255/40R18 Tire Size Specifications
This tire size 255/40R18 fits 4 vehicles in our database.
Everything to know about the 255/40R18 tire size
Size geometry
A 255/40R18 tire has a 255mm section width and a 40% aspect ratio, mounted on a 18-inch rim. Sidewall height works out to 102.0mm (4.02") and overall outside diameter is 661.2mm (26.03"). At highway speed the tire completes about 481 revolutions per kilometre â your speedometer and odometer were calibrated against this number.
Direct substitute sizes
If 255/40R18 is unavailable, the closest same-diameter substitutes on the same rim are 245/42R18 and 265/38R18. Both keep your speedometer reading within 1% â safe for daily use, ABS, and stability control. Always verify load and speed ratings before swapping.
Plus / minus sizing options
For a 255/40R18 you can upsize to 265/34R19 (plus-one) to fit a larger wheel without changing the speedometer reading, or downsize to 245/47R17 (minus-one) for a softer ride or winter setup. Both stay inside the Âą3% diameter tolerance that ABS and TPMS systems expect.
Vehicle compatibility
4 vehicles in our database run the 255/40R18 tire size from the factory. Aftermarket fitment depends on rim width, offset, and clearance â match these specs to your wheel before purchasing tires.