Trailer tires pressure

[colbysmith]

[colbysmith]

This reply, from Kenda Tire company:

Hello Colby,
We suggest running trailer tires at the max cold inflation pressure marked on the sidewall of your tire. For the load range of your tires that is best pressure to run them at. If you have any further questions please let me know.
Thanks,
Matthew​ White
Warranty Administrator
American Kenda Rubber Industrial Co., LTD
330-526-2658 Direct
330‑526‑2651 Main
330-494-0955 Fax

Goodyear and Trailer King just sent me a generic weight chart without any recommendations.

[thataway]

All travel trailers, camping trailers and 5th wheel RV trailers have the following information on a plaque fixed to the trailer:
1. Empty Weight – The weight of the trailer without any cargo or fluids; also called Dry Weight or Unloaded Weight

2. GVWR – The maximum weight a trailer is rated to weigh, including cargo, fluids, etc.
3. Load Capacity – The total weight of the cargo a trailer is rated to carry
on a plaque somewhere in the vehicle. This plaque also will indicate the tire size and what Pressure to which it should be inflated. This is a known amount--sample vehicles are weighed as they leave the production line. Engineers have calculated the Load Capacity (many are very low; only a few hundred pounds--after you add water, (Black water, Grey Water and Fresh Water)--also propane tanks. The owner is cautioned to never exceed the GVWR! The tire inflation pressure (not necessarily Max capacity,) although it may be max capacity is clearly labeled in each Recreational trailer.

Fast forward for this Magic ST trailer tire. The exact same tire is used in your boat trailer. The trailer and tire manufactures know that the average boater:
1. Never weighs the trailer, boat and gear put aboard.
2. Never gave a thought to the capacity of the trailer.
3. The dealer is going to include the cheapest, barely acceptable GVRW trailer . I have seen it in several new boats I have purchased, other than C Dory--and in the used C Dory's I have owned.
4. Often this is compounded by boat builders giving very optimistic boat weights, and weights which the average boater may find when trailering.

So the people who give advice are going to CYA. Give the answer which will give the least problems. That is to inflate the tire to its's max capacity. This is fine, and certainly easier than weight of the boat and gear aboard.

Now Colby I believe has the same trailer from Load Rite that I had. Surprise! It has one of those capacity tags on the frame. Mine says use 225 x 75 x 15 tires load range D. Inflate to 65 PSI (which in fact is the max cold inflation pressure.).

Some of us are cautious--and upgrade our trailer to Endurance Load Range E--same size tire. That tire has a max rating of 80 PSI--25 PSI over the 65PSI which is given on the trailer frame! So, if Colby is cautions and upgrades his trailer tires to Load Range E-and has the tire which is capable of running at 80 PSI, go against the trailer manufacture's capacity plate, and inflate the "Bouncing Ball Betty" boat trailer up to 80 PSI? The 65 PSI rates the tire to carry 2540# (single trailer on each axle.), where the 80 PSI is going to allow carrying 2830#. ( that much weight might overload the axle and trailer frame)

Bear in mind that this is exactly the same tire, which an RV manufacture to put a specific number and inflation pressure (which often is different than the max capacity of the trailer tire.)

On the Float On Trailer I had for the Tom Cat, we used 16" wheels, and the trailer was rated for a little over 13,000 lbs. The real weight was about 10,200 loaded and ready to go, so we used the inflation for that specific weight.

Yes it is far easier and it probably reduces the tire builder and trailer builder's liability by saying it is OK to go Max pressure. If you don't want to weight the trailer with boat and gear aboard that is fine.

Colby apparently felt I didn't know the difference between LT, P and ST tires. I have been towing boat trailers for over 70 years. I have owned RV's continuously for over 60 years(VW Campers to 45' Diesel Powered max size Motor home), I first drove heavy trucks (and lite trucks over) 70 years ago--and my summer job in high school and college was driving trucks which had a payload from 20,000 lbs to 50,000 lbs (Class in the Calif. mountains on gravel and dirt roads and included river fords. We checked the tires on all of these vehicles at least daily when in use--including checking pressures. After difficult runs, we rechecked the tires in mid day.

Do what is comfortable for you--and be safe!

[ssobol]

If you change to a different tire (even a higher capacity one) aren't you now operating the trailer outside of its design specification (i.e. what's on the data plate)? Does the data plate say if you are using D tires inflate to X psi and if using E tires inflate to Y psi? Otherwise, you are just guessing.

[colbysmith]

Bob, I wasn’t trying to insult your intelligence, and I apologize if you took it that way. I think both you and I are pretty wise about trailers, tires and brakes. And tact isn’t exactly my forte. I didn’t mean you didn’t know the difference between ST, P and LT. But you started discussing RV’s and trucks, and I’m pretty sure you’re not running ST’s on those. (I take RV's to mean motorized, such as a Motorhome, but I guess it includes campers too, so already some confusion on my part when discussing RV's.) I would never recommend running max psi in a LT or P tire. And I know the tire manufacturers don’t. The fact is most of the tire manufacturers and trailer shops do recommend running ST’s at their max rated pressure. I’m pretty sure the reasons for that have been stated clearly in this thread. Colby

[san juanderer]

Yikes ! How such a relatively simple topic has generated such a massive response. Some people type so much, must be like controling a verbal conversation. It is a ST tire on a boat trailer, inflate it to setting specified on side of tire. Enough said !

[colbysmith]

Thinking more about psi in our trailer tires, these thoughts/questions come to mind. And actually, as I think about them, I'm beginning to wonder if it's worth while to upgrade to LR E tires given they are still under rated to support the load of both axles on one side if a tire fails. Just doesn't seem to make since to upgrade for that reason, if running them at a lower PSI than max.

(Oh, and I did look up what's considered overinflation. Looks like 20 psi above what's needed for the load carried.)

How do the following affect the weight on each wheel?

Wind affect? I've frequently towed in cross winds of 10-15 mph+.
I know the wheel temperatures run a little warmer on the down wind side.

What about cornering?

Centering of the boat on the trailer?

Weight distribution in the boat. (Does it float level?)

Especially on dual axle trailers, when turning in a tight parking lot that places extra stress on the sidewalls, what roll does tire inflation play?

How much more firmness is provided in a higher load range tire due to more belts (ply), and how does this relate in roughness of ride? (I.e. is it the higher psi, or the addition of plys.)

Is there any reason really to upgrade load categories to provide more buffer on a dual axle trailer in case one tire blows? And if so, will running lower psi in the higher load category tire reduce from it's capibility to support that load short term? Colby

Late addition:

[C-Wolfe]

[T.R. Bauer]

I was pretty close to giving up on the craziness of this....I worked in the service department at a large RV dealership in Washington for a few years. The recommendation (it was 20 + years ago but doubt it really changed) is that if you upgrade tires to a higher rating, you should put 5-10 pounds more air in it than the lower rated tire you replaced and no more - regardless if it was a trailer or diesel pusher.

It might be hard to believe, but during that time I changed about 5 zillion tires on trailers or motorhomes.....We sold Monaco, Montana, Jayco, Winnebago, and few others at the time. You'd be surprised how close trailers are to the max GVW before ANYTHING is added. And the tires are......the smallest, cheapest, and lightest duty ones they could get away with.

So.....I do not blame E-trailer or any of the experts connected at the hip of risk management saying fill it on up because that tire probably doesn't have a prayer even at max PSI with how people overload the rigs. With that said, on the other side, I have seen more than 1 premium coach (with well meaning owners) roll in with washer and drier or cabinet carriage bolts ripped out of the wall/floor because of the jarring of having high load range tires filled all the way up to 125 or whatever psi because it says to fill it up to that on the side of the tire. And somebody did it because they thought they were doing the right thing. Most of the time though, I will concede, the only obvious repercussion was leaky shocks, broken springs, broken brackets, empty cabinets, and a pissed off family with a wrecked vacation.

Commercial tires on the other hand....the have a minimum rating because they realize there is such a thing.....And it's just as important as the max.

So, like I said before, do what you want and even after all this dialog I still agree with Bob. It's your money and your trailer. Use your brain and do what you think is best - it probably is

[Chester]

The knee jerk max pressure instruction likely is from the legal side of the tire manufacturers business'. They see liability from overloaded trailers, low tires, high speeds, neglect and stupidity. In the case of sellers and installers, uneducated habits and the near impossibility of knowing what the customer will haul drive max pressure advice too.

The engineers don't work up tire pressure charts just for kicks. (Read this again.)
My vehicle's tires are inflated to the pressures on the door jam, not the max tire pressure on the sidewall.

Over inflated trailers damage the loads and trailers themselves due to road shock. As pointed out above, RVs too.

[Chester]

FWIW small trailer tire pressure charts have disappeared from the web.
Your copy of Chapman Piloting has one though.

[colbysmith]

[thataway]

[alainP]

Bob, could you give me an idea of what that was with your 25?

[colbysmith]