What is the diameter difference between 255/35R18 and 275/35R18?

255/35R18 has an overall diameter of 25.03 inches (636 mm). 275/35R18 is 25.58 inches (650 mm). That's a 0.55 inch (14 mm) difference — 275/35R18 is taller.

Will 275/35R18 cause speedometer error on a car fitted with 255/35R18?

Swapping 255/35R18 for 275/35R18 produces a speedometer error of about 2.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61.3 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

255/35R18 turns 806 revs per mile. 275/35R18 turns 788 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

255/35R18 has a sidewall of 89 mm (3.51 in). 275/35R18 sidewall is 96 mm (3.79 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 275/35R18 a safe plus-size upgrade from 255/35R18?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.2%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/35R18 vs 275/35R18

Overall diameter, sidewall, revs per mile, and speedometer error — 275/35R18 is the taller tire, with a 2.2% speedo delta when swapping.

255/35R18

25.03in

636 mm overall diameter

275/35R18

25.58in

650 mm overall diameter

Diameter Δ

0.55 in

Speedo error

2.2%

255/35R18 revs/mi

806

275/35R18 revs/mi

788

Within the ±3% overall-diameter band usually considered safe for plus-sizing — speedometer and ABS calibration should stay close to factory.

Full spec

Side by side

Metric	255/35R18	275/35R18
Section width	255 mm	275 mm
Aspect ratio	35	35
Wheel diameter	18″	18″
Sidewall height	89 mm	96 mm
Overall diameter	25.03 in (636 mm)	25.58 in (650 mm)
Circumference	78.63 in	80.36 in
Revolutions / mile	806	788

Other comparisons for these sizes

245/40R18 vs 255/35R18 255/35R18 vs 265/30R19 255/35R18 vs 265/35R18 255/35R18 vs 255/40R18 265/35R18 vs 275/35R18 275/35R18 vs 285/30R19 275/35R18 vs 275/30R19 275/35R18 vs 275/40R18

FAQ

Frequently asked

What is the diameter difference between 255/35R18 and 275/35R18?: 255/35R18 has an overall diameter of 25.03 inches (636 mm). 275/35R18 is 25.58 inches (650 mm). That's a 0.55 inch (14 mm) difference — 275/35R18 is taller.
Will 275/35R18 cause speedometer error on a car fitted with 255/35R18?: Swapping 255/35R18 for 275/35R18 produces a speedometer error of about 2.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61.3 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 255/35R18 turns 806 revs per mile. 275/35R18 turns 788 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 255/35R18 has a sidewall of 89 mm (3.51 in). 275/35R18 sidewall is 96 mm (3.79 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 275/35R18 a safe plus-size upgrade from 255/35R18?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.2%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.