Tire Size Box

215/30R20 vs 215/40R20

215/40R20 compared with 215/30R20

+6.8% diameter, 0.0" width

215/40R20 is 26.77" tall vs 25.08". More than the 3% rule of thumb, so check carefully before switching.

25.1"20" rim2.5"8.5" wide
215/30R20 (solid) compared with 215/40R20 (dashed outline), drawn to scale

With 215/40R20 tires, when your speedometer says 60 mph you are really going

64.1 mph

215/40R20 is +1.69 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/30R20215/40R20Difference%
Overall diameter25.08"26.77"+1.69"+6.8%
Section width8.46"8.46"0.00"0.0%
Sidewall height2.54"3.39"+0.85"+33.3%
Circumference78.79"84.11"+5.32"+6.8%
Revolutions per mile804.2753.3−50.9−6.3%

Speedometer difference

If your vehicle came with 215/30R20 and you fit 215/40R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.1 mph+4.1 mph
65 mph69.4 mph+4.4 mph
70 mph74.7 mph+4.7 mph
75 mph80.1 mph+5.1 mph
80 mph85.4 mph+5.4 mph

Each size on its own

Questions

Which is bigger, 215/30R20 or 215/40R20?
215/40R20 is taller by 1.69 inches (26.77" vs 25.08"). 215/30R20 is the same width.
Can I replace 215/30R20 with 215/40R20?
It is not recommended without checking carefully. The diameter difference is +6.8%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 215/40R20 change my speedometer?
When your speedometer reads 60 mph with 215/40R20 fitted (calibrated for 215/30R20), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 215/40R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.85 inches of ground clearance at the axle.

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