Tire pressure question.

[Thomcat316]

OK, so the Litehouse has 800 miles under the floor pan, and the "4.80x12" tires I purchased from the local trailer supply seem to have magically turned into 5.30x12.... Go figure.

They also have an odd wear pattern.


There's two shoulders and three ribs here. If you look closely at the "bottom" rib in the photo you'll see that there's a ghostly remnant of the circumferential yellow stripe that still runs over the blocks of the rib. The only wear on the tire is on the center rib.

To me, this says "overinflated". Currently I'm running 25PSI in the tire, and the entire casing remains cool to the touch after hours at 60-70MPH except for the center rib, which is warm.

Should I deflate things still further? Should I get radial tires? Any other suggestions?

[proformance]

I'll through my two cents in as I have spent many years looking at tread wear to determine proper inflation, caster and camber.

1) You will need to put more miles on your trailer before you reach any positive conclusion. It will require several hundred miles before your tires begin to break in.

2) Yes, if the tire is only warm in the center, then the center is your primary contact patch. In a perfect world, the tire should have equal temperature across the entire surface.

3) The tire pressure requirements will change based on load. If your trailer was fully loaded during this test, then yes, I would recommend reducing the tire pressure approx 5psi (Provided the tires have broken in.)

4) You can get down to approx 15psi safely on a trailer without loosing a bead. (under most applications). But, if you add significant weight, you will need to increase pressure.

5) Real world observation; While driving, note the sidewall deflection while transition up/down driveway lips, over speed bumps, off curbs, across pot-holes, rounding corners at considerable speed and traveling straight at or just above normal highway speeds. (A video camera mounted to your TV or trailer will provide you with video to review under safe condition rather than hanging your head out the window while someone else drives.) A) Some deflection is good. You want to see the sidewall deflect minimally with the small obstructions and significantly more with the larger obstructions. But, not deflect greater than 30% (approx) of the normal sidewall height with severe obstructions (Too much deflection represents to little PSI, No deflection represents to much PSI) B) Also, you do not want the width of the tire at the sidewall, to decrease (narrow) with highway speeds (this indicates to little PSI.) C) You want to insure that while cornering at significant cornering speeds, the tire does not roll to the side more than approx 15% of its width. (Too much roll could blow a bead.)

6) You may never see proper tire wear if your tires are rated for a load significantly greater than the actual weight of your trailer. As the tire rotates, the centrifugal force influences the contact patch of the tire. It may be your trailer may not have enough weight to overcome the centrifugal force resulting in the center of the tire always experiencing the greatest load/wear.

The most accurate method of identifying proper tire inflation is observing tire real deflection under normal and abnormal driving conditions -and- measuring actual tire temperatures across the surface of the tire immediately upon stopping the vehicle.

[Thomcat316]

I'd like to thank you for taking the time to produce the most concise and informative single-source bit of information I've been able to finsd on the whole of the Web - seriously, I searched a *lot* before asking this one.

More questions, though...

1) You will need to put more miles on your trailer before you reach any positive conclusion. It will require several hundred miles before your tires begin to break in.

2) Yes, if the tire is only warm in the center, then the center is your primary contact patch. In a perfect world, the tire should have equal temperature across the entire surface.

3) The tire pressure requirements will change based on load. If your trailer was fully loaded during this test, then yes, I would recommend reducing the tire pressure approx 5psi (Provided the tires have broken in.)

It's been about 1200 miles now, and at 25PSI there's still no noticeable wear, and the contact patch is still less than an inch out of five or so. I think I'll plan on going to 20PSI for the next trip and see what happens then. The fenders aren't installed yet, so it's really simple to hand-check tire temperatures at rest stops, and it's still "cool tire with warm center bead" all the time - no flexural/frictional heating in the carcass at all.

4) You can get down to approx 15psi safely on a trailer without loosing a bead. (under most applications). But, if you add significant weight, you will need to increase pressure.

This is what makes me ask questions - I'm pretty close to 15PSI already, and the trailer's still a bit bouncy and the tire's still round in cross section. Would radial passenger car tires (145SR12) hold a flatter cross section better with light loads, or should I start adding strategically placed sandbags?

5) Real world observation; While driving, note the sidewall deflection while transition up/down driveway lips, over speed bumps, off curbs, across pot-holes, rounding corners at considerable speed and traveling straight at or just above normal highway speeds. (A video camera mounted to your TV or trailer will provide you with video to review under safe condition rather than hanging your head out the window while someone else drives.) A) Some deflection is good. You want to see the sidewall deflect minimally with the small obstructions and significantly more with the larger obstructions. But, not deflect greater than 30% (approx) of the normal sidewall height with severe obstructions (Too much deflection represents to little PSI, No deflection represents to much PSI) B) Also, you do not want the width of the tire at the sidewall, to decrease (narrow) with highway speeds (this indicates to little PSI.) C) You want to insure that while cornering at significant cornering speeds, the tire does not roll to the side more than approx 15% of its width. (Too much roll could blow a bead.)

Haven't had a chance to rig the GoPro Hero and go do a cloverleaf and short freeway run yet, but best I can tell from looks back in the mirror there's little or no deflection going on.

6) You may never see proper tire wear if your tires are rated for a load significantly greater than the actual weight of your trailer. As the tire rotates, the centrifugal force influences the contact patch of the tire. It may be your trailer may not have enough weight to overcome the centrifugal force resulting in the center of the tire always experiencing the greatest load/wear.

I'll be happy to wear tires funny, just so long as I have a reasonable confidence that I'm not likely to either shake the trailer to pieces or lose a bead on an onramp.

Might have some nice low-mile wheels/tires for sale soon!

[bdosborn]

An old jeepers trick for establishing the PSI needed for your vehicle:

Draw a chalk line across your tire and drive around the block. Add or subtract pressure till the chalk line wears completely away across the tread.

FWIW,
Bruce

[Maureenm]

Hi knowledgable trailer people, I think this is the thread to answer my question...my trailer is new to me and know little about it's origins, but I have a tire pressure question. My tires are "obsolete" I've been tole
D, but they are what I have for now. 6.0-16. I checked the pressure and one side was 6.0 and the other was 8.5. Well, these numbers kind of freaked me out. I just read about 15 or 20 psi being feasible, so that made me feel a little better as I was under the impression that trailer tires had much higher psi typically. My trailer is pretty light(760) so I plan to add some air in the morning and see how it goes,but not sure what to start with. These tires have a tread more like a tractor, so I figure that probably makes a difference. Any advice would be helpful. I do plan to replace these soon, but not immediately.
Thanks, maureen

[John Palmer]

Hi knowledgable trailer people, I think this is the thread to answer my question...my trailer is new to me and know little about it's origins, but I have a tire pressure question. My tires are "obsolete" I've been tole
D, but they are what I have for now. 6.0-16. I checked the pressure and one side was 6.0 and the other was 8.5. Well, these numbers kind of freaked me out. I just read about 15 or 20 psi being feasible, so that made me feel a little better as I was under the impression that trailer tires had much higher psi typically. My trailer is pretty light(760) so I plan to add some air in the morning and see how it goes,but not sure what to start with. These tires have a tread more like a tractor, so I figure that probably makes a difference. Any advice would be helpful. I do plan to replace these soon, but not immediately.
Thanks, maureen

15 to 18#'s is fine for your 760 pound trailer. You can find new 6.00 by 16 vintage tires at Coker Tire.

[Maureenm]

Thanks, John. I had a trip planned so I went with 19psi as they looked good, and it worked out fine, but I think will contact coker's. In the meantime, I found out they are willy's military jeep tires. Appreciate the help.
Maureen

[Thomcat316]

5,300 miles later, with less than 500 lbs. all-up on my 5.30x12 tires running at 25PSI, and I've still not rubbed the little molding nibs off the outer rows of tread. Tread temps peak at "warm" in the middle, with the tread edges being "cool" and the sidewalls being "a little warm". Anyone ever use an infrared thermometer to measure sidewall temps? What's "too hot"?

The trailer bounces very little as long as it's weighted to over 400 lbs. - I think it helps that 50 lbs. of that is a futon mattress (mass damper deluxe...). Empty requires avoiding bumps.

Thanks to all for the info so far, and especially to Bruce for pointing out the tire chalk trick - I'll use it when I fully load the trailer in October for the trade shows.

Happy Camping!
Whitney

[dguff]

It may not be relevant for today's tires but the instructions on the decal inside the door of a 1947 KIt called for inflation pressures of 12 to 15 psi. They originally had bias ply tube type tires of 16 or 15" size.

Jerome

[ubear7]

Shouldn't 5.30x12 have an 80 psi? I have 2 trailers one for a golf cart and the one for the teardrop both came with 5.30x12 and require 80 psi.

[Wolffarmer]

Back in my motorcycling days we would determine the needed PSI by taking a reading. Then riding untill things warmed up pretty good. Check the pressure again. If the pressure did not rise by 5 lbs then the starting pressure was to high. If the pressure increased more than 5 lbs then the starting pressure was to low. I have not tried this with the trailer. I just feel the tire and watch the wear pattern. Those of us using tire sizes of a car can probably run 25 pounds or less. And the lower you can safely run the smoother the ride is for the trailer

Randy

[Shadow Catcher]

I don't know that normal rules apply to trailer tires some or all of the time. From what I can glean trailer tires are a total different animal which is one of the reasons I've asked about using conventional automotive tires. The literature tells you that during hot periods you need to raise the temperature in the tires by 10 pounds. I had that reiterated to me By a Goodyear tire expert.
Frankly the level of end product of hay through male bovine is pretty incredible, and on top of this the fact that the vast majority of them are made in China that Goodyear exec they are also end product from digestive processes.