235/65R18 vs 255/50R20

255/50R20 is 0.0% taller (+0.01 in) and 0.79 in wider than 235/65R18.

Same height

255/50R20 and 235/65R18 are the same overall diameter, so the speedometer stays accurate.

	235/65R18	255/50R20	Change
Diameter	30.03″	30.04″	+0.01″+0.0%
Width	9.25″	10.04″	+0.79″+8.5%
Sidewall	6.01″	5.02″	−0.99″−16.5%
Circumference	94.3″	94.4″	+0.0″+0.0%
Wheel	18″	20″	+2″
Revs per mile	672	671	−0

235/65R18255/50R20

Change sizes Speedometer table Gearing

Speedometer shows 60 mph60.0mph

Real speed on 255/50R20.

Ground clearance+0.01in

Change in height under the axle.

Width per side+0.39in

On the same wheel, split inboard and outboard.

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235/65R18 or 255/50R20?

Can I use 255/50R20 instead of 235/65R18?

255/50R20 and 235/65R18 are the same overall diameter, so the speedometer stays accurate. 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 255/50R20 you are really doing 60.0 mph if the speedometer was set up for 235/65R18. Going the other way, 235/65R18 would make it read 60.0 mph at a real 60.

How much ground clearance does it change?

Half the diameter difference: +0.01 in (+0 mm) under the axle.

Other comparisons

30x9.50R15 vs 235/65R18 235/70R17 vs 235/65R18 235/60R18 vs 235/65R18 235/65R18 vs 255/60R18 245/60R18 vs 235/65R18 235/65R18 vs 265/60R18 255/55R18 vs 235/65R18 235/65R18 vs 255/65R18 225/60R18 vs 235/65R18 235/65R18 vs 265/65R18 235/65R18 vs 255/55R19 235/65R18 vs 255/65R17 235/65R18 vs 255/70R16 30x9.50R15 vs 255/50R20 255/50R20 vs 255/70R16 235/70R17 vs 255/50R20 255/50R20 vs 255/65R17 255/50R20 vs 255/60R18