Pulsing rear wheels with traction loss. New Diff and bearings same problem

[ryank382]

Hey all,

I've been trying to get to the bottom of this for over a year. I may have even posted about it before but nothing worked and I've come across some new information that may help.

Basically if I have traction fully off (NOT MDM) and im going straight, the moment I lose traction I get fast pulsing booming/banging noises similar to when you get wheel hop. I does not happen if the tail is sliding around a corner. Only when going straight. I had someone record whats happening from the outside in slow motion and as you can see the rate of spin of the rear wheels is changing back and forth or "pulsing"

I have a 6mt with solid rear subframe bushings, poly diff mounts, sways, Ohlin R&T coils and recently got a new OEM spec diff from diffsonline. Still having the issue. I really thought the diff was the problem.

I spoke to someone recently who suggested that maybe the ABS is messing around with it. and that maybe because I coded euro MDM in the car its confusing the system. Or when the steering angle sensor reads straight something happens with the traction control even though its fully off. IDK but really hoping for some insight and what I can do next to finally remedy this.

TIA

[Redd]

It looks to me that it's ABS/DSC related. It looks and sounds like ABS/DSC is pulsing the rear brakes for some reason. I'd try the following:

1. Undo whatever MDM changes/coding you made. Go back to stock.

2. Do DSC module reset.

Good luck and pls keep us posted.

[amrazM]

Whats your tire pressure in the rear? the rear wheels are not fully slipping, my car did the same thing with solid sf and poly diff bushings. I coded out tpms and dropped the tire pressure considerably to around 23psi iirc and it stopped doing it.

[MineralWhiteF80]

I think this is still considered "wheel hop" or a type of "tire shake", and 99% chance it's simply caused by the tire's ability to grip based on its tire pressure, pavement conditions, and the car's suspension geometry. It doesn't have anything to do with traction control or ABS intervening.

I've been down that rabbit hole before with my e90 M3, e92 M3, f80 M3, and f82 M4. My consensus is that ALL my cars have a tendency to do this in a lot of straight, off-the-line acceleration scenarios in first and second gears. And that is with stock suspension/lowering springs/coilovers and a lot of 200 or 300 treadwear tires. The only thing that really changes the wheel hop is tire pressures, suspension stiffness, and tire carcass temperature (hot tires tend to wheel hop less).

Edit: And just to add... there are so many factors that play a part in this annoying topic that it's hard to compare other peoples experiences to what your car is actually doing because car setups and conditions can be very different. For example, in my M4 with 590 whp, if I just floor it in 1st gear going 5mph, it will wheel hop like crazy and I think the rear subframe has left the vehicle, but if I'm in 3rd gear doing 50mph and floor it, the tires will light up once boost ramps in and the tire spin is super smooth. I can floor it 2nd gear at 30mph and sometimes it wheel hops bad and some times it's nice and smooth.

I bet if you unplugged all your wheel speed sensors or pulled DSC/ABS fuses you would still get this wheel hop.

[ryank382]

Originally Posted by Redd

It looks to me that it's ABS/DSC related. It looks and sounds like ABS/DSC is pulsing the rear brakes for some reason. I'd try the following:

1. Undo whatever MDM changes/coding you made. Go back to stock.

2. Do DSC module reset.

Good luck and pls keep us posted.

Ty will speak to my shop about undoing the coding and see if it helps. Will take some time to get in the shop unfortunately.

Originally Posted by amrazM

Whats your tire pressure in the rear? the rear wheels are not fully slipping, my car did the same thing with solid sf and poly diff bushings. I coded out tpms and dropped the tire pressure considerably to around 23psi iirc and it stopped doing it.

Originally Posted by MineralWhiteF80

I think this is still considered "wheel hop" or a type of "tire shake", and 99% chance it's simply caused by the tire's ability to grip based on its tire pressure, pavement conditions, and the car's suspension geometry. It doesn't have anything to do with traction control or ABS intervening.

I've been down that rabbit hole before with my e90 M3, e92 M3, f80 M3, and f82 M4. My consensus is that ALL my cars have a tendency to do this in a lot of straight, off-the-line acceleration scenarios in first and second gears. And that is with stock suspension/lowering springs/coilovers and a lot of 200 or 300 treadwear tires. The only thing that really changes the wheel hop is tire pressures, suspension stiffness, and tire carcass temperature (hot tires tend to wheel hop less).

Edit: And just to add... there are so many factors that play a part in this annoying topic that it's hard to compare other peoples experiences to what your car is actually doing because car setups and conditions can be very different. For example, in my M4 with 590 whp, if I just floor it in 1st gear going 5mph, it will wheel hop like crazy and I think the rear subframe has left the vehicle, but if I'm in 3rd gear doing 50mph and floor it, the tires will light up once boost ramps in and the tire spin is super smooth. I can floor it 2nd gear at 30mph and sometimes it wheel hops bad and some times it's nice and smooth.

I bet if you unplugged all your wheel speed sensors or pulled DSC/ABS fuses you would still get this wheel hop.

Thank you for responses but I've tried messing around with tire pressure already (23psi is really low i wouldnt go that low) but even on different roads, with different tire pressures, and even in rainy or wet conditions, i get the same symptoms consistently every single time in the same way. Traction fully off, WOT, going straight. and im not bouncing off the rev limiter lol

[nurburgracer]

Great video! Do you see this both rear wheels or just the left? What diff fluid are you running?

[MineralWhiteF80]

Originally Posted by ryank382

Thank you for responses but I've tried messing around with tire pressure already (23psi is really low i wouldnt go that low) but even on different roads, with different tire pressures, and even in rainy or wet conditions, i get the same symptoms consistently every single time in the same way. Traction fully off, WOT, going straight. and im not bouncing off the rev limiter lol

It's unlikely you will ever completely eliminate the wheel hop because these cars (and most independent suspension RWD cars in general) all have wheel hop problems, but some combinations of suspension components, tire compounds, suspension geometry (stiffness/alignment) are more prone to it than others. All you can try to do is minimize it as much as you can, mainly through suspension stiffness, tire compounds, and tire pressures.

Only video I can offer is the very first post on my Instagram in my F80 M3, totally stock other than lowering springs. If you listen carefully, you can hear the wheel hop through first gear. If the video quality was better and you slowed it down, it would look just like your youtube video:
add instagram dot com in front of this: /p/BauZNrRjAWi/?utm_source=ig_web_copy_link&igshid=MzRlODBiNWFlZA ==

[zdubz777]

Glad I haven’t done the solid subframe bushings yet. I was under the impression that was the best fix for this.

[ryank382]

Originally Posted by nurburgracer

Great video! Do you see this both rear wheels or just the left? What diff fluid are you running?

OEM fluid. I havnt physically seen the other wheel with my eyes but the sound and sensation is coming from both sides when inside the car.

Originally Posted by MineralWhiteF80

It's unlikely you will ever completely eliminate the wheel hop because these cars (and most independent suspension RWD cars in general) all have wheel hop problems, but some combinations of suspension components, tire compounds, suspension geometry (stiffness/alignment) are more prone to it than others. All you can try to do is minimize it as much as you can, mainly through suspension stiffness, tire compounds, and tire pressures.

Only video I can offer is the very first post on my Instagram in my F80 M3, totally stock other than lowering springs. If you listen carefully, you can hear the wheel hop through first gear. If the video quality was better and you slowed it down, it would look just like your youtube video:
add instagram dot com in front of this: /p/BauZNrRjAWi/?utm_source=ig_web_copy_link&igshid=MzRlODBiNWFlZA ==

It’s so weird because I’ve tried so many different variations of things and nothing has made it better or worse even slightly. It’s exactly the same symptoms. Before this car I had an F80 and I currently also own an M Roadster and neither of those cars has this problem. My f80 was on stock suspension, KW club sports and KW V3 and never had this problem. Super sports and potenza RE11s. But that’s a significantly more rigid and competent vehicle when it comes to chassis and suspension

Also from what I can see the insta vid is just your tires fighting for traction. I get a very concerning banging noise in the cabin

[ryank382]

Originally Posted by zdubz777

Glad I haven’t done the solid subframe bushings yet. I was under the impression that was the best fix for this.

Forgot to quote and respond to this. I read everywhere that people fixed their wheel hop with this solution that’s why I did it. It might still work for you. From what it seems like I’m dealing with a very unique issue

My schedule is so hectic but once I get a chance I’m going to stop by my shop to get the euro MDM or abs/DSC looked at.

[omgzirra_exe]

the coding has no affect to wheel hop...

also the ride height of the car plays a factor. the rear axle must be off its normal geometry, it probably struggling to correct its geometry under acceleration.

the downside to being that slammed in the rear you put more strain on th cv joints. wouldnt hurt to check them.

shove a gopro under your car facing one of the rear axles and you can probably see how it reacts under acceleration..

also zdubz777 still get it done, the benefit of the SSB is beneficial in more ways than none.

[nurburgracer]

Any update on this OP?

[amrazM]

have you inspected the ball joints and bushings on the rear control arms? this doesnt seem electronic

[DrFerry]

Originally Posted by ryank382

Hey all,

I've been trying to get to the bottom of this for over a year. I may have even posted about it before but nothing worked and I've come across some new information that may help.

Basically if I have traction fully off (NOT MDM) and im going straight, the moment I lose traction I get fast pulsing booming/banging noises similar to when you get wheel hop. I does not happen if the tail is sliding around a corner. Only when going straight. I had someone record whats happening from the outside in slow motion and as you can see the rate of spin of the rear wheels is changing back and forth or "pulsing"

I have a 6mt with solid rear subframe bushings, poly diff mounts, sways, Ohlin R&T coils and recently got a new OEM spec diff from diffsonline. Still having the issue. I really thought the diff was the problem.

I spoke to someone recently who suggested that maybe the ABS is messing around with it. and that maybe because I coded euro MDM in the car its confusing the system. Or when the steering angle sensor reads straight something happens with the traction control even though its fully off. IDK but really hoping for some insight and what I can do next to finally remedy this.

TIA

The mechanics of wheel hop / axle tramp requires quite a technical answer. I’ll do my best to be brief. Simply put; wheel hop results from the tire gripping the surface and loading the suspension, then losing grip and unloading the suspension. The forces and torques generated by the tire’s grip on the road (circumferentially and longitudinally) act to cause rearward weight transfer - as the vehicle ‘squats’ (compresses) down causing ride height to be reduced and dynamic alignment changes (gain negative camber and gain toe-in).

The first thing to keep in mind is the pneumatic tire has spring rates in the vertical, circumferential and longitudinal directions. All of these spring rates are affected by inflation pressure on the order of about 85%. A tire’s structural stiffness (i.e. without any air in it) is roughly 15% and results from the tire’s components such as its bead, carcasse body plies, steel and cap under tread belt architecture. Consequently, inflation pressure can play a big role in reducing wheel hop.

I see in the video the tire’s rate of rotation changes as the tire grips and then slips (un-grips) on the road surface. I can also see the road surface is slightly wet (more than damp). When the tire is in a state of gripping the road, the suspension and its bushings are loaded into compression and deflected respectively. Then the opposite happens when the tire un-grips, i.e. the tire slips, its rotational rate increases momentarily, and the suspension unloads (rebounds).

The large tractive forces generated by the tire are released when the tire slips and the suspension momentarily becomes unloaded causing the rear bushings to relax and the vehicle ride height to momentarily increase. You can think of this like a tight watch spring suddenly being released. This cyclic grip and un-grip (stick / slip) situation then repeats itself. The violence of the process causes the sub-frame bushings to move (compress and decompress) as well as the differential to move i.e. bounce around as its bushings are deformed. The banging you hear is quite possible the differential hitting the sub-frame housing, the trunk floor or both.

The torque from the drive shafts works to twist, or wind up, the tire (see photo of a drag tire below) because the tire has a circumferential stiffness and spring rate. When the tire slips and becomes less loaded, its sidewall height also increases slightly (a few millimeters) - further exacerbating the upward ‘jacking motion’ of the vehicle from its prior squatted position - and further adding to momentary forward weight transfer.

The shock absorber settings, tire inflation pressure, grip capacity of the tire, suspension design (anti-squat or not) bushing hardness and bushing deflection, all play a role in wheel hop / axle tramp. Each of the aforementioned must be addressed individually until wheel hop is reduced. I’m providing some links below, which explain the concept perhaps, better than I can. PS: It’s possible the E9X M3 uses anti-squat rear suspension link geometry, but I don’t know for sure.

Mitigation Suggestions:
1) Lower the rear tire pressures to increase tire contact patch size (adds grip). Suggest 28psi cold and work up from there (reduces handling and load carrying capabilities).
2) Reduce shock absorber bump setting (use softest bump = EDC Comfort setting) to aid rearward weight transfer at launch
3) Replace the OEM sub-frame bushings with solid bushings
4) Replace the OEM differential bushings with harder bushings
5) Use a stickier tire (UTQG tread wear <=100) - adds grip. (Drag radial or extreme summer tire).
6) Increase the rear shock absorber rebound setting (use hardest rebound). Only possible with double adjustable shocks

Wheel Hop – Causes, Effects and Cures
https://nasaspeed.news/tech/suspensi...cts-and-cures/
.
Wheel Hop Explained and Steps for Fixing
https://carnewscast.com/wheel-hop-ex...ps-for-fixing/
.
Wheel Hop Explained
https://execollection.com/2019/06/19...hop-explained/
.

.

[ryank382]

Originally Posted by nurburgracer

Any update on this OP?

Originally Posted by amrazM

have you inspected the ball joints and bushings on the rear control arms? this doesnt seem electronic

Sorry guys no update as of yet have been swamped with work and don’t have the technical experience to be able to inspect components and understand exactly what’s going on. For the record car only has 40-45k miles. I need to bring the car back to my shop

Originally Posted by DrFerry

The mechanics of wheel hop / axle tramp requires quite a technical answer. I’ll do my best to be brief. Simply put; wheel hop results from the tire gripping the surface and loading the suspension, then losing grip and unloading the suspension. The forces and torques generated by the tire’s grip on the road (circumferentially and longitudinally) act to cause rearward weight transfer - as the vehicle ‘squats’ (compresses) down causing ride height to be reduced and dynamic alignment changes (gain negative camber and gain toe-in).

The first thing to keep in mind is the pneumatic tire has spring rates in the vertical, circumferential and longitudinal directions. All of these spring rates are affected by inflation pressure on the order of about 85%. A tire’s structural stiffness (i.e. without any air in it) is roughly 15% and results from the tire’s components such as its bead, carcasse body plies, steel and cap under tread belt architecture. Consequently, inflation pressure can play a big role in reducing wheel hop.

I see in the video the tire’s rate of rotation changes as the tire grips and then slips (un-grips) on the road surface. I can also see the road surface is slightly wet (more than damp). When the tire is in a state of gripping the road, the suspension and its bushings are loaded into compression and deflected respectively. Then the opposite happens when the tire un-grips, i.e. the tire slips, its rotational rate increases momentarily, and the suspension unloads (rebounds).

The large tractive forces generated by the tire are released when the tire slips and [...]

I appreciate the detailed explanation and response. The video may have had damp asphalt but this happens regardless of road conditions and tire pressure. I’ve addressed the subframe and diff bearings and I run the same tire thousands of people run but don’t know a single example of a car with the same problem as me. I’m on Ohlin road and track coils and I can’t adjust rebound/compression individually. I’ve already decreased stiffness by 2 clicks but maybe that’s not enough. I’m still not convinced that is the issue though.