What is the diameter difference between 275/65R18 and 285/65R18?

275/65R18 has an overall diameter of 32.07 inches (815 mm). 285/65R18 is 32.59 inches (828 mm). That's a 0.51 inch (13 mm) difference — 285/65R18 is taller.

Will 285/65R18 cause speedometer error on a car fitted with 275/65R18?

Swapping 275/65R18 for 285/65R18 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

275/65R18 turns 629 revs per mile. 285/65R18 turns 619 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

275/65R18 has a sidewall of 179 mm (7.04 in). 285/65R18 sidewall is 185 mm (7.29 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 285/65R18 a safe plus-size upgrade from 275/65R18?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.6%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

275/65R18 vs 285/65R18

Overall diameter, sidewall, revs per mile, and speedometer error — 285/65R18 is the taller tire, with a 1.6% speedo delta when swapping.

275/65R18

32.07in

815 mm overall diameter

285/65R18

32.59in

828 mm overall diameter

Diameter Δ

0.51 in

Speedo error

1.6%

275/65R18 revs/mi

629

285/65R18 revs/mi

619

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	275/65R18	285/65R18
Section width	275 mm	285 mm
Aspect ratio	65	65
Wheel diameter	18″	18″
Sidewall height	179 mm	185 mm
Overall diameter	32.07 in (815 mm)	32.59 in (828 mm)
Circumference	100.77 in	102.37 in
Revolutions / mile	629	619

Other comparisons for these sizes

265/70R17 vs 275/65R18 285/65R18 vs 305/55R20

FAQ

Frequently asked

What is the diameter difference between 275/65R18 and 285/65R18?: 275/65R18 has an overall diameter of 32.07 inches (815 mm). 285/65R18 is 32.59 inches (828 mm). That's a 0.51 inch (13 mm) difference — 285/65R18 is taller.
Will 285/65R18 cause speedometer error on a car fitted with 275/65R18?: Swapping 275/65R18 for 285/65R18 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 275/65R18 turns 629 revs per mile. 285/65R18 turns 619 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 275/65R18 has a sidewall of 179 mm (7.04 in). 285/65R18 sidewall is 185 mm (7.29 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 285/65R18 a safe plus-size upgrade from 275/65R18?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.6%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.