Tire Size Box

165/65R15 vs 235/40R16

235/40R16 compared with 165/65R15

−0.2% diameter, +2.8" width

235/40R16 is 23.40" tall vs 23.44". Within the 3% rule, so usually interchangeable.

23.4"15" rim4.2"6.5" wide
165/65R15 (solid) compared with 235/40R16 (dashed outline), drawn to scale

With 235/40R16 tires, when your speedometer says 60 mph you are really going

59.9 mph

235/40R16 is −0.04 inches (−0.2%) in overall diameter. That is within the 3% most shops and makers allow.

165/65R15235/40R16Difference%
Overall diameter23.44"23.40"−0.04"−0.2%
Section width6.50"9.25"+2.76"+42.4%
Sidewall height4.22"3.70"−0.52"−12.4%
Circumference73.65"73.52"−0.14"−0.2%
Revolutions per mile860.2861.8+1.6+0.2%

Speedometer difference

If your vehicle came with 165/65R15 and you fit 235/40R16, 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, 165/65R15 or 235/40R16?
165/65R15 is taller by 0.04 inches (23.44" vs 23.40"). 235/40R16 is wider by 2.76 inches.
Can I replace 165/65R15 with 235/40R16?
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 235/40R16 change my speedometer?
When your speedometer reads 60 mph with 235/40R16 fitted (calibrated for 165/65R15), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.2%.
Will 235/40R16 lift my vehicle?
Ride height changes by half the diameter difference: −0.02 inches of ground clearance at the axle.

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