305/78R21 Tire Size Specifications
This tire size 305/78R21 fits 0 vehicles in our database.
Everything to know about the 305/78R21 tire size
Size geometry
A 305/78R21 tire has a 305mm section width and a 78% aspect ratio, mounted on a 21-inch rim. Sidewall height works out to 237.9mm (9.37") and overall outside diameter is 1009.2mm (39.73"). At highway speed the tire completes about 315 revolutions per kilometre â your speedometer and odometer were calibrated against this number.
Direct substitute sizes
If 305/78R21 is unavailable, the closest same-diameter substitutes on the same rim are 295/81R21 and 315/76R21. Both keep your speedometer reading within 1% â safe for daily use, ABS, and stability control. Always verify load and speed ratings before swapping.
Plus / minus sizing options
For a 305/78R21 you can upsize to 315/71R22 (plus-one) to fit a larger wheel without changing the speedometer reading, or downsize to 295/85R20 (minus-one) for a softer ride or winter setup. Both stay inside the Âą3% diameter tolerance that ABS and TPMS systems expect.
Vehicle compatibility
0 vehicles in our database run the 305/78R21 tire size from the factory. Aftermarket fitment depends on rim width, offset, and clearance â match these specs to your wheel before purchasing tires.
Vehicles Using 305/78R21
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