Replacing Trailer Tire Size PR 6 LR 78-15

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Question:

I am replacing the tires on an old trailer from the 20s that has been sitting at my grandparents forever. I am not sure what I should be looking for to replace them, but this is all the information I was able to get off the tires. Tire info Uniroyal PR 6 LR 78-15 Thanks for your help.

asked by: Jon

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Expert Reply:

The modern tire size equivalent to your 78-15 is the size ST205/75-15 like the part # AM10245. This is a Load Range D tire with the capacity of 2,150 lbs at 65 psi.

For a Load Range C in this size you would want the part # AM10244 instead. This tire has a capacity of 1,820 lbs at 50 psi. As long as you go with a tire that has enough weight capacity for your trailer when loaded it doesn't matter which Load Range you go with.

You should note that trailer tires should always be inflated to their max psi rating in order for them to have their full capacity.

expert reply by: Jameson C

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Answer 1

Load range B trailer tires are going to have a lower capacity than C load range tires. Basically that, psi rating, and the ply rating are the only differences. A higher load range tire would last a little longer than lower load ranges of the same…

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Answer 2

In order to determine the torque rating for the lug nuts on your trailer you will need to know check out the chart I attached that shows all of the torque specs for all the trailer lugs available based on stud size, wheel material and wheel size.

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Answer 3

The difference between an load range C and load range D tire in the same size is the capacity and psi rating. The two tires will still have the same dimensions and fit on the same wheel. The D rated tire has a higher capacity. For a ST175/80D13 like…

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Answer 4

Your math is correct in your trailer weight load example. If a fully-loaded tandem axle trailer weighs 4000-lbs then each of the 4 tires will bear 1/4th of that load, or 1000-lbs. In this case a tire rated for 1300-lbs would provide a good safety…

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Answer 5

The three most common lug stud sizes for a trailer are 1/2"-20, 9/16"-18, and 5/8"-18. In order to make sure you get the correct lug nuts you need to measure the lug studs on the trailer now as we have no way to look this up for…

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Answer 6

To find the load capacity for your axle you should look on the trailer VIN plate or sticker that lists the VIN number. The weight rating of the axle should be listed on that same plate or sticker. Also, the axle could have a tag or plate on it that…

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Answer 7

The 12 inch tires that we carry are rated for 65 miles per hour. Any faster than that for extended periods and the excessive heat build up will cause tire failure. To get a tire with a higher speed rating you would have to go up in size. That also…

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Answer 8

Even though I cannot comment specifically on the grease you used because I am not familiar with it, I can tell you the best grease for trailer bearings is a a grease with a rating of GC-LB, which just means it is made to withstand very high…

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Answer 9

To determine the size of the hub assembly you need to purchase you have to determine which bearings are in the old assembly. If the old assembly has L44649 inner bearings, you would use the hub you chose #8-258-5UC1. If the inner bearings are marked…

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Answer 10

A BT8 spindle would have a diameter of .99 of an inch where the bearings would both install and would have a diameter of 1.24 where the great seal would ride. That would require a hub part #AKIHUB-440-2-1K for an idler hub. A BTR spindle would have…

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Answer 11

The closest radial tire size I would have to replace the 4.80-12 bias tire size is the Kenda Karrier S-Trail ST145R12 Radial Trailer Tire #AM10130. The 4.80-12 bias tire is 20.7 inches tall and 4.9 inches wide. The 145R12 radial tire is 21.3 inches…

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Answer 12

The Kenda 4.80-12 Bias Trailer Tire with 12" Galvanized Wheel - 5 on 4-1/2 - Load Range B #AM30590 have a max speed of 65 mph. When trailer tires are not speed rated with a letter, the default is 65 mph max. I've attached an article to…

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Replacing Trailer Tire Size PR 6 LR 78-15

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