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295/45R20 vs 315/40R21 tire size comparison

295/45R20315/40R21

315/40R21 is 0.4 in (1.54%) taller than 295/45R20 and 0.8 in wider. They fit different wheels: 295/45R20 a 20-inch wheel and 315/40R21 a 21-inch wheel.

295/45R20 and 315/40R21 side by side

+0.4 in / +1.54%295/45R20: 30.5 in tall, solid line315/40R21: 30.9 in tall, dashed line295/45R20Width 11.6 in (295 mm)Sidewall 5.2 in (133 mm)315/40R21Width 12.4 in (315 mm)Sidewall 5.0 in (126 mm)
295/45R20 is drawn with a solid line and 315/40R21 with a dashed line. In each drawing both tires are to the same scale; the tread shoulder and bead curves are simplified. The table below has the same numbers.
Dimensions of 295/45R20 and 315/40R21, with the difference (315/40R21 minus 295/45R20)
Measurement295/45R20315/40R21DifferenceDifference %
Section width11.6 in (295 mm)12.4 in (315 mm)+0.8 in (+20 mm)+6.78%
Sidewall height5.2 in (133 mm)5.0 in (126 mm)-0.2 in (-7 mm)-5.08%
Wheel (rim) diameter20.0 in (508 mm)21.0 in (533 mm)+1.0 in (+25 mm)+5.00%
Overall diameter30.5 in (774 mm)30.9 in (785 mm)+0.4 in (+11 mm)+1.54%
Circumference95.7 in (2430 mm)97.1 in (2467 mm)+1.4 in (+37 mm)+1.54%
Revolutions per mile662652-10-1.52%

Differences are 315/40R21 minus 295/45R20; percentages are relative to 295/45R20. These are nominal design dimensions. Real tires vary by brand, tread depth, wheel width, load and pressure.

The overall diameter differs by 1.54%, which is within the common 3% rule of thumb.

The rule of thumb keeps a replacement size within about 3% of the original overall diameter. It covers diameter only. It is not a fit, load or safety check, because width, wheel diameter, load capacity and clearance matter too. Confirm any size change with your vehicle's owner's manual or a tire professional.

Speedometer difference

When the speedometer reads 60 mph on a vehicle built for 295/45R20, the actual speed on 315/40R21 is about 60.9 mph. When it reads 60 mph on a vehicle built for 315/40R21, the actual speed on 295/45R20 is about 59.1 mph. These figures assume the speedometer is accurate on the original size and use nominal dimensions, so treat them as estimates.

Actual speed for a given speedometer reading, 295/45R20 against 315/40R21
Speedometer readsActual on 315/40R21 (built for 295/45R20)Actual on 295/45R20 (built for 315/40R21)
20 mph20.3 mph19.7 mph
30 mph30.5 mph29.5 mph
40 mph40.6 mph39.4 mph
50 mph50.8 mph49.2 mph
60 mph60.9 mph59.1 mph
70 mph71.1 mph68.9 mph
80 mph81.2 mph78.8 mph

A common rule of thumb is to keep a replacement size within about 3% of the original overall diameter. Check the tire placard on the driver's door jamb and your owner's manual for the sizes your vehicle was built for. Confirm any size change with your vehicle's owner's manual or a tire professional.

Which vehicles use each size?

These vehicles list the size among their verified sizes, by trim. Open one to see all of its sizes.

Check it in the calculator

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Shop for 295/45R20 or 315/40R21 tires

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Other comparisons with 295/45R20

Side-by-side dimensions and speedometer difference for sizes close to 295/45R20 in overall diameter.

Other comparisons with 315/40R21

Side-by-side dimensions and speedometer difference for sizes close to 315/40R21 in overall diameter.

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