Last weekend I had to replace two tyres on my car as they were wearing down. It cost £85.50 each to replace them. I was told that usually the back wheels wear away at half the rate of the front tyres. Given that the car has done 25,000 miles, it means that for every 50,000 miles I should have bought 6 new tyres. 6 tyres will cost £513. £513 into 50,000 miles is £0.01026.
Put it another way, my tyres wear away at a rate of just over 1 penny per mile driven.
Or, in terms of fuel costs, it would be like adding roughly 9p to a litre of petrol.