18"/382mm

The sizing of racing chair tyres is peculiar...please check your wheel size before ordering.

Although called 18" tyres, this size has a measured diameter: 

382mm + (2 x 18mm) = 418mm / 16.4"

If your wheel + tyre combination measures just over 18" in diameter, don't look here. You need to look at the 20" tyre section....don't ask, it's complicated...