Tire Size Box

295/45R20 vs 345/35R21

345/35R21 compared with 295/45R20

+0.2% diameter, +2.0" width

345/35R21 is 30.51" tall vs 30.45". Within the 3% rule, so usually interchangeable.

30.5"20" rim5.2"11.6" wide
295/45R20 (solid) compared with 345/35R21 (dashed outline), drawn to scale

With 345/35R21 tires, when your speedometer says 60 mph you are really going

60.1 mph

345/35R21 is +0.06 inches (+0.2%) in overall diameter. That is within the 3% most shops and makers allow.

295/45R20345/35R21Difference%
Overall diameter30.45"30.51"+0.06"+0.2%
Section width11.61"13.58"+1.97"+16.9%
Sidewall height5.23"4.75"−0.47"−9.0%
Circumference95.67"95.84"+0.17"+0.2%
Revolutions per mile662.3661.1−1.2−0.2%

Speedometer difference

If your vehicle came with 295/45R20 and you fit 345/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.1 mph+0.1 mph
40 mph40.1 mph+0.1 mph
50 mph50.1 mph+0.1 mph
60 mph60.1 mph+0.1 mph
65 mph65.1 mph+0.1 mph
70 mph70.1 mph+0.1 mph
75 mph75.1 mph+0.1 mph
80 mph80.1 mph+0.1 mph

Each size on its own

Questions

Which is bigger, 295/45R20 or 345/35R21?
345/35R21 is taller by 0.06 inches (30.51" vs 30.45"). 345/35R21 is wider by 1.97 inches.
Can I replace 295/45R20 with 345/35R21?
Usually, yes. The diameter difference is +0.2%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 345/35R21 change my speedometer?
When your speedometer reads 60 mph with 345/35R21 fitted (calibrated for 295/45R20), your real speed is 60.1 mph. Your odometer will under-count miles by about 0.2%.
Will 345/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.03 inches of ground clearance at the axle.

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