TireSizesFinder

245/40R20 vs 245/45R20

245/45R20 is 0.96 in (24.5 mm) taller than 245/40R20, a +3.48% diameter difference. With the speedometer set for 245/40R20, an indicated 60 mph is 62.1 mph on 245/45R20.

Is this a safe swap?

Diameter difference +3.48%: outside the ±3% guideline

By overall diameter alone, 245/45R20 falls outside the ±3% range commonly used as a guideline when replacing 245/40R20; speedometer and ride-height changes are larger. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 245/40R20 (27.72 in) vs 245/45R20 (28.68 in)245/40R2027.72 in × 9.65 in245/45R2028.68 in × 9.65 in
Side profile and tread width, drawn to the same scale.
245/40R20 vs 245/45R20 differences
Measurement245/40R20245/45R20Difference% diff
Overall diameter27.72 in (704.0 mm)28.68 in (728.5 mm)+0.96 in (+24.5 mm)+3.48%
Sidewall height3.86 in (98.0 mm)4.34 in (110.3 mm)+0.48 in (+12.3 mm)+12.50%
Section width9.65 in (245.0 mm)9.65 in (245.0 mm)0.00 in (0.0 mm)0.00%
Circumference87.07 in (2,211.7 mm)90.10 in (2,288.7 mm)+3.03 in (+77.0 mm)+3.48%
Revolutions per mile728703−24−3.36%
True speed with the speedometer calibrated for 245/40R20
IndicatedActual on 245/40R20Actual on 245/45R20Difference
30 mph30.0 mph31.0 mph+1.0 mph
60 mph60.0 mph62.1 mph+2.1 mph
75 mph75.0 mph77.6 mph+2.6 mph

Ride-height change: 245/45R20 raises the vehicle by 0.48 in (12.3 mm) at the axle (half the +24.5 mm diameter difference).

245/45R20 is 0.96 in taller than 245/40R20 and the same width, a 3.48% difference in overall diameter.

With the speedometer calibrated for 245/40R20, an indicated 60 mph is actually 62.1 mph on 245/45R20, and revolutions per mile change from 728 to 703.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 245/40R20

Other comparisons with 245/45R20

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.