Tire Size Box

195/40R17 vs 195/35R18

195/35R18 compared with 195/40R17

+1.0% diameter, 0.0" width

195/35R18 is 23.37" tall vs 23.14". Within the 3% rule, so usually interchangeable.

23.1"17" rim3.1"7.7" wide
195/40R17 (solid) compared with 195/35R18 (dashed outline), drawn to scale

With 195/35R18 tires, when your speedometer says 60 mph you are really going

60.6 mph

195/35R18 is +0.23 inches (+1.0%) in overall diameter. That is within the 3% most shops and makers allow.

195/40R17195/35R18Difference%
Overall diameter23.14"23.37"+0.23"+1.0%
Section width7.68"7.68"0.00"0.0%
Sidewall height3.07"2.69"−0.38"−12.5%
Circumference72.70"73.43"+0.73"+1.0%
Revolutions per mile871.5862.8−8.7−1.0%

Speedometer difference

If your vehicle came with 195/40R17 and you fit 195/35R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.2 mph+0.2 mph
30 mph30.3 mph+0.3 mph
40 mph40.4 mph+0.4 mph
50 mph50.5 mph+0.5 mph
60 mph60.6 mph+0.6 mph
65 mph65.7 mph+0.7 mph
70 mph70.7 mph+0.7 mph
75 mph75.8 mph+0.8 mph
80 mph80.8 mph+0.8 mph

Each size on its own

Questions

Which is bigger, 195/40R17 or 195/35R18?
195/35R18 is taller by 0.23 inches (23.37" vs 23.14"). 195/40R17 is the same width.
Can I replace 195/40R17 with 195/35R18?
Usually, yes. The diameter difference is +1.0%, 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 195/35R18 change my speedometer?
When your speedometer reads 60 mph with 195/35R18 fitted (calibrated for 195/40R17), your real speed is 60.6 mph. Your odometer will under-count miles by about 1.0%.
Will 195/35R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.12 inches of ground clearance at the axle.

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