Tire Size Box

295/35R17 vs 225/40R18

225/40R18 compared with 295/35R17

−0.2% diameter, −2.8" width

225/40R18 is 25.09" tall vs 25.13". Within the 3% rule, so usually interchangeable.

25.1"17" rim4.1"11.6" wide
295/35R17 (solid) compared with 225/40R18 (dashed outline), drawn to scale

With 225/40R18 tires, when your speedometer says 60 mph you are really going

59.9 mph

225/40R18 is −0.04 inches (−0.2%) in overall diameter. That is within the 3% most shops and makers allow.

295/35R17225/40R18Difference%
Overall diameter25.13"25.09"−0.04"−0.2%
Section width11.61"8.86"−2.76"−23.7%
Sidewall height4.06"3.54"−0.52"−12.8%
Circumference78.95"78.81"−0.14"−0.2%
Revolutions per mile802.6803.9+1.4+0.2%

Speedometer difference

If your vehicle came with 295/35R17 and you fit 225/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph29.9 mph−0.1 mph
40 mph39.9 mph−0.1 mph
50 mph49.9 mph−0.1 mph
60 mph59.9 mph−0.1 mph
65 mph64.9 mph−0.1 mph
70 mph69.9 mph−0.1 mph
75 mph74.9 mph−0.1 mph
80 mph79.9 mph−0.1 mph

Each size on its own

Questions

Which is bigger, 295/35R17 or 225/40R18?
295/35R17 is taller by 0.04 inches (25.13" vs 25.09"). 295/35R17 is wider by 2.76 inches.
Can I replace 295/35R17 with 225/40R18?
Usually, yes. The diameter difference is −0.2%, 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 225/40R18 change my speedometer?
When your speedometer reads 60 mph with 225/40R18 fitted (calibrated for 295/35R17), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.2%.
Will 225/40R18 lift my vehicle?
Ride height changes by half the diameter difference: −0.02 inches of ground clearance at the axle.

Other comparisons