I recall seeing this term bandied about on the forums when I was buying a sportscar. Specifically in reference to rear engined/rwd 911.
I get it and I also understand how the old turbos could cause some code browns.
Moving on to the matter at hand, however…
Isn’t liftoff oversteer exactly how we rotate, generally? So wouldn’t that make the 911 the ultimate cornering vehicle?
I’d say no for the kart because there’s a lot less (Arguably close to zero) front/rear load transfer in a kart when you lift off.
Caster is what does the work on entry in a kart.
No, a kart rotates through inputs. When you lift off throttle in a kart, you take the force away that is twisting the frame and getting the inside rear wheel unloaded.
In that sense, a kart drives more like a dirt car, where you have to have some input or load going through the kart to get it to rotate. If you don’t throttle down in a dirt car, the thing plows and understeers like crazy.
911 lift off oversteer is generally mid-corner but they definitely dont handle like a kart. Though, there are definitely similar techniques used for completely different purposes. I would say my Mustang is much more similar to my Kart then my 911s. That isnt to say the 911 isnt a better handling car but its certainly different. 911s tend to push on entry but luckly you can usually transfer load onto the front on entry and get it to bite this is more/less noticeable on different models but would say its a general trait.
Really? I notice this big time. I use this load transfer all the time to begin turn in. There’s a huge diff approaching a sweeper and trying it flat or with kart neutral (will slide laterally off). Shifting weight to fronts via braking and then rotate. There’s no suspension so it’s a quick transition.
Or am I misunderstanding?
I should go try a car track day.
Feel like putting some meat on this? How does caster do the work?
What you’re probably feeling is a combination of caster and reduction in power at turn in. The caster helps unload the inside rear wheel, transferring the load diagonally to it’s front end counterpart. It may feel like lift-off oversteer or a lift-off type behavior, but it’s more to do with the unique geometry of a kart.
If you still have a kart, turn it full lock one way on the ground and see how much the opposite wheel comes up. That will give you an exaggerated sense of how the caster angle influences the load transfer from inside rear to outside front wheel. You should be able to ping-pong the chassis from corner to corner.
Sure, but that’s not lift-off oversteer though
How does one define it? In order to rotate the kart there has to be a moment of transition. The act of letting off throttle (neutral) accompanied by brake coming down (forward) results in wheel lift as kart settles on its nose. The lift bit allows the back to unstick. Turn in initiates a (generally) very subtle and controlled bit of oversteer which separates tire from rubber briefly, which is then re-engaged with rubber as power comes in. Sorta playing catch with the balance of the kart.
What’s lift off oversteer in a car?
I’m driving a rear engines car fast into a corner, I’m feeding power through the car, at apex I realize I’m carrying too much speed and will run out wide, so I lift off. At this point thebalance changes, to a more neutral status. The rears which were getting the grip suddenly go light. And we fall off the track? The trick then is to just let it run out and resist the urge to put power back down else you zing totally?
Whose got cones and a big ass parking lot we can play in?
By this do you mean that unless you have power going through the chassis, the dirt car wants to flat slide? Like the fronts will just skip along not finding purchase? The fronts in a sprint dirt car seem to hop along not doing much most of the time but they do seem to do something.
This is not lift-off oversteer because it is braking-induced. Lift-off is specifically from engine-braking alone. At least with my 206, that’s negligible compared to my Elise where it is dramatic.
Aha! Progress! So I send the 911 into the corner without braking but the engine braking is what is sending weight forwards. That makes sense.
An overly aggressive downshift could cause one to get unglued? Similar thing ?
Engine braking is nonexistent in karts afaik
Not flat slide, purely understeering. You’re right, the front wheels don’t do much, that’s why you need to be on throttle to turn because you’re turning with the throttle. Powersliding essentially.
The car has lift-off oversteer because the rear wheels are no longer trying to drive the car in a straight line, the weight moves forward a bit, and the rear lightens and allows for rotation. If you’ve ever driven a FWD car aggressively, you could feel it pretty distinctly. Some FWD cars get super light in the rear when you lift. In the rear engine 911, it’s from the heavy booty wanting to overtake the front wheels. If you took a car to a skid pad and drove in a circle with throttle on and then lifted off, you’d feel the rear want to swing around. That’s lift-off oversteer. If you did that in a kart, you would not feel the rear wanting to swing around.
As James noted, the caster driving the inside front wheel down into the track and jacking the weight has a far larger effect on the kart’s cornering ability than the very small weight transfer forward.
I looked at my data yesterday and my LonAcc Gs were at most about -0.5 Gs in hard braking zones. By contrast, a 911 GT3 seems to hit about -1.5 Gs under braking. Just to illustrate how little decel a rear-brake kart actually has compared to a track car.
Not quite, if you aren’t rev matching. Without rev matching, the energy for the higher rotational energy of the engine has to come from somewhere, and this comes from the car’s kinetic energy. In other words, the car slows down to speed the engine up. Rev-matching means this energy comes from gasoline, and the car doesn’t have to lose momentum. This is why you can chirp the rears if you don’t rev match.
Either way, the higher the engine rpm, the higher the engine drag, the greater the engine braking. All else being the same. For a kart, it is wrong to say there’s no engine braking. It just isn’t considerable.
That’s a relatable description and makes sense.
Not under ideal circumstances. But in others, definitely. Extreme example is the “shift lock”. A technique used to lock (or at least rapidly deccelarate) the rear wheels by downshifting aggressively in drifting.
But that’s not lift off oversteer of course
I define it as oversteer that can be caused by the load transfer from rear to front when lifting off. It really doesn’t happen in karts because that kind of load transfer is so minimal compared to a suspended vehicle with a mass in the four figure territory.
I think the main reason it’s talked about is that it’s the main cause of crashes for newcomers. They lift off for confidence and then all hell breaks loose.
meanwhile on r/idiots in cars, we get to see the 5% that have the “pin it” involuntary reaction to stressors.
So, in conclusion, I need to go to the ETS parking lot with Nick and learn all about lift off oversteer since I clearly have not experienced it in my car yet. It’s time for new tires anyways.