Will 175/80-13 Tires Fit in Place of 185/80-13 Tires on a Cox Tilting Boat Trailer

Question

Question:

I am replacing radial sized p185/80-13 mounted on a 5 on 4.5 wheel. Its on an old steel COX tilting boat trailer that carries a 19 foot ODay Mariner centerboard sailboat that weights 1350 lbs. I dont know the weight of the trailer. Will a 175/80-13 radial with D rating handle the load? I am new to trailering and therefore dont know how to assure myself otherwise.

asked by: Tony D

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Expert Reply:

First, if your current tires have a P in front of the size that indicates they are likely passenger vehicle tires which should not be used on trailer due to the differences in construction. If they are trailer tires, they should have ST in front of the size.

A 185/80-13 is a trailer tire size. Check the trailer tongue for a plate that lists the capacities and should also list the tire size the manufacturer uses for the trailer. That is the size you would ideally want to stay with.

Both a 175/80-13 and 185/80-13 will fit the same size wheels (4-1/2 to 5-1/2 inch wide) and they are about the same diameter (between 24 and 24-1/2 inches).

The major difference is the capacity. A 175 tops out at 1,610 pounds for a load range D, # AM10210. A 185 tops out at 1,725 pounds for a load range D, # AM1ST79. If you go with the smaller size you need to be sure that it can handle the gross trailer weight.

Since the two different sizes will fit the same wheels you do not have to also replace the wheels. But if you want to I recommend # AM3S334 for a 185 with galvanized wheel or # AM32001HWTB for a 175 with aluminum wheel. Aluminum is corrosion resistant and looks sharp. Galvanized is more corrosion resistant, but you lose some appearance. Both wheels have a 5 on 4-1/2 bolt pattern.

expert reply by: Michael H

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Answer 1

In height or total diameter, a 185/80-13 and 175/80-13 like part #AM1ST77 only differ by about 5/8 of an inch. The 185 would have a diameter of 24.65 inches while the 175 would have a diameter of 24.02 inches. The section width, or thickness of the…

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Answer 2

It is okay to have different load range tires on each axle of a tandem axle trailer on a temporary basis but I do not recommend using the trailer in this configuration in the long term. Also, it is never a good idea to mix tires of different sizes.…

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Answer 3

Oddly enough for the directional trailer wheels we carry such as #AM20259 there isn't a left and a right. There is just the one so if you were to use 2 of them the appearances of them would not match unless you had more than one axle. Then…

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Answer 4

The load range D on the Loadstar ST185/80D13 #AM1ST79 actually gives you a higher weight rating than the C load range. For this size D is 1,710 lbs at 65 psi while C is 1,480 lbs at 50 psi. It doesn't hurt to have a tire that is rated for more…

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Answer 5

The 4.80X12 2 ply tire at 60 psi that you have is a Load Range B tire. The other 4 ply tire at 90 psi should be a Load Range C tire. When the inflation pressure is higher that will indicate a higher load range. The Load Range B tire should have a…

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Answer 6

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 7

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 8

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 9

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 10

Good morning, Cliff. As of today (3/27/24) we are expecting the #KE33JR tire/wheel combo to be in stock in about 2 weeks. Hopefully this means we can take our own pictures and put them on the site within maybe about 3-4 weeks from now. What I can…

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Answer 11

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 12

The two sizes you mentioned are pretty similar and fit many of the same 15 inch wheels. The 205/75-15 fits rim widths of 5 inch to 6-1/2 inch whereas the 225/75-15 fits widths that are 5 inch to 6 inch. The 205 is 27.1 inches tall and the 225 is 28.4…

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