Tyre Wear - Stepping / Sawtoothing

[NickSw]

Wife's '08 SR180 although the problem is likely not restricted to any make/model.

For a little while she has noticed a rumbling coming from the back end. Difficult to pin point exactly. Took the car out for a spin and def. heard/felt it. Noticeable at any speed and seems to happen at 1 revolution of the tyre, I tried 10 - 80mph.

First thought was a wheel bearing on the way out.

Car for mot at an independant garage this week. Mentioned the prob to them and asked if they would have a look whilst it was up in the air.

Their diagnosis is rear tyres stepping/sawtoothing. I've looked but can't see any sign of uneven or abnormal tyre wear. The tyres have only done a few thousand miles and have plenty of tread left, certainly 5-6mm.

Writing this makes me remember that the car went in to the same garage when swmbo first noticed the rumble, about 6 months ago. They then diagnosed rear tyres. These were pretty well clapped out and so I had both rears replaced. Can't remember make of tyres but probably same as original. Can confirm if of any interest. This slightly lessened the problem but has not cured it.

I'm wondering whether to swap the wheels corner to corner (can't remember if they are directional tyres). Also wondering if a full alignment check might be called for. Also wondering if it could be a wheel bearing after all.

Anyone have any thoughts on this or similar experiences please.

Nick.

[Cyker]

First thought is the tracking/toe/whatever-the-heck-it's-called on the rear wheels is off and they aren't running properly straight, but if that was the case I'd expect noticeable crabbing!

[Big Auris]

Suggest that you have tread separation on the tyre casing, this can cause the tyre to warp or create a gumboil effect on the periphery of tyre generally caused by cheap tyres but not always the case. By jacking the car up and spinning the wheel these faults can be very obviously seen. Is the wheel Bolts tight ????? all these faults will show up at a lower speed.

Big Auris