Although most tyres are made to very high quality standards, there are still variations in the thickness of the rubber, the steel belts and the radial webbing that form the structure. One consequence of the variations is a slight weight difference around the tyre. This is well known and easily cured by balancing the wheel and tyre.

A less well known effect of the variability is something called run-out – a measure of how straight the tyre will run if fitted to a wheel and allowed to roll along a flat level surface. Some will run straight and true, others will veer to the left or right in varying degrees. You will see an indication of this on most new tyres – have you ever noticed coloured lines running around the tread on your new tyre? Some of these are to give the tyre distributors easy to read information about where the tyre should be shipped to, but one of them will be a run-out indicator – usually red or blue, and the extreme left or right hand line. The nearer to the centre it is, the straighter the tyre will run, and which side of the centre it is denotes the direction of the run-out.

A steering problem can arise if both tyres on the front axle happen to run out significantly in the same direction. (To be technically accurate, there are two types of run-out – radial run-out is where the hole isn’t exactly in the centre of the tyre and some tyre fitters will have heard of this. We’re talking about side or lateral run-out here). Ideally, when you’re buying new tyres you should select two with run-out of about the same amount, but in opposite directions – in other words, with the coloured lines both to the inside of the centre of the tyre, or both to the outside. That way the two will cancel each other out and you’ll get straight steering. Needless to say, few garages or tyre fitters seem to pay this much attention when fitting the tyres and of course the helpful coloured run-out indicators often wear off in the first few miles. (You might also get the technicians staring at you in disbelief when you explain this to them!)

What can you do now the run-out indicators are no longer visible on your tyres? Well, try swapping one tyre only from the back to the front and see if it makes a difference. If not, try swapping both. Check to see if your tyres are directional –if they’re not you can try diagonal swaps as well. It’s all trial and error now I’m afraid, but at least you’ll know what to look out for when you buy new tyres.

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