What is the diameter difference between 255/40R19 and 255/35R20?

255/40R19 has an overall diameter of 27.03 inches (687 mm). 255/35R20 is 27.03 inches (687 mm). That's a 0 inch (0 mm) difference — 255/35R20 is shorter.

Will 255/35R20 cause speedometer error on a car fitted with 255/40R19?

Swapping 255/40R19 for 255/35R20 produces a speedometer error of about 0%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 60 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

255/40R19 turns 746 revs per mile. 255/35R20 turns 746 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

255/40R19 has a sidewall of 102 mm (4.02 in). 255/35R20 sidewall is 89 mm (3.51 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 255/35R20 a safe plus-size upgrade from 255/40R19?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

255/40R19 vs 255/35R20

Overall diameter, sidewall, revs per mile, and speedometer error — 255/40R19 is the taller tire, with a 0% speedo delta when swapping.

255/40R19

27.03in

687 mm overall diameter

255/35R20

27.03in

687 mm overall diameter

Diameter Δ

0 in

Speedo error

255/40R19 revs/mi

746

255/35R20 revs/mi

746

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	255/40R19	255/35R20
Section width	255 mm	255 mm
Aspect ratio	40	35
Wheel diameter	19″	20″
Sidewall height	102 mm	89 mm
Overall diameter	27.03 in (687 mm)	27.03 in (687 mm)
Circumference	84.92 in	84.91 in
Revolutions / mile	746	746

Other comparisons for these sizes

235/45R18 vs 255/35R20 245/45R18 vs 255/40R19 255/45R18 vs 255/40R19 245/40R19 vs 255/35R20 245/40R19 vs 255/40R19 245/45R19 vs 255/40R19 255/35R19 vs 255/40R19 255/40R19 vs 265/35R20 255/40R19 vs 275/30R21 255/40R19 vs 265/35R19

FAQ

Frequently asked

What is the diameter difference between 255/40R19 and 255/35R20?: 255/40R19 has an overall diameter of 27.03 inches (687 mm). 255/35R20 is 27.03 inches (687 mm). That's a 0 inch (0 mm) difference — 255/35R20 is shorter.
Will 255/35R20 cause speedometer error on a car fitted with 255/40R19?: Swapping 255/40R19 for 255/35R20 produces a speedometer error of about 0%. Your speedometer will read higher than your actual speed — a 60 mph indicated reading is really 60 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 255/40R19 turns 746 revs per mile. 255/35R20 turns 746 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 255/40R19 has a sidewall of 102 mm (4.02 in). 255/35R20 sidewall is 89 mm (3.51 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 255/35R20 a safe plus-size upgrade from 255/40R19?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 0%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.