37x12.50R20 tire size
A flotation size: 37.0 inches tall and 12.5 inches wide on a 20-inch wheel. Below: what it measures, what it swaps with, and which trucks run it from the factory.
Sizes that swap with 37x12.50R20
Within 3% of the original diameter — close enough to fit without a recalibration or clearance work on most trucks.
| Size | Diameter | Difference | Width |
|---|---|---|---|
| 37x12.50R17 | 37.00" | same height | 12.5" |
| 37x12.50R18 | 37.00" | same height | 12.5" |
| 37x13.50R22 | 37.00" | same height | 13.5" |
| 38x13.50R17 | 38.00" | +1.00" (+2.7%) | 13.5" |
| 38x13.50R18 | 38.00" | +1.00" (+2.7%) | 13.5" |
| 38x13.50R20 | 38.00" | +1.00" (+2.7%) | 13.5" |
Plus and minus sizing
Same overall height on a different wheel. Going down a wheel size buys sidewall for off-road; going up is usually about looks. Gearing and speedometer stay put either way.
Compare 37x12.50R20 against your current size
Tire size comparison
Diameter change, speedometer error, and whether it will rub.
37.0" tall · 12.5" wide
37.0" tall · 12.5" wide
Diameter and width are close enough to stock that this is a bolt-on swap on an unmodified truck.
- Within the range normally treated as a direct swap — no clearance work expected.
Reading this size
37x12.50R20 is written the flotation way, which states the numbers directly: 37 inches tall, 12.50 inches wide, on a 20-inch wheel. No arithmetic needed — which is why off-road tires are usually sold this way.
That last figure is the one that matters when you change size. The speedometer, odometer, transmission shift points and stability control all assume the factory diameter, so staying within a few percent keeps everything calibrated. Width matters for clearance rather than gearing — it decides whether the tire touches the suspension at full lock.
Common questions
How tall is a 37x12.50R20 tire?
37.00 inches in overall diameter, with a 8.50-inch sidewall on a 20-inch wheel. Section width is 12.50 inches (317.5mm), and it turns about 545 times per mile. Real tires vary from the nominal figure by up to half an inch depending on brand and tread.
What is equivalent to a 37x12.50R20?
The closest common size is 37x12.50R17 at 37.00 inches — effectively identical. Anything within about 3% of the original diameter swaps on without upsetting the speedometer badly or needing a tune.
Will 37x12.50R20 fit my truck?
We do not have it listed as a factory size on the trucks we cover, so treat it as an upgrade size. Put your current size into the calculator on this page to see the diameter change and whether it is likely to rub.
Does going to 37x12.50R20 affect my speedometer?
Only if the overall diameter changes. The speedometer counts wheel rotations and multiplies by the factory tire circumference, so a larger tire makes the truck travel further per rotation than the gauge assumes and the display reads low. Around 3% is where transmission shift points and stability control calibration start to matter, and most modern trucks can be recalibrated for the new size.