3 wheel at CMP turn 12

[jhelgesen]

Just got this pic in from a friend.

Did all that work to the suspension, torsions, sways, shocks, and still 3 wheel through turn 12.

[DUK]

Just my observation, but maybe too much rebound in the front or your suspension is hanging up?

[Steve@Rennsport]

Yessir, they tend to do that,...

Without question, I'd need to know all the details of your suspension to offer any construction suggestions but generally speaking, lifting the inside front wheels is caused by:

1) Insufficient rear roll stiffness

2) Front roll center too far below ground

[jhelgesen]

I'd be glad to offer what I have for a suspension:

23 and 31 torsions
31 and 27 SRP sways
revalved bilsteins
polygraphite bushings
car weight, 2400 pounds

A arms swung free when I did the suspension upgrade a few months ago. Car lifted the front with old setup of 21 and 26's and out of the box bilsteins.

When I've asked at the track, most of the 911 guys at cmp would tell me "thats the fast way around that corner", but I still have to wonder, wouldn't it be better to have both fronts on the ground for steering.

[Steve@Rennsport]

Hi John:

These cars WILL momentarily lift the inside front wheels when hard on the throttle exiting a corner, but only an inch or less,..

Your torsion bars look close, but I'd ask which swaybar is which???

The 27mm one should be in front and the 31mm one needs to be on the rear.

We raise the front spindles (or use an RSR, JRZ, or Moton strut) to raise the front roll center back up above ground level after lowering. The reduces lateral weight transfer and keeps the inside front tire on the ground where it belongs.

Indeed, 4-wheeled cars stick better than 3-wheeled ones.

[jhelgesen]

This is interesting Steve, I went with SRP's recomendation and have the 31mm bar in the front, and the 27 bar in the rear.

That particular corner is a very hard second gear turn.

[2.7RACER]

My question is: Was the car understeering in that particular corner?
I've always evaluated my suspension settings by first determining what my car is doing in any particular corner, along with the affect of the line I take through each corner.
Whether the tire is 4 inches in the air or just skimming the suface, it isn't doing any work.
Soften the front or stiffen the rear and see what happens at other corners.
Is the pic taken in a decreasing radius corner?
With a stiffer rear, some oversteer could cause the car to rotate better at this corner, with of course the attendant oversteer at other corners as well.
It becomes a matter of how confident you are with the car.
Hey, I'm not anywhere close to an expert about these things, but that is my view with my experience.

[jhelgesen]

Car doesn't really understeer, feel planted around the track.

Guess I would have to ask how to stiffen the rear more. Haven't corner balanced the car yet, so don't know the weight balance front to back. Would raising the rear of the car with the adjustable spring plates move some weight?

[jaydubya]

How about "too much front swaybar"? They are adjustable so try softening the front swaybar.

[jluetjen]

John; here's some food for thought on the subject of lifting a front wheel in a 911. (Be sure to follow the references to the earlier threads too!)

[jaydubya]

Originally posted by jluetjen
John; here's some food for thought on the subject of lifting a front wheel in a 911.

Thanks for that link. From an article referenced in that thread:

http://www.turnfast.com/tech_handling/handling_antiroll.shtml

As with all good things, more is better only to a point. Because the anti-roll bar connects the left and right sides, this reduces the independence of independent suspension. Too stiff a bar, and you can cause too much loss in the ability of the left or the right wheel to independently respond to road surface imperfections. The purpose of suspension is to maintain maximum tire contact with the road. The purpose of independent suspension is to allow the left and right wheels to each seek that contact separately. The left wheel may need to be going down when the right needs to be going up. If they were tied together as with the old floating rear axles, one or both of the wheels is not achieving maximum contact. In fact, too stiff an anti-roll bar can actually cause an inside wheel to lift completely off the ground during hard cornering.

[jluetjen]

Be sure to read all of the threads and links. Don't necessarily take the first bit of information as being truth. There's a lot of information there -- some of it conflicting, and when you've finished reading, you'll need to chose your strategy.

[Jandrews]

Some good advice here.

I had a similar situation. I run 23/31 and was carrying my inside front wheel 4" off the ground through hard corners. The trick for me was just as Steve suggested...less stiffness in the front.

Those Sways sound huge to me, but my car is a tad lighter. Still, wow...27 and 31 sways?! In any case, I would soften the front and see what happens. Any movement to free up the flex in the front will help move that inside tire closer to the ground.


JA

[jaydubya]

Jleutjen - Yep, have read it all before.

My personal experience - when someone tells me my inside front wheel is lifting I reduce the front swaybar stiffness (and sometimes the rear swaybar stiffness at the same time, depending on how the car feels to me in terms of balance). This puts the front wheel back on the ground. As Steve mentioned, increasing rear stiffness will help as well, but possibly at the expense of rear adhesion, depending on how stiff the rear of the car is already.

Whether keeping the inside front wheel on the ground is any faster or slower or makes any difference at all in terms of corner exit speed is another issue altogether, and as one can see from the previous threads on this topic, hotly contested. Personally I find that my car is much more predictable and easier to drive out of turns at the limit when both front wheels stay in contact during corner exit.

Cheers,

Jeff