Hi. I've only owned a Q7 for 9 months. I've already had two punctures. The garage I have taken the car to insist they can't change just one tyre and at least two should be changed. That's a cost in excess of £600 every time this happens.

Any advice please?

It's all about having the same level of grip on both sides of the car, so if you have to brake hard in the wet, the car pulls up straight.

 

If you have a new tyre with 8mm of tread on one side of the car and a part-worn one with 4mm of tread on the other side, the old tyre will aquaplane before the new tyre, so if these tyres are on the front, you are likely to spin the car.  This is because the front tyres do most of the stopping when you brake.

You shouldn't run tyres with more than 2mm tread difference on the same axle.  The car will pull due to the difference in radius between tyres.  However, the tyre only needs changing if the puncture is near the edges or has gone in at an angle or the tyre is damaged due to being run-flat.