Tire Size Box

225/35R18 vs 225/45R18

225/45R18 compared with 225/35R18

+7.3% diameter, 0.0" width

225/45R18 is 25.97" tall vs 24.20". More than the 3% rule of thumb, so check carefully before switching.

24.2"18" rim3.1"8.9" wide
225/35R18 (solid) compared with 225/45R18 (dashed outline), drawn to scale

With 225/45R18 tires, when your speedometer says 60 mph you are really going

64.4 mph

225/45R18 is +1.77 inches (+7.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/35R18225/45R18Difference%
Overall diameter24.20"25.97"+1.77"+7.3%
Section width8.86"8.86"0.00"0.0%
Sidewall height3.10"3.99"+0.89"+28.6%
Circumference76.03"81.59"+5.57"+7.3%
Revolutions per mile833.4776.5−56.8−6.8%

Speedometer difference

If your vehicle came with 225/35R18 and you fit 225/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph42.9 mph+2.9 mph
50 mph53.7 mph+3.7 mph
60 mph64.4 mph+4.4 mph
65 mph69.8 mph+4.8 mph
70 mph75.1 mph+5.1 mph
75 mph80.5 mph+5.5 mph
80 mph85.9 mph+5.9 mph

Each size on its own

Questions

Which is bigger, 225/35R18 or 225/45R18?
225/45R18 is taller by 1.77 inches (25.97" vs 24.20"). 225/35R18 is the same width.
Can I replace 225/35R18 with 225/45R18?
It is not recommended without checking carefully. The diameter difference is +7.3%, 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 225/45R18 change my speedometer?
When your speedometer reads 60 mph with 225/45R18 fitted (calibrated for 225/35R18), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.3%.
Will 225/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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