Is 305/45R22 bigger than 275/60R20?

305/45R22 is 0.19 inches shorter and 30 mm wider. In overall diameter that is −0.56%, which stays inside the ±3% rule of thumb for a substitution.

How much will 305/45R22 throw off my speedometer?

Every reading scales by 0.99439. An indicated 60 mph becomes 59.7 mph, and every 100 miles on the odometer is really 99.4 miles.

How much does 305/45R22 change ground clearance over 275/60R20?

The axle centerline moves by 0.09 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 305/45R22 fit where 275/60R20 fits?

Nothing derived from the size code can answer that. Clearance depends on wheel offset, suspension travel and body dimensions that no tire size contains. This page tells you exactly what changes dimensionally, which is the part that can be calculated.

275/60R20 vs 305/45R22

305/45R22 is −0.19″ in overall diameter and +30 mm in section width against 275/60R20 — a diameter change of −0.56%, which stays inside the ±3% substitution rule. An indicated 60 mph would really be 59.7 mph.

Within 3%

Every dimension

Difference between 275/60R20 and 305/45R22
Dimension	275/60R20 → 305/45R22	Change
Overall diameter	32.99″ → 32.81″	−0.19″ (−0.56%)
Section width	275 mm → 305 mm	+30 mm (+10.91%)
Sidewall height	165.0 mm → 137.3 mm	−27.8 mm
Rolling circumference	103.65″ → 103.07″	−0.58″
Revolutions per mile	611.3 → 614.7	+3.4
Axle height / clearance	16.50″ → 16.40″	−0.09″

275/60R20275 mm

305/45R22305 mm

275/60R20 32.99″305/45R22 32.81″

Which is taller, 275/60R20 or 305/45R22?

275/60R20 is the taller of the two, at 32.99″ against 32.81″. The gap is 0.19 inches, or 4.7 mm.

Both are metric sizes, so neither states its height directly. Both figures below are derived from the section width, aspect ratio and wheel diameter in the code. 275/60R20 is 275 mm wide with a 165.0 mm sidewall on a 20″ wheel; 305/45R22 is 305 mm wide with a 137.3 mm sidewall on a 22″ wheel.

What the speedometer will read

Indicated versus actual speed after the size change
Speedometer reads	Actual speed	Error
25 mph	24.9 mph	−0.1 mph
40 mph	39.8 mph	−0.2 mph
55 mph	54.7 mph	−0.3 mph
60 mph	59.7 mph	−0.3 mph
70 mph	69.6 mph	−0.4 mph
80 mph	79.6 mph	−0.4 mph

Fitting 305/45R22 in place of 275/60R20 multiplies every speed and distance reading by 0.99439. Over 10,000 indicated miles the odometer is out by −56 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 275/60R20 would need 3.71 to keep the same engine speed on 305/45R22. Work it out for your own axle ratio.

Full specification of each size

275/60R20

Derived dimensions for 275/60R20
Dimension	Metric	Imperial
Section width	275.0 mm	10.83″
Sidewall height	165.0 mm	6.50″
Wheel diameter	508.0 mm	20.0″
Overall diameter	838.0 mm	32.99″
Rolling circumference	2,632.7 mm	103.65″
Revolutions per mile	379.8 / km	611.3 / mile
Measuring rim (estimate)	216 mm	8.5″

305/45R22

Derived dimensions for 305/45R22
Dimension	Metric	Imperial
Section width	305.0 mm	12.01″
Sidewall height	137.3 mm	5.40″
Wheel diameter	558.8 mm	22.0″
Overall diameter	833.3 mm	32.81″
Rolling circumference	2,617.9 mm	103.07″
Revolutions per mile	382.0 / km	614.7 / mile
Measuring rim (estimate)	254 mm	10″

Rim widths differ too: 275/60R20 is designed for 8″–9.5″ and 305/45R22 for 9.5″–11″. Their measuring rims differ, so the same wheel will not be ideal for both.

Can you swap one for the other?

Inside the ±3% rule

The diameter difference of −0.56% is within the ±3% that fitters use as the boundary for a substitution, so the speedometer, odometer and wheel-speed-derived systems stay close enough to calibration. The section width difference of +30 mm is a separate question and is the one that decides whether it rubs.

Neither figure says anything about physical fitment. Whether 305/45R22 clears the strut, the fender liner and the steering stops depends on wheel offset and suspension geometry that a size code does not encode. For maintenance rather than sizing, Car Basics covers tire care.