[morritse]

Ran something over in the middle of the road a couple days ago and popped my right rear tire.

Replaced the tire but have since been getting a slow pulsing sound from the front end at 80-85MPH.

It seems to increase in frequency when i turn right and decrease when i turn left. It also changes pitch with speed.

What does this sound like to you guys? The replacement tire should be close enough in treadwear to the other one.

Does it sound like an alignment or balance issue? or something worse. Car is an f32 xdrive

[Wires]

That sounds alignment related. Best case just needs an alignment, worst case, damaged stuff in the front end. A competent shop would be able to confirm.

[yupetc]

I've experienced something similar before, but mine turned out to be one of the belly covers came loose because few bolts went missing; and a loose piece of undercover can flap upon higher speed driving. Anyways, you may want to look under and inspect in a wider area to see what's loose. If not, then look into the other suspension components.

[morritse]

Checked alignment which was fine.

The tech noted that there is a 3mm tread depth difference between the 2 rear tires.

Is that enough to cause these symptoms?

[Wires]

BMW spec is no more than 4/32" = 3.175mm difference between tires, so that should be fine.

[Wires]

Are they the same tire size on all 4-corners? You could try swapping a front to that new back location to check if they are.

[morritse]

Originally Posted by Wires

Are they the same tire size on all 4-corners? You could try swapping a front to that new back location to check if they are.

I'm going to move the low tread one up front and see if it changes. It is AWD so probably not a good idea either way

[Wires]

Originally Posted by morritse

I'm going to move the low tread one up front and see if it changes. It is AWD so probably not a good idea either way

Apparently tire shops can "shave" a tire down to match the rest. I've never did this, but others have mentioned it.

[morritse]

The pulsing is around 1 pulse per second at 80mph and maybe goes to 2 per second by 85mph.

maybe difference in diameter is causing some constructive interference with different rotating distances making those pulses.

I'm going to check wheel balances and replace the 4mm tread tire if that doesn't fix it.

I guess it could be a bearing, but it seems too coincidental that it started happening immediately after hitting something and replacing 1 tire.

[morritse]

Found all the wheel weights missing from the right front tire.


I would expect this to cause a sounds once every tire vibration, not only once/second

[morritse]

Rotates and balanced all wheels, no change. This is so frustrating

[morritse]

https://youtube.com/shorts/JdyquGp_cr4?feature=share

[morritse]

New wheels and tires didn't resolve the issue, gonna look at wheel bearings next but if those are fine I'm stumped.

[Wires]

When mine had a bad front wheel bearing it sounded a lot like one front tire out of alignment. That might be your deal as well.

[morritse]

All the bearing themselves were fine. We did notice that the front right wheel wobbles significantly at speeds. The wheel and tire are brand new, so either the wheel is bent, or something else is causing it to wobble.

If the latter is true, what could it be if not the bearing?

[agentorange]

Could it be an aerodynamic issue? Maybe one of the undertray pieces is loose and vibrating at particular speeds to to the way the air moves under the car.

[morritse]

Originally Posted by agentorange

Could it be an aerodynamic issue? Maybe one of the undertray pieces is loose and vibrating at particular speeds to to the way the air moves under the car.

It's possible. It's been to a couple shops and neither of them noticed anything like that...

I'll specifically mention it next time.

[morritse]

So a tech rode with me and he could hear obvious bearing noises coming from below the passenger seat.

If I drove and move my head over there I can too now. That axle also had some play in it so going to replace those both.

I think the pulsing noises I have been hearing is from the front right wheel spinning slightly slower than the front left because more friction, and I was hearing the interference pattern of those 2 frequencies.

I'll let you guys know if the problem is fixed but I'm 90% sure this will do it.

[morritse]

Wheel bearing and/or axle fixed the problem.