38x12.50-17 Tire Size

All You Need to Know About 38x12.50-17 Tires

A 38x12.50-17 tire is a non-radial flotation tire with a nominal 38-inch overall diameter, a 12.5-inch section width, and a 17-inch wheel diameter. The 38x12.50-17 occupies a specialty position between the common 37-inch and 40-inch off-road tire categories. Like the 37x12.50-17, the absence of "R" in the 38x12.50-17 designation indicates non-radial construction - typically bias-ply - rather than the radial architecture used in modern truck tires.

38x12.50-17 Size Quick Specs

• Nominal overall diameter: ~38 inches (actual diameter varies ±1-2% by manufacturer)
• Nominal section width: ~12.5 inches
• Construction type: Bias-ply or non-radial specialty
• Wheel diameter: 17 inches
• Approximate sidewall height: ~10.5 inches
• Recommended wheel width range: 8.5-11.0 inches
• Standard measuring rim: 17x10

What 38x12.50-17 Means

• 38 = nominal tire diameter in inches
• 12.50 = nominal section width in inches
• 17 = wheel diameter in inches
• No "R" = non-radial construction

The 38x12.50-17 uses the same traditional flotation size notation as the 37x12.50-17 and other non-R flotation sizes. The 38-inch diameter is the distinguishing figure - one nominal inch larger than 37x12.50-17 - and represents a meaningful step in terms of required vehicle modification, axle clearance, and off-road capability.

38x12.50-17 vs 37x12.50-17: Direct Comparison

The 38x12.50-17 adds one nominal inch of diameter and approximately 0.5 inch of axle clearance compared with the 37x12.50-17. Both sizes share a 12.5-inch section width, so width-related fitment differences between 38x12.50-17 and 37x12.50-17 are minimal. The additional diameter on the 38x12.50-17 improves obstacle rollover and breakover angle over the 37x12.50-17, but the difference is smaller than the step between 35-inch and 37-inch sizes.

Where 38x12.50-17 Fits in the Off-Road Tire Market

The 38x12.50-17 is not a high-volume commercial size. It does not fit neatly into the mass-market 37-inch or 40-inch categories, which means:

• Fewer manufacturers produce 38x12.50-17 compared with 37x12.50-17 or 40x13.50-17
• Retail availability of 38x12.50-17 is more limited than adjacent sizes
• 38x12.50-17 is primarily found in specialty off-road catalogs and military-surplus tire markets

Vehicles running 38x12.50-17 are typically purpose-built off-road rigs rather than daily drivers. The 38x12.50-17's diameter places it firmly in the heavy-modification category, requiring lift, trimming, and clearance work comparable to or exceeding what a 37x12.50-17 demands.

Clearance and Fitment Considerations for 38x12.50-17

A 38x12.50-17 requires at least as much suspension lift and body clearance as a 37x12.50-17, and in many cases more. The 38x12.50-17's one additional inch of diameter over the 37x12.50-17 can expose fitment gaps in builds that were engineered precisely around 37-inch clearances. Common modifications required for 38x12.50-17 include:

• Suspension lift sufficient to clear a 38-inch diameter at full compression - often 5–6 inches minimum on most platforms
• Fender trimming beyond what a 37x12.50-17 typically requires
• Bump-stop relocation to prevent 38x12.50-17 tire contact with the frame or inner fender at full droop
• Re-evaluation of steering geometry at increased ride height

Drivetrain and Gearing Effects of Running 38x12.50-17

A 38x12.50-17 tire has a rolling circumference of approximately 119 inches, based on its 38-inch nominal diameter. Compared with a 37x12.50-17 (approximately 116-inch circumference), the 38x12.50-17 increases rolling circumference by roughly 3 inches - approximately a 2.7% difference. Against factory tire sizes, the departure is larger: a 38x12.50-17 fitted to a vehicle with 33-inch stock tires represents a 15% rolling circumference increase, significantly affecting effective axle ratio, acceleration, transmission behavior, and drivetrain load. Re-gearing is standard practice on dedicated builds running 38x12.50-17 tires.