Tire Size Box

315/75R17 vs 295/75R18

295/75R18 compared with 315/75R17

−0.5% diameter, −0.8" width

295/75R18 is 35.42" tall vs 35.60". Within the 3% rule, so usually interchangeable.

35.6"17" rim9.3"12.4" wide
315/75R17 (solid) compared with 295/75R18 (dashed outline), drawn to scale

With 295/75R18 tires, when your speedometer says 60 mph you are really going

59.7 mph

295/75R18 is −0.18 inches (−0.5%) in overall diameter. That is within the 3% most shops and makers allow.

315/75R17295/75R18Difference%
Overall diameter35.60"35.42"−0.18"−0.5%
Section width12.40"11.61"−0.79"−6.3%
Sidewall height9.30"8.71"−0.59"−6.3%
Circumference111.85"111.28"−0.57"−0.5%
Revolutions per mile566.5569.4+2.9+0.5%

Speedometer difference

If your vehicle came with 315/75R17 and you fit 295/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph19.9 mph−0.1 mph
30 mph29.8 mph−0.2 mph
40 mph39.8 mph−0.2 mph
50 mph49.7 mph−0.3 mph
60 mph59.7 mph−0.3 mph
65 mph64.7 mph−0.3 mph
70 mph69.6 mph−0.4 mph
75 mph74.6 mph−0.4 mph
80 mph79.6 mph−0.4 mph

Each size on its own

Questions

Which is bigger, 315/75R17 or 295/75R18?
315/75R17 is taller by 0.18 inches (35.60" vs 35.42"). 315/75R17 is wider by 0.79 inches.
Can I replace 315/75R17 with 295/75R18?
Usually, yes. The diameter difference is −0.5%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 295/75R18 change my speedometer?
When your speedometer reads 60 mph with 295/75R18 fitted (calibrated for 315/75R17), your real speed is 59.7 mph. Your odometer will over-count miles by about 0.5%.
Will 295/75R18 lift my vehicle?
Ride height changes by half the diameter difference: −0.09 inches of ground clearance at the axle.

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