Tire Size Box

245/35R18 vs 245/45R18

245/45R18 compared with 245/35R18

+7.8% diameter, 0.0" width

245/45R18 is 26.68" tall vs 24.75". More than the 3% rule of thumb, so check carefully before switching.

24.8"18" rim3.4"9.6" wide
245/35R18 (solid) compared with 245/45R18 (dashed outline), drawn to scale

With 245/45R18 tires, when your speedometer says 60 mph you are really going

64.7 mph

245/45R18 is +1.93 inches (+7.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/35R18245/45R18Difference%
Overall diameter24.75"26.68"+1.93"+7.8%
Section width9.65"9.65"0.00"0.0%
Sidewall height3.38"4.34"+0.96"+28.6%
Circumference77.76"83.82"+6.06"+7.8%
Revolutions per mile814.8755.9−58.9−7.2%

Speedometer difference

If your vehicle came with 245/35R18 and you fit 245/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.3 mph+2.3 mph
40 mph43.1 mph+3.1 mph
50 mph53.9 mph+3.9 mph
60 mph64.7 mph+4.7 mph
65 mph70.1 mph+5.1 mph
70 mph75.5 mph+5.5 mph
75 mph80.8 mph+5.8 mph
80 mph86.2 mph+6.2 mph

Each size on its own

Questions

Which is bigger, 245/35R18 or 245/45R18?
245/45R18 is taller by 1.93 inches (26.68" vs 24.75"). 245/35R18 is the same width.
Can I replace 245/35R18 with 245/45R18?
It is not recommended without checking carefully. The diameter difference is +7.8%, 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 245/45R18 change my speedometer?
When your speedometer reads 60 mph with 245/45R18 fitted (calibrated for 245/35R18), your real speed is 64.7 mph. Your odometer will under-count miles by about 7.8%.
Will 245/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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