mgordon18

I was taking a cloverleaf a little aggressively this evening and on the last part of the turn I experienced our cars' famous understeer. Not much, but it did start to plow.

I wasn't going quite fast enough for the situation to turn ugly but it did bring a question to my mind: If I keep my foot in it, I risk understeering so much that I could hit the curb. If I lift off to try to tuck the nose back in, I risk having the rear end step out...also risking a curb hit.

What's the right play when you find yourself with understeer on a curbed, one lane road?

1990nein

Well once you're understeering the first thing you need to do is regain front grip. You have a number of options.

1. Straighten the steering wheel. I find jiggling a centered wheel helps me "find" the grip faster and also reduces the chances/viciousness of snap oversteer.
2. Lift off the throttle. Doing so will shift the weight of the car forward, pushing the front tires down to help them grip
3. Use your brakes to shift the weight of the car forward. Similar effect on grip of pushing the front tires down, but remember using the brakes will also use a portion of the front grip you are trying to regain.
4. Keep your eyes looking up ahead and don't let target fixation get the best of you. You will always go where you look so avoid that tendency to look where the car is going and look where you want to go.

mgordon18

Well this was out of the question, since I was in a cloverleaf turn. Straightening the steering wheel would have put me off the road!
I took a 1-day car control clinic earlier this year which included a few runs on a skidpad, simulating almost my exact situation (sans curbs). Lifting off the throttle was the way to not only tuck the nose back in (as you state), but also the way to slide the rear tires out and possibly spin.

But I guess this is where the finesse comes in... The idea is to lift off the throttle enough to get grip up front, but not enough to slide the rear end out.

What if I were to lift off until the nose tucks in and then get back on the gas to put weight back on the rear to keep it from stepping out?

Yes!

7500rpm

Understeering can occurs when you go too fast into a corner, try to accelerate inside a corner, try to turn a tighter radius in a corner, or a combination of two or more of the above. The dynamics overwhelmed the front tires and you have to do the opposite to reduce or eliminate the under steer. Since you've already gone into the corner a little too hot, you need to reduce speed and/or reduce your steering angle. You are right that sudden lift off may induce oversteer so we usually ease off, rather than lift off. As Pho mentioned, you might have to straighten the steering a little instead of the instinctive reaction to turn even more. When neither seem sufficient to eliminate your understeering, the brakes are your last resort.

wwest

NEVER turn PSM off..???

If PSM was on and it allowed you to get into that situation, without itself correcting (rear braking, possibly differentially so, typically, in this case), then you need dealer PSM service.

1990nein

You have no alternative, it's just physics. Your tires have 100% traction at any time - portions of it can be allocated towards acceleration, braking, or turning inputs - but you only have 100% total traction. If you exceed 100%, your tires will not grip; aids aside, accelerate past 100% and you will peel out, brake past 100% and you will lock up, turn past 100% and you will spin out. If you exceed 100% traction, you have to reduce your inputs until you regain grip.

What happens when you stomp the gas and start to peel out? You exceed the grip limit, so you have to reduce throttle input until the tires gain traction.

When you're trying to turn, but the car isn't turning, it means there is not enough front grip available. The only way to make some available is to reduce turning input until you regain traction (or hold the steering wheel there until the wheels scrub and reduce speed enough to regain traction); turning more attempts to use grip that doesn't exist.


Yes try not to think of it as "when in this situation, gas" or "when the car does this, brake." Think of the throttle and brakes as tools to apply newton's laws; your goal is to keep the car's weight and traction evenly distributed while maintaining as much momentum through the corner as you can.

Yes the 911 is very rewarding when you do this properly, but keep in mind any corner will involve a multitude of mental calculations involving how much brake, gas, and steering to input based on the current weight and traction distribution. So again, please don't think "when here, do this" because it involves quite a bit more and you can get yourself into trouble with one-size-fits-all solutions (I know from experience). Our top racing drivers have not become pros by memorizing a textbook of "when here, do this," but rather have developed a very good understanding of what to do based on what they see and feel.

mattyf

Understeer scrubs off speed so it's already helping slow you down a bit. As others mentioned I would ease off throttle slightly in combination with straightening the wheel a bit until the front starts to grab again.

There's an incredibly tricky freeway onramp near my house that I practice on religiously. It's a decreasing radius with an upslope. Very hard to drive it fast without plowing.

I haven't noticed PSM intervention during understeer only had it intervene on oversteer, so I don't think anything is wrong with your PSM.

mhm993

Dont forget, that "i risk oversteer" is precisely what you need to do in a controlled way to get out of the front pushing.
It's not about hard and fast rules (never lift) but about finese (lift just enough to move the weight and get the car turning)
We do this drill all the time with kids at teen survival. None of them ever has any idea that when the car pushes, a light lift brings them back into control.

mgordon18

That is, in fact, what I ended up doing. Instinctively, I backed off as most people would when they realize they're going too fast for a given turn. But I also had in my mind, "don't lift too much!" So I was able to get back on track without causing even the PSM to kick in, let alone any real havoc.

I'm glad to know that I basically did the right thing. That skidpad exercise from the clinic really helps give that feeling of understeer/oversteer and allows you to understand how one plays off of the other via the throttle.

But I'll tell you: that low frequency hum of the front wheels plowing really gets the adrenaline going...

dasams

Were you running at constant speed or accelerating when understeer began? I suspect the latter as that's when the weight shifts to the rear. As you've noted, a light lift to settle the car will return neutral steering.

mgordon18

I was indeed accelerating. I thought the ramp was going to straighten out, but it had one more turn in it. I didn't floor it, but I was definitely easing on to the throttle when I realized I had to instead hold the turn.

It also felt like a decreasing radius turn, but I checked out the satellite, and it looks pretty consistent from space.