37x12.50R20 — the heavy-duty 37
The only 37 in this catalogue whose recorded platforms are work trucks rather than off-road vehicles.
Flotation (imperial) notation · Flotation (imperial)
- Overall diameter
- 37.00 in
- 940 mm
- Section width
- 12.50 in
- 318 mm
- Sidewall height
- 8.50 in
- 216 mm
- Aspect ratio
- 68.0%
- sidewall as a share of width
- Wheel diameter
- 20 in
- the hole in the middle
- Circumference
- 116.2 in
- 2952 mm
- Revolutions per mile
- 545.1
- geometric, not measured
- Revolutions per km
- 338.7
- geometric, not measured
- Typical load index
- 108–128
- 2205–3968 lb per tire
Flotation sizes are almost always LT construction, so they share the light-truck band. Speed symbols run low because the aggressive tread patterns these sizes are sold in are rated against heat build-up, not against sustained high speed.
The load-index range shown is the band this CLASS of size is typically produced in — not a list of what is in stock for this exact size today. Load index and speed symbol are printed on the sidewall of the specific tire you are holding, and the required minimum is on the placard of the specific vehicle you are fitting. Read both.
Nearest real sizes in metric notation, same wheel
- 325/60R2035.35 in tall-1.65 in
- 295/65R2035.10 in tall-1.90 in
- 285/65R2034.59 in tall-2.41 in
Compare any two sizes, including ones this site has no page for, in the comparison tool.
Platforms recorded with this size
The fourth-generation F-250 Super Duty, the fourth-generation Ram 2500 and the fourth-generation Silverado 2500HD all name 37x12.50R20 as a common upgrade. None ships it.
Those three are the only vehicles in the catalogue that reach 37 in on a factory 20-inch wheel, and their reason for being able to is that they start higher than anything else. A heavy-duty pickup leaves the factory between 33.46 in and 34.07 in, so a 37 is a step of three inches rather than five.
What it costs those three
| Coming from | Diameter | Step | Actual speed at an indicated 70 mph |
|---|---|---|---|
| 285/60R20 | 33.46 in | +3.54 in (10.56%) | 77.4 mph |
| 275/65R20 | 34.07 in | +2.93 in (8.58%) | 76.0 mph |
| 295/65R20 | 35.10 in | +1.90 in (5.42%) | 73.8 mph |
| 35x12.50R20 | 35.00 in | +2.00 in (5.71%) | 74.0 mph |
The bottom two rows are the ones that make this size viable on a work truck. Both of those are themselves upgrades these platforms list, so the 37 is frequently a second step rather than a first one, and taken from that position it is a five per cent change rather than a ten per cent one.
Its own wheel, above and below
38x13.50R20 is the only larger size catalogued on a 20-inch wheel: +1.00 in, 2.70%, and 1.00 in wider at 13.50 in. It is the smallest step between two adjacent flotation sizes anywhere here.
Downward, 35x12.50R20 is 2.00 in shorter on identical section width, and 325/60R20 is 1.65 in shorter while being 0.30 in wider — the only metric code on this wheel that beats a 12.50 flotation tire for stance.
The casing, and what a 20-inch wheel leaves of it
8.50 in of sidewall is the shallowest of the four 37s catalogued. 37x12.50R17 and 37x13.50R17 both carry 10.00 in, and 37x12.50R18 carries 9.50 in, all at the same 37.00 in of overall diameter.
For a truck that spends its time loaded, that difference is the substance of the wheel-size decision, and none of it appears in any figure the size code produces. This size is also set against a common heavy-duty starting point in the 275/70R18 comparison.
Related
- 275/70R18 vs 37x12.50R20
- 325/60R2035.35 in tall
- 295/65R2035.10 in tall
- 285/65R2034.59 in tall
Class: Flotation (imperial). Every figure above is computed from the size code, not stored — see how these numbers are calculated.