M3 corner/high speed stability issues

[backagain]

Originally Posted by mm767cap

It's not the back end, it's the front end. It's when you LIFT the throttle in the corner. I have experienced trailing throttle oversteer in cars before, but this is a new one for me. I'm experiencing it on every corner, so it's not tramlining. To answer the posters question about whether it's bad or not: it's pretty prominent on my car. Might not be for everyone, but for me, it's quite significant.

One thing that I WILL say is that I tried the suggestion of turning off the traction control, and I DID notice a marked improvement in the behavior. So at least for me it appears to be a traction control issue.

I know it sounds like we just don't know what we are talking about here, but I've owned an E46, P car, NSX, ISF, Jaguar F-Type R Coupe etc. and always enjoyed playing with the limits in corners. This is a new behavior that I've never experienced in a car before. It is indeed rather un-nerving. As I said before, the first time it happened I thought the front tires had unbeaded from the rims as the car pushed into a strong understeer

"Three principal differences between power oversteer and trailing throttle oversteer are:

• Trailing throttle oversteer requires the rear tires to be close to their grip limit, whereas power oversteer can still happen when the car is not at the grip limit if it has enough rear wheel torque.
• Trailing throttle oversteer, once mastered, can be applied more smoothly and to a lesser extent than power oversteer. Power oversteer typically results in a drift even in skilled driver's hands, whereas trailing throttle oversteer does much less so.
• Power oversteer can often be recovered from simply by reducing throttle. With trailing throttle oversteer, reducing throttle does nothing. The car must physically decelerate to where the rear tires grip again. For this reason trailing throttle oversteer is often regarded as more dangerous than power oversteer, even though power oversteer can result in loss of control of the vehicle as well."

Because the backend is losing traction in trailing throttle oversteer (more so that power oversteer), the DSC is intervening, therefore, twitching.

[Wills2]

My car always feels twitchy on entry to high speed corners on the first application of steering input then settles.

It is a tad unnerving though, the PS4S have made it worse I'm not keen on the front end they give the car.

[Ilikemike]

Originally Posted by Colinv6

My comp m3 with ACS springs (dealer fitted before collection) doesn't feel quite right on high speed bends, it can feel very unnerving, not twitchy as in the back end coming round,
But a feeling of for a second or 2 you don't really have control over the car very much.

Same here, kind of the feeling that there is a very thin layer of air between the road and the rubber and that chaos (into the guard rail) is about to happen.... Unsettling and I have not experienced this in 45 years of driving in any other car. I thought maybe it is the steering so, I'm having the front thrust bushings changed to ball joints (Dinan) as a first step to see if that improves my understanding, it could also be the particular road surface: I notice it on especially well travelled highways and not so much on back roads where the grip is phenomenal.

[CanAutM3]

Originally Posted by backagain

• With trailing throttle oversteer, reducing throttle does nothing. The car must physically decelerate to where the rear tires grip again. For this reason trailing throttle oversteer is often regarded as more dangerous than power oversteer, even though power oversteer can result in loss of control of the vehicle as well."

I don't fully agree with this bullet. Trailing throttle oversteer can be overcome rather easily by applying some throttle to transfer some weight back onto the rear wheels and therefore increase their grip.

The reason trailing throttle oversteer is so dangerous is because it is an unnatural reflex for most drivers to have to accelerate to recover from an "out of control" situation.

[CanAutM3]

After reading so many of the comments about "the rear feeling twitchy", maybe it is related to the fact that the F8X's rear subframe is solidly bolted to the body instead of being isolated with bushings, like on the vast majotity of cars. Because of this, the rear end communicates directly whatever it is doing with no damping effect. I actually very much like that trait of the F8X and makes it very enjoyable to drive on track.

[mm767cap]

Originally Posted by backagain

"Three principal differences between power oversteer and trailing throttle oversteer are:

• Trailing throttle oversteer requires the rear tires to be close to their grip limit, whereas power oversteer can still happen when the car is not at the grip limit if it has enough rear wheel torque.
• Trailing throttle oversteer, once mastered, can be applied more smoothly and to a lesser extent than power oversteer. Power oversteer typically results in a drift even in skilled driver's hands, whereas trailing throttle oversteer does much less so.
• Power oversteer can often be recovered from simply by reducing throttle. With trailing throttle oversteer, reducing throttle does nothing. The car must physically decelerate to where the rear tires grip again. For this reason trailing throttle oversteer is often regarded as more dangerous than power oversteer, even though power oversteer can result in loss of control of the vehicle as well."

Because the backend is losing traction in trailing throttle oversteer (more so that power oversteer), the DSC is intervening, therefore, twitching.

I must not have been clear. I'm not getting oversteer. I'm getting understeer when you lift the throttle a little mid corner. The back end remains completely planted. It's the FRONT end that's losing grip. My reference to trailing throttle oversteer was merely to say that I've experienced that in the past on other cars, so wouldn't be surprised to see it show up. This is more like "trailing throttle understeer", which I don't think is a thing.

[mm767cap]

Originally Posted by CanAutM3

After reading so many of the comments about "the rear feeling twitchy", maybe it is related to the fact that the F8X's rear subframe is solidly bolted to the body instead of being isolated with bushings, like on the vast majotity of cars. Because of this, the rear end communicates directly whatever it is doing with no damping effect. I actually very much like that trait of the F8X and makes it very enjoyable to drive on track.

I don't think the original OP is talking about a twitchy back end. I know my back end isn't twitchy at all. It's the front end. The back end is firmly planted.

[mm767cap]

Originally Posted by Wills2

My car always feels twitchy on entry to high speed corners on the first application of steering input then settles.

It is a tad unnerving though, the PS4S have made it worse I'm not keen on the front end they give the car.

Interesting. Mine feels rock solid in the entry. And solid as long as I don't modulate the throttle. If I give it more throttle it feels solid and predictable. It's when I lift that things get weird. I haven't noticed much difference between the PSS and the PS4S so interesting to hear this is happening with your new tires

[backagain]

Originally Posted by mm767cap

I must not have been clear. I'm not getting oversteer. I'm getting understeer when you lift the throttle a little mid corner. The back end remains completely planted. It's the FRONT end that's losing grip. My reference to trailing throttle oversteer was merely to say that I've experienced that in the past on other cars, so wouldn't be surprised to see it show up. This is more like "trailing throttle understeer", which I don't think is a thing.

Got you.

I've never experienced this type of understeer with my F80. I've experimented with various amount of throttle steering and breaking at different turning speeds. As long as the inputs are smooth, the car's behavior is predictable. If the balance is interrupted abruptly, it let you know instantly.

[CanAutM3]

Originally Posted by mm767cap

I must not have been clear. I'm not getting oversteer. I'm getting understeer when you lift the throttle a little mid corner. The back end remains completely planted. It's the FRONT end that's losing grip. My reference to trailing throttle oversteer was merely to say that I've experienced that in the past on other cars, so wouldn't be surprised to see it show up. This is more like "trailing throttle understeer", which I don't think is a thing.

One thing I think could be causing this odd behaviour is the DSC applying the front outside brake in anticipation of a trailing throttle oversteer due to the sudden mid-corner lift-off. It is contrary to vehicle dynamics principles to have understeer increase with throttle lift-off. It could also explain why this behaviour is not present with DSC off and why it feels like the car is "rolling over" the front outside tire (it becomes very loaded in such a scenario).

That is a big reason I hate DSC (even Euro-MDM) at the track: because it prevents any type of throttle steer. When you do a quick lift to tuck the nose in, all you get is more push with the car going slower .

[Wills2]

Originally Posted by mm767cap

Interesting. Mine feels rock solid in the entry. And solid as long as I don't modulate the throttle. If I give it more throttle it feels solid and predictable. It's when I lift that things get weird. I haven't noticed much difference between the PSS and the PS4S so interesting to hear this is happening with your new tires

Apart from the increased grip/traction off the line (but don't we always get that from a new tyre vs. shagged out old ones) I'm not impressed with the steering response from the PS4S, they are also not supplying the correct load index for the fronts either for our cars on 19" I wonder if that is the issue, as the front feels a tad bouncy under load through the corner and tends to wash out, the rear is very good though.

Either that or my car is buggered after 45k in 16 months.

[CanAutM3]

Originally Posted by Wills2

Apart from the increased grip/traction off the line (but don't we always get that from a new tyre vs. shagged out old ones) I'm not impressed with the steering response from the PS4S, they are also not supplying the correct load index for the fronts either for our cars on 19" I wonder if that is the issue, as the front feels a tad bouncy under load through the corner and tends to wash out, the rear is very good though.

Either that or my car is buggered after 45k in 16 months.

That could be because the PS4S you installed up front were not designed specifically as front tires for a RWD car.

[TRZ06]

Originally Posted by CanAutM3

One thing I think could be causing this odd behaviour is the DSC applying the front outside brake in anticipation of a trailing throttle oversteer due to the sudden mid-corner lift-off. It is contrary to vehicle dynamics principles to have understeer increase with throttle lift-off. It could also explain why this behaviour is not present with DSC off and why it feels like the car is "rolling over" the front outside tire (it becomes very loaded in such a scenario).

That is a big reason I hate DSC (even Euro-MDM) at the track: because it prevents any type of throttle steer. When you do a quick lift to tuck the nose in, all you get is more push with the car going slower .

That most definitely a possibility.

The algorithm is not very intuitive on this car.

It steps in way prematurely.

There is an on-ramp that I like to take near me and the system in MDM mode will come in way early. If I turn everything off, I can get an extra 10mph in the corner and I am not even at the limits yet. That tells you just how ultra conservative it is.

[mechanic75]

Originally Posted by mm767cap

I must not have been clear. I'm not getting oversteer. I'm getting understeer when you lift the throttle a little mid corner. The back end remains completely planted. It's the FRONT end that's losing grip. My reference to trailing throttle oversteer was merely to say that I've experienced that in the past on other cars, so wouldn't be surprised to see it show up. This is more like "trailing throttle understeer", which I don't think is a thing.

This is exactly what I experience. I referred to it as lift off understeer to my SA. It is low speed and partial to light throttle on a gentle radius bend. I initially thought it was a very tight diff or dodgy diff that wasn't opening quick enough and hence still driving the car forwards. It was like the front hit a patch of black ice or standing water suddenly then regains grip.

It happened first about 500 yards after collecting my car from new as there is a perfect bend down the road from dealers. About 30 mph and slowing to a stop sign. It was wet.

I got a professional alignment and it has made a big difference but I still think the diff was the biggest factor as it was sudden and unnatural. I haven't noticed it in a long time that it scares me but I'll keep a closer eye on it.

[F83]

Originally Posted by mm767cap

It's not the back end, it's the front end. It's when you LIFT the throttle in the corner. I have experienced trailing throttle oversteer in cars before, but this is a new one for me. I'm experiencing it on every corner, so it's not tramlining. To answer the posters question about whether it's bad or not: it's pretty prominent on my car. Might not be for everyone, but for me, it's quite significant.

One thing that I WILL say is that I tried the suggestion of turning off the traction control, and I DID notice a marked improvement in the behavior. So at least for me it appears to be a traction control issue.

I know it sounds like we just don't know what we are talking about here, but I've owned an E46, P car, NSX, ISF, Jaguar F-Type R Coupe etc. and always enjoyed playing with the limits in corners. This is a new behavior that I've never experienced in a car before. It is indeed rather un-nerving. As I said before, the first time it happened I thought the front tires had unbeaded from the rims as the car pushed into a strong understeer

Hmm. Sounds like a TC software glitch. I've not experienced (in my 15 with probably different software). It's fully planted through the turns. But you should report it.

[Wills2]

Originally Posted by CanAutM3

That could be because the PS4S you installed up front were not designed specifically as front tires for a RWD car.

I think you're right, I had the choice in front of me either star rated MPSS or the PS4S, I think I chose badly.

But then again anyone choosing the PS4S will have made the same mistake as me.

[Racer20]

Originally Posted by CanAutM3

I got alll the improvements you describe by getting a good alignmnet done

Yup. I have had my car aligned every spring since I got it, and this is exactly what I feel after the alignment as well.

[OF Hero]

Originally Posted by CanAutM3

That could be because the PS4S you installed up front were not designed specifically as front tires for a RWD car.

Aren't these new Michelins getting incredible reviews, though? There's a big thread in the tire section and everybody seems to love them. Or were you specifically referring to the load rating on the 19" models only?

[mm767cap]

Originally Posted by Wills2

Apart from the increased grip/traction off the line (but don't we always get that from a new tyre vs. shagged out old ones) I'm not impressed with the steering response from the PS4S, they are also not supplying the correct load index for the fronts either for our cars on 19" I wonder if that is the issue, as the front feels a tad bouncy under load through the corner and tends to wash out, the rear is very good though.

Either that or my car is buggered after 45k in 16 months.

Hahahahaha!!! That's some good driving!!!! I had the same issue with the PSS, so for me it isn't tire specific. Now I wish I had paid more attention to he difference in tires before I mounted up the PS4S!!

[mm767cap]

Originally Posted by CanAutM3

One thing I think could be causing this odd behaviour is the DSC applying the front outside brake in anticipation of a trailing throttle oversteer due to the sudden mid-corner lift-off. It is contrary to vehicle dynamics principles to have understeer increase with throttle lift-off. It could also explain why this behaviour is not present with DSC off and why it feels like the car is "rolling over" the front outside tire (it becomes very loaded in such a scenario).

That is a big reason I hate DSC (even Euro-MDM) at the track: because it prevents any type of throttle steer. When you do a quick lift to tuck the nose in, all you get is more push with the car going slower .

I think you might be on to something here. I entered a long corner last night, relaxed the throttle, got my understeer. Mid-corner turned off DSC and tried the same move. Understeer largely gone.

Will definitely report this to my SA. Thanks for the all the feedback here guys!

[CanAutM3]

Originally Posted by OF Hero

Aren't these new Michelins getting incredible reviews, though? There's a big thread in the tire section and everybody seems to love them. Or were you specifically referring to the load rating on the 19" models only?

I am not saying that the PS4S is not an improvement over the PSS in general (I recently changed from PSS to PS4S on our S4). What I am saying is that potentially (and likely), the PS4S Wills2 has in front of his car are not SPECIFICALLY designed as a FRONT tire for a RWD car. The stock 255 PSS or even the 265/35R19 (M0) I have on my car are indeed designed specifically as a front tire for a RWD car to be mounted on the 9" wide wheels. Usually, front tires are designed with a rounder contact patch to improve steering response while rear tires are designed with squarer contact patch to improve traction. This could explain why he is experiencing less steering response with the PS4S than he did with his previous tire.

[Iceman1]

Originally Posted by CanAutM3

^ This

What made a big difference for me is getting a GOOD alignment done on my car. What I mean by a GOOD alignment, is one done by a shop that will take the time to go back and forth between adjustments points do get it "exactly" (meaning as close as possible) to your specified settings and not just within factory specification. It seems the F8X roll off the factory floor with a fair bit of variance in terms of alignment. After the alignment, my car felt so much more planted and stable.

What specs did you align to? (Camber/caster/toe settings)