Why Do 911s Lift Inside Front In Corners

[jyl]

In photos of autocrosses, I often see 911s with the inside front tire lifted off the ground. Looks like of goofy, and I seldom see photos of 944s / 914s doing the same "lift the leg" thing.

This shouldn't happen, should it? What's the cause? Does it mean the rear swaybar isn't stiff enough, or something like that?

[JSDSKI]

911's are very territorial

[scottb]

JSDSKI: Shouldn't that mean that a rear tire comes off the ground?

[masraum]

When the body leans to one side and you are on the throttle as you often are in a corner in a 911 the weight transfer is to the opposite rear tire. This in itself would not cause the tire to lift, but the sway bar is actually what lifts the tire. since the weight transfer to the outside tire causes that suspension to compress which in turn twists the sway bar, the twisting of the sway bar actually helps to lift the opposite tire.

[cary]

Because it looks cool..........

[YTNUKLR]

There was some AutoX photo of a flared, badass looking 914 with deep wheels. I recall it had a front lift.

[ted]

Lifts a wheel... looks cool but really isnt.
Good traction but may need heavier rear torsion bars and or sway bars.
Put slicks on a stock 911 and you'll have a tricyle too.

[widebody911]

It's not a 911-specific thing.

I've seen it on other makes of cars as well - like the M3 lightweight that blasted past SCCAITA and I in turn 1 last time I was @ Thunderhill.

It's a function of chassis and suspension rigidity.

[yelcab1]

I saw an old alfa romeo Guiletto did that on Grizzly Peak in front of The Wall. Nothing special about 911 at all. Drive almost any car fast enough around a corner and it will do that too.

[Dantilla]

I've seen plenty of front wheel drives lift the rear corner under trail braking upon turn in.

[Superman]

Umm. I think it has to do with the placement of the engine in the car. Front wheel drive cars lift their rear legs.

[smestas]

My local German auto repair shops runner car has a licence plate that reads "UP ON 3".

I've also see this alot on Water cooled VW's but usually on the inside rear tire.

[jluetjen]

I'll try not to be too long winded, but the short answer is because of the car's weight distribution, the relationship between the CG height and the roll center heights, and the suspension tuning (ie: T-bar and sway bar stiffness and their ratio front to back). The fact that it does lift at all suggests that the chassis itself is stiff enough to transfer the forces to the front sway bar -- which is a good thing. Also the fact that it does lift is not really detrimental to the handling since the inside wheel on the light end of a car rarely provides any cornering forces to speak of. Besides, as everyone will always remind you, the 911 is an "Oversteering" car, so your car's cornering potential is most likely limited by the rear end, not the front. (Larger rear tires may change this though!). It's not unusual nor specific to rear engined cars, NASCAR cars always do this (and they are front Engined) at places like Watkins Glen while going through the S's.

BTW, As a result of the forces provide by wider and stickier tires, Porsche changed the rear suspension geometry on the Carrera RSR's and Turbos which made these cars far less likely to lift the front end. The problem was not so much the front tire in the air, but that the lean in the back was moving the rear suspension into a bad zone in it's camber curve. Carroll Smith describes it well when he says that the rear end is "falling over". So Porsche raised the rear roll center and increased the rear camber gain on the "Turbo trailing arm" suspension which helped a lot. A side affect is that it is that you will rarely see a Turbo lift a front tire very high. Note that this is not a "Perfect" solution since it has other side affects which the earlier suspension did not have, namely that it wears the tires out faster in street use and it apparently makes the car "dartier" which many drivers find unsettling in day-to-day use.

[A Quiet Boom]

Interesting discussion here! I find that my car, with the reduced weight of fiberglass bumpers, tneds to easliy push the frontend under acceleration during cornering. If I jab the throttle hard when the front tires are planted I can force over steer and of course I have the famous trailing throttle oversteer which I found to the most unsettling handling trait to get used to. In the past I've always had high powered front engine rear drive cars which understeered until you hit the gas. I know a lot about drag racing suspensions but very little about sportscar/road racing suspensions so expect a lot of questions from me in this area in the future. Interesting note: I've been playing EA games Need For Speed V - Porsche Unleashed for about a year or so, winning the factory driver in both automatic and manual trans mode as well as winning every series in evolution mode, I've found that driving the RS in the game has made me more aware of my real car. In fact I believe that playing the game has improved my driving ability as much as real seat time has if not more. Next summer I plan to go to my first DE events and I just can't wait to push the car in the controlled enviroment of a race track, one thing I find really cool about the 911 is that mine is basically a stock suspension and having had 14+ years experience driving fox-body mustangs on back country roads I can almost double my corning speed in the 911 vs. the Mustang's that I practically grew up driving (first one at 18) this says a lot because I am very comfortable with the Mustang chassis and know right where it's limits are but I'm relatively new to the 911, I can only imagine how much I'll improve with more seat time and some DE's under my belt. The 911 very much reminds me of my 12HP Kohler powered go-cart I had as a kid in which four wheel drifts were the norm and throttle-induced oversteer were essential for some of the corners on the "track" my brother and I laid out in the woods behind my parents house. It is easy to see why so many people love these cars, once you learn to drive them they are a blast!

[masraum]

Henry Watts - Secrets of Solo Racing
Paul Frere - Sports Car and Competition Driving

Both of these books offer lots of the scientific and/or mechanical info of what is going on when you drive a car in anything but a straight line. Great books if you can enjoy some otherwise dry reading.