've never seen a 911 lift an inside rear tire. They lift the inside front all the time. You sure you heard it right, that they said rear?

JR

[sbrown.nw]

They said rear and I double checked. Wish I had a pict...

[rfloz]

Originally Posted by white78911

I went to 17x7.5&9 Rota Foxes with new and stickier tires (Kumho XS - love them) but I noticed immediately more understeer. Had the front sway bar tightened and the rear bar loosened. Much more balanced maybe to a touch of oversteer.

Scott

Normally one would stiffen the rear bar and/or loosen the front bar to counteract understeer.

As to lifting the rear wheel - is this on entry with lots of late braking? You may be pitching the car into the turn a little too hard. The norm, as mentioned above, is inside front wheel lift on exit under acceleration.

[sbrown.nw]

rfloz, that could be it.

- Smoother turn in?
- Loosen rear sway bar?
- Earlier braking?
- All of the above?

Scott

[sbrown.nw]

One more thing rfloz. The comment you said about tightening the sway bar - that is what I thought needed to be done, but I could swear I heard my suspension expert state loosen the rear and tighten the front. The car did dial out understeer / plowing on 90 deg turns (changing from one street to another). I have the Weltmeister bars - does a loosening action / adjustment actually make them tighter in stiffness?

Scott

[911st]

Getting a 911 to turn in at slow speeds is an effort.
I suspect your rear tires are 255's, what size are you running in front?

For autoX you want/need a bunch of neg camber up front (say around-3 ).

Second, for autoX you often want the rear stiff so it will come around easyer (rotate).

It also helps to set up the front with some toe out.

Often newer AutoX drivers are just going to fast to make a turn and push through it.

I to have a lot to learn about autoX.

[rfloz]

First, if your inside rear wheel is lifting you should have massive wheelspin accelerating out of the corner, especially considering you have no LSD. Do you? If not, why not?

Second, if you have inside rear wheel lift it is generally a sign of too much rear roll stiffness or too little front roll stiffness. See Fred Puhn's How to Make your Car Handle.

"Generally" because if there are overriding mechanical issues (tall front wheel drive cars or blown struts come to mind), or driving issues (see above) they can produce similar results even in a well set up car.

So, before making more suspension changes you might want to make sure your front struts are working properly.

Then, my suggestion would be to have an expert auto-crosser drive your car. You can then watch from the outside and see if there is really a problem. And, you can watch from inside the car to see what the expert is doing differently than what you are doing. I have found this to be very enlightening, not to mention humbling, when you see how fast your car can really go.

What makes auto-cross so difficult is things come at you very fast. This makes sorting out driver vs. car issues tough.

And yes, these things do understeer in low speed corners at auto-cross speeds (I switched from a Mustang, massive understeer, to a 911 and expected wild oversteer. Surprise - lots of low speed understeer!) . But, understeer usually manifests itself as front end washout, i.e., front wheel sliding, not rear wheel lift.

[sbrown.nw]

This sounds like what could be happening (from autoX and racing forum).

Scott

Originally Posted by 175K911

You sure it's actually lifting, and not just getting light and spinning?

In tighter 2nd gear turns on the track, I only have a few inches of tread on the inside tire touching the ground, but with the Guard LSD I get plenty of bite to power out. And this is with 23/33 torsions and 25mm Tarett sways: