I’ve seen this question enough to warrant a webpage. Here goes!!

Please Note:

• You need to check the wheel for its width. It should be on the back side of the wheel in this format: 6.5K – where the number is the width in inches and the letter is configuration of the flange.
• Below I am only quoting the “Single” load carrying capacity, not the dual, as most travel trailers use either single or tandem axles, both of which have single tires at the end of the axle.
• The “-” in the size means the tire is a bias ply tire. Sometimes the letter “D” (for diagonal) is used in its place. For reference: “R” = Radial and “B” = Bias Belted. It is OK to use radials in place of the original bias ply tire. You’ll not likely find any Bias Belted tires in any kind of tire. They were an experiment that didn’t work!

7.00-15: Important Statistics

A 7.00-15 is 29.6″ in diameter, with a width of 8.0″ on a 5.50″ wide wheel with an allowable rim width range of 5″ to 6.5″. The load carrying capacity is 2040# single at 65 psi for a Load Range D (8 PR).

ST205/90-15: Important Statistics

An ST205/90-15 has a 29.5″ diameter, with a width of 8.0″ on a 5.50″ wide wheel with an allowable rim width range to 5″ to 6.5″. It has a load carrying capacity of 2600# single at 65 psi for a LR D (8 PR)

This is closest to the original tire. It has substantially more load carrying capacity, so less inflation pressure can be used. See the link below for the procedure.

• Use caution using a different inflation pressure as the old trailers were frequently sized too small in the tire department.

ST225/75R15: Important Statistics

An ST225/75R15 is 28.3″ in diameter, 8.8″ wide on a 6.00″ wide wheel with an allowable rim width range of 6″ to 7.5″. It has a load carrying capacity of 2540# single at 65 psi for a LR D (8 PR).

This tire is likely too wide for the stock rim, but the size is readily available. Many people have used this size.

The tire is also wider than the 7.00-15, even on the narrower rim. You’ll need to check side clearance. You’ll need at least 1 1/2″ on both sides as measured with the 7.00-15 in place.

It has substantially more load carrying capacity, so less inflation pressure can be used. See the link below for the procedure.

• Use caution using a different inflation pressure as the old trailers were frequently sized too small in the tire department.

ST205/75R15: Important Statistics

An ST205/75R15 is 27.1″ in diameter with a width of 8.00″ on a 5.50″ rim, with an allowable rim width range of 5″ to 7″. In a Load Range D, the load carrying capacity is 2150# at 65 psi.

This makes the ST205/75R15 about 2 1/2″ smaller in diameter than the 7.00-15. Everything else is comparable, including the inflation pressure (load carrying capacity)

For more information:

It would do you well to read my webpage on ST tires: ST Tires – Barry’s Tire Tech

You’ll also want to do the Pressure Buildup Test: Pressure Build up Test – Barry’s Tire Tech