Track report

[4play]

Originally Posted by Lienrocs

You could try running a little more pressure in the rear as well. They're big and heavy cars.

Completely different tire/suspension so I'm not sure how relevant it is but I was running around 32 pounds on A052's and the car didn't have the grip that it did with 38 pounds at all four corners.

I tried a range from 32-36psi on the rears without much success.

Fronts seemed pretty happy anywhere from 35-41psi.

It was tough to change pressures on the fly because we only had 30 min sessions and the track went from 41F/wet to 63F/dry across a few sessions. You couldn't stop in the hot pits, so any pressure changes in real time would have cost 1/2 the session.

And, as usual with a track day, two of the five 30 minute sessions were red flagged due to cars breaking.

[Secret Chimp]

Originally Posted by 4play

Fronts are 275/35/19 AMG GT R Sport Cup 2s, was running ~35 psi hot.

Rears are 305/30/20 458 Speciale Sport Cup 2s, was running ~32 psi hot.

Just a thought...If the tires you are using are truly specc'd for two different cars, even though both are Cup 2's, one might might be a softer compound than the other. If your fronts are a bit softer than the rears, that will upset balance on corner entry.

There seems to be general consensus that the Star spec Cup 2's that are OEM for the GTS are a bit harder than off the shelf Cup 2's. It's not too out there to believe that the tire manufacturer tweaks the compounds for other model-specific tires.

[FormulaMMM]

Originally Posted by 4play

I tried a range from 32-36psi on the rears without much success.

Fronts seemed pretty happy anywhere from 35-41psi.

It was tough to change pressures on the fly because we only had 30 min sessions and the track went from 41F/wet to 63F/dry across a few sessions. You couldn't stop in the hot pits, so any pressure changes in real time would have cost 1/2 the session.

And, as usual with a track day, two of the five 30 minute sessions were red flagged due to cars breaking.

Originally Posted by Secret Chimp

Just a thought...If the tires you are using are truly specc'd for two different cars, even though both are Cup 2's, one might might be a softer compound than the other. If your fronts are a bit softer than the rears, that will upset balance on corner entry.

There seems to be general consensus that the Star spec Cup 2's that are OEM for the GTS are a bit harder than off the shelf Cup 2's. It's not too out there to believe that the tire manufacturer tweaks the compounds for other model-specific tires.

It's true on the tires and Cup 2 vary substantially. Speciale spec should be ok, but keep in mind it was tuned to that car -- weight, dampers, etc. Accordingly, you might need to go outside of BMW recommended track damper specs to get the most out of that tire and it will never be a perfect fit.

I run Supercar 3R, but in "generic" sizing, so not tuned to the 1LE like Cup 2 K spec is to Speciale.

Suggest ride height is probably the main answer. then damper adjustments from there.

Mentioned my old E9X Fall Line track alignment. It wasn't livable on the street so we upped it probably similar to the difference between GTS street vs. track settings. It wasn't nearly as planted.

Apparently small differences can fundamentally transform handling on track.

[FormulaMMM]

Finally got the GTS out on track, been a full year. Was well behind the car for the first couple of sessions but after mind & muscle memory returned it was as rewarding and exhausting as ever. What a car. Proper, fire breathing track car.

No media this time, gopro still isn’t filtered right anyways. But a look at telemetry of two fastest laps to date for some findings. Shaved about 2/10ths this time out vs previous best last summer. No component changes, but damper adjustments.

Went into this track day with the primary goal of finding rear traction. The front has always been pinned, even before plates and while chunking original Cup 2’s, so no changes required there. The guidance/methodology here resonated with me http://speed.academy/which-way-do-i-...ers-hard-soft/ With starting point BMW recommended track spec, I adjusted:

+2 front rebound to 2 open. (To influence rear traction per that article’s recommendations.)
-4 rear rebound to 8 open. (With 16 clicks available, 8 open is the halfway point.)

+1 rear low speed compression to 0 open.
+3 rear high speed compression to 6 open. (This now equals the front high speed compression setting.)

Home track is by and large smooth, with just a couple of bumps that can unsettle the car. One rough exit curbing area in particular that’s bit me a handful of times even with the wheel fully unwound.

Takeaway is that the reduction in rebound has increased rear traction under power. I was getting to full throttle more sharply and confidently out of certain corners with the new settings. When the back end let’s loose now it’s more of a progressive, usable, E9X gen style, controlled power oversteer. Small amount of opposite lock, stay all the way in the throttle, and it digs out of the corner. And the unpredictable snap oversteer over that rough exit curbing is gone as far as I can tell.

On telemetry (orange line is the faster, latest lap) the sharper throttle pick ups are in the rectangles. Don’t think all of that was there for the taking before. Was also driving a different style at points – slower in, fast out, more square racing line that prioritizes straight speeds (circles). Can tell I’ve been retrained driving a rear-engine car for the past 12 months.

For those unfamiliar with telemetry, the time delta at each point in the laps is shown at bottom. Illustrates how different cornering approaches and vehicle setups can gain and lose tenths over the course of the lap.



So, softening rear rebound for more traction under power seems like the ticket to me. Downside: Maybe less corner entry stick and pace. If that’s accurate and it’s not me just being rusty and wimpy, probably a worthwhile exchange with the GTS’s power vs the sustained corner momentum approach.

Only thing I’d like to improve now is a reduction in some mid-corner oversteer in the track’s two third gear hairpins (50-60 mph). The back end gets twitchy under sustained load mid-corner. Maybe additional damper adjustments could assist, or just cheat and up the mechanical grip with some slicks…

Returning to the GTS one thing that really struck me – it’s damn near impossible to overdrive. It’s a better athlete than you are. Rewards aggression, seeking the limit more than any other car I’ve driven. Encourages you to drive to and expand driver limits as opposed to the car’s limitations. It’s a mental and physical driving challenge.

Few other notes:

Aim SOLO 2 LED’s quit about halfway through the day. Just stopped giving me the red or green according to +/- to day’s best and no +/- time delta on the screen either. Would just show each previous lap time the whole session. Not the first time it’s happened, don’t know cause. Lights are enabled in settings. +/- best screen just goes fully on the fritz. Rolling lap screen, everything else seems normal.

AP Racing kit + Ferodo continues to impress and deafen.

Buddy drove the GTS for a couple of sessions, emerged with that hair on fire look, concluded it was the most fantastic machine he’s every tracked.

Ran through a couple gallons of water, added some character to the paint, dusted up the orangeys.

[Gomeler]

Good stuff on trying to tame the rear. I don't have the car/my notes on me, but.. I think I settled on almost exactly the same settings you did in an attempt to settle the power oversteer coming out of 3rd gear corners. It's such a fun engineering problem, I wish I had more time to poke at it.

[FormulaMMM]

Originally Posted by Gomeler

Good stuff on trying to tame the rear. I don't have the car/my notes on me, but.. I think I settled on almost exactly the same settings you did in an attempt to settle the power oversteer coming out of 3rd gear corners. It's such a fun engineering problem, I wish I had more time to poke at it.

Nice, thanks dude. That’s good to hear. Think softening rear rebound holds water in theory & practice –

To the extent that low & high compressions are occurring, you’re slowing the damper’s reaction = less snap, less skittery, etc. Just an overall reduction in damper energy/nervousness. That's what the back end needs, to just chill out a bit. And with 16 clicks on offer that seems to imply a lot of adjustability.

Turns out my terrible in car footage is good for something – it captured that snap oversteer I was referring to in the latest update (0:50 – 0:53). I ran this same line over the bumpy exit curbing dozens of times with the softened rear rebound and didn’t experience this once last time out.

To test where softening might become counterproductive, I reduced rear rebound -2 more clicks midway through the day to 10 open. My impression (butt dyno fwiw) was that slowed the car’s reactions a bit too much in certain sectors, possibly cut down on front end bite and overall rotation, which is crazy considering the dynamics of other settings, i.e., ready to spin 360s…

Fun engineering problem for sure. 3 ways on your 235? Let me know if you find any sweet spots that you think could apply.

[MadM2C]

Curious on your best lap time at Gingerman and alignment specs?

[Gomeler]

Is that recording on the Goodyear SuperCar 3s? Moving from the Cup 2 to the Toyo RR reduced those micro-corrections coming out of every corner. Even with my prior adjustments I'm still seeking as you said: "more of a progressive, usable, E9X gen style, controlled power oversteer".

I think I was close, I was able to power through a lot of the tail wagging instead of having the car immediately snap oversteer. It's a rewarding platform when you set a PB, but it really makes you work for it.

I honestly have been under the M235iR once, and that was mostly to see if I could fit an 18x11(I don't think I can ). I believe it has non-reservoir 2-way KW coilovers. Starting on Monday I'll be tearing into it with the goal of getting it out to the track on the 27th or 28th of July. Just need to double check everything, mark some bolts, and flush the brakes.

[FormulaMMM]

Originally Posted by Gomeler

Is that recording on the Goodyear SuperCar 3s? Moving from the Cup 2 to the Toyo RR reduced those micro-corrections coming out of every corner. Even with my prior adjustments I'm still seeking as you said: "more of a progressive, usable, E9X gen style, controlled power oversteer".

I think I was close, I was able to power through a lot of the tail wagging instead of having the car immediately snap oversteer. It's a rewarding platform when you set a PB, but it really makes you work for it.

I honestly have been under the M235iR once, and that was mostly to see if I could fit an 18x11(I don't think I can ). I believe it has non-reservoir 2-way KW coilovers. Starting on Monday I'll be tearing into it with the goal of getting it out to the track on the 27th or 28th of July. Just need to double check everything, mark some bolts, and flush the brakes.

Yeah, all of the corrections are with Supercar 3R, OE sizes, stock wheels. The constant back end movement and corrections still aren't anywhere near gone from mid corner to corner exit. Just seems full throttle availability, that traction moment arrives earlier and more clearly now. And then no snap surprises after that.

Added rubber (and/or slicks) would help tame more for sure, and be faster. For now I'm stubbornly hanging onto the OE wheels and tire sizes because I sense that they contribute to the communicativeness, sharpness. The 20" in back in particular.

Agreed, it's a rewarding but massively challenging platform approaching the limit. No PB's by accident, you know you've been through it.

Look forward to following 235 progress, thing is sweet!

Originally Posted by MadM2C

Curious on your best lap time at Gingerman and alignment specs?

Alignment is just stock lowered ride height, plus GC camber plates at max -. Not sure how much more adjustability there is with all stock components front & rear.

Best so far is a 1:37.6 (telemetry above). Maybe there's a 36 in the car in spring/fall conditions if I slam a red bull and really put one together.

Experienced driver and in the area? Looking for some additions to make rent affordable sometime in the offseason. Let me know if you'd be interested and I'd be happy to message you if we put something together.

[CanAutM3]

Originally Posted by FormulaMMM

Finally got the GTS out on track, been a full year. Was well behind the car for the first couple of sessions but after mind & muscle memory returned it was as rewarding and exhausting as ever. What a car. Proper, fire breathing track car.

No media this time, gopro still isn’t filtered right anyways. But a look at telemetry of two fastest laps to date for some findings. Shaved about 2/10ths this time out vs previous best last summer. No component changes, but damper adjustments.

Went into this track day with the primary goal of finding rear traction. The front has always been pinned, even before plates and while chunking original Cup 2’s, so no changes required there. The guidance/methodology here resonated with me http://speed.academy/which-way-do-i-...ers-hard-soft/ With starting point BMW recommended track spec, I adjusted:

+2 front rebound to 2 open. (To influence rear traction per that article’s recommendations.)
-4 rear rebound to 8 open. (With 16 clicks available, 8 open is the halfway point.)

+1 rear low speed compression to 0 open.
+3 rear high speed compression to 6 open. (This now equals the front high speed compression setting.)

Home track is by and large smooth, with just a couple of bumps that can unsettle the car. One rough exit curbing area in particular that’s bit me a handful of times even with the wheel fully unwound.

Takeaway is that the reduction in rebound has increased rear traction under power. I was getting to full throttle more sharply and confidently out of certain corners with the new settings. When the back end let’s loose now it’s more of a progressive, usable, E9X gen style, controlled power oversteer. Small amount of opposite lock, stay all the way in the throttle, and it digs out of the corner. And the unpredictable snap oversteer over that rough exit curbing is gone as far as I can tell.

On telemetry (orange line is the faster, latest lap) the sharper throttle pick ups are in the rectangles. Don’t think all of that was there for the taking before. Was also driving a different style at points – slower in, fast out, more square racing line that prioritizes straight speeds (circles). Can tell I’ve been retrained driving a rear-engine car for the past 12 months.

For those unfamiliar with telemetry, the time delta at each point in the laps is shown at bottom. Illustrates how different cornering approaches and vehicle setups can gain and lose tenths over the course of the lap.



So, softening rear rebound for more traction under power seems like the ticket to me. Downside: Maybe less corner entry stick and pace. If that’s accurate and it’s not me just being rusty and wimpy, probably a worthwhile exchange with the GTS’s power vs the sustained corner momentum approach.

Only thing I’d like to improve now is a reduction in some mid-corner oversteer in the track’s two third gear hairpins (50-60 mph). The back end gets twitchy under sustained load mid-corner. Maybe additional damper adjustments could assist, or just cheat and up the mechanical grip with some slicks…

Returning to the GTS one thing that really struck me – it’s damn near impossible to overdrive. It’s a better athlete than you are. Rewards aggression, seeking the limit more than any other car I’ve driven. Encourages you to drive to and expand driver limits as opposed to the car’s limitations. It’s a mental and physical driving challenge.

Few other notes:

Aim SOLO 2 LED’s quit about halfway through the day. Just stopped giving me the red or green according to +/- to day’s best and no +/- time delta on the screen either. Would just show each previous lap time the whole session. Not the first time it’s happened, don’t know cause. Lights are enabled in settings. +/- best screen just goes fully on the fritz. Rolling lap screen, everything else seems normal.

AP Racing kit + Ferodo continues to impress and deafen.

Buddy drove the GTS for a couple of sessions, emerged with that hair on fire look, concluded it was the most fantastic machine he’s every tracked.

Ran through a couple gallons of water, added some character to the paint, dusted up the orangeys.

Great, something to geek out about

Looking at the telemetry data seems to point out that most of your gains were achieved under braking, with the slower entry speeds actually causing you to loose time. Further, could it be possible that your feeling of sharper throttle application is simply the result of slower apex speeds (less used lateral traction results in more available longitudinal traction)? Something to ponder.

[FormulaMMM]

Originally Posted by CanAutM3

Great, something to geek out about

Looking at the telemetry data seems to point out that most of your gains were achieved under braking, with the slower entry speeds actually causing you to loose time. Further, could it be possible that your feeling of sharper throttle application is simply the result of slower apex speeds (less used lateral traction results in more available longitudinal traction)? Something to ponder.

Thanks for geeking with me!

Definitely, where there are the sizable gaps in min corner speeds, that’s the case. Was driving a different style at points, rear-engine has apparently rewired me. But I do think the car was made more amenable to that approach with the damper adjustments. So, part my updated instincts, maybe also part my driving to suit the car, what it “wanted” to do.

The two corners that left the greatest impression were T1 (~750 mark on telemetry) and T6 (~4500 mark).

In T1, min speed was only about 1.5 mph slower, and I’ve been through there at both higher and lower speeds but can’t recall ever pinning the throttle quite that convincingly. It’s just a brief 3rd gear acceleration zone before braking for T2, but I was 3.5 mph up (telemetry above at the ~900 mark).

Check this out – here’s comparison to another reasonably quick lap. The difference in the brief T1 to T2 acceleration zone here is 4.7 mph despite equal cornering speeds.



And then for T6 (4500 mark) – just 1.5 mph difference in min cornering speed, but again a much stronger throttle application as shown by the steeper acceleration curve. The rough exit curbing of this corner is also where that snap oversteer used to occur, but I didn’t get that once this time around.

More testing required for conclusive findings, for sure. If I had the place to myself, I’d actually spin rear rebound 16 clicks to full open, run some laps, then set +16 to full closed. Just to get a strong impression of the different dynamics at both ends of the range.

I’m envious of the race teams that get to fiddle with dampers for hour-plus practice sessions. As opposed to 20 minute sessions, 20 cars on a 2 mile track... A 14 psi range intra-session complicates further with the GTS. To really make damper headway/conclusions I’d bring the tires up to pressure & temp with initial settings, run a couple of hot laps. Into the pits, adjust, out lap, 1-2 more hot laps, then repeat. Hopefully, I’ll have that chance at some point.

[JustAnothaM4]

Did you guys swap the the standard brake booster when going the AP Racing route? Any coding needed?

[FormulaMMM]

Originally Posted by Project M4GTS

Did you guys swap the the standard brake booster when going the AP Racing route? Any coding needed?

Nope.

[JustAnothaM4]

Originally Posted by FormulaMMM

Nope.

Interesting…I just finished the install and the pedal feel compared to CCB is is different.

[FormulaMMM]

Originally Posted by Project M4GTS

Interesting…I just finished the install and the pedal feel compared to CCB is is different.

That's true and to be expected, especially right after install. Very little bite. What pads? You'll need to bed to wake up the system, if you haven't already. See recommended guidance from AP Racing and pad manufacturer

[rcompound]

I have been using AP brakes for the past 3 years and AP brakes is one of the best decisions I have made with the GTS. The Ferodo DS 1.11 pads last, great initial engagement, no fade ever, and the best brakes I have ever had on a car including Porsche OE which I think is the gold standard.

I did not change the brake booster.

[JustAnothaM4]

Anybody going to the BMW CCA event at Road Atlanta this weekend?

[Buckeye///M]

Originally Posted by Project M4GTS

Anybody going to the BMW CCA event at Road Atlanta this weekend?

I’ll be there. Looking forward to seeing some F82’s at the track!

[JustAnothaM4]

Originally Posted by Buckeye///M

I’ll be there. Looking forward to seeing some F82’s at the track!

Hell yeah! See you there.

[schnell325]

Absolutely awesome to see the few GTSs in North America getting together!

[SYT_Shadow]

A couple more GTS will be joining the track world soon! Gotta represent!

[daveishi]

Just wanted to share a couple shots a friend got of me at Buttonwillow last weekend, thought they really highlighted the GTS features well!