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Seems you are overdue for new ball joints and bushings based on the service history. That bushing on the front strut arm does degrade and it has a big impact on dynamic toe. Since you are tracking, I’m going to assume you care about chassis dynamics. Going with balls would be better but you need to replace the ball joints too so get new arms, beat on the car and then upgrade the bushing to balls later.

you seem to be describing massive understeer, which is better than massive oversteer otherwise you’d be dead already. Your pads could be contributing this since the frictional coefficient in the front is different than the rear (if you’re running stock in the back). ABS thresholds and brake balance are set with stock pads so this could be part of the issue, but your tires may also be shot since there are only so many heat cycles the tire can take and then you just get crap for grip.
rear calipers were 100 F warmer than front thus know traction control is working with DWS tires on the wheels with pressure sensors
75-80% of all braking is done by the fronts, it’s true that the front brakes have better heat dissipation due to air flow, but 100F hotter in the rear is a not good, that’s a big difference. I could see the other way around very easily. It’s very likely the car is activating DSC while you are tracking because it’s sensing you have excessive under or over steer. Short rear pad life and hot rear brakes usually are a result of a lot of DSC intervention to yaw the car because it thinks you’re losing it. I’ve gone through an entire OE Rear brake pad down to the backing plate in 30 mins on test car on a track at the proving grounds. It was a Dodge Challenger, all nannies on the whole time. Beginning mileage was 700 miles. Stock M5 pads will hold up pretty well.

Do you drive it on track with no DSC? (I would not recommend this unless you’re really dialed in to the car the track and your skill level is up there). TC doesn’t make the rear caliper heat up, unless you’re doing massive powerslides, which TC would outright prevent that by cutting throttle and DSC would then brake one of the rear wheels to straighten out.
 

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Very informative
Stock rear pads but down 50% thickness which is usually when I throw them away since in my Brembo 4 piston caliper 928 too much heat gets transferred to pistons and fluid lots of boiling instances when pads too thin, they are insulators after all.

i drive in mDynamic mode in dry dsc in wet

till I know alignment , front end , rear shocks are good will not venture to everything off
 

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I had a tank slapper braking in wet previous event on Corsa tires With DSC on under braking

It seemed the rear tires were being braked out of sync with my steering corrections.

changed to mDynamic better under braking but worse under acceleration

still learning the car

perhaps turning everything off is the solution, let my raw driving skills shine through LOL

just remembered Corsa’s tires are 3/8 of an inch smaller in diameter than oem.
 

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Braking distances much shorter with Corsa tires
Better stick means more weight transfer
Thus brake balance closer to optimum with high bite dtc60 on front

stock worn low grip front tires do not allow the required weight transfer to front for dtc60 to be able to work in a balanced fashion with lower friction Stock rear pads
 

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80 min is a long time for one session no? I’d run out of fuel in the M5.

So that means DSC is always on, MDM just allows for greater yaw angle before intervening. That’s likely why you have 100F difference. You should also check or reset your steering angle sensor. If that is off by a few degrees then it can cause wacky DSC interventions, this is how the car knows what angle is commanded. Easy to do in ISTA.

an unbalanced car is a slow car and it can be very dangerous. You can’t drive fast if you do not have confidence in the car. OEs purposely dial in understeer otherwise it turns in to an 80s 911 Turbo. Are you a late braker?

DSC light should blink anytime it intervenes. Don’t look at the light though, that will make you slower for sure, use perhipeal vision.
 

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I started with a full tank of fuel , shifted at 7,000 instead of 8,200
Since I was the only guy on track the wet corner worker and track Marshal would have“reasoned” with me to let everybody go home once I came into pits. Thus dragged it out.
The other 18 Drive Club members (typically NASCAR caged Corvettes on Hoosier’s ) went home at lunch time before the rains came.
Strangly I did not see the vetted on track much thus in my dry morning sessions was only having to watch for caged 3 series BMW’s to let by

unlike HPDE events one gets 8 sessions 50 minutes long which is great.

I was watching for checkers or black flags since I had so many Aquaplaning moments at a 100+ mph on the 2 shorter Straights with elevation changes.
I still got to see 120 mph in the wet (15 mph down from 6.0 ) on front straight which is well drained and level.

One of the reasons I like this 3.2 mile track is in oder to fit in 23 turns the straights are relatively short thus feel comfortable with no Hans and 5 point harness.

While at VIR McLarens are hitting 190 mph at that speed protective gear does not add much to survival equation
 

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Yes I am a late braker went through a lot of Ferrodo pads in my 928 at Gingerman in the 1990’s but where only $75 from distributor back then.
Gave up on 928 boiled brake fluid to easily

m5 has reliable brakes just wished they made dct70 pads for it
 

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Discussion Starter #288
I run DTC60 on a dry track. Ever since I put them in they vibrate a lot under heavy braking. With my conti's I can engage the ABS at will for an entire session.

The DSC uses the rear brakes and will eat them alive 2to1. Turn off the DSC, P500 and drive. At higher speeds its a lot harder to get the car to over steer. If you shift less and keep the RPM's lower on corner exit that will help control the power as well.
 

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80 min is a long time for one session no? I’d run out of fuel in the M5.

DSC light should blink anytime it intervenes. Don’t look at the light though, that will make you slower for sure, use perhipeal vision.
Per my cell phone log I called the track general manager at 1:29 pm when I came back from lunch to ask if track is still open since no cars or trailers remained on site, a ghost town .
Then called my wife at 2:53 that I was heading out to come home.
In my time estimate I should have probably allowed a minute or 2 to get my car to garage 4 minutes to check brake temperatures 2 or 3 minutes to close up and head home in my other car
Let’s say a better track time estimate is 70 minutes.

Are you talking about the DSC light on lower part of center stack console area?

I was looking at dash for any flashing lights but could see none when on the Conti’s
 

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I run DTC60 on a dry track. Ever since I put them in they vibrate a lot under heavy braking. With my conti's I can engage the ABS at will for an entire session.

The DSC uses the rear brakes and will eat them alive 2to1. Turn off the DSC, P500 and drive. At higher speeds its a lot harder to get the car to over steer. If you shift less and keep the RPM's lower on corner exit that will help control the power as well.
I have zero vibration under braking when on Corsa tires , perhaps due to no flat spotting in 3,000 miles. I do not know the history of the 33,000 mile front Conti’s I think I will just throw them out , the soft side walls may hide flat spots if balanced well.
but flat spots are more noticeable under hard braking
Tire may also have internal damage, not going to chance running them at speed anymore

good tip on turning off dsc, I have a 6-speed manual
I guess P600 would be clutch less shifting
Got good at that in my past 1987 5.0 mustang
 

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So maybe you’re just getting ABS pulsation, I guess I’d not characterize it as vibration, but I can see it being described that way.
DSC (in non MDM) should intervene when you late brake since it senses the car is yawing but brake pedal pressure is high and you have steering angle dialed in. It simply prevents your attempt to trail brake, which is what it’s supposed to do, it’s braking one of the rears to reduce the yaw rate. MDM will allow reasonable trail braking.

In general, late braking is bad but kinda normal driver response. you will carry too much speed in the corner, miss your apex, and not have the car set up for exit and you won’t be able to get on the gas as quickly. It can take a long time to get it right and not over slow the car either, but slow in really is fast out. There’s a bigger penalty with a car this heavy. When you do drive with no DSC just make sure you are not excessively late braking. It’s not hard to go from understeer to oversteer when carrying too much speed into a corner. The S85 is weak on torque so power oversteer on exit isn’t a big concern.

It really helps that you’re always at the same track so you can nail down your brake and turn in points. They move as you get faster though. Since you have a 6MT there’s the additional complexity of downshifting, rev matching, clutch let out etc. If you drive the same way with MDM off you probably will spin, otherwise there’d be no reason for DSC to activate. Only street cars have DSC and ABS, so that’s why you have little company when it’s raining.
 

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If I am experiencing abs vibration that is the first time I have
no feedback in brake pedal.

the other thing is all cars I have driven to point of abs engaging the rate of deceleration eases up. That did not Happen rate of retardation still could be slightly increased with increasing pedal pressure.

The strongest deceleration is achieved modulating brake up to but not Into abs mode.
If abs was disabled one could do threshold braking achieving an even higher deceleration than abs assisted

Thanks, you gave me a lot to think about at the next event, confident once on Corsa’s all will be good even in the rain
 

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Ok I was assuming you had some serious vibration, it wasn’t clear to me that the major issue seemed to be poor front end grip under decel. Flat spotting or any tire/wheel vibration or imbalance issue would also be present when not braking. Same with wheel bearing. Flat spotting really isn’t a big thing anymore on modern steel or composite belted radials. A Hunter Roadforce balancer will diagnose that. Bad bushings, damaged control arm or bad ball joints can result in pedal and steering wheel feedback under aggressive braking. It’s the bushing when it goes away under light braking, since light braking won’t make the front toe-in. Warped rotors will always have pedal feedback at any level of brake effort.

It best to always wear your Hans when on track, it substantial reduces the risk of neck injuries anyone who’s ever been in an accident on a track never regrets having it on. I know I don’t. I switched to the Simpson one two years ago, and prefer it since doesn’t rely on dual shoulder belts, so it’s better for street cars that have standard 3 point belts.
 
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