[ozmartini]

Hey guys, recently noticed new wheel hop in my car. 2021 M2C, bought it new, have had it for 16 months now, around 14k miles. Around 2 months ago noticed I started getting wheel hop on my winter wheels/tires which used to break away smoothly...figured its probably just a problem with my winter set. Put on summer tires (entirely stock setup) and it's still getting wheel hop instead of breaking away smoothly. Just back in October car was breaking traction smoothly; now it hops all over the place. The car does need an alignment since someone hit the front wheel back in December; could that be the issue? I really know nothing about suspension in general so any advice would help, thanks!

[M2C-NLUSA]

Originally Posted by ozmartini

Hey guys, recently noticed new wheel hop in my car. 2021 M2C, bought it new, have had it for 16 months now, around 14k miles. Around 2 months ago noticed I started getting wheel hop on my winter wheels/tires which used to break away smoothly...figured its probably just a problem with my winter set. Put on summer tires (entirely stock setup) and it's still getting wheel hop instead of breaking away smoothly. Just back in October car was breaking traction smoothly; now it hops all over the place. The car does need an alignment since someone hit the front wheel back in December; could that be the issue? I really know nothing about suspension in general so any advice would help, thanks!

It's a known issue with the 2 series. You're not alone in having it.

[ozmartini]

But is this something that can be fixed? I was just gonna take it to the dealer to do the alignment, would they be able to do anything about it?

[Up4speed]

wheel hop is exaggerated by many variables. As tires age, they tend to get harder, and thus more wheel hop. Also, a summer tire will hop more in cold weather. Certain tire brands do it more.
When I had old Pirellis on one of my cars, they would hop so bad that it would scare me on a slow sharp turn (ackermann effect). It completely went away when I put new Michelin MP4S on (by the way, MP4S do it less than PSS)
Tire pressures, and street surface also has some effect.
So realistically, what I'm trying to say is that tires will do this, and it's hard to narrow down why it happens. Wheel alignment isn't generally one of the reasons, as far as I know.

[DanG]

I have only experienced wheel hop on wet roads when I accelerate too fast.

[ozmartini]

Originally Posted by Up4speed

wheel hop is exaggerated by many variables. As tires age, they tend to get harder, and thus more wheel hop. Also, a summer tire will hop more in cold weather. Certain tire brands do it more.
When I had old Pirellis on one of my cars, they would hop so bad that it would scare me on a slow sharp turn (ackermann effect). It completely went away when I put new Michelin MP4S on (by the way, MP4S do it less than PSS)
Tire pressures, and street surface also has some effect.
So realistically, what I'm trying to say is that tires will do this, and it's hard to narrow down why it happens. Wheel alignment isn't generally one of the reasons, as far as I know.

So you're saying it's probably just the tires? I want to believe that but the fact that it started doing this on my winter tires and has now carried on to my summer tires makes me think it's something else.

[Telluride]

Does DSC exacerbate wheel hop? It's happened a few times on my car but always when I'm in MDM mode. I've not experienced when driving with DSC off. Guessing the difference is from MDM limiting how much/how long wheel spin can go on... and how this may help rear tires to alternate between grip and spin.

For any engineers/techs, wheel hop cannot be a surprise to BMW. How much of this can the drivetrain handle on a prolonged basis? I'm never searching for wheel hop... rather thinking about the strain put on the drivetrain, drive shaft, rear end, etc. when it has happened.

[ozmartini]

Originally Posted by Telluride

Does DSC exacerbate wheel hop? It's happened a few times on my car but always when I'm in MDM mode. I've not experienced when driving with DSC off. Guessing the difference is from MDM limiting how much/how long wheel spin can go on... and how this may help rear tires to alternate between grip and spin.

For any engineers/techs, wheel hop cannot be a surprise to BMW. How much of this can the drivetrain handle on a prolonged basis? I'm never searching for wheel hop... rather thinking about the strain put on the drivetrain, drive shaft, rear end, etc. when it has happened.

Honestly I haven't tried breaking traction with DSC completely off; only in MDM. Generally I don't hoon around too much, but it's just jarring when you try to and the car behaves completely differently than it used to. It's still pretty cold out though, and it could be I'm just prematurely worrying about this; I was just wondering if it does become a problem if it's something you can fix.

[(K)]

I was just going to ask what settings you normally drive in. I consider myself fairly competent with my footwork but I can never get Sport+ to be smooth on anything but smooth roads. Sport+ throttle feels like an all or nothing affair and it feels like it fights the stability control rather than cooperate with it.

[Up4speed]

Originally Posted by ozmartini

So you're saying it's probably just the tires? I want to believe that but the fact that it started doing this on my winter tires and has now carried on to my summer tires makes me think it's something else.

It's really hard for me to say, especially not being in the car. As I mentioned, it can be so many things, and probably a few more that I forgot about, or didn't know about. So, realistically, all I am saying is that you don't need to jump to conclusions that there is a legitimate problem, but I'm also saying that it may be a problem (other than tires) as well.
Unfortunately, I'm saying a lot of nothing! lol
But I can say, that in my experience, it was always the tires when I had a problem with wheel hop in any of my cars.

[David1]

Every recent BMW I have owned has had wheel hop. Normal operation for rear wheel drive cars with independent rear suspension.

[MMMBRAP]

My car is bone stock and this happens to me, and I don't even track the car, or go nuts with it. Doubt that this is something that can be "fixed".

[Moflow]

I agree with David and MMMBRAP. My 350Z had wheel hop roughly as bad as this car. I live in the northwest where its wet most of the time and wheel hop is just a thing that happens if you want independent rear suspension. It's annoying, but you just learn to drive around it.

[agent_orange]

Generally the sure way to eliminate wheel hop in any independent rear rwd car is to have all spherical bearings in the rear suspension, i.e. no elastomer bushings, and a solid mounted diff. And by solid I don't mean firmer rubber or poly bushings.
Whether this is practical for a street car or not is a whole other matter though.

[bitcore]

Originally Posted by agent_orange

Generally the sure way to eliminate wheel hop in any independent rear rwd car is to have all spherical bearings in the rear suspension, i.e. no elastomer bushings, and a solid mounted diff. And by solid I don't mean firmer rubber or poly bushings.
Whether this is practical for a street car or not is a whole other matter though.

From what I understand, agent orange is right, and this is probably the best path to go down to really resolve the issue. Deflection and "wind-up" in the suspension, subframe, diff, driveshaft and axles themselves is actually most of the cause of wheel hop in the first place. And we all know that BMW likes to rubber-mount damn near everything under the car body. Everything is a spring, to some degree, with the right amount of load.

Under load, the entire suspension deflects and distorts - not only along the axis of the rear springs and shocks (squat), but in complex ways where it compresses/twists control arms/loads bushings. Drive axles twist and "wind up" like a torsion spring. Compliance in the tire rubber tread/sidewall itself also contributes to this stored energy.

Taking a look at what wheel hop IS, you can then see ways to reduce it: Once the tire loses traction under forward thrust, grip 'falls off the cliff', and this stored energy in the entire suspension/driveline is rapidly released until the energy is fully released, where wheel speed slows down enough for grip to suddenly restore. The lose-grip/restore-grip process repeats at a resonant frequency according to all of the components involved, and tends to amplify pretty badly to where you feel/hear the juddering and risk breaking something. One way to stop the hop is powering through it to get wheel speed up incredibly high, but you'll often break something on the way there (spider gears, pinion, axles, CV joints, diff case... It's really violent and these parts are not cheap)

It's a complicated problem with many variables. Some are easier to control/adjust than others. Pretty much every thing you can do to mitigate the issue seems to really be about either changing the resonant frequency of the wheel hop, or reducing the ability of the suspension system itself to store energy as an elastic spring at all (exclusive of the actual spring/damper)

• Make the suspension/driveline components so stiff that there is no elastic wind-up in the suspension (Replace bushings with bearings, solid mounts for subframe/diff mounts, upgrade axles/half-shafts to be beefier and thusly store less energy as a torsion spring)
• Change the grip characteristics of the road surface or tire: change air pressure, change tire compound, change tire size, change wheel diameter, change alignment [A LOT such that it's not a practical option], change the surface you are driving on (go somewhere else, add grip modifiers like drag strip prep or wet the surface with water)
• Apply something to dampen the effects: Adjust springs/shock combination to help reduce the severity or change resonant frequency
• Add or subtract mass from unsprung weight to help change the resonant frequency: change wheels, different brakes, lighter/heavier control arms, etc.

On some cars, it can be super easy and well-known "fix"... But on M2's I think it's a more complicated problem to "solve" since so many of the rear axle components are suspended with rubber bushings, which add elastic compliance, and thusly store energy like a spring does. I haven't heard of many simple success stories. I'd love to know if there's a few really nice bang-for-buck "fixes" on our platform.

Personally, my desire to fix this is for having fun, not really for accelerating from a dig, not for drag, and not for track racing. General hooning. If I want to lay some rubber, I typically have to get the thing sliding sideways so that the tires are always past the grip-cliff in a vector that is very stiff (sideways!), and the problem goes away. Breaking traction in a straight line usually causes crazy hop and I have to back out immediately, which is no fun!

[Bumpinjeep]

Or, just wait until the weather gets warmer. Over in the PWN, it's still in the 30s at night. Tires get harder the colder it gets and lose contact with the pavement. Wait until it's in the 60s or warmer, warm up the tires properly and try it again. I would bet you wont get any hop and will be happy again.

[Telluride]

Originally Posted by bitcore

From what I understand, agent orange is right, and this is probably the best path to go down to really resolve the issue. Deflection and "wind-up" in the suspension, subframe, diff, driveshaft and axles themselves is actually most of the cause of wheel hop in the first place. And we all know...

Both educational and plenty of food for thought. Thanks for taking the time and chiming in.

[Wolfman’s Brother]

Originally Posted by bitcore

I typically have to get the thing sliding sideways so that the tires are always past the grip-cliff in a vector that is very stiff (sideways!), and the problem goes away. Breaking traction in a straight line usually causes crazy hop and I have to back out immediately, which is no fun!

This is my experience as well. Light wheel spin in a straight line hops like mad. Sideways, smooth as butter.

[jdubm2c]

Originally Posted by ozmartini

So you're saying it's probably just the tires? I want to believe that but the fact that it started doing this on my winter tires and has now carried on to my summer tires makes me think it's something else.

What tire pressure are you running? Sometimes installers/dealers way over-inflate the tires, which might exascerbate the car's inherent problem.

[ozmartini]

Thank you all for your thoughtful/helpful responses; I really learned a lot from you guys and truly appreciate it! Had no idea that there were so many factors that go into this.

[ozmartini]

Originally Posted by jdubm2c

What tire pressure are you running? Sometimes installers/dealers way over-inflate the tires, which might exascerbate the car's inherent problem.

Running 34/35 all around. It's also still pretty cold in Chicago, hasn't really been above 50's since I put the summers back on.