305/30R21 Tire Size Specifications & Compatible Vehicles
Overall Diameter
716.4 mm
Section Width
305 mm
Sidewall Height
91.5 mm
Circumference
2250.6 mm
Revs/Mile
715
Rim Diameter
21"
Inch Equivalent
28.2x12R21
Rim Width (ETRTO)
9.5" – 12.0"
Alternative Tire Sizes
These tire sizes are within 3% overall diameter of 305/30R21 and may be used as replacements:
Understanding 305/30R21
The tire size 305/30R21 means the tire has a section width of 305mm, an aspect ratio of 30% (the sidewall height is 30% of the width), and fits a 21-inch rim.
Sidewall Height = 305 x 0.3 = 91.5 mm
Overall Diameter = (91.5 x 2) + (21 x 25.4) = 716.4 mm
Circumference = 716.4 x π = 2250.6 mm
Overall Diameter = (91.5 x 2) + (21 x 25.4) = 716.4 mm
Circumference = 716.4 x π = 2250.6 mm
Frequently Asked Questions
The 305/30R21 is a standard tire size. Check your vehicle door jamb sticker or owner manual to confirm compatibility.
A 305/30R21 tire has an overall diameter of 716.4mm (28.2 inches). The sidewall height is 91.5mm, and the total circumference is 2251mm.
For 305/30R21 tires, the ETRTO recommended rim width is 10.5". The acceptable range is 9.5" minimum to 12.0" maximum. Using a rim outside this range can cause improper bead seating and unsafe handling.
Yes, as long as the replacement tire overall diameter is within 3% of the 305/30R21 716.4mm diameter. Compatible alternatives include 175/45R22, 225/35R22, 315/25R22. Use our Tire Size Calculator to compare any two sizes.