Tire Size Box

305/40R22 vs 305/45R22

305/45R22 compared with 305/40R22

+3.8% diameter, 0.0" width

305/45R22 is 32.81" tall vs 31.61". More than the 3% rule of thumb, so check carefully before switching.

31.6"22" rim4.8"12.0" wide
305/40R22 (solid) compared with 305/45R22 (dashed outline), drawn to scale

With 305/45R22 tires, when your speedometer says 60 mph you are really going

62.3 mph

305/45R22 is +1.20 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/40R22305/45R22Difference%
Overall diameter31.61"32.81"+1.20"+3.8%
Section width12.01"12.01"0.00"0.0%
Sidewall height4.80"5.40"+0.60"+12.5%
Circumference99.29"103.07"+3.77"+3.8%
Revolutions per mile638.1614.7−23.4−3.7%

Speedometer difference

If your vehicle came with 305/40R22 and you fit 305/45R22, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 305/40R22 or 305/45R22?
305/45R22 is taller by 1.20 inches (32.81" vs 31.61"). 305/40R22 is the same width.
Can I replace 305/40R22 with 305/45R22?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 305/45R22 change my speedometer?
When your speedometer reads 60 mph with 305/45R22 fitted (calibrated for 305/40R22), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 305/45R22 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

Other comparisons