SidewallerTire & wheel calculators

255/35R18 vs 255/40R18

255/40R18 is 4.0% taller (+1.00 in) and the same width than 255/35R18.

Caution
Check before you buy

255/40R18 is 4.0% taller than 255/35R18. It often still fits, but expect a noticeable speedometer error and check clearance at full steering lock.

255/35R18255/40R18Change
Diameter25.03″26.03″+1.00″+4.0%
Width10.04″10.04″0.00″0.0%
Sidewall3.51″4.02″+0.50″+14.3%
Circumference78.6″81.8″+3.2″+4.0%
Wheel18″18″Same
Revs per mile806775−31
SideTread
255/35R18255/40R18
Speedometer shows 60 mph62.4mph

Real speed on 255/40R18.

Ground clearance+0.50in

Change in height under the axle.

Width per side0.00in

On the same wheel, split inboard and outboard.

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255/35R18 or 255/40R18?

Can I use 255/40R18 instead of 255/35R18?

255/40R18 is 4.0% taller than 255/35R18. It often still fits, but expect a noticeable speedometer error and check clearance at full steering lock. Also match or beat the original load index and speed rating, and check that the wheel width suits the new tire.

Will my speedometer be off?

At an indicated 60 mph on 255/40R18 you are really doing 62.4 mph if the speedometer was set up for 255/35R18. Going the other way, 255/35R18 would make it read 57.7 mph at a real 60.

How much ground clearance does it change?

Half the diameter difference: +0.50 in (+13 mm) under the axle.

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