What is the diameter difference between 235/50R18 and 245/45R19?

235/50R18 has an overall diameter of 27.25 inches (692 mm). 245/45R19 is 27.68 inches (703 mm). That's a 0.43 inch (11 mm) difference — 245/45R19 is taller.

Will 245/45R19 cause speedometer error on a car fitted with 235/50R18?

Swapping 235/50R18 for 245/45R19 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.9 mph. Anything under 3% is usually acceptable without recalibration.

How many revolutions per mile does each size do?

235/50R18 turns 740 revs per mile. 245/45R19 turns 729 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.

What's the sidewall height difference?

235/50R18 has a sidewall of 118 mm (4.63 in). 245/45R19 sidewall is 110 mm (4.34 in). Lower-profile sidewalls give sharper steering response but less bump compliance.

Is 245/45R19 a safe plus-size upgrade from 235/50R18?

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

235/50R18 vs 245/45R19

Overall diameter, sidewall, revs per mile, and speedometer error — 245/45R19 is the taller tire, with a 1.6% speedo delta when swapping.

235/50R18

27.25in

692 mm overall diameter

245/45R19

27.68in

703 mm overall diameter

Diameter Δ

0.43 in

Speedo error

1.6%

235/50R18 revs/mi

740

245/45R19 revs/mi

729

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	235/50R18	245/45R19
Section width	235 mm	245 mm
Aspect ratio	50	45
Wheel diameter	18″	19″
Sidewall height	118 mm	110 mm
Overall diameter	27.25 in (692 mm)	27.68 in (703 mm)
Circumference	85.61 in	86.96 in
Revolutions / mile	740	729

Other comparisons for these sizes

215/60R16 vs 235/50R18 235/55R17 vs 235/50R18 235/45R18 vs 235/50R18 235/50R18 vs 245/45R18 245/40R19 vs 245/45R19 245/45R19 vs 265/35R21 245/45R19 vs 255/40R19

FAQ

Frequently asked

What is the diameter difference between 235/50R18 and 245/45R19?: 235/50R18 has an overall diameter of 27.25 inches (692 mm). 245/45R19 is 27.68 inches (703 mm). That's a 0.43 inch (11 mm) difference — 245/45R19 is taller.
Will 245/45R19 cause speedometer error on a car fitted with 235/50R18?: Swapping 235/50R18 for 245/45R19 produces a speedometer error of about 1.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 60.9 mph. Anything under 3% is usually acceptable without recalibration.
How many revolutions per mile does each size do?: 235/50R18 turns 740 revs per mile. 245/45R19 turns 729 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
What's the sidewall height difference?: 235/50R18 has a sidewall of 118 mm (4.63 in). 245/45R19 sidewall is 110 mm (4.34 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
Is 245/45R19 a safe plus-size upgrade from 235/50R18?: 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.