Tire size
305/30 R20
Full dimensions and a live comparison calculator for the 305/30 R20 tire size.
Overall diameter
691.0 mm
27.20″
Sidewall height
91.5 mm
Circumference
2.171 m
Revs / km
460.7
Section width
305 mm
Aspect ratio
30%
Rim diameter
20″
508.0 mm
Radius
345.5 mm
What does 305/30 R20 mean?
The 305 is the section width in millimetres, measured sidewall to sidewall. The 30 is the aspect ratio — sidewall height as a percentage of width, so the sidewall here is 91.5 mm. The R20 means a radial-construction tire designed for a 20-inch wheel rim. Together these give an overall diameter of 691 mm.
Compare 305/30 R20 with another size
Current Tire
New Tire
Ground line · scaled comparison
Not Recommended
Over 5% — speedometer & ABS may misread
Diameter change
-56.7 mm
-8.21%
Speedometer at 100
91.8 km/h
-8.21% error
Ground clearance
-28.4 mm
ride height delta
Sidewall change
+9.8 mm
revs/km: 501.8
Permalink for this comparison:
/compare/305-30-r20-vs-225-45-r17Common alternatives to 305/30 R20
These sizes are within a few percent overall diameter — usually safe on the same vehicle from a speedometer-error standpoint.
Compare 305/30 R20 with popular upgrades
Plus-size upgrades from 305/30 R20
Fitment safety note
Overall diameter, speedometer error and circumference are only part of the picture. Physical clearance, wheel offset (ET), hub bore, suspension geometry, load index and your manufacturer's recommendation all decide whether a size is truly safe on your car. Always cross-check with the vehicle manual or a qualified fitter before changing tire size.