Vibration after car has been sitting?

[matthugie]

I searched but didn't see anything relevant. When I leave the car sitting for a few days and then drive it, for the first 10-15 minutes or so there is a vibration that seems to be coming from the rear somewhere. If the car hasn't been sitting for more than a day it doesn't have any abnormal vibrations. It's worst when I first start driving, gets worse the faster the car goes, but progressively gets better until it just goes away. I did have the driveshaft out a couple months ago to replace the gas tank, but it drove fine for a 24 hour autox and 2 day event at VIR with no issues last month. The fact that it appears to only be related to not driving the car and that it just goes away on its own has me stumped as to what it could be.

The car: 88 325is - s52 swap with g260. Trans mounts, guibo, and CSB replaced at time of swap (~2 years ago). All urethane bushings in the rear (subframe, trailing arm, and diff mount) done about 1.5 years ago. Wheels are fairly new Apex Arc8's with 235 ZII's, maybe 2 months old.

Thanks guys.

[dustyperez]

could be the tires, they will get a flat spot if they sit too long and as they warm up it goes away.

[matthugie]

could be the tires, they will get a flat spot if they sit too long and as they warm up it goes away.

That's the only thing I could think of, but they shouldn't be getting flat spots after 2 days. The cold tire pressures are 34psi front and 35psi rear, so they aren't low on pressure. If I was leaving it sitting for extended periods of time that would make more sense, but I drive it a couple times a week. I drove it Tuesday after it sat for a few days and had it happen, and then drove it last night and it happened again. On the way to work this morning there was nothing.

[e30rapidic]

flat spots on the tires. Even my F150 does it

[matthugie]

Well, that's 4/4 on flat spots on tires (including offline convos). Guess my first thought was correct and I shouldn't have second guessed it. Thanks guys.

[dwight]

Check shocks

[reelizmpro]

I was going to suggest tires, lost wheel weight or bent wheels. All of the above can throw wheels out of balance. Swapping wheels with a new or known good set can help troubleshoot.

[hillbarry]

Its the tires my friend.

[matthugie]

Check shocks

Shocks are fairly new, maybe 5k on them.

I was going to suggest tires, lost wheel weight or bent wheels. All of the above can throw wheels out of balance. Swapping wheels with a new or known good set can help troubleshoot.

The vibration goes away, which throws out bends or lost weights, unless they are somehow balancing themselves out when moving. Still leaves tires, which appears to be the consensus. Thanks.

[LJ851]

Does it seem to be getting more noticeable as the temps are dropping?

[dirtbag30]

old, hard, dryrotted tires.