Boatmate 18" tire pressure?

[RTS]

Most of the heat generated in tires while you are running down the highway comes from the flexing/unflexing of the side wall as the tire rotates. Flexed at the bottom, unflexed at the top. Much like taking a paper clip and bending it back and forth...it will heat up.

Another reason to run max pressure in trailer tires....the sidewall flex, therefore heat build up, is minimized.

Edited April 30, 2014 by RTS

[RTS]

You decided to get all scientific here. So, when you put the tire on the trailer and load it up with a boat, this causes a portion of the tire to flatten on the ground. This will certainly change the "V" in PV=nrT as the tire flattens and the rubber flexes. T is always changing. I would expect to see P change. How much? I have no idea. Common senses would suggest that if you stacked several tons of lead into the boat while on the trailer, eventually those tires will burst like a squeezed balloon. My instincts are telling me that internal tire pressure does increase with trailer load, but that is a mere (educated???) guess.

Actually, what is happening here is more like the bottom of the tire flexes, and the rest of the tire 'unflexes'...leaving the internal Volume unchanged....just 'rearranged'.

[Cory]

I was taught that a perfect sphere provides the largest volume for a given surface area. As soon as you deviate at all from the perfect sphere, your volume drops for a fixed surface area. I suspect this is true for the toroid shape of a tire. As soon as you deviate from the perfect doughnut shape, the internal volume drops and the tire rubber must stretch to accommodate, which means a rise in internal pressure to force the rubber to stretch. I'm not saying there are large deviations in the scenario we are discussing (it may only be a couple psi, which is probably within the error of most tire gauges--I have no idea how much deviation there would be), but I standby my gut feeling that internal pressure rises as you add weight on the tire. The question in my mind is how much.

This just makes sense from the perspective of squeezing a balloon until it pops. As you squeeze it, it changes to a less ideal shape, causing the rubber to bulge until the increasing pressure pops the balloon.

Edited April 30, 2014 by Cory

[saidainc]

I agree with the 50psi cold but I run them at 75psi because I like a challenge.

[TheKiwi]

I agree with the 50psi cold but I run them at 75psi because I like a challenge.

[saidainc]

[old skool malibu]

Ok thanks TMC. 50 psi it is then!

[SmoothWaterMan]

Cory, oldjeep is correct.

The balloon analogy does not correlate, for the tire does not stretch, expand, or otherwise enlarge or shrink itself with air pressure or weight. By squeezing the balloon you are changing the volume of the balloon, and in return the pressure goes up and tries to expand the balloon to regain it's original volume. Once the balloon stretches itself to it's limit it breaks.

A balloon in place of a tire will do the same thing. Due to not having steel belts or thick rubber holding it's volume the same, a balloon will compress and change it's volume. A tire is mechanically strong enough to overcome the weight and while it will "deform" by changing shape, it will not stretch and change it's volume. Volume of air in the tire must change to change pressure (if temp remains constant).

An underrated tire for a load will most certainly pop like a balloon, for the weight will overcome the mechanical limits of the tire, and in it's attempt to stretch, it will blow.

Just good info to know.

pb.