Trailer tire inflation?

[Hokiefyd]

I just put new tires on my 5x8 open bed utility trailer. ST175/80R13s. They are Load Range D, for 1,620 pounds @ 65 psi. Most of the time, the load in my trailer consists of leaves/limbs, walk-behind lawn mowers, and the occasional lawn tractor. The trailer weights about 600 pounds, and it's rare that I have another 900 pounds in it (1,500 total).

Can I run these tires at much less inflation pressure to save the trailer from bouncing down the road when empty? I get that I need 65 psi in them if I want to load them to 1,620 pounds each, but when they're rolling around with nearly nothing on them, I gather that I can keep them at less than that.

They're Kenda Karrier trailer radials. So far, they seem to roll smooth. A friend has a set from 2006 on his pop-up camper and likes them.

 

[jrmason]

Virtually all trailer tire manufacturers recommend running at max inflation all the time regardless of load. ST tires have a different carcass than passenger tires and the lower tire inflation can potentially heat the tires up, which is coincidentally the leading cause of failures in ST tires.
With that being said, a few pounds under shouldn't hurt anything but I wouldn't get too carried away.

 

[ls1mike]

Max pressure all the time in trailer tires. Low pressure equals heat, heat equals stress equals blowout.

 

[IndyIan]

I usually run them a bit lower than max if I'm not carrying a big load. I have run them much lower when carrying something semi delicate, like a large appliance that I don't want beat to khrap in a bouncy trailer. Even at nearly half max psi, I didn't find the tires heating up at 55mph with a 1/3 load on.
I guess the main thing is that you can't have a lot of sidewall deflection when just rolling with a trailer tire. Then they heat up and die.

 

[CapriRacer]

As a general rule, every vehicle ought to have a vehicle tire placard, which lists the original tire size and the proper inflation pressure for that size. That includes trailers.

- BUT -

that does not include homemade vehicles, and I'll bet there is a lower limit on GVW where the federal regulations don't apply.

Also as a general rule, the ST tires on trailers are sized such that they should be inflated to the max on the sidewall. That means the total load carrying capacity of the tires ought to be just a bit over the GVW.

With that in mind, let's do the math.

The load carrying capacity of an ST175/80R13 is 1620# at 65 psi. There are 2 on the trailer. The tongue weight is supposed to be between 10% and 15%, so that mean the trailer can weigh as high as 3726#.

If the trailer weighs 600# empty - and if I remember the rule of thumb correctly, payloads on trailers generally are twice what the empty trailer weighs - so the GVW of the trailer would be 600#*3 = 1800#.

I think things aren't lining up. Here's what I suspect:

1) If this is a homemade trailer, that it was made using what parts were available - and that would include tires and wheels.

2) If this isn't a homemade trailer, that the original tires had less load carrying capacity - for example passenger car tires.

So examining #2 for a second, a 175/70R13 has a load carrying capacity of 1047# at 35 psi, so 2 would be 2094#. If I adjust the load capacity because it is on a trailer by dividing by 1.1, I get the total weight of the vehicle 2303#. That makes much more sense.

So Hoke, tell us more about this trailer. Homemade? Are you the original owner? Does it have a vehicle tire placard? How old is it.

 

[Donald]

Max pressure listed on sidewall unless the manufacturer of the trailer recommends a different PSI.

 

[Hokiefyd]

Originally Posted By: CapriRacer
2) If this isn't a homemade trailer, that the original tires had less load carrying capacity - for example passenger car tires.

So examining #2 for a second, a 175/70R13 has a load carrying capacity of 1047# at 35 psi, so 2 would be 2094#. If I adjust the load capacity because it is on a trailer by dividing by 1.1, I get the total weight of the vehicle 2303#. That makes much more sense.

So Hoke, tell us more about this trailer. Homemade? Are you the original owner? Does it have a vehicle tire placard? How old is it.


I suspect it's #2. It's not a home-made trailer, but the tires and wheels that were on it were P-metric 205/65R15s on 15" wheels. The wheels have a "passenger car" type backspacing, and the axle is wide enough to space the tires right at the edge of the fender. I looked at using OTS 14" trailer tires/wheels, but the backspacing of regular trailer wheels set them too far out of the fenders. So I looked at the narrower trailer tires, and the 13s fit the fenders well.

The 205/65R15s have a load index of 92, or about 1,389 pounds. De-rate that 10% for trailer use, and we're looking at 1,250 pounds each (2,500 pounds total). The trailer has a 3,000 pound axle. I don't know about the leaf springs. They use shackles at both ends, and aren't the cheaper slipper springs. I'm only guessing at the 600 pound empty weight. I can barely scootch the trailer sideways across my slippery garage floor, but only if I repeatedly lift-lift-lift on the back so that it bounces a little bit. It's a pretty sturdy trailer. The title lists it as a 2000 model. The original owner is a co-worker of mine, so I know it's legit.

I decided that I'd prefer to use trailer tires on it, rather than the passenger car tires. Even the small ST 13" tires are rated for more weight than what I assume the original P-metric tires are. Even at only 35 psi, there is absolutely no sidewall bulge in the ST 13" tires.

This is a picture of the trailer, with its original wheels/tires:

This is a picture of it from the fall, with some 13" trailer tires I borrowed from a friend to test the fit:

I don't use the ramp on it anymore. I have some 2x10s with the steel bolt-on ramp ends for if I need to load something on it. The rampwind sail was a real drag (har har).

 

[Boss302fan]

I have always run my trailer tires at 50PSI...

 

[philipp10]

Originally Posted By: Hokiefyd
I just put new tires on my 5x8 open bed utility trailer. ST175/80R13s. They are Load Range D, for 1,620 pounds @ 65 psi. Most of the time, the load in my trailer consists of leaves/limbs, walk-behind lawn mowers, and the occasional lawn tractor. The trailer weights about 600 pounds, and it's rare that I have another 900 pounds in it (1,500 total).

Can I run these tires at much less inflation pressure to save the trailer from bouncing down the road when empty? I get that I need 65 psi in them if I want to load them to 1,620 pounds each, but when they're rolling around with nearly nothing on them, I gather that I can keep them at less than that.

They're Kenda Karrier trailer radials. So far, they seem to roll smooth. A friend has a set from 2006 on his pop-up camper and likes them.


If they are not loaded they are not going to heat up as there would be no sidewall deflection.

 

[CKN]

Have you ever watch other 13" inch tires spinning at highway speeds? If you have you would know to inflate them to maximum inflation.

So please inflate to maximum to keep you and others safe.

 

[Dexters]

You don't have to go max pressure.

http://hmcclub.homestead.com/Goodyear_Tire_Inflation___Load_Charts.pdf

 

[Dexters]

Originally Posted By: Dexters
You don't have to go max pressure.

http://hmcclub.homestead.com/Goodyear_Tire_Inflation___Load_Charts.pdf



I should clarify. Your TV doesn't have to be max pressure. Your trailer tires should be max pressure BUT get a good digital pressure reader and understand the effects of temperature on tire pressure.

 

[CapriRacer]

Hokie,

Thanks for the update.

Yup, we are talking about a complex situation. The trailer likely started life with passenger car tires and now has ST tires on it.

At 35 psi, those ST tires have a load carrying capacity of 1100## - so 2 would be 2200. I think tires shouldn't be asked to operate at more than 85% of their rated capacity so the load on the tires shouldn't be higher than 1870 - which is about what I think the GVW of the trailer is.

So I think 35 psi would be fine. But to be more certain, I'd do a pressure buildup test. The next time you operate the trailer in the worst condition, check to see if you get more than 10% pressure buildup. If not, the starting pressure is OK.

 

[jrmason]

ST tires have higher ratings because they are not a passenger tire. "P" and "LT" tires are passenger tires and have a completely different load rating system. ST tires also don't have to meet the same safety standards that passenger tires do, and are almost always made by the lowest bidder. (Chinese). Even if its a name you recognize, its almost guaranteed to be made by an over seas company.

Also, ST tires have a very short service life. In 3 years time, 1/3 of an ST's tire capacity is lost. The combined capacity of all of the tires should exceed the loaded trailer weight by 20 percent. ST tires are only rated for 65 mph. For these reasons, I prefer an LT tire over an ST tire on my 14k lb GVW tilt trailer.

 

[Hokiefyd]

Originally Posted By: CapriRacer
Yup, we are talking about a complex situation. The trailer likely started life with passenger car tires and now has ST tires on it.

At 35 psi, those ST tires have a load carrying capacity of 1100## - so 2 would be 2200. I think tires shouldn't be asked to operate at more than 85% of their rated capacity so the load on the tires shouldn't be higher than 1870 - which is about what I think the GVW of the trailer is.


My decision to use ST tires instead of passenger car tires was more in line with me wanting to do "the correct thing" by running trailer tires on a trailer, rather than trying to get additional load capacity out of them.

It sounds like I might be just as well off with the passenger car tires. A P195/65R15 (I use that size because it's easier to find and less expensive than the P205/65R15 that came with it) has a load index of 89, which is 1,279 pounds. If I de-rate those by 15%, that's right at 1,100 pounds, which could be at least what the GVW of the trailer is anyway.

I may go ahead and keep the 15" wheels that came with the trailer and store them. I'll see how the ST tires do over time, and when it's time to replace them, I may go back to the P-metric tires. With as much as I carry in this trailer, it probably doesn't make much of a difference anyway...and even decent American-made P-metric tires are a good sight cheaper than Chinese ST tires.

 

[EdwardC]

I am not positive if this was mentioned as I just skimmed the posts, but an option for you could be to remove one of the leaf springs if you're routinely running with significantly less weight than the intended design of the trailer.

If you wanted to spend some money, you could add some shocks to the suspension to even out the bounciness.

I've seen this a lot of tear drop trailer forums, here's an example: http://outbackteardrop.com/body8.html