Tire Size Box

305/40R18 vs 295/45R18

295/45R18 compared with 305/40R18

+3.1% diameter, −0.4" width

295/45R18 is 28.45" tall vs 27.61". More than the 3% rule of thumb, so check carefully before switching.

27.6"18" rim4.8"12.0" wide
305/40R18 (solid) compared with 295/45R18 (dashed outline), drawn to scale

With 295/45R18 tires, when your speedometer says 60 mph you are really going

61.8 mph

295/45R18 is +0.85 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/40R18295/45R18Difference%
Overall diameter27.61"28.45"+0.85"+3.1%
Section width12.01"11.61"−0.39"−3.3%
Sidewall height4.80"5.23"+0.42"+8.8%
Circumference86.73"89.39"+2.66"+3.1%
Revolutions per mile730.6708.8−21.7−3.0%

Speedometer difference

If your vehicle came with 305/40R18 and you fit 295/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 305/40R18 or 295/45R18?
295/45R18 is taller by 0.85 inches (28.45" vs 27.61"). 305/40R18 is wider by 0.39 inches.
Can I replace 305/40R18 with 295/45R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 295/45R18 change my speedometer?
When your speedometer reads 60 mph with 295/45R18 fitted (calibrated for 305/40R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 295/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

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