T145/80R17 Tire Size

T145/80R17 Spare Tire: The Radial Compact Spare on 17-Inch Wheels

T145/80R17 is a temporary spare tire distinguished from most compact spares by its radial construction - indicated by the R in the size - rather than the diagonal (bias-ply) construction found in the more common T135/80D17. This is the defining characteristic of the T145/80R17 size and the primary reason a buyer or technician would search for it specifically.

T145/80R17 Quick Specs

What Each Part of the T145/80R17 Size Means

• T - Temporary use
• 145 - Tire width in millimeters
• 80 - Aspect ratio
• R - Radial construction
• 17 - Wheel diameter

T145/80R17 vs T145/80D17: Construction Is the Only Difference

Both sizes have identical dimensions - 145 mm wide, 80% aspect ratio, 17-inch wheel. The sole difference is the construction method.

T145/80R17 uses radial construction, where internal cord plies run perpendicular to the direction of travel. This is the same construction used in all modern regular tires.

T145/80D17 uses diagonal (bias-ply) construction, where cord plies run at an angle across the tire. This is the traditional construction found in most compact spares.

Always use the exact construction type specified on the spare wheel or in the vehicle owner's manual. Substituting one for the other without verification can affect handling and load behavior.

Do Radial Spare Tires Have the Same Speed Limit as Diagonal Ones?

Yes. Despite radial construction being more heat-tolerant than diagonal in regular tires, T145/80R17 carries the same 50 mph / 50-mile limits as its diagonal counterpart T145/80D17. The limiting factor for temporary spares isn't the construction method - it's the narrower section width, reduced tread depth, and lighter carcass relative to the regular tire it replaces. These structural compromises apply to both construction types equally.