Why does my steering wheel wibble wobble?

QI can feel a vibration through the steering of my Toyota Corolla, both at low and high speeds. What is causing it?

John Macdonald, Kilmarnock

Ed says

AThe most obvious suspicion is that one or both of the front wheels is out-of-balance. Try to detect if it comes from the left or right alone, which isolates it to that particular wheel. Simple imbalance is easy to diagnose because it's usually most noticeable at a certain speed, often around 50-70mph and it more-or-less goes away if you slow down or speed up by about 10mph. Having the wheel(s) balanced should cure this.

Look out, though, for other issues. Low speed vibration (with or without high speed wobble) may mean the wheel or tyre is distorted.

Find a stretch of very smooth asphalt (if you can!). Hold the steering loosely. Slowly accelerate from rest until the wobble comes on. If the steering wheel twitches slightly from side to side then the wheel is bent, or the tyre carcass is distorted. Jack up the wheel and rotate it, watching the tread and the rim. Look for a side to side twitch as it goes around.

Up to a few millimetres is OK, but any more ideally requires a new wheel or tyre. If the problem is more of a bumpbump-bump felt through the suspension, then the tread of the tyre may be detaching from the carcass. Often you'll see a patch of tread that's worn more than the rest and a bulge can sometimes be felt as you run the ball of your hand across the width of the tyre. Replace the tyre. If the whole body of the car bumps or twitches at low speed, but not the steering, then one of the rear wheels or tyres is responsible.

Tyres can be damaged by kerbing, pot holes or having gone flat – while driving or parked up. Age is a killer, especially if the car does a low annual mileage. The tyres may be cracked, perished, or have flat-spotted while standing. Sometimes, though, poorlymade tyres can start to distort at a relatively early stage in their life. If they were fitted as a complete set, consider replacing all four – they may all go west, one after the other, over a short period of time.