Trailer tires - Fiberglass RV


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Old 07-11-2007, 06:51 PM   #1
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After our first Boler trip, I told the forum how crazy the trip was, with things bouncing everywhere! Many people told us to check the axle. Just wanted to update everyone. Our friendly neighbourhood mechanic said he thought the axle was probably okay. mentioned that we could maybe lower the tire pressure, to see if that would help. We had just bought new
ST175/80R13, already mounted, and just put them on. Actually checked the pressure today, before we pulled out of the driveway, and there was 55 lbs!. Yikes. Hopefully the ride will now be smoother--we brought the pressure down to about 25. Just letting you know, for interest sake.
I'm beginning to wonder of our venture into Bolering is a little rockier than most.....
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Old 07-11-2007, 07:16 PM   #2
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I assumed you checked the recommended tire pressure? On my boat trailer the recommended pressure is considerably higher than on the car (which is 36.)

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Old 07-11-2007, 09:35 PM   #3
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Quote:
Our friendly neighbourhood mechanic said he thought the axle was probably okay. mentioned that we could maybe lower the tire pressure, to see if that would help.

Actually checked the pressure today, before we pulled out of the driveway, and there was 55 lbs!. Yikes.

Hopefully the ride will now be smoother--we brought the pressure down to about 25. Just letting you know, for interest sake.

I'm beginning to wonder of our venture into Bolering is a little rockier than most.....
Trailer tires are SUPPOSED TO be at a higher pressure.
You could damage your sidewalls at a mere 25 lbs!

My 5.30 x 12" Fiber Stream tires are supposed to be inflated to [b]80 LBS cold.
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Old 07-11-2007, 09:42 PM   #4
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Check your sidewalls for the proper pressure!

Trailer tires are supposed to be high, as everyone else said..I would hate to see you with a blow out or worse!
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Old 07-11-2007, 10:47 PM   #5
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I would be interested to know what preasure I should keep the 13 inch tires at on my 13ft Burro if anyone knows off hand.
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Old 07-11-2007, 11:22 PM   #6
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Dave,
Depends on what type tire. As Gina said it should be on the sidewall.
My Scamp 13 has USA Trail and they are set to 50psi.
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Old 07-12-2007, 01:47 PM   #7
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Hold on here -- Trailer and truck tires (ST and LT) are not the same as automobile tires, where it is recommended that one normally run at the max pressure (but not always, see door label below; Ford sez use 30 front and 35 rear, but the tires say 42...; a 99 Mountaineer with the same tires sez 26 on both front and rear).

Think about this; if I get a Load Range B tire on my Egg when it was new, I might run it at the sidewall max of 35psi. Later I decide to replace it with a Load Range C tire which has a sidewall max of 55 psi. If I follow most of the advice above, I would increase the pressure to 50 psi and now my trailer is subjected to a rougher ride.

Later, I manage to find some Load Range D tires which have a sidewall pressure of 65 psi, so I jack them up to that. I have now come awfully close to doubling the tire pressures under the same trailer. Why don't I quit fooling around with rubber and get some solid steel wheels...

Tires are actually intended to carry a load and be part of the suspension.

See the Goodyear Load/Inflation Chart and you can see that I could have the above scenario with 14" tires.

All of that said, there is some wisdom in the advice to run at higher psi; you are far more likely to damage a tire at low psi than high (bounce damage and a few broken rivets are better than the ditch) and if you are careless about checking pressures, starting at higher ones gives you a little leeway.

For example, I believe the tire pressures Ford put on the Mountaineeer are too low, considering the neglect the average driver likely gives to things like that; my personal opinion is that Ford set it lower to give a nicer ride to the SUV than the truck and that set up the Explorer/Firestone Fiasco.
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Old 07-12-2007, 02:15 PM   #8
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I was interrupted while posting this, and Pete has beaten me to the major points... but here's my version anyway...

Yes, trailer tires are typically run at higher pressures than passenger car tires... but in both cases the correct pressure depends on the tire and the load. The pressure must be at least high enough to support the required load, but still within the maximum (which is marked on the sidewall of the tire).

The specification of "ST175/80R13" describes the type and size of the tire, but not the load range or pressure rating. The load range for trailer tires (and most light truck and commercial truck/trailer tires) is given as a range letter, from "A" to whatever. For each load range, there's a typical pressure, and a corresponding load capacity; essentially, the higher ranges can carry more load because they are constructed to withstand higher pressures.

There are essentially no load range A tires, but the ST175/80R13 could be load range B or C, or higher. Load range B tires would usually have a maximum inflation pressure of 35 PSI, but they might not have enough load capacity. The tires might be load range C, and for that range the max pressure is normally 50 PSI. They could even be load range D (65 PSI), E (80 PSI, like Frederick's), etc.

Here's another link to the often-referenced Goodyear Marathon Load/Inflation Tables web page. The pressure and load capacity for a given size don't really change by brand. According to the document there, a load range B ST175/80R13 could carry 1100 lb per tire at its max of 35 psi, a load range C could carry the same at that pressure, of up to 1360 lb at 50 psi. Down at 25 PSI, they're good for only 905 lb per tire.

25 PSI might be enough for the Boler. Higher pressure, even if not needed for load capacity, may help lower rolling resistance and thus reduce heat buildup, or improve control, but overdoing it isn't good for ride or control.
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Old 07-12-2007, 04:13 PM   #9
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Here is Carlisle's tire maintenance and inflation guide.

Carlisle

According to them I'm dead on with 50psi for the Carlisle USA Trail 13 ST.
They also make a position statement in here: "Maximum load range only is attained when the tire is at its maximum air pressure. There is no advantage to taking air out of the tire. With maximum pressure, the tire will perform and wear better, and you will get better gas mileage. Reduce the psi and you compromise the functionality of the tire. This is the position we take on this."

This is a pretty well-written guide and basically would apply to any trailer tire maintenance. I guess it's all arguable, but I'm following their published stuff.

Dave, again depends on brand and type of tire you have and then look up the manufacturers recommendations.
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Old 07-12-2007, 05:10 PM   #10
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My tires are:
Milestar brand M-108
Radial
ST 175/80R13
Load Range C
Max Load 1360 Lbs at 50Psi cold

Now that I have this I'll look them up...
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Old 07-12-2007, 07:26 PM   #11
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Quote:
According to them I'm dead on with 50psi for the Carlisle USA Trail 13 ST.
They also make a position statement in here: "Maximum load range only is attained when the tire is at its maximum air pressure. [b]There is no advantage to taking air out of the tire. With maximum pressure, the tire will perform and wear better, and you will get better gas mileage. Reduce the psi and you compromise the functionality of the tire. This is the position we take on this."
I'm not questioning the suitability of 50 PSI for Greg's specific situation, but the part I've highlighted of the Carlisle statement is simply ridiculous. Despite the lack of an engine, the dynamics of vehicle behaviour are not different for trailers than for any other vehicle. The very highest pressure the tire can take is not automatically the optimal one for the situation, any more than it is for tires on cars or trucks.

We - as the general trailer-towing public - have very low expectations of trailer dynamics (response, traction, ride...) and thus are happy with small rock-hard tires. We have higher expectations for our motor vehicles, and are thus willing to spend more for the tires, and specify and operate them differently.
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Old 07-12-2007, 08:29 PM   #12
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I thought that was an interesting statement too Brian. I thought Carlisles stuff would inject some good discussion.

Where this will show up again is very much like the Ford Explorer blowout and rollover suits awhile back. If you blow a Carlisle tire and roll or have damage or personal injury and the courts establish you ran only 34 psi against manufacturers recommendations, then they have a back door out of litigation, or a reduced award at best.
Ford countered the lawsuits with under inflation and lack of following the manufacturers recommendations.

I especially like the part where right below their inflation/load table they said that the table basically was informational only and not a recommendation to reduce pressure.
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Old 07-13-2007, 12:14 PM   #13
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I strongly suspect that Carlisle has gone the total-pressure route because of the problems they were having with tire blowouts a few years back. It was bad enough that Scamp (and Casita?) stopped using them as original equipment on the trailers (Like Ford, Scamp had a fender sticker recommending reduced pressures) and they quickly earned a bad RV reputation on all the RV groups.

Everyone then switched to Goodyear Marathons and they now have a less-than-pristine reputation...

Hmm, could it be the owners, not the tires?

Clearly, the trailer manf, like the vehicle manf, wants a nice ride and high pressures work against that, while the tire manf wants a cool tire and low pressures (and high speeds) work against that.

As owners, our goal is to find a happy medium, but we need always bear in mind that when in doubt, use the higher pressures because they have less serious consequences.
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Old 07-13-2007, 01:33 PM   #14
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Quote:
...when in doubt, use the higher pressures...
I agree: err on the side of higher pressure, and therefore higher capacity, while staying within the tire's limits. This applies to trailers as it does to any vehicle; it is even more important with trailers because they so commonly push the tires close to their limits, leaving less margin for error than a typical car, for instance.
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