Tire Size Box

315/35R17 vs 315/40R17

315/40R17 compared with 315/35R17

+4.8% diameter, 0.0" width

315/40R17 is 26.92" tall vs 25.68". More than the 3% rule of thumb, so check carefully before switching.

25.7"17" rim4.3"12.4" wide
315/35R17 (solid) compared with 315/40R17 (dashed outline), drawn to scale

With 315/40R17 tires, when your speedometer says 60 mph you are really going

62.9 mph

315/40R17 is +1.24 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/35R17315/40R17Difference%
Overall diameter25.68"26.92"+1.24"+4.8%
Section width12.40"12.40"0.00"0.0%
Sidewall height4.34"4.96"+0.62"+14.3%
Circumference80.68"84.58"+3.90"+4.8%
Revolutions per mile785.3749.2−36.2−4.6%

Speedometer difference

If your vehicle came with 315/35R17 and you fit 315/40R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.4 mph+3.4 mph
75 mph78.6 mph+3.6 mph
80 mph83.9 mph+3.9 mph

Each size on its own

Questions

Which is bigger, 315/35R17 or 315/40R17?
315/40R17 is taller by 1.24 inches (26.92" vs 25.68"). 315/35R17 is the same width.
Can I replace 315/35R17 with 315/40R17?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 315/40R17 change my speedometer?
When your speedometer reads 60 mph with 315/40R17 fitted (calibrated for 315/35R17), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 315/40R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.62 inches of ground clearance at the axle.

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