Tire Size Box

195/35R18 vs 195/40R18

195/40R18 compared with 195/35R18

+3.3% diameter, 0.0" width

195/40R18 is 24.14" tall vs 23.37". More than the 3% rule of thumb, so check carefully before switching.

23.4"18" rim2.7"7.7" wide
195/35R18 (solid) compared with 195/40R18 (dashed outline), drawn to scale

With 195/40R18 tires, when your speedometer says 60 mph you are really going

62.0 mph

195/40R18 is +0.77 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

195/35R18195/40R18Difference%
Overall diameter23.37"24.14"+0.77"+3.3%
Section width7.68"7.68"0.00"0.0%
Sidewall height2.69"3.07"+0.38"+14.3%
Circumference73.43"75.84"+2.41"+3.3%
Revolutions per mile862.8835.4−27.4−3.2%

Speedometer difference

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

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph62.0 mph+2.0 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 195/35R18 or 195/40R18?
195/40R18 is taller by 0.77 inches (24.14" vs 23.37"). 195/35R18 is the same width.
Can I replace 195/35R18 with 195/40R18?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 195/40R18 change my speedometer?
When your speedometer reads 60 mph with 195/40R18 fitted (calibrated for 195/35R18), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 195/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.38 inches of ground clearance at the axle.

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