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Why Does Trailer Tire Weight Rating Drop When Used in Dual Tire Setup

Question:

I know you have answered questions about load capacity of single tire dual axle trailer tires, but I have a dual tire dual axle trailer, if the load capacity of the tire is 3500lbs that would mean the total trailer load capacity with 8 tires would be 28k?

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Expert Reply:

Good question. Trailers that use dual tires on both sides of the same axle, so that a tandem axle trailer with two such axles has a total of 8 tires, will often have a lower per-tire rating for that dual-tire setup. In other words, the total capacity will be less than 8 times the single tire rating.

For example, one single Provider ST235/80R16 Radial Trailer Tire # PRG80235 has a weight rating of 4080-lbs when it is used as the one tire on each end of the axle. But if it is used in a dual-tire setup with 2 tires on each end of the axle then the rating for each tire drops to 3640-lbs. 8 of these in a dual-tire setup would mean a total capacity of 8 x 3640-lbs, or 29,120-lbs.

The reason for this is that in dual-tire applications the load on each of the tires in a pair is never exactly the same. Roads have a crowned (gently arched) profile which tends to put more of the axle load on the inner tires. Industry standard practice is to de-rate a tire by 10% in dual tire installations.

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