40X12.50R17 Tire Size

All You Need to Know About 40X12.50R17 Tires

A 40X12.50R17 tire is a radial flotation tire with a nominal 40-inch overall diameter, a 12.5-inch section width, and a 17-inch wheel diameter. It sits in the same 40-inch diameter class as the 40X13.50R17 but is one inch narrower in section width, making it a more fitment-friendly choice for vehicles that need a 40-inch diameter but cannot accommodate the wider 13.5-inch section.

40X12.50R17 is a limited-availability size, and significantly fewer models are produced compared with 40X13.50R17 or the well-stocked 37X12.50R17 below it.

40X12.50R17 Size Quick Specs

The following specifications reflect the 40X12.50R17 size class. Because this is a limited-production size, confirmed data points are drawn from specific published manufacturer specs rather than averaged across a large pool of models; always verify the exact figures for the specific tire you are purchasing.

Note on 40X12.50R17 actual diameter: Like all flotation tires, 40X12.50R17 tires measure smaller than their nominal stated size. The Toyo Open Country R/T Pro publishes an inflated diameter of 39.8". Always use the manufacturer's published inflated diameter for speedometer calibration and clearance planning, not the nominal 40-inch name.

What 40X12.50R17 Means - Notation Explained

• 40 = nominal tire height in inches
• 12.50 = nominal tire width in inches
• R = radial construction
• 17 = wheel diameter in inches

The absence of an "LT" suffix in the base 40X12.50R17 size designation means a standard flotation casing. Many confirmed production in this size is LT-designated (40X12.50R17LT), following the same pattern as the broader 40-inch flotation family, where the LT version is the common form. When shopping, verify whether a listed tire carries an LT designation, as LT and non-LT versions have different load capacities and inflation pressure limits.

40X12.50R17 vs 40X13.50R17 - Width Difference

Both 40X13.50R17 and 40X12.50R17 tires share the same nominal 40-inch diameter and radial construction on a 17-inch wheel. The difference is section width - one inch narrower on the 40X12.50R17.

The 40X12.50R17 is one inch narrower than the 40X13.50R17. That narrower section affects fitment in several practical ways: the inboard sidewall requires less clearance from the leaf spring, control arm, and inner liner; the tire places less lateral stress on wheel bearings; and the narrower section width reduces the fender clearance requirement, making 40X12.50R17 a viable option on vehicles that cannot clear a 13.5-inch section at 40-inch diameter. The tradeoff is a slightly smaller contact footprint in soft terrain, where the wider 13.5-inch section provides more flotation. Wheel offset requirements also differ: the narrower 12.5-inch section is less sensitive to offset changes because it extends less far inboard and outboard than a 13.5-inch tire on the same backspace.

40X12.50R17 vs 37X12.50R17 - Height Difference

Both 40X12.50R17 and 37X12.50R17 are 12.5-inch-wide radial flotation tires on 17-inch wheels. The 40X12.50R17 is three inches taller in nominal diameter.

The step from 37X12.50R17 to 40X12.50R17 carries the same diameter-driven consequences as any 37-to-40-inch upgrade: the 40-inch tire's larger circumference (~125.6" versus ~116" for a 37-inch) alters the effective gear ratio, reduces engine RPM at a given road speed, and adds rotating mass. On most truck and Jeep platforms, this step requires suspension lift, fender clearance modifications, and gear ratio correction. The narrower 12.5-inch width at least means that offset and inboard clearance concerns are less acute than on the wider 40X13.50R17.

40X12.50R17 Availability

40X12.50R17 is a limited-availability size. The confirmed production in this size includes the Toyo Open Country R/T Pro - a rugged-terrain (hybrid AT/MT) tire rated Load Range C (6-ply, 35 psi maximum, 39.8" actual inflated diameter, 8.0"-10.5" approved rim width range). This tire carries a 45,000-mile tread warranty and is a DOT-legal street and off-road tire.

The BFGoodrich Baja T/A KR3 is also produced in a 40x12.5R17 format, but this is a competition-only, non-DOT desert racing tire - it is not street-legal and is not applicable to standard truck or Jeep builds. It should not be confused with the street-legal 40X12.50R17 options.

Buyers should confirm current availability before selecting this size, as the selection remains narrow. For buyers who need a wider range of model options - M/T, A/T, and LT-rated choices - the 40X13.50R17 offers substantially more selection across brands, including Nitto, Toyo, Mickey Thompson, Milestar, and others.

Fitment Requirements for 40X12.50R17

40X12.50R17 carries the same diameter-based fitment demands as any 40-inch tire on a 17-inch wheel, with slightly reduced width clearance concerns compared to the 40X13.50R17:

• 4"–6"+ suspension lift on most platforms - the 40-inch diameter will not clear factory or mildly lifted fender openings
• Fender clearance modifications - the 40-inch diameter typically requires trimming or aftermarket flares, though the 12.5-inch section width reduces the lateral clearance demand compared to a 13.5-inch tire
• Axle regearing - the 40-inch rolling circumference (~125.6") alters the effective gear ratio; most Jeep and truck platforms require gearing correction (typically 4.56 or lower) to restore drivability
• Approved rim width: 8.0"–10.5" per the Toyo Open Country R/T Pro published spec - verify for the specific tire model purchased
• Steering and brake assessment - the increased rotating mass at 40-inch diameter raises braking distances and load on steering components, regardless of section width