What is the diameter difference between 255/35R18 and 265/30R19?

255/35R18 has an overall diameter of 25.03 inches (636 mm). 265/30R19 is 25.26 inches (642 mm). That's a 0.23 inch (6 mm) difference — 265/30R19 is taller.

Will 265/30R19 cause speedometer error on a car fitted with 255/35R18?

Swapping 255/35R18 for 265/30R19 produces a speedometer error of about 0.9%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.6 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. 265/30R19 turns 798 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). 265/30R19 sidewall is 80 mm (3.13 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 265/30R19 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 0.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/35R18 vs 265/30R19

Overall diameter, sidewall, revs per mile, and speedometer error — 265/30R19 is the taller tire, with a 0.9% speedo delta when swapping.

255/35R18

25.03in

636 mm overall diameter

265/30R19

25.26in

642 mm overall diameter

Diameter Δ

0.23 in

Speedo error

0.9%

255/35R18 revs/mi

806

265/30R19 revs/mi

798

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	265/30R19
Section width	255 mm	265 mm
Aspect ratio	35	30
Wheel diameter	18″	19″
Sidewall height	89 mm	80 mm
Overall diameter	25.03 in (636 mm)	25.26 in (642 mm)
Circumference	78.63 in	79.36 in
Revolutions / mile	806	798

Other comparisons for these sizes

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

FAQ

Frequently asked

What is the diameter difference between 255/35R18 and 265/30R19?: 255/35R18 has an overall diameter of 25.03 inches (636 mm). 265/30R19 is 25.26 inches (642 mm). That's a 0.23 inch (6 mm) difference — 265/30R19 is taller.
Will 265/30R19 cause speedometer error on a car fitted with 255/35R18?: Swapping 255/35R18 for 265/30R19 produces a speedometer error of about 0.9%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.6 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. 265/30R19 turns 798 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). 265/30R19 sidewall is 80 mm (3.13 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 265/30R19 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 0.9%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.