What is the diameter difference between 255/40R18 and 265/35R18?

255/40R18 has an overall diameter of 26.03 inches (661 mm). 265/35R18 is 25.3 inches (643 mm). That's a 0.73 inch (19 mm) difference — 265/35R18 is shorter.

Will 265/35R18 cause speedometer error on a car fitted with 255/40R18?

Swapping 255/40R18 for 265/35R18 produces a speedometer error of about 2.8%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.3 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

255/40R18 turns 775 revs per mile. 265/35R18 turns 797 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

255/40R18 has a sidewall of 102 mm (4.02 in). 265/35R18 sidewall is 93 mm (3.65 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 265/35R18 a safe plus-size upgrade from 255/40R18?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.8%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/40R18 vs 265/35R18

Overall diameter, sidewall, revs per mile, and speedometer error — 255/40R18 is the taller tire, with a 2.8% speedo delta when swapping.

255/40R18

26.03in

661 mm overall diameter

265/35R18

25.3in

643 mm overall diameter

Diameter Δ

0.73 in

Speedo error

2.8%

255/40R18 revs/mi

775

265/35R18 revs/mi

797

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	255/40R18	265/35R18
Section width	255 mm	265 mm
Aspect ratio	40	35
Wheel diameter	18″	18″
Sidewall height	102 mm	93 mm
Overall diameter	26.03 in (661 mm)	25.3 in (643 mm)
Circumference	81.78 in	79.49 in
Revolutions / mile	775	797

Other comparisons for these sizes

245/45R17 vs 255/40R18 235/40R18 vs 255/40R18 245/40R18 vs 255/40R18 245/45R18 vs 255/40R18 255/35R18 vs 265/35R18 255/35R18 vs 255/40R18 255/40R18 vs 265/35R19 255/40R18 vs 255/35R19 255/40R18 vs 275/30R20 255/40R18 vs 275/40R18

FAQ

Frequently asked

What is the diameter difference between 255/40R18 and 265/35R18?: 255/40R18 has an overall diameter of 26.03 inches (661 mm). 265/35R18 is 25.3 inches (643 mm). That's a 0.73 inch (19 mm) difference — 265/35R18 is shorter.
Will 265/35R18 cause speedometer error on a car fitted with 255/40R18?: Swapping 255/40R18 for 265/35R18 produces a speedometer error of about 2.8%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 58.3 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 255/40R18 turns 775 revs per mile. 265/35R18 turns 797 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 255/40R18 has a sidewall of 102 mm (4.02 in). 265/35R18 sidewall is 93 mm (3.65 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 265/35R18 a safe plus-size upgrade from 255/40R18?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 2.8%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.