305/55R20 vs 33x12.50R20

305/55R20 is 0.2" taller than 33x12.50R20 (0.6%)

Diameter difference−0.63%diameter 33.21" → 33.00"
305/55R2033x12.50R20
305/55R2033x12.50R20Difference
Overall diameter33.21"33.00"−0.21"
Section width12.01"12.50"+0.49"
Sidewall height6.60"6.50"−0.10"
Circumference104.3"103.7"−0.7"
Revolutions per mile607611+4
Wheel diameter20"20"±0"

Speedometer

ShowsActualDiff
30 mph29.8 mph−0.2
45 mph44.7 mph−0.3
60 mph59.6 mph−0.4
70 mph69.6 mph−0.4
80 mph79.5 mph−0.5

Gear ratio to match

CurrentEquivalent
3.423.40
3.553.53
3.733.71
4.104.07

33x12.50R20 is 0.21" shorter than 305/55R20, a −0.63% change in diameter, inside the 3% range most shops treat as a safe swap.

Ground clearance changes by 0.10" (half the diameter change), and the tire needs 0.10" less room above it.

33x12.50R20 is 0.49" wider. On the same wheel offset about half of that, 0.25", moves toward the suspension and half toward the fender.

Both fit a 20" wheel; the sidewall is 0.10" shorter on 33x12.50R20.

Details: 305/55R20 in inches · 33x12.50R20 in inches · change sizes in the calculator

FAQ

What is the difference between 305/55R20 and 33x12.50R20?

33x12.50R20 is 0.21" shorter (−0.63%) and 0.49" wider than 305/55R20.

Will 33x12.50R20 change my speedometer?

Yes, by −0.63%. When the speedometer shows 60 mph you would be going 59.6 mph.

Can I replace 305/55R20 with 33x12.50R20?

Often yes: the diameter change of −0.6% is within the common 3% guideline. Check the load index, speed rating and clearance.