truffle shuffle under hard braking

[marksae]

Another possible cause could be toe changes as the rear suspension unloads, aka bump steer.

[bigjae1976]

When you go into the braking zone there's a distinct wiggle in the rear end that feels like its about the spin. Is that what you are talking about? I put the Stoptech BBK on and it was no more.

I never got to experiment but my theory (which I am confident to be true) is when the rear end squats, the rear suspension is supposed to toe in to provide stability under acceleration. So when you brake hard and take all of the weight off the rear, the suspension will toe out and cause that unstable feeling. Never got into on a different BBK thread...that is precisely the reason why a rear BBK is a big upgrade on this car.

Your E46 M3 was the opposite. When the rear end squats the rear toes out which is why you dial toe in on your static alignment settings.

If you look through my post history, I made the same mistake...you cannot apply the standard E36/E46 suspension formula to an E9X M3 in a lot of cases. I still find a lot of tuners and performance shops doing that. They recommend putting coilovers on...a standard E46 M3 approach...you really should be putting on a 4 wheel BBK first for the best improvement in handling.

[Sebringjetta]

Originally Posted by RickyBobby

Are those NT01's new?
Sounds like tread squirm. It goes away after two days of use.

approx. 2 days on them....

[Sebringjetta]

Originally Posted by bigjae1976;15560850When

you go into the braking zone there's a distinct wiggle in the rear end that feels like its about the spin. Is that what you are talking about?

that is exactly what im referring to....well i just bought a new f/r bbk....so will find out next month...thank you for the help my friend!!!!!!!!!!!!

[1MOREMOD]

Originally Posted by PrimeBMW

What you are describing sounds similar to what people experienced years ago when the first round of folks took their car to the track the E9* M3. Maybe some more will speak up. If memory serves me right it happened more often with lowering springs or even the first Dinan set ups. But with that said it is something that happens with the stock suspension when run with stickier tires and/or aggressive pad compounds. Sure you can drive around it, lower pressures, change pad compounds, etc... But I think it may be happening because the springs are a little soft and the nose is diving, thus there is less weight on the rear tires. Then the tail wags a little. Get some real coilovers with stiffer springs and it will most likely go away.........you know you want them anyway!

i would agree with this. i had same issue on stock e90 suspension. only happened on really hard braking zones. i always just drove around it after being used to such bad brake shudder from smoking my stock rotors early on this waggle seemed like nothing.

[skxf430]

What is the toe setting on your alignment?

[Sebringjetta]

Originally Posted by skxf430

What is the toe setting on your alignment?

-1.8 FRONT
-1.5 REAR

this will be more aggressive here next month after picking up a set of CO SUSP.

[skxf430]

Those are your camber settings.

What is the toe settings for the front and rear?

[Sebringjetta]

Originally Posted by skxf430

Those are your camber settings.

What is the toe settings for the front and rear?

ya sorry didnt read your orig quote correctly....ill have to look and see what the toe was...dont recall that off hand....

[skxf430]

Some cars like the Z06 need to run with a little toe in so under hard braking the car doesn't wiggle. You want to make sure you have a little toe in and not toe out.

[Sebringjetta]

Originally Posted by skxf430

Some cars like the Z06 need to run with a little toe in so under hard braking the car doesn't wiggle. You want to make sure you have a little toe in and not toe out.

will take a look thank you

[Triple M]

They recommend keeping the toe neutral upfront and definite a rear adjustable toe arm if the car is dropped. It also depends on the plane of the straight line, flat, downhill, uphill (COTA turn 1), crest straight (e.g before corkscrew at laguna seca, had a scary moment there in a spec Miata) or off camber straight. If it's a flat straight your problem will be somewhere between BBK/Alignment. Hence the suspension/brake setup difference for different tracks when it comes to the pros.

[bigjae1976]

Originally Posted by Triple M

They recommend keeping the toe neutral upfront and definite a rear adjustable toe arm if the car is dropped. It also depends on the plane of the straight line, flat, downhill, uphill (COTA turn 1), crest straight (e.g before corkscrew at laguna seca, had a scary moment there in a spec Miata) or off camber straight. If it's a flat straight your problem will be somewhere between BBK/Alignment. Hence the suspension/brake setup difference for different tracks when it comes to the pros.

I don't think the front suspension is the issue in this case although more front spring will help the weight transfer.

I'd also look at how you are braking. I think there are some instructors that teach you do not have to get on the brakes smoothly. In some cars, correct. In the E9X M3? Ain't no way.

I looked at my spec sheet, my rear toe was set at .10 toe in on each side...I think that's %. For reference, I run .12 on my E46.

[skxf430]

Toe in on the rear should help stabilize under hard braking.

[Sebringjetta]

Originally Posted by skxf430

Toe in on the rear should help stabilize under hard braking.

[Triple M]

Originally Posted by bigjae1976

I don't think the front suspension is the issue in this case although more front spring will help the weight transfer.

I'd also look at how you are braking. I think there are some instructors that teach you do not have to get on the brakes smoothly. In some cars, correct. In the E9X M3? Ain't no way.

I looked at my spec sheet, my rear toe was set at .10 toe in on each side...I think that's %. For reference, I run .12 on my E46.

+1
Tad bit toe in in the rear. Some instructor don't clarify that initial pressure on threshold breaking is "smooth heavy" 90% as opposed to "sudden slam" 100% (which would cause a full lock in a car without ABS). Braking by far is the hardest thing I've ever had to learn, and I'm still working on perfecting after all this years.

[SenorFunkyPants]

Originally Posted by bigjae1976

I looked at my spec sheet, my rear toe was set at .10 toe in on each side...I think that's %. For reference, I run .12 on my E46.

0.10 would usually be a function of a degree, in this case 10 minutes or 1/6 of a degree of toe in...(60 minutes in one degree)
I think the std spec for total rear toe in is 0.10' +- 0.12'
AIUI under acceleration the rear wheels tend to toe out so the ideal would be to have the rear toe set such that you get 0 degrees toe when accelerating (for zero tyre scrub) returning to toe in when off throttle and braking to stabilize the rear.
If you had one rear tyre toeing differently to the other then the rear tyres would tend to try to steer the car under braking (and acceleration). If the rear toe is out you would expect to see asymmetrical tyre wear between the two rear tyres.
Certainly in pre ABS 911s you didn't want to instantly "slam" on the brakes as the weight transfer to the front suspension rapidly compressed the front springs and then you got a sort of bounce back which momentarily reduced the weight over the front axle and caused the front brakes to lock up - don't know if you can get the same with the E9x M3.

[M3SQRD]

If you are talking about the front end skipping as you turn in while braking then these will address your problem:

http://store.bimmerworld.com/bimmerw...kit-p1860.aspx

I tried to address this issue by making single variable changes - alignment changes, rebound/compression changes, tire pressures, etc. - but nothing really addressed the problem until I installed the front lower control arm bearings. Now the car feels great while braking and starting to enter a corner because the car no longer has that skipping feeling toward the outside of the corner!

[bigjae1976]

Originally Posted by SenorFunkyPants

0.10 would usually be a function of a degree, in this case 10 minutes or 1/6 of a degree of toe in...(60 minutes in one degree)
I think the std spec for total rear toe in is 0.10' +- 0.12'
AIUI under acceleration the rear wheels tend to toe out so the ideal would be to have the rear toe set such that you get 0 degrees toe when accelerating (for zero tyre scrub) returning to toe in when off throttle and braking to stabilize the rear.

Yeah, not an expert on how to read the measurements. I get confused on that pretty easily.

BUT in regards to the rear wheels...I'm think the opposite is true under acceleration.

If you get the car sideways it VERY much wants to get straight once you get back on the gas. Many moons ago when I did a drifting practice, I had an ex-formula drift guy as an instructor. He took my car out and had a lot of trouble keeping it sideways which really surprised him...he was familiar with BMWs.

I think the car toes in when the rear squats. If you look at the rear suspension design it is quite different from the E36/E46. There's no lateral trailing arm in the E9X. And the E9X M3 toe arm is behind the axle unlike the E36/E46 which has the toe arm in front.

So the toe changes in the E9X M3 rear suspension should be the opposite. I can put my car on an alignment rack this weekend and see if this is the case. I'm quite curious.

If my theory is correct, the rear tires will toe outwards under braking.

Originally Posted by Triple M

+1
Tad bit toe in in the rear. Some instructor don't clarify that initial pressure on threshold breaking is "smooth heavy" 90% as opposed to "sudden slam" 100% (which would cause a full lock in a car without ABS). Braking by far is the hardest thing I've ever had to learn, and I'm still working on perfecting after all this years.

I think the common mistake that intermediate and newer advanced drivers make is throwing out the anchor every time they step on the brakes. Its the common transition going from I brake, I turn in, I step on gas to using the controls to balance the car through the turn.

Not saying that this is OP's issue but something to think about.

[leo95se]

Originally Posted by PrimeBMW

What you are describing sounds similar to what people experienced years ago when the first round of folks took their car to the track the E9* M3. Maybe some more will speak up. If memory serves me right it happened more often with lowering springs or even the first Dinan set ups. But with that said it is something that happens with the stock suspension when run with stickier tires and/or aggressive pad compounds. Sure you can drive around it, lower pressures, change pad compounds, etc... But I think it may be happening because the springs are a little soft and the nose is diving, thus there is less weight on the rear tires. Then the tail wags a little. Get some real coilovers with stiffer springs and it will most likely go away.........you know you want them anyway!

agreed.. its a common thing. disheartening but fun!

[SenorFunkyPants]

Originally Posted by bigjae1976

So the toe changes in the E9X M3 rear suspension should be the opposite. I can put my car on an alignment rack this weekend and see if this is the case. I'm quite curious.
If my theory is correct, the rear tires will toe outwards under braking.

It will be interesting to see what you get.
It would be an undesirable characteristic if the rear wheels did indeed toe out during braking...as that would make the rear less stable.

With 0.10' toe in on each rear wheel (total 0.20') you are nearly at the maximum of the stock total rear toe spec of 0.22' toe in.
I have 0.04' on each side of my (road car use only) M3 and that works really well for spirited driving even on very bumpy country roads.
Maybe might be worth trying something similar? Might help the car turn in a bit easier?

[Billj747]

Originally Posted by bigjae1976

When you go into the braking zone there's a distinct wiggle in the rear end that feels like its about the spin. Is that what you are talking about? I put the Stoptech BBK on and it was no more.

I never got to experiment but my theory (which I am confident to be true) is when the rear end squats, the rear suspension is supposed to toe in to provide stability under acceleration. So when you brake hard and take all of the weight off the rear, the suspension will toe out and cause that unstable feeling. Never got into on a different BBK thread...that is precisely the reason why a rear BBK is a big upgrade on this car.

Your E46 M3 was the opposite. When the rear end squats the rear toes out which is why you dial toe in on your static alignment settings.

If you look through my post history, I made the same mistake...you cannot apply the standard E36/E46 suspension formula to an E9X M3 in a lot of cases. I still find a lot of tuners and performance shops doing that. They recommend putting coilovers on...a standard E46 M3 approach...you really should be putting on a 4 wheel BBK first for the best improvement in handling.

I'm not sure i'd agree. Are you saying a F&R BBK would have a better (more forward bias) to fix the rear end wagging under braking?

When you had the issue and it was solved by the F&R BBK, did you use the same pads F&R pre and post BBK?

I still think the OPs issue is too aggressive of a rear pad for the stock brakes. Since he's going BBK, if he runs a less aggressive rear pad and/or if the caliper piston sizes are balanced and he runs the same pads F&R, I think his issue will go away.