What is the diameter difference between 245/40R19 and 245/45R19?

245/40R19 has an overall diameter of 26.72 inches (679 mm). 245/45R19 is 27.68 inches (703 mm). That's a 0.96 inch (25 mm) difference — 245/45R19 is taller.

Will 245/45R19 cause speedometer error on a car fitted with 245/40R19?

Swapping 245/40R19 for 245/45R19 produces a speedometer error of about 3.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.2 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. 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?

245/40R19 has a sidewall of 98 mm (3.86 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 245/40R19?

A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 3.6%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.

Tire size comparison

245/40R19 vs 245/45R19

Overall diameter, sidewall, revs per mile, and speedometer error — 245/45R19 is the taller tire, with a 3.6% speedo delta when swapping.

245/40R19

26.72in

679 mm overall diameter

245/45R19

27.68in

703 mm overall diameter

Diameter Δ

0.96 in

Speedo error

3.6%

245/40R19 revs/mi

755

245/45R19 revs/mi

729

Outside the typical ±3% safe plus-size band — you may want speedometer recalibration, and this change can affect ABS or traction control behaviour.

Full spec

Side by side

Metric	245/40R19	245/45R19
Section width	245 mm	245 mm
Aspect ratio	40	45
Wheel diameter	19″	19″
Sidewall height	98 mm	110 mm
Overall diameter	26.72 in (679 mm)	27.68 in (703 mm)
Circumference	83.93 in	86.96 in
Revolutions / mile	755	729

Other comparisons for these sizes

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

FAQ

Frequently asked

What is the diameter difference between 245/40R19 and 245/45R19?: 245/40R19 has an overall diameter of 26.72 inches (679 mm). 245/45R19 is 27.68 inches (703 mm). That's a 0.96 inch (25 mm) difference — 245/45R19 is taller.
Will 245/45R19 cause speedometer error on a car fitted with 245/40R19?: Swapping 245/40R19 for 245/45R19 produces a speedometer error of about 3.6%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 62.2 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. 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?: 245/40R19 has a sidewall of 98 mm (3.86 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 245/40R19?: A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 3.6%. This swap is outside the typical ±3% safe range and may require speedometer recalibration or affect ABS / traction control behaviour.