How to determine tire rating?

[DrD]

I have a shorlandr tandem axle trailer. Currently there are four ST175D80 load range C, 5 lug tires / wheels on it. The boat's trailer weight is 3700 lbs, and the trailer itself weighs 1580 lbs. How do I calculate the minimum tire rating? Would radials be the best choice?

Is the rating = (boat weight + trailer weight) / 4 wheels ?

Are these tires underrated for this setup?

Thanks.

-Dale-

 

[tashasdaddy]

Re: How to determine tire rating?

your running 13 inch wheels, this load is at the very top of your tires rating of1360 . with out changing wheels, i'd go with a Carlisle St1858Od13C rating 1480. to go higher in rating you will have to go to a 14 inch wheel.

 

[Silvertip]

Re: How to determine tire rating?

Staying with the 13" tires provides a 640 pound reserve. While that may seem adequate, consider that the boat weight is normally listed "dry" meaning no fuel, no batteries, not gear, no people, and no adult beverages. I suspect you have at least a 30 gallon fuel tank so there is 200 pounds. Couple of batteries, etc., and you can see you ware quickly at the capacity of tire. Run them even a couple pounds light on air and they will be overloaded. I agree with Tash that you would be better served with 14" wheels and tires that provide a little more reserve.

 

[DrD]

Re: How to determine tire rating?

If I were to change out to 14" wheels:

a. Would they fit this trailer?
b. What tire would be a good choice?
c. Radial or Bias?
d. Should I stay with the ST175d14 or
should I use a ST185d14?

Thanks again,

-Dale-

 

[tashasdaddy]

Re: How to determine tire rating?

a radial tire once mounted and use needs to turn the same direction at high speed. on the same side of the trailer. the bias ply tire can be swopped from side to side. but don't run 1 radial and 1 bias, i use a bias for a spare, and only run a short distance till the radial is repaired. look at this load ratings. i'd go with Part # 4123 it's as ST205/75D14 1760 lb rated. with 5 lug rim
http://www.championtrailers.com/tires_on_rims.html

 

[Silvertip]

Re: How to determine tire rating?

We can't see your trailer and we don't have a model number so we have no idea how much room you have under the fenders. Measure the diameter of your existing tire. Your tire dealer can provide the diameter of whatever size you want. You will need enough clearance to allow for the difference in diameter.

 

[bruceb58]

Re: How to determine tire rating?

Like Silvertip said, you will need to make sure that larger tires will fit under your fender. Make sure you examine how high the tire will go up if your other tire was flat. Best way is to jack up one of the tires completely so that the equilizer has tilted all the way up and measure the gap between your existing tire and the fender.

I am not sure what you mean by sticking with the 175d14. That is not a common size for a 14" tire. 205 is usually the minimum width for a 14" tire.

If you use radials, you can rotate them from side to side. It was a myth that you couldn't, started way back in the early 70's when radials first hit the market. The exception to this are tires with directional tread patterns which would not apply to trailer tires.

As far as radials vs bias ply...a big advantage of radials is that they wear longer. Most trailer tires are changed because of age before they wear out.

Tires should be changed at 4-6 year intervals no matter what the tread wear. This applys to your car and motorcycle as well.

 

[Texasmark]

Re: How to determine tire rating?

Couple of things.

Early on in the life of American built radials there were problems of separation do to incorrect rotation. Today that is not the case and new vehicle owners manuals show them crossed as they were back in the bias ply days; at least mine do and have since '97 that I know of. I have done it for as long as I can remember and have had zero problems.

If you can get a higher load range you can stay with your current 13" diameter. A full service tire shop (or look on www) should be able to order you whatever you want in the higher ply ratings. Lotta folks out there internationally making lots of different tires.

A trailer rating I don't think is necessary. I think "trailer use only" warnings mean that the tire has not passed/been tested to or whatever for passenger service. Surely those are more stringent tests.
No reason you couldn't use a P or LT radial tires on your trailer; course the P would be 4 ply and I suppose that is where you already are.

If you do go with larger tires, in addition to what Bruce said is the flexing of the springs under load (deflect) and upon impact. You have to add space for deflection along with the tandem travel distance. But, I have found that trailer springs don't deflect all that much; like maybe a couple of inches and load a couple of inches.

A 14" P rated radial is probably about the same carrying capacity as a 13" C rated trailer tire so you really should stay with trailer ratings and C or better when you go to 14". Don't know if a 14" LT tire is available. Doubt it.

Only had one trailer that ate tires; it was custom made and they didn't get the caster/camber of the trailer correct.

Usually you can examine your tires for the tell-tell cracking, indicating that the plasticizers have quit functioning and signalling that it's time for a change. Lack of use (which keeps the placticizers moving through the rubber, ozone from sun shining on the tire, and sitting on damp ground (dirt), all contribute to premature tire degredation. Now don't ask me what damp dirt has to do with it, but I have numerous examples where it's obvious that the tire degraded prematurely where it was in contact with it.

Only lost one tire in my life on a trailer. Was dad's trailer and I was 10ish, didn't know about these things although I do remember that I did notice that the tires had checkerboard all over them. We were coming back from a trip at about 60 mph at the time. Pieces of it came off and you could hear them hitting the fender. Don't remember if it had blown out or not by the time we got stopped and did something about it. What? I don't remember. I doubt that we had a spare.

Speaking of spares, if you change tire dia, don't forget to get a new spare also.

HTH,

Mark

 

[Silvertip]

Re: How to determine tire rating?

I strongly urge you NOT to use "P" (passenger) designated tires. Go to any tire store and push on the sidewall of a "P" tire and then do the same to an "ST" (special trailer) designated tire. You will find the sidewall much stiffer. That's to handle the effects of sway and the stiffer spring rates than found on cars. Trailers don't have shock absorbes either so the sidewall takes a beating from vertical (bouncing) forces. Trailer tires also typically carry 50 psi pressure where car tires are much lower so heat build-up will be an issue. I know people use "P" designated tires on trailers. That does not make it safe even if they are new.