Fleet tyre specialist Tyreserve estimates that the price of the average tyre bought by fleets has risen by about 15% this year.
It says the fact that fleets are buying larger and more specialist tyres is the overriding factor driving the increase.
Tyreserve estimates that UK fleets this year have spent about £297 million on tyres - an increase of £39 million from last year.
General manager David Goodyear said: 'This rise is almost entirely thanks to a trend that sees each new model rolling out on larger tyres than the last.
'We are in a situation where 17-inch tyres are becoming the norm on upper-medium cars and 15-inch or 16-inch tyres are standard on lower-medium models. Even superminis are creeping up to 14 and 15 inches.'
Goodyear stresses that these larger tyres may provide better grip and can have a positive effect on ride and handling for many vehicles, but the main impetus towards larger tyres is coming from vehicle stylists.
He added: 'Most cars look better on bigger wheels but the advantages are mainly cosmetic. However, moving up from a 16 to 17 inch wheel can increase the tyre bill for the life of a car by 20% and it is fleets that are paying the bill.'