Grinding Noise from rear on track driving

[sanename]

Howdy everyone!! First time poster but have been following this forum. I have a 2018 F80 M3 6MT which I started tracking since last year (5 events) and hooked on to it. This year I made some changes to the car Ohlins R&T coilovers + carbotech Brake pads + Continental ECF 275/35/18 square setup (brand new TA5R wheels and tires).

I was at PittRace last weekend and after couple of aggressive laps the car started having grinding noise coming from the rear. Happened at turn (12/13/14 section), I pitted and checked everything, went back in and had the same issue started at the same section. I switched back to stock wheels, the car ran fine without any issues. The ECF wheels do not have TPMS, could this be causing the issue? I checked for code and see that there is error code 4829F, Wheel acceleration sensor - rear right - sensor 4 -- value - implausible. The wheels and tire are brand new so no bends or issues with them.

This happened to me once more in VIR last month and when i bring the car to the paddock turn it off and restart everything was fine. I had the car throughly inspected by quantum speedworks at VIR and they could not find anything wrong with it. I ran with the ECF wheels but had no issues on day 2 but since it had rained that day, i was easy on the laps.

Any idea what could be going wrong, the car runs fine with stock wheels. Do I need TPMS on the track wheels?

Any guidance would help. Thanks!

[M3SQRD]

Originally Posted by sanename

Howdy everyone!! First time poster but have been following this forum. I have a 2018 F80 M3 6MT which I started tracking since last year (5 events) and hooked on to it. This year I made some changes to the car Ohlins R&T coilovers + carbotech Brake pads + Continental ECF 275/35/18 square setup (brand new TA5R wheels and tires).

I was at PittRace last weekend and after couple of aggressive laps the car started having grinding noise coming from the rear. Happened at turn (12/13/14 section), I pitted and checked everything, went back in and had the same issue started at the same section. I switched back to stock wheels, the car ran fine without any issues. The ECF wheels do not have TPMS, could this be causing the issue? I checked for code and see that there is error code 4829F, Wheel acceleration sensor - rear right - sensor 4 -- value - implausible. The wheels and tire are brand new so no bends or issues with them.

This happened to me once more in VIR last month and when i bring the car to the paddock turn it off and restart everything was fine. I had the car throughly inspected by quantum speedworks at VIR and they could not find anything wrong with it. I ran with the ECF wheels but had no issues on day 2 but since it had rained that day, i was easy on the laps.

Any idea what could be going wrong, the car runs fine with stock wheels. Do I need TPMS on the track wheels?

Any guidance would help. Thanks!

Did you have edc before installing the R&T? I’m asking because an acceleration sensor is for edc input to the edc controller which determines how much damping force should be applied. Did you tie it somewhere that it could get pulled on and/or be hit by the tire? It has nothing to do with TPMS.

[sanename]

Yes, I had EDC before and I used the EDC cancellation kit when I installed the coilovers. I did check if the wire is getting in the way, everything looks fine

[dvas]

Agree that this has nothing to do with TPMS. I run without the TPMS sensors in my track wheels without issue.

I think it's interesting that you get the noise with the track wheels but not the stock wheels. Do you pull a lot less G's on the stock setup compared your track setup? Do you notice the noise in both left and right turns? What mode do you run the car in?

I would try to conclusively rule out that the track wheels and the general track wheel setup as being the culprit. Start with the easy stuff and make sure there is no rubbing inside the wheel wells. Check the wheels for trueness (I understand that they're new but you never know), as well as, spacers or studs that you may be running. Check your wheel bearings as well and rear suspension components to ensure they are true and everything is torqued. If none of that seems to be an issue, perhaps it has something to do with the diff.

[SYT_Shadow]

nothing to do with TPMS for sure

You describe 'grinding', but if there's no metal to metal contact on the wheel-car you may need the friction washers.
That it goes away changing wheels tells me it's either physical rubbing, which you should be able to see on the wheel easily, or you need the washers:
https://www.fcpeuro.com/products/bmw...BoC1XAQAvD_BwE

[sanename]

Originally Posted by dvas

Agree that this has nothing to do with TPMS. I run without the TPMS sensors in my track wheels without issue.

I think it's interesting that you get the noise with the track wheels but not the stock wheels. Do you pull a lot less G's on the stock setup compared your track setup? Do you notice the noise in both left and right turns? What mode do you run the car in?

I would try to conclusively rule out that the track wheels and the general track wheel setup as being the culprit. Start with the easy stuff and make sure there is no rubbing inside the wheel wells. Check the wheels for trueness (I understand that they're new but you never know), as well as, spacers or studs that you may be running. Check your wheel bearings as well and rear suspension components to ensure they are true and everything is torqued. If none of that seems to be an issue, perhaps it has something to do with the diff.

It happened on a fast speed right turn but the noise exist once it started. I run everything in comfort mode, ohlins are set at 10 clicks, checked the wheels and there seem to be no rubbing or dent. Will get the balance checked on them and the rear suspension

One thing I am suspecting is the issue with diff bushing mentioned in this video

[sanename]

Originally Posted by SYT_Shadow

nothing to do with TPMS for sure

You describe 'grinding', but if there's no metal to metal contact on the wheel-car you may need the friction washers.
That it goes away changing wheels tells me it's either physical rubbing, which you should be able to see on the wheel easily, or you need the washers:
https://www.fcpeuro.com/products/bmw...BoC1XAQAvD_BwE

Grinding doesnt feel like metal to metal contact but more of a vibration coming from the back as if the diff is low on fluid

[dvas]

Originally Posted by sanename

It happened on a fast speed right turn but the noise exist once it started. [/url]

I'm not sure what you mean by this.

Originally Posted by sanename

I run everything in comfort mode, ohlins are set at 10 clicks, checked the wheels and there seem to be no rubbing or dent. Will get the balance checked on them and the rear suspension

One thing I am suspecting is the issue with diff bushing mentioned in this video

If you are running in comfort mode on track, I presume that you are not advanced/instructor/etc. It's of course not a dig as we all start as green novices and build from there. But the takeaway that is important is that you are probably not pulling max Gs in the corners, and yet you are still getting the grinding noise in the rear. I personally would want to address the issue before going back on track as I've seen more than one car end up in a wall after loosing a wheel and have myself had to cut track days short due to broken studs on more than one occasion.

It still seems fishy to me that your OEM wheel/tire setup doesn't produce the same issue. But, if you've had your track wheel/tire setup checked, wheel bearings, and suspension components (by a repudiable shop as some places really could not care less - or gloss over - on this sort of thing - I've had Ferraris show up to FCA track events with 1mm of front brake pads and with a shop signoff), then possibly it does have something to do with the diff and/or subframe - though I lean that this is unlikely. If after checking all of the aforementioned easy stuff, you still have this issue unresolved, I would suggest to contact BMW USA directly and have a conversation with them. . I've had good luck with them working with me to resolve known issues (even those not under warranty or recall) when I've just been encouraging of my multiple BMW ownership and the BMW brand. Perhaps, with the right conversation, BMW USA would be willing to comp you a diagnosis at one of the dealers.

[sanename]

Update on this, i got the car inspected and nothing seems to be wrong with the car itself. The wheels needed to be balanced hopefully that might be the cause of the vibrations.

I may have used the wrong word (grinding), it is more of a execssive vibration than grinding, no metal to metal contact, the wheels are not rubbing with anything. I will get the friction washers syt_shadow mentioned.