Could Radial Trailer Tire be used As Spare for Tire Size ST225/75D15


I have 4 St225 75 D15 tires on my travel trailer can I get a 225 75 R15 as a spare to go with them?


Helpful Expert Reply:

You currently have bias ply tire based on the letter D in your tire size ST225/75D15 and the other size you mentioned is a radial based on the R in the size. Ideally you run the same construction style for all tires including the spare but in an emergency situation you could use a radial to replace a bias ply.

The main difference between a radial ply and a bias ply tire is how the tire is constructed. The cords inside a bias ply tire run at a 32 degree angle to the direction of travel, and the cords on a radial tire run at a 90 degree angle to the direction of travel, or across the tire from wheel lip to wheel lip.

A radial tire flexes more than a bias tire, giving it better ground contact, traction, stability, and tread wear.

A radial tire will normally run cooler than a bias ply tire, especially when the tire is under a load. A tire that runs cooler will last longer.

helpful expert reply by:
Jameson C

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