Tire pressure

[UncleWillie]

Re: Tire pressure

I prefer to run my vehicles at max tire pressure because I prefer the stiff ride over a soft ride.

It will also increase your MPG.

Yea! That too!
The Pluses of inflating the tires to max outweigh the minuses.

Has anyone ever worn out a trailer tire by putting so many miles on them that they wore out the treads before they failed in some other way?

 

[ricohman]

Re: Tire pressure

So two things... First, keep in mind rims have a max pressure also. You do NOT want to exceed that, unless you enjoy metal shrapnel... I've seen rims with max psi less than 80 psi...

Second, the OP is less than half the max load. I know people often disagree with this, but give me a second... Imagine your tire at max load, max psi. The angle of sidewall and size of footprint is what the tire is designed for. You want those two variables to be the same, no matter what the load. The only variable you control is the psi in the tire. Running max psi when a tire is loaded to less than half of capacity puts the tire way outside of its design spec. Your footprint on the ground is miniscule, you will wear the center of the tire extremely quickly and the available traction is greatly reduced. (assuming bias ply, radials are actually much more tolerant of higher psi when compared to load.)

So i'm curious, why do vehicle manufacturers never, EVER recommend max tire psi on the doorpost placard? Because your ride would suck, tire lifetime would be greatly reduced, and you would not have nearly as much control. But yet for some reason people think it is ok with trailer tires that are at half their max load.

Trailer tires and vehicle tires are two very different things. You can't really compare the two when talking about air pressure. ST are constructed with stiffer sidewalls and less tread depth and have more load capacity than even a comparable LT tire. Built for trailers and to run cool are the design spec. Ride and comfort aren't near the top of the list.

 

[smokeonthewater]

Re: Tire pressure

Trailer tires (and lt tires) generally DON'T state max tire pressure but rather state max LOAD @ xx psi......

Along with do not exceed xx psi to seat bead

 

[agallant80]

Re: Tire pressure

We'll I'll say this. Last season new trailer new tires I thought 65PSI was too much and ran the tires at 45 PSI. End of season replaced all 4 tires on the trailer. It took $600 for me to understand that I should run at max PSI

 

[Home Cookin']

Re: Tire pressure

per previous discussions, and reference to greater sidewall strength, trailer tires require a lot more pressure than seems right b/c the sidewalls are exposed to greater sideways roll pressure from the centrifugal force.

However, in this case I wonder about his having a light load yet complying with "max pressure at max load". If the two were independent, then pressure would be the same for any load, but it is expressed as if there is a relationship, which suggests lower pressure for lower loads would be OK--but since we don't know the ratios under max, may as well be safe.

 

[JimS123]

Re: Tire pressure

per previous discussions, and reference to greater sidewall strength, trailer tires require a lot more pressure than seems right b/c the sidewalls are exposed to greater sideways roll pressure from the centrifugal force.

I've never been able to understand this. What's the difference between a trailer tire and the rear tires on a front wheel drive car? Rotational force should be the same, so where does centrifugal force eminate from?

 

[tpenfield]

Re: Tire pressure

I raised the question about tire pressure, because of how car tire pressure recommendations are specified more based on the vehicle and its more known load range versus the tire's rated maximum pressure.

i would assume that with trailers, the load is much more of an unknown and quite variable, so the tire's rating is more of the benchmark.

 

[UncleWillie]

Re: Tire pressure

I've never been able to understand this. What's the difference between a trailer tire and the rear tires on a front wheel drive car? Rotational force should be the same, so where does centrifugal force emanate from?

There is no difference.

Compare a P205/75R14 at 44psi and 1532 lb Load
..... to a ST205/75R14 at 50psi and 1760 lb Load

A 13.6% Pressure difference and a 14.9% Load difference.

The real difference is in the sidewall.
The Auto tire is designed to handle the inertial* cornering forces of aggressive maneuvering.
The auto tire will roll on the sidewall during turns, the ST Tire will not tolerate that.
The Special Trailer tire assumes you will NOT be doing hard maneuvering while in tow.

-----------------------
* The side force in a turn is due to Inertia.
Centrifugal Force is a Fictitious/Imaginary force.
The term is in common use by the public to describe the apparent reaction to the Centripetal force.

 

[bigdee]

Re: Tire pressure

I've never been able to understand this. What's the difference between a trailer tire and the rear tires on a front wheel drive car?

Apples and oranges. Trailer tires are designed with stiff sidewalls that will not tolerate much flexing. Automobile tires are designed to flex for traction and ride comfort.

 

[JimS123]

Re: Tire pressure

There is no difference.

Compare a P205/75R14 at 44psi and 1532 lb Load
..... to a ST205/75R14 at 50psi and 1760 lb Load

A 13.6% Pressure difference and a 14.9% Load difference.

The real difference is in the sidewall.
The Auto tire is designed to handle the inertial* cornering forces of aggressive maneuvering.
The auto tire will roll on the sidewall during turns, the ST Tire will not tolerate that.
The Special Trailer tire assumes you will NOT be doing hard maneuvering while in tow.

-----------------------
* The side force in a turn is due to Inertia.
Centrifugal Force is a Fictitious/Imaginary force.
The term is in common use by the public to describe the apparent reaction to the Centripetal force.

Good explanation. So now I understand why you shouldn't use an ST tire on a car (duh!), but why not use a car tire on a trailer?

 

[JimS123]

Re: Tire pressure

Apples and oranges. Trailer tires are designed with stiff sidewalls that will not tolerate much flexing. Automobile tires are designed to flex for traction and ride comfort.

Yup. Well, I chose to have my baby (boat) ride in comfort.....lol

 

[ricohman]

Re: Tire pressure

Good explanation. So now I understand why you shouldn't use an ST tire on a car (duh!), but why not use a car tire on a trailer?

Because a comparable size ST tire can take nearly 40% more load than a car tire.

 

[bruceb58]

Re: Tire pressure

Because a comparable size ST tire can take nearly 40% more load than a car tire.

Yep. Just try to find a passenger car tire in a 14" size that will have a 1900 load rating. They don't make them!

 

[ricohman]

Re: Tire pressure

Yep. Just try to find a passenger car tire in a 14" size that will have a 1900 load rating. They don't make them!

Nope, they sure don't.
I've seen many small home-made utility trailers running worn out auto tires. But these things are usually used for short trips and light loads. Lots of guys save their old car tires for the "trailer".
But buying new car tires and putting them on a boat trailer makes no sense.

 

[bigdee]

Re: Tire pressure

Good explanation. So now I understand why you shouldn't use an ST tire on a car (duh!), but why not use a car tire on a trailer?

If you rode in a trailer you would understand why! You certainly can run car tires on a lightly loaded trailer, for instance a jon boat or small utility trailer.

 

[Home Cookin']

Re: Tire pressure

so what to do about those trailers made from the chopped-off back end of a pick-up truck? Car or trailer tires?

 

[JimS123]

Re: Tire pressure

Because a comparable size ST tire can take nearly 40% more load than a car tire.

Ahaaaa....there's the rub.

If the load rating of a car tire(s) exceed the capacity of the trailer there is no reason why the car tire (or LT)
won't work. If that's the case you'll be running on "good" tires that will last reasonably long.

OTOH, of the capacity requires the load rating of an ST you'll be stuck with STs and have to replace them every 3 years because STs have poor service life.

Bottom line is that its a capacity thing not a sidewall thing. Otherwise we'd put ST high strength sidewall tires on the rear of the car and just forbid anyone from riding in the back seat.....LOL.

 

[JimS123]

Re: Tire pressure

But buying new car tires and putting them on a boat trailer makes no sense.

My brand new tandem boat trailer came from the factory with car tires. They lasted for years. The capacity x 4 exceeded the trailer capacity by a reasonable margin.

 

[bruceb58]

Re: Tire pressure

My trailer came with 205/75/14 tires. It is rated at 7K. Passenger tires in that size are rated at 1500#. 1500 x 4 = 6000.

So, you may say, why not just go up to 15" tires! Problem is they only go up to 1600# per tire!

At least with 15" you can use a light truck tire as an alternative.

 

[ricohman]

Re: Tire pressure

Ahaaaa....there's the rub.

If the load rating of a car tire(s) exceed the capacity of the trailer there is no reason why the car tire (or LT)
won't work. If that's the case you'll be running on "good" tires that will last reasonably long.

OTOH, of the capacity requires the load rating of an ST you'll be stuck with STs and have to replace them every 3 years because STs have poor service life.

Bottom line is that its a capacity thing not a sidewall thing. Otherwise we'd put ST high strength sidewall tires on the rear of the car and just forbid anyone from riding in the back seat.....LOL.

Car tires are designed for cars. And are designed to work with a suspension and steering components. Double axle ST tires shrug off tight turns at low speeds and you can leave them "loaded" for lengths of time. Auto tires seem to nearly fold off the bead.
Do that with auto tires and the sidewalls start to come apart. Although I was a kid at sears when I sold tires, I used a lot of what I learned when I became a mechanic.
Just because the load rating matches does not make any auto tire fit for trailer use. People use them and I'm sure lots have no trouble. Trailer tires are designed they way they are for good reason.