[TrackClub]

Originally Posted by N Camarolina

It most definitely IS possible to spin in Sport 1 with all 4 wheels on the asphalt in dry conditions on OEM SC3s. I've managed to do it twice so far under trail braking, and I suspect the cause was a bit too abrupt final release of the brake pedal when near the apex (lots of steering dialed in).

The first time was VIR turn 3, where the induced rotation was beautifully slow and the ECS intervened to catch the rear (successfully) right as I was about to add some counter steer. If I hadn't mentally paused to admire the rotation I had induced, I probably could have added some throttle while opening the wheel to settle the rear and the ECS may not have even intervened.

The second time was at VIR turn 4, where the induced rotation was much faster. This was under aggressive trail braking (where I recorded 1.5 lateral G while still having some longitudonal G from slowing the car). The ECS started trying to catch the rear about 1/4 second before I added opposite steering lock. I overcorrected slightly, but without the countersteer, I do not believe the ECS would have successfully caught the rear, as the yaw rate was quite high.

Word to the wise: When you start practicing and playing with trail braking, be prepared for oversteer and do not assume that ECS will save you, even in PTM Sport 1.

Agree: it is posssible to lose a car with any nanny. But, it takes a bit of trying

From what you describe, I suspect you engage brakes way too much on corner entry, which is not really producing trail braking per se, but massive amount of understeer, with the fronts sliding, especially with steering lock being added on. Then, when the car slows down closer to the apex and the fronts finally REGAIN GRIP, the rears get violently loose. This is a classic case of snap oversteer.

Often times, the initial understeer puts a driver to sleep, until the fronts regain traction. This is also a classic situation in the wet. So...watch for understeer, as it is not always a benign thing and is capable of causing some truly spectacular wrecks...

Cheers!

[N Camarolina]

Originally Posted by TrackClub

Agree: it is posssible to lose a car with any nanny. But, it takes a bit of trying

From what you describe, I suspect you engage brakes way too much on corner entry, which is not really producing trail braking per se, but massive amount of understeer, with the fronts sliding, especially with steering lock being added on. Then, when the car slows down closer to the apex and the fronts finally REGAIN GRIP, the rears get violently loose. This is a classic case of snap oversteer.

Often times, the initial understeer puts a driver to sleep, until the fronts regain traction. This is also a classic situation in the wet. So...watch for understeer, as it is not always a benign thing and is capable of causing some truly spectacular wrecks...

Cheers!

Thank you for your thoughts Trakclub. I always appreciate your analysis.

I'm pretty certain it's not understeer (massive or otherwise). At my last track day two weeks ago at VIR I finally entered T1 with a few mph too many under trail braking, asked too much from the front tires, and had the car understeer. I simply opened the wheel a little (still under braking) so the ratio of lateral grip request was lower. Blew the racing line but easily, but had room to keep the car on the asphalt and kept the rear end planted.

Normally under trail braking with the extra weight on the front and the car and the speed in check, the front tires have extra grip and the car pivots amazingly well (on a dime in the best examples), and smoothly (not violently). But I also notice that I seem to sometimes get a little bit of extra pivot (yaw) when I release the last bit of brake pedal, near the apex. Normally it's fine and the back end stays under control behind me without ECS intervening. Every once in a while, though, this extra pivot winds up being too much for the rear traction and back end will start to step out.

The PDR data on PI Toolbox seems to suggest the extra yaw on brake release is more pronounced when the brake pedal is released (too) quickly. In the example where I had the back end step out while trail braking into turn 4, I released the last 18% of pedal considerably faster than what I had done up to that point and the yaw rate during that time climbed from 34% to 38% without any additional steering input, and this immediately preceded the rear losing traction. I would have thought that at that moment the weight transfer rearward would tend to stop any rotation immediately and perhaps initiate understeer, but clearly that's not what is happening.

[TrackClub]

Originally Posted by N Camarolina

Thank you for your thoughts Trakclub. I always appreciate your analysis.

I'm pretty certain it's not understeer (massive or otherwise). At my last track day two weeks ago at VIR I finally entered T1 with a few mph too many under trail braking, asked too much from the front tires, and had the car understeer. I simply opened the wheel a little (still under braking) so the ratio of lateral grip request was lower. Blew the racing line but easily, but had room to keep the car on the asphalt and kept the rear end planted.

Normally under trail braking with the extra weight on the front and the car and the speed in check, the front tires have extra grip and the car pivots amazingly well (on a dime in the best examples), and smoothly (not violently). But I also notice that I seem to sometimes get a little bit of extra pivot (yaw) when I release the last bit of brake pedal, near the apex. Normally it's fine and the back end stays under control behind me without ECS intervening. Every once in a while, though, this extra pivot winds up being too much for the rear traction and back end will start to step out.

The PDR data on PI Toolbox seems to suggest the extra yaw on brake release is more pronounced when the brake pedal is released (too) quickly. In the example where I had the back end step out while trail braking into turn 4, I released the last 18% of pedal considerably faster than what I had done up to that point and the yaw rate during that time climbed from 34% to 38% without any additional steering input, and this immediately preceded the rear losing traction. I would have thought that at that moment the weight transfer rearward would tend to stop any rotation immediately and perhaps initiate understeer, but clearly that's not what is happening.

What you are describing seems completely opposite to what one would expect with a too fast a brake release UNLESS the rears are already at the limit and by moving weight to the rear (by releasing the brake quickly) you induce loss of traction there. Amd hence the slide. Assuming your ESC is working properly applying brakes to a correct wheel to reduce yaw, I would say you are waaay overdriving the car sir And ESC let's you exceed limits until you exceed the ESC. Solution? Move up to PTM Race and assume direct control of yaw, based on what the car is ACTUALLY doing vs what ESC is preventing the car from doing due to your overdriving (meaning: you don't feel what the car is doing balance wise, as ESC is masking the exceeded limits, until its own corrective limits are exceeded).
I can tell you without a shadow of a doubt, that the car feels VERY different balance wise between Sport1 and Race. It is capable of very fast laps under BOTH settings, but it requires an adjustment from a driver. In my strictly personal opinion, the car is clearly safer in Sport1, but not necessarily easier to drive fast, as its feedback is muted by ESC (as one would fully expect). Hope this makes sense. Cheers and have fun!

[cdrptrks]

Originally Posted by TrackClub

ESC let's you exceed limits until you exceed the ESC. Solution? Move up to PTM Race and assume direct control of yaw, based on what the car is ACTUALLY doing vs what ESC is preventing the car from doing due to your overdriving (meaning: you don't feel what the car is doing balance wise, as ESC is masking the exceeded limits, until its own corrective limits are exceeded).
I can tell you without a shadow of a doubt, that the car feels VERY different balance wise between Sport1 and Race.

Agreed plus I would add that sometimes even PTM Race will reduce my feeling of what the car is doing on corner exits so I usually prefer to drive with everything off to have a better feel for what the rear is doing but VIR is probably not a great track to try everything off for the first time due to high consequences for mistakes in some places.

Lately I have started switching to Sport 2 (from all off or Race) on hot days during the session whenever the tires start to get hot/greasy and slide more. I can hear the exhaust note change when Sport 2 is intervening most of the time but I usually can't tell when Race is intervening without reviewing the PDR video afterwards so I prefer Sport 2 in that situation plus it was designed for use on hot tires. I have also been experimenting with purposely inducing oversteer with abrupt throttle in slow low risk corners while in Sport 2 to rotate the car for a moment before PTM stops the slide but I need to compare data to see if there is actually any advantage from this.

[5.M0NSTER]

Fully agree with your comments here. I love the feel of the car in Race. Breakaway at the limits is progressive and communicative. Gives you plenty of heads up in most cases so you can counter steer or use the pedals to manage the weight transfer.

I usually stay in Race even with hot tires. It becomes more of a handful and I know Sport2 would be faster. I just like to slide and enjoy the Alpha chassis balance and rigidity.

[egslaw]

Thank you to all that answered. Unfortunately, your suggestions did not seem to work on my car so I'll be headed to dealer to try to resolve. Probably user error!

Originally Posted by MakCamaro

To lock in the right mode, simply use the mode up/down button on the center console. There is no need to press the SEL button on the right side of the steering wheel to enter it. If I recall correctly this has been discussed earlier in this thread.

[TrackClub]

Originally Posted by egslaw

Thank you to all that answered. Unfortunately, your suggestions did not seem to work on my car so I'll be headed to dealer to try to resolve. Probably user error!

Just to make sure: have you gone to the very first page of this thread? It has all the info in one single post and I have kept it pretty current. You may wish to read it and re read it again in necesssary and then practice on your car when stationary. Why? Because the chance is, that a dealer will be clueless - unfortunately. Not a dig towards hard working folks (some friends work that profession), but these cars are pretty rare and dealers do not get a chance to drive them at all, never mind setting them up. Also, maybe find some Youtube vids on how to set up PTM etc for visuals if you really have trouble. Fingers crossed for y either way. Cheers!

[TrackClub]

Originally Posted by cdrptrks

Agreed plus I would add that sometimes even PTM Race will reduce my feeling of what the car is doing on corner exits so I usually prefer to drive with everything off to have a better feel for what the rear is doing but VIR is probably not a great track to try everything off for the first time due to high consequences for mistakes in some places.

Lately I have started switching to Sport 2 (from all off or Race) on hot days during the session whenever the tires start to get hot/greasy and slide more. I can hear the exhaust note change when Sport 2 is intervening most of the time but I usually can't tell when Race is intervening without reviewing the PDR video afterwards so I prefer Sport 2 in that situation plus it was designed for use on hot tires. I have also been experimenting with purposely inducing oversteer with abrupt throttle in slow low risk corners while in Sport 2 to rotate the car for a moment before PTM stops the slide but I need to compare data to see if there is actually any advantage from this.

Very similar experience here: i am usually rather progressive with throttle and cannot really feel TC, especially in high speed sweepers. OTOH, in such corners, TC is of limited value imo and it is quite possible to completely lose the rear on exit due to high G forces and possibility of equally high yaw breaking traction. Anyhow, the GM engineer did a wonderful job describing benefits of different PTM modes and I can completely understand how Sport 2 would be better for hot rubber. TC is dynamically adjustable in many race cars for this very reason: tire deg. Having said that, like Monster above, I usually stay in Race (I tend to use Sport 1 only when giving rides to public). Cheers!

[wakespeak]

Wow until I read this thread I didn't realize how much traction control is part of the RACE setting in PTM. I had thought the eLSD was helping but no throttle management with some Stabilitrak.

I have been fighting the PTM. You can indeed mash the throttle when you don't think you can in RACE as it turns out. I have been modulating the throttle more then I have needed to, like at turn 19 at COTA which is easy to otherwise dangerously oversteer on throttle. I have just floored it on some occasions at the apex of turn 19 and thought the car was down on power because the tail didn't get loose..

Focusing on slip angles, opening up your hands is the right way to leverage the PTM in RACE. Aim for smooth, consistent racing line and let the car handle the throttle for the most part. The only exception is when the tires are close to "done" or they are cold. In those conditions sport 1/2 could be better if you are working with the PTM.

While that is safer I like ability to rotate the car with the throttle a bit more. Now that I understand better the PTM's intentions, it will be interesting next time.

[TrackClub]

Originally Posted by wakespeak

Wow until I read this thread I didn't realize how much traction control is part of the RACE setting in PTM. I had thought the eLSD was helping but no throttle management with some Stabilitrak.

I have been fighting the PTM. You can indeed mash the throttle when you don't think you can in RACE as it turns out. I have been modulating the throttle more then I have needed to, like at turn 19 at COTA which is easy to otherwise dangerously oversteer on throttle. I have just floored it on some occasions at the apex of turn 19 and thought the car was down on power because the tail didn't get loose..

Focusing on slip angles, opening up your hands is the right way to leverage the PTM in RACE. Aim for smooth, consistent racing line and let the car handle the throttle for the most part. The only exception is when the tires are close to "done" or they are cold. In those conditions sport 1/2 could be better if you are working with the PTM.

While that is safer I like ability to rotate the car with the throttle a bit more. Now that I understand better the PTM's intentions, it will be interesting next time.

Very well said! However, per my post above, it also depends how much slip angle one already carries out of mid corner. TC will not prevent big skip angles/yaw from exceeding traction. It just maximizes forward acceleration (preventing unnecessary tire over slip). Hence, if the slip angle is high, the car may still spin out on exit. Got caught a couple of times and needed to apply big and multiple corrections to keep it under control.
But, it all depends on how much speed one carries into a corner and especially in a mid corner phase. Cheers!

[wakespeak]

Originally Posted by TrackClub

Very well said! However, per my post above, it also depends how much slip angle one already carries out of mid corner. TC will not prevent big skip angles/yaw from exceeding traction. It just maximizes forward acceleration (preventing unnecessary tire over slip). Hence, if the slip angle is high, the car may still spin out on exit. Got caught a couple of times and needed to apply big and multiple corrections to keep it under control.
But, it all depends on how much speed one carries into a corner and especially in a mid corner phase. Cheers!

Thanks - yep RACE will still get you sideways. Its just that I now know why i didn't go sideways when I went to full throttle and thought I would.

[TrackClub]

Originally Posted by wakespeak

Thanks - yep RACE will still get you sideways. Its just that I now know why i didn't go sideways when I went to full throttle and thought I would.

Got ya! Just in case you have not read the very first post (since updated with all subsequent comments etc), check out the GM engineer's discussion about PTM, which I have included there. Very good stuff. Cheers and happy motoring!

[KirillWA]

Kudos to the author, this is such a great guidance, collected in one place.

I'm doing autocross, ~1 minute for a single lap, and PTM Sport 1 is my choice.

[TrackClub]

Originally Posted by KirillWA

Kudos to the author, this is such a great guidance, collected in one place.

I'm doing autocross, ~1 minute for a single lap, and PTM Sport 1 is my choice.

Thank you for your kind words sir!

If the car starts to feel a bit too tight during rotations, don't hesitate to try Race (after you get comfy with the balance overall). Cheers and have fun in your competitions!