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What tire pressure? What load rating?

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  • What tire pressure? What load rating?

    I have a single axle trailer carrying a 2500 lb boat. The tires are 20.5 x8.0-10. Do I inflate to the tire pressure listed on the trailer (60 lbs) or the max tire pressure listed on the tires (90 lbs)? What load rating do I need? C? D? E?

    Thanks, Mike


  • #2
    Re: What tire pressure? What load rating?

    Put 90 pounds of air in a load range "B, C, or D" tire and you will have shrapnel in your face. 90 PSI goes ONLY into load range "E" tires of your size. The sidewall of the tire carries maximum tire inflation pressure. For trailers, inflate the tire to that pressure. The sidewall of the tire also indicates the maximum load the tire can handle. Multiply that number by 2 since you have two tires. A Load Range "E" tire is has a 1535# load rating. A Load Range "D" would be 1320# @ 70 PSI max which puts you right at the load you indicated. If your all up weight (trailer, boat, full of fuel, all of the gear, batteries, etc) is 2500# on a single axle trailer you need load range "E".

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    • #3
      Re: What tire pressure? What load rating?

      I am going to guess that the original tires had a maximum pressure of 60 PSI but they were replaced with higher load-rated tires with a higher maximum pressure. Start with 90 PSI. If the trailer bounces too much, lower it but don't go below 60 PSI. But chances are you'll be fine at 90.
      Bob, Orange County NY
      '88 Bayliner 1700 Capri Bowrider, 85 HP Force O/B, "Sea Weasel"
      Want a vessel safety check? Click here. Want to join the Coast Guard Auxiliary? Click here.
      Disclaimer: Although I am a member of the USCG Auxiliary, the opinions and advice in my replies are my own and do not necessarily reflect CG or CG Auxiliary policy or regulations unless so specified.

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      • #4
        Re: What tire pressure? What load rating?

        Go with the max pressure on the tire. Watch how the tire is wearing. If the center seems to be wearing more, drop the pressure a little.

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        • #5
          Re: What tire pressure? What load rating?

          The poster indicated he had a 2500# load. That "requires" a minimum load range "D" tire and to support that load the tire needs to be at 70 PSI. Underinflation is what causes heat -- heat causes tread separation and blow outs. Even a load range "E" tire cannot be deflated to 60 PSI as that represents a 35% reduction and certain tire failure. It's all about the numbers folks.

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          • #6
            Re: What tire pressure? What load rating?

            Originally posted by Silvertip View Post
            The poster indicated he had a 2500# load. That "requires" a minimum load range "D" tire and to support that load the tire needs to be at 70 PSI. Underinflation is what causes heat -- heat causes tread separation and blow outs. Even a load range "E" tire cannot be deflated to 60 PSI as that represents a 35% reduction and certain tire failure. It's all about the numbers folks.

            I agree about the over or under inflation thing. The tire has the max pressure and maximum weight it is designed to carry. That means the tire needs to be inflated to xx psi to hold xxxx lbs. It the tires are over inflated, the centers will be what is supporting that weight instead of it being evenly distributed across the tread of the tire. That creates heat also and can cause issues as well. That is why it is important to pay attention to what the tires are telling you. If your tires wear more on the center of the tread it is over inflated. If the wear is on the outsides of the tread it is under inflated. You want them to wear straight across if possible.The tires will last and preform better that way. If the MAX psi on a tire is 90 it will not end the world if you run them at 85 to achieve proper tire wear.

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            • #7
              Re: What tire pressure? What load rating?

              Originally posted by Silvertip View Post
              The poster indicated he had a 2500# load. That "requires" a minimum load range "D" tire and to support that load the tire needs to be at 70 PSI. Underinflation is what causes heat -- heat causes tread separation and blow outs. Even a load range "E" tire cannot be deflated to 60 PSI as that represents a 35% reduction and certain tire failure. It's all about the numbers folks.
              You're right about load range D tires in that size. How could the trailer manufacturer then recommend 60 PSI? Could the trailer have originally been equipped with larger tires?
              Bob, Orange County NY
              '88 Bayliner 1700 Capri Bowrider, 85 HP Force O/B, "Sea Weasel"
              Want a vessel safety check? Click here. Want to join the Coast Guard Auxiliary? Click here.
              Disclaimer: Although I am a member of the USCG Auxiliary, the opinions and advice in my replies are my own and do not necessarily reflect CG or CG Auxiliary policy or regulations unless so specified.

              Comment



              • #8
                Re: What tire pressure? What load rating?

                If you are running the original load (boat) on the original size and weight rating tires that the trailer was designed for, just do the 60 PSI. If you change the tires size or capacity you need to look up the carry capacity of the OE tires and then figure the correct pressure for that weight on the replacement tires.
                It is ok to check by weighing the trailer and making changes, but be sure you haven't over loaded the tires, brakes, springs, axles, or tow vehicle when you find out that weight.
                1989 Baja Sunsport 196, Mercruiser 5.7, Alpha 1
                Moultonborough Neck, Lake Winnipesaukee, NH

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                • #9
                  Re: What tire pressure? What load rating?

                  Over inflation does not cause heat but it will cause tread wear. But this discussion is not about over inflation which is inflating a tire to a value higher than the label on the sidewall. This is about load capacity and the tire pressure required to carry that load. Even with load range "E" tires in this application, the max load at 90 PSI is 3070#. This poster has a 2500# load. The poster asked what load range does he need. The answer is obvious -- in that tire size, absolute minimum is load range D and they better be inflated to 70 PSI or they would be underinflated for the load. Load range E would provide a suitable safety margin. I take it you would suggest he deflate the tires to get a better ride and more even tire wear! That is simply rediculous since deflating a load range D tire that is already at the limit of its capacity would now be at a critical point, heat goes up and you risk a blow out. Trailer tires are not like car tires. Boat trailers are typically loaded very near the maximum capacity of tires and springs. Underinflating tires is simply dangerous and is the prime reason for tire failure.

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                  • #10
                    Re: What tire pressure? What load rating?

                    If he is running load range D tires there would not be a need to run the pressure a little low since the tire would be running flatter treadwise. If he goes with an E rated tire there is a little margin to play with on tire pressure. But what do I know. I only pull my boat daily which weighs about the same as his. I am still running the same tires for the last 2 years. When I was younger I worked in the tire manufacturing industry, now I commercial fish.

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                    • #11
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                      Thanks for all of the replies

                      I bought the boat and trailer, both used, from a dealer four years ago. I replaced both tires last year but wasn't sure if I needed the E load rating or not but I bought them anyway to be on the safe side....glad I did. The weight of my boat is at the upper limit of the trailer capacity so I think I'll run the tires at the rated pressure.

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