Tire Size Box

205/35R18 vs 205/45R18

205/45R18 compared with 205/35R18

+6.8% diameter, 0.0" width

205/45R18 is 25.26" tall vs 23.65". More than the 3% rule of thumb, so check carefully before switching.

23.6"18" rim2.8"8.1" wide
205/35R18 (solid) compared with 205/45R18 (dashed outline), drawn to scale

With 205/45R18 tires, when your speedometer says 60 mph you are really going

64.1 mph

205/45R18 is +1.61 inches (+6.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/35R18205/45R18Difference%
Overall diameter23.65"25.26"+1.61"+6.8%
Section width8.07"8.07"0.00"0.0%
Sidewall height2.82"3.63"+0.81"+28.6%
Circumference74.30"79.37"+5.07"+6.8%
Revolutions per mile852.8798.3−54.5−6.4%

Speedometer difference

If your vehicle came with 205/35R18 and you fit 205/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.4 mph+3.4 mph
60 mph64.1 mph+4.1 mph
65 mph69.4 mph+4.4 mph
70 mph74.8 mph+4.8 mph
75 mph80.1 mph+5.1 mph
80 mph85.5 mph+5.5 mph

Each size on its own

Questions

Which is bigger, 205/35R18 or 205/45R18?
205/45R18 is taller by 1.61 inches (25.26" vs 23.65"). 205/35R18 is the same width.
Can I replace 205/35R18 with 205/45R18?
It is not recommended without checking carefully. The diameter difference is +6.8%, 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 205/45R18 change my speedometer?
When your speedometer reads 60 mph with 205/45R18 fitted (calibrated for 205/35R18), your real speed is 64.1 mph. Your odometer will under-count miles by about 6.8%.
Will 205/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.81 inches of ground clearance at the axle.

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