[SEAT TIME RULES]

Originally Posted by kpaso

Wow, great to know.

I also wonder if people running -2.5 to -3 rear camber are more inclined to get this with less rear tire contacting the ground under heavy braking in a straight line?

That's a lot of Neg Camber in the rear of ANY BMW.

Unless you have to run that much for fender clearance I see no benefit going past 2.2-2.3.

Have you done pyrometer tests to dial in your camber front and rear yet?

I'm still dialing in my setup so I can't give any specific direction on a M2 yet, but the little I've tested at 2.0 seems close to optimal

[AWC-F87]

Originally Posted by SEAT TIME RULES

That's a lot of Neg Camber in the rear of ANY BMW.

Unless you have to run that much for fender clearance I see no benefit going past 2.2-2.3.

Have you done pyrometer tests to dial in your camber front and rear yet?

I'm still dialing in my setup so I can't give any specific direction on a M2 yet, but the little I've tested at 2.0 seems close to optimal

What do you mean pyrometer to dial In camber?

[tux2005]

Using a pyrometer to measure tire temps across the width of the tire, the camber should be ideal when the temps are equal across the entire tire. If the inside is hotter then there's too much camber and you're overheating the inside. If the centre of the tire was higher than either shoulder then too high of a tire pressure and it should be lowered (or the opposite if shoulders are hotter).

[AWC-F87]

Originally Posted by tux2005

Using a pyrometer to measure tire temps across the width of the tire, the camber should be ideal when the temps are equal across the entire tire. If the inside is hotter then there's too much camber and you're overheating the inside. If the centre of the tire was higher than either shoulder then too high of a tire pressure and it should be lowered (or the opposite if shoulders are hotter).

Thank you, I had a feeling that's what you meant but thank you for the explanation

[kpaso]

Originally Posted by SEAT TIME RULES

That's a lot of Neg Camber in the rear of ANY BMW.

Unless you have to run that much for fender clearance I see no benefit going past 2.2-2.3.

Have you done pyrometer tests to dial in your camber front and rear yet?

I'm still dialing in my setup so I can't give any specific direction on a M2 yet, but the little I've tested at 2.0 seems close to optimal

I don't personally run that much but I've seen some people post up some crazy camber numbers on here before.

[TUNEDM3]

Run a more aggressive brake pad compound in the rear then in the front to remedy the rear wag under heavy braking.

[SEAT TIME RULES]

Originally Posted by TUNEDM3

Run a more aggressive brake pad compound in the rear then in the front to remedy the rear wag under heavy braking.

THIS!!!

[SEAT TIME RULES]

Originally Posted by tux2005

Using a pyrometer to measure tire temps across the width of the tire, the camber should be ideal when the temps are equal across the entire tire. If the inside is hotter then there's too much camber and you're overheating the inside. If the centre of the tire was higher than either shoulder then too high of a tire pressure and it should be lowered (or the opposite if shoulders are hotter).

If you use a pyrometer make sure its the internal probe kind. Otherwise its crap.

Make sure you take the readings as soon as you exit the car in the pit area.

3 readings...Inside, middle and outside.

On street tires (RE71R's, Yoko A052's,) maybe 3.0-3.2 is ideal. On true R compounds like a Hoosier R7, BFG R1, NT-01 you will need more camber. Probably 3.3-3.5 degrees. I've been setting up BMW's for track and Solo 2 work for 20+ years now. This is assuming you have an decent aftermarket C/O setup and proper spring rates as well

[Got f1?]

Based on my limited track experience which is also limited to Mid-Ohio, I can say I have definitely encountered it on the back straight barking for the turn. Thats from about 135-140 down to 60 or so. Rear got really unsettled.

I have coilovers and track pads. What I found after talking to others at the track is that while rear toe can play a part, in my experience that weekend, it turned out to be the track. It eventually went away. Not sure if more rubber down did something or the heat of the day smoothed it?

For those that felt it, were you driving more than over a couple hours of the day? Several days, hot, etc?

[bentom2]

Originally Posted by Got f1?

Based on my limited track experience which is also limited to Mid-Ohio, I can say I have definitely encountered it on the back straight barking for the turn. Thats from about 135-140 down to 60 or so. Rear got really unsettled.

I have coilovers and track pads. What I found after talking to others at the track is that while rear toe can play a part, in my experience that weekend, it turned out to be the track. It eventually went away. Not sure if more rubber down did something or the heat of the day smoothed it?

For those that felt it, were you driving more than over a couple hours of the day? Several days, hot, etc?

I experienced it on tracks, multiple days at each track, throughout the days before I made a bunch of suspension changes and it largely went away, as I believe I mentioned earlier in this thread.

Before the suspension changes though, I did notice that straddling an asphalt seam in the braking zone made it worse, so was able to decrease the effect by getting all 4 tires on the same asphalt section, but it didn’t go away completely.

Also, the way I applied the brakes had an impact. A light initial application to transfer weight, followed by dropping anchor, decreased the effect quite a bit compared with going straight to max braking.

Based on my experience with straddling the seam, I can see how perhaps a differential in braking traction left to right on a green track could also lead to the tail wagging a bit more than once the tire rubber had been laid down on the line.

[richard in NC]

Originally Posted by bentom2

Also, the way I applied the brakes had an impact. A light initial application to transfer weight, followed by dropping anchor, decreased the effect quite a bit compared with going straight to max braking.

This! My braking points were sooner but my confidence went up. Not eliminated but less unsettled-ness....

[grinchmas]

I've had this issue and it was improved by popping in the Bimmerworld Front Upper Control Arm bearings. Also improves steering feel in my opinion as well!

[jmg]

Originally Posted by AWC-F87

I don't notice the wag under acceleration only hard braking.
Coming down the front straight of big willow at 140 and threshold braking into trailing for turn 1 it is not a good feeling having the car wag around.

I'm curious if anyone has felt a difference with suspension settings, stiffer/softer?

I may start looking into more rigid bushings as well.

I had this happen to me in my M3 CS on the front straight at Big Willow. Turned out my alignment was all out of whack. Front and rear camber and toe were off from each other left to right.

[AWC-F87]

Originally Posted by jmg

I had this happen to me in my M3 CS on the front straight at Big Willow. Turned out my alignment was all out of whack. Front and rear camber and toe were off from each other left to right.

Monday my car goes in for the spl parts install and a fresh alignment. I'm going to tell them to make sure everything is super square.

Many people don't realize how gnarly big willow is lol

[pal]

Originally Posted by TUNEDM3

Run a more aggressive brake pad compound in the rear then in the front to remedy the rear wag under heavy braking.

This ^^

I'm surprised nobody else mentioned this. Increasing the rear brake bias helps reduce the dive under braking and stabilizes the rear end. On my TT RS and prior to that in the Z4M Coupe (with StopTech 4 pistons all around), I ran a slightly more aggressive Cf pad in the rear.

Alignment and spherical bushing links are certainly a good idea for a heavily tracked car, but brake bias is part of the equation to stabilize the rear end.

Having tracked a Z4M and TT RS for the last 10+ years, I find the M2's wheelbase long. It's funny when I see posts calling it short. It's a big car and about the size of the e46

[jmg]

Originally Posted by pal

This ^^

I'm surprised nobody else mentioned this. Increasing the rear brake bias helps reduce the dive under braking and stabilizes the rear end. On my TT RS and prior to that in the Z4M Coupe (with StopTech 4 pistons all around), I ran a slightly more aggressive Cf pad in the rear.

Alignment and spherical bushing links are certainly a good idea for a heavily tracked car, but brake bias is part of the equation to stabilize the rear end.

Having tracked a Z4M and TT RS for the last 10+ years, I find the M2's wheelbase long. It's funny when I see posts calling it short. It's a big car and about the size of the e46

You can also corner balance the and adjust rake if you have coils, but IMHO those and brake bias are fixes to be done AFTER checking and fixing the alignment.

[pruettfan]

Sticky tires pretty much cures the issue. Once I started using Cup2 or equivalent that issue pretty much resolved itself everywhere but Laguna down the hill from turn 1.

[clutchdj]

Yes noticed this at the end of straight at thunderbolt towards the end of my last sessions. At the time was on mpss that I had cooked lol. I need a bit more toe in on the rear axle. Overall not frightening but I could feel it. On mp coilovers.

[asciimike]

Reviving this thread because I had this experience yesterday.

The rear wag is _really_ pronounced under high speed braking going from 130-140 to 70-80, and in a few cases I'm countersteering to handle it. Nothing unmanagable, but definitely unsettling when committing to high speed corners.

I run sport+ (not full DSC off), have euro MDM and am not seeing intervention, but haven't done any of the "magical" brake tuning discussed in a few of the other threads (e.g. https://f87.bimmerpost.com/forums/sh...php?t=1885341; though I admit I didn't experience the weird pedal inconsistency this time and don't think it's related).

I'm running 295 square RE71RS with -3.5 in the front and somewhere between -2.5 and -3 in the rear. Brake system wise, my day yesterday was with Ferrodo DS 3.12s and Ti shims, with stock rotors/calipers.

I've also got rear toe links, and had to play around with them for stability (I had some serious acceleration instability issues until I played with rear toe a bit more--potentially I have to keep going on this to solve the tail wagging?)

I experienced this with Hawk DTC-60s and no front spherical bearings on AO52s, so I don't think it's tires or pads.

My mechanic thought it might be tire pressure related (too high in the rear) or toe related. It decreased a bit over the course of the day (as I dialed in my tire pressures better), suggesting environmental conditions, though also may have been changes in my driving style.

Any other thoughts? Keep playing with rear toe? Any other ways of adjusting brake bias in software (or in the brake system), as I can't really add grippier pads in the rear (or maybe I can if I switch mfgrs?).

[D.Yooras]

Originally Posted by asciimike

Reviving this thread because I had this experience yesterday.

The rear wag is _really_ pronounced under high speed braking going from 130-140 to 70-80, and in a few cases I'm countersteering to handle it. Nothing unmanagable, but definitely unsettling when committing to high speed corners.

I run sport+ (not full DSC off), have euro MDM and am not seeing intervention, but haven't done any of the "magical" brake tuning discussed in a few of the other threads (e.g. https://f87.bimmerpost.com/forums/sh...php?t=1885341; though I admit I didn't experience the weird pedal inconsistency this time and don't think it's related).

I'm running 295 square RE71RS with -3.5 in the front and somewhere between -2.5 and -3 in the rear. Brake system wise, my day yesterday was with Ferrodo DS 3.12s and Ti shims, with stock rotors/calipers.

I've also got rear toe links, and had to play around with them for stability (I had some serious acceleration instability issues until I played with rear toe a bit more--potentially I have to keep going on this to solve the tail wagging?)

I experienced this with Hawk DTC-60s and no front spherical bearings on AO52s, so I don't think it's tires or pads.

My mechanic thought it might be tire pressure related (too high in the rear) or toe related. It decreased a bit over the course of the day (as I dialed in my tire pressures better), suggesting environmental conditions, though also may have been changes in my driving style.

Any other thoughts? Keep playing with rear toe? Any other ways of adjusting brake bias in software (or in the brake system), as I can't really add grippier pads in the rear (or maybe I can if I switch mfgrs?).

Proper track driving should be done with DSC off, especially for evaluation of weird issues like this, there are just too many variables to deal with to pin point the problem with DSC on at any level. That said there are a few very important factors here:

1) CAMBER THRUST: Your alignment should have done with driver ballast in the car to ensure rear camber is the same side to side when driving. If there is much of a deviation in rear camber you can be experiencing camber thrust both under braking an acceleration.

2) ALIGNMENT ANGLES: Too much camber makes the problem worse, rear toe should be set to static toe in of somewhere around 3-6mm. Any less and toe can get negative (toe out) under braking, much more and you'll have trouble putting down power exiting slow speed corners. Side note, be very careful with adjustable controls in the rear end of this chassis, changing the length of the arms relative to the factory arms will change far more than just basic alignment angles. Do not ever allow the arms to be different lengths side to side as that will change the dynamics of each side during suspension travel.

3) DSC EMERGENCY BRAKING: The goal of DSC is to make the car safe to drive on public roads. That's not to say you can't use it on the track but there are aspects of it that work well on the road that won't work on the track. In particular, the emergency braking parameter referred to in the other threads does a few things, like changing the brake pedal position and stroke required to achieve max braking, but it also changes the brake force distribution to individual wheels. This increases stability and maximizes straight line braking which in turn reduces the braking distances of emergency stop benchmarks. This benchmark is very important for the European market, especially in German with the Autobahn roadways.

It's highly likely heavy braking at the track is activating this parameter and causes the ABS modulator to minimize the yaw during braking to keep the rear axle in line with the front one. It does this through changing the brake force distribution to each wheel to achieve minimal yaw, great for the road, bad for the track. This is especially true in corners that require braking while turning where the system will be continuously "hunting" for the best braking force to keep the back end going "straight."

[Daytona_550]

I have experienced the same tail wagging on very hard braking. I think my biggest problem might be too much front brake bias because I run AP front brake kit and stock rear calipers (all four on Ferodo DS1.11 pads). I suspect nannies are working overtime to keep braking in the rear even, and the side to side rear brake application leads to the wagging tail.

Might be in the market for an AP kit for the rear in the near future.

[bentom2]

Originally Posted by Daytona_550

I have experienced the same tail wagging on very hard braking. I think my biggest problem might be too much front brake bias because I run AP front brake kit and stock rear calipers (all four on Ferodo DS1.11 pads). I suspect nannies are working overtime to keep braking in the rear even, and the side to side rear brake application leads to the wagging tail.

Might be in the market for an AP kit for the rear in the near future.

I run the same brake setup and have used 1.11 in the past.I also drive both with and without stability control depending how I’m feeling, conditions, and familiarity with the track.

The tail wag went away after I changed out the front torque arm bushings, rear toe links, and installed coilovers. I did them all at once, so couldn’t tell you which actually was the cause, but the car has been stable under hard braking since.