What is the diameter difference between 245/40R19 and 255/40R19?

245/40R19 has an overall diameter of 26.72 inches (679 mm). 255/40R19 is 27.03 inches (687 mm). That's a 0.31 inch (8 mm) difference — 255/40R19 is taller.

Will 255/40R19 cause speedometer error on a car fitted with 245/40R19?

Swapping 245/40R19 for 255/40R19 produces a speedometer error of about 1.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.7 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

245/40R19 turns 755 revs per mile. 255/40R19 turns 746 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

245/40R19 has a sidewall of 98 mm (3.86 in). 255/40R19 sidewall is 102 mm (4.02 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 255/40R19 a safe plus-size upgrade from 245/40R19?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.2%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.

Tire size comparison

245/40R19 vs 255/40R19

Overall diameter, sidewall, revs per mile, and speedometer error — 255/40R19 is the taller tire, with a 1.2% speedo delta when swapping.

245/40R19

26.72in

679 mm overall diameter

255/40R19

27.03in

687 mm overall diameter

Diameter Δ

0.31 in

Speedo error

1.2%

245/40R19 revs/mi

755

255/40R19 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	245/40R19	255/40R19
Section width	245 mm	255 mm
Aspect ratio	40	40
Wheel diameter	19″	19″
Sidewall height	98 mm	102 mm
Overall diameter	26.72 in (679 mm)	27.03 in (687 mm)
Circumference	83.93 in	84.92 in
Revolutions / mile	755	746

Other comparisons for these sizes

225/50R17 vs 245/40R19 235/45R18 vs 245/40R19 245/45R18 vs 255/40R19 245/45R18 vs 245/40R19 255/45R18 vs 255/40R19 225/40R19 vs 245/40R19 245/35R19 vs 245/40R19 245/40R19 vs 255/35R20 245/40R19 vs 245/35R20 245/40R19 vs 245/45R19

FAQ

Frequently asked

What is the diameter difference between 245/40R19 and 255/40R19?: 245/40R19 has an overall diameter of 26.72 inches (679 mm). 255/40R19 is 27.03 inches (687 mm). That's a 0.31 inch (8 mm) difference — 255/40R19 is taller.
Will 255/40R19 cause speedometer error on a car fitted with 245/40R19?: Swapping 245/40R19 for 255/40R19 produces a speedometer error of about 1.2%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.7 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 245/40R19 turns 755 revs per mile. 255/40R19 turns 746 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 245/40R19 has a sidewall of 98 mm (3.86 in). 255/40R19 sidewall is 102 mm (4.02 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 255/40R19 a safe plus-size upgrade from 245/40R19?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.2%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.