Highway vibration

[Alexlind123]

After starting a new job which requires a section of highway commute, a vibration which starts at ~78mph became bothersome. The vibration is fairly low frequency, in fact the term "shimmy" might be applicable. The axis of vibration is up/down or front/back, not side to side. I can feel it in the steering wheel, but the whole car has a shake.

Does anyone have any idea what might be causing this? Where should i start looking? If you want more information, just let me know.

[bmwrp8]

I have the exact same problem..don't really know whats wrong but i'm thinking guibo...let's see what other say

[Morgenster]

Same here, although mine gets better at 80 mph. Ifeel it much more in the seat and gearstick than the wheel.

[J.DeFeo]

I also have an identical problem that surfaces around 68 MPH and clear up around 80. It's also heavily dependant on road surface, but still manifests on brand new, freshly paved highway. I'm also thinking guibo/center bearing maybe transmission/engine mounts.

[Morgenster]

Same here, although mine gets better at 80 mph. Ifeel it much more in the seat and gearstick than the wheel.

Forgot to add this: it also seems to be slightly random but mostly when cold started and gets better with 30 mins of driving.

[632 Regal]

most shakes/vibrations/shimies etc that dont manifest until above appx 70mph are out of round tires. Shimmies below 70 are usually out of balance tires.

[632 Regal]

flat spotting, some tires do it when new and gradually dont when aged a little bit.
Forgot to add this: it also seems to be slightly random but mostly when cold started and gets better with 30 mins of driving.

[Morgenster]

I think I'll check if it's worst on mondays because my car sits longest in weekends. What exactly is "out of round" or "out of balance"? I have a vague idea about it, but wouldn't know how to check.

[Podmore]

'Out of round' refers to a tyre which is not perfectly symmetrical around the circumference - not quite circular. A tyre can be perfectly balanced but out of round and it will exhibit a harmonic vibration at certain speeds. An out of balance tyre has a little more weight at certain points of the circumference than others; this will also exhibit a harmonic vibration at certain speeds. You can see an out of round tyre when it's on the balancer - the tread will hop up and down a bit. No fix for an out of round tyre, throw it away. To get your tyres perfectly balanced, get them to balance the rim without the tyre on it first, then they should fit the tyre and rebalance the whole assembly. A new tyre will have a spot marked on it which is the heavy spot - this should then be diametrically opposite the heavy spot on the rim. When the rim weight is then removed and the wheel/tyre balanced together, the minimum compensatory weight can be used, leading to the best balance possible.

[Morgenster]

'Out of round' refers to a tyre which is not perfectly symmetrical around the circumference - not quite circular. A tyre can be perfectly balanced but out of round and it will exhibit a harmonic vibration at certain speeds. An out of balance tyre has a little more weight at certain points of the circumference than others; this will also exhibit a harmonic vibration at certain speeds. You can see an out of round tyre when it's on the balancer - the tread will hop up and down a bit. No fix for an out of round tyre, throw it away. To get your tyres perfectly balanced, get them to balance the rim without the tyre on it first, then they should fit the tyre and rebalance the whole assembly. A new tyre will have a spot marked on it which is the heavy spot - this should then be diametrically opposite the heavy spot on the rim. When the rim weight is then removed and the wheel/tyre balanced together, the minimum compensatory weight can be used, leading to the best balance possible.

How delightfully comprehensive and handy! I know what to check on next ime I have tires switched. Many thanks!
Come to think of it, I didn't notice any increase in vibrations today after the car 's been sitting for the weekend, so I don't think flat-spotting is the issue here.