Shaking when accelerating

[Tibje]

Hello,

When the car is mounted with 18 inch rims with winter tyres, I have no problems.
When the car is mounted with 21 inch rims with summer tyres and while accelerating (semi) hard, the car shakes/falters.

Does anyone know what the problem could be?

It’s an xDrive.

Thanks!

[6coupe]

Balancing and/or warped wheels. Most likely balancing issue.

[Walt White Coupe]

If it just happens when accelerating, it has nothing to do with balance or warping. Bark up another tree.

[murph914]

Are the tires square? Meaning same size front and back? If not, what sizes are you running?

[6coupe]

Originally Posted by Walt White Coupe

If it just happens when accelerating, it has nothing to do with balance or warping. Bark up another tree.

Effects of an out of balance wheel will increase with rotational speed, but would remain once at high speed, not just accelerating to it.

[Walt White Coupe]

Not completely true. An out of balance wheel will shake the most at two resonant frequencies. The first is around 40 mph and shake will increase as you approach that speed and then when you pass it, the shake will slowly decrease and will then start to increase again as you approach around 80 mph. And it will decrease again as you pass 80 mph. Now if you get to 160 mph it will really shake.

We need a little more info from the OP about when the shake occurs.

[Tibje]

When I accelerate slowly, nothing shakes/happens.

It feels more like a heart skipping a beat, while beating very fast.

The BMW garage says it is the VTC (Variabel Traction Control or something like that) because it is an xDrive but they couldn’t explain why this doesn’t happen on the 18 inch rims.

After having some bad experiences with the garage, I come to you guys for help.

Btw: there are no warming signs flashing or error messages.

[Tibje]

Originally Posted by murph914

Are the tires square? Meaning same size front and back? If not, what sizes are you running?

Front: 245/35R20
Back: 275/30R20

BMW official rims: 20” LM rim V 356 liquid black

[murph914]

Front: 245/35R20 84" 2134 mm
Back: 275/30R20 83.2" 2113 mm

looks like those are pretty. Close. With what BMW told you the easiest explanation is something is off with the 20" wheel's circumference. When the Revs/ mile are off front to back the xdrive goes a little wonky. But it does not appear that should be an issue here.

Bad wheels can do all kinds of weird things at load and rpm. 6coupe's info about harmonics is right, but I have had issues with sidewalls and bent wheels that would get worse with more weight on the tires.

Go for the low hanging fruit first and make sure the tires and wheels are all good. Swap them out if you can. If the 18 tires have the same circumference can those be swapped out without hurting the xdrive?

Next up you get into some more expensive repairs. Transfer case would be one.

I actually had an issue that I brought to BMW for several times. They put chassis ears on the car and replaced several wheel bearings, swapped out rims, and did an alignment before giving up. Just before the warranty expired the diff exploded (I have a 650i). The gear locked and the driveshaft splines stripped. That was about 20k miles ago and the car has been fine since.

Sorry I can't point to a smoking gun. You're going to need to do some more checking first. Hopefully something stupid.

[Tibje]

Originally Posted by murph914

Front: 245/35R20 84" 2134 mm
Back: 275/30R20 83.2" 2113 mm

looks like those are pretty. Close. With what BMW told you the easiest explanation is something is off with the 20" wheel's circumference. When the Revs/ mile are off front to back the xdrive goes a little wonky. But it does not appear that should be an issue here.

Bad wheels can do all kinds of weird things at load and rpm. 6coupe's info about harmonics is right, but I have had issues with sidewalls and bent wheels that would get worse with more weight on the tires.

Go for the low hanging fruit first and make sure the tires and wheels are all good. Swap them out if you can. If the 18 tires have the same circumference can those be swapped out without hurting the xdrive?

Next up you get into some more expensive repairs. Transfer case would be one.

I actually had an issue that I brought to BMW for several times. They put chassis ears on the car and replaced several wheel bearings, swapped out rims, and did an alignment before giving up. Just before the warranty expired the diff exploded (I have a 650i). The gear locked and the driveshaft splines stripped. That was about 20k miles ago and the car has been fine since.

Sorry I can't point to a smoking gun. You're going to need to do some more checking first. Hopefully something stupid.

Originally Posted by murph914

Front: 245/35R20 84" 2134 mm
Back: 275/30R20 83.2" 2113 mm

looks like those are pretty. Close. With what BMW told you the easiest explanation is something is off with the 20" wheel's circumference. When the Revs/ mile are off front to back the xdrive goes a little wonky. But it does not appear that should be an issue here.

Bad wheels can do all kinds of weird things at load and rpm. 6coupe's info about harmonics is right, but I have had issues with sidewalls and bent wheels that would get worse with more weight on the tires.

Go for the low hanging fruit first and make sure the tires and wheels are all good. Swap them out if you can. If the 18 tires have the same circumference can those be swapped out without hurting the xdrive?

Next up you get into some more expensive repairs. Transfer case would be one.

I actually had an issue that I brought to BMW for several times. They put chassis ears on the car and replaced several wheel bearings, swapped out rims, and did an alignment before giving up. Just before the warranty expired the diff exploded (I have a 650i). The gear locked and the driveshaft splines stripped. That was about 20k miles ago and the car has been fine since.

Sorry I can't point to a smoking gun. You're going to need to do some more checking first. Hopefully something stupid.

Thanks for the advice. I'll look further in to it and will keep you posted!

[gjohnsen]

You can actually pull the 4x4 fuse to check if the transfer case is broken. If it runs completely smooth without the fuse, you know what to blame.

Had transfer case changed on a F01 and my 6 series GC. Both at low mileage. It is one day of labor and the cost of the part. The germans call it VTG. (Verteilergetriebe). I had i covered under warranty. The total cost is about 8000$ without warranty...

[doughboy650gc]

@tibje did you ever find out the cause of the shaking? I have the same thing