Tire pressure on new trailer tires - Fiberglass RV


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Old 09-03-2009, 08:58 PM   #1
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Trailer: 1999 Scamp 13 ft and 2003 Bigfoot 17 ft (15B17CB)
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We got 2 new Towmax tires for the Bigfoot, but are confused as to what PSI to use for trailering. The local tire place only put 32 PSI because that's what the trailer sticker says. The max on the sidewall is 65 PSI. They look low to me, but it's hard to tell with radials. I get opinions that differ from my usual "experts" from 32 to 65. I've heard low pressure is the number one reason for failure, so we want to avoid that.
I searched the archives for info, but I may have missed it.
Any help appreciated.
Tony and Darlene
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Old 09-03-2009, 09:06 PM   #2
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The local tire place only put 32 PSI because that's what the trailer sticker says. The max on the sidewall is 65 PSI.
Any help appreciated.
Tony and Darlene
I say go with what is on the sidewall. I goofed up with my car a while back and used what the sticker said instead of the tire (which was hard to find and read anyway) I was running them grossly under inflated. Mechanic at reputable alignment shop straightened me out - he said follow tire mfr recommendations, ignore car sticker and handbook - they're generic. Might be the same for trailers.

I'm running Carlisle radial trailer tires at 60 psi (at stated on tire) with no problem. Rolls nice.
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Old 09-03-2009, 09:32 PM   #3
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I'd go with what it says on the sidewall too (and I do!). Unless you're got the EXACT same tire now as what came with the trailer. After all, sidewall info comes from the tire manufacturer and I'd think they'd know best what PSI should run on their tires.

Your mileage may vary.
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Old 09-03-2009, 10:39 PM   #4
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Casita put 32 pounds of air in the two new wheels and tires I bought from them back in May, 2003.

Thanks to this forum I found out that was way to little pressure.
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Old 09-03-2009, 11:21 PM   #5
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65 PSI is max-- that's when you are approaching the weight limit of the tire (the one the tire manufacturer put on the sidewall) Normally I would say about 50 would do. If you go down to 32, it is way underinflated and the sidewalls will flex too much, and the tire casing (sidewalls) will get warm (actually hot). This will cause a blowout--- running your tires at max makes them a lot stiffer (they won't overheat tho, usually) but then the cushioning effect provided by the tires (that's why solid rubber tires were done away with) will be to the point of almost nonexistant. Now, did I confuse you all? Larry
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Old 09-04-2009, 05:14 AM   #6
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Hi Tony,

You didn't mention the weight of your trailer or the tire size. Take a look at a load/inflation table. Assuming ST225/75R15 tires, load capacity for each tire is 1760# at 35 psi, 1880# at 40 psi, 2020# at 45 psi, 2150 at 50 psi, 2270# at 55 psi, 2380# at 60 psi and 2540# at 65 psi. You can't go over 50 psi unless you have D load range tires.

The axle weight for our trailer is 3100# with tanks empty, but I would allow for at least 3600#, 1800 for each tire, meaning you could get by with 40 psi. I put 55 psi in mine to be on the safe side. Ours came with C load range, but I upgraded to D Marathons with the yellow circle. Our trailer is a little "over gross". Yours may be as well.
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Old 09-04-2009, 07:10 AM   #7
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Larry and Carrie have it right, whats written on the side is max, I'd try it at 50-55 lbs fully loaded on your size trailer, at 65 lbs you'll probably have to nail everything down because of vibration
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Old 09-04-2009, 07:18 AM   #8
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Quote:
Hi Tony,

You didn't mention the weight of your trailer or the tire size. Take a look at a load/inflation table. Assuming ST225/75R15 tires, load capacity for each tire is 1760# at 35 psi, 1880# at 40 psi, 2020# at 45 psi, 2150 at 50 psi, 2270# at 55 psi, 2380# at 60 psi and 2540# at 65 psi. You can't go over 50 psi unless you have D load range tires.

The axle weight for our trailer is 3100# with tanks empty, but I would allow for at least 3600#, 1800 for each tire, meaning you could get by with 40 psi. I put 55 psi in mine to be on the safe side. Ours came with C load range, but I upgraded to D Marathons with the yellow circle. Our trailer is a little "over gross". Yours may be as well.
I believe that this is Goodyear’s the load/inflation table which Bob mentioned: http://www.goodyear.com/rv/pdf/rv_inflation.pdf

I found it to be a lonely case of manufacturer data in this trailer tire pressure World of opinions. Sidewall tire data specifically states the maximum tire pressure and as it is with car or truck tires it is not a recommended tire pressure.

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Old 09-04-2009, 11:07 AM   #9
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Trailer: 1999 Scamp 13 ft and 2003 Bigfoot 17 ft (15B17CB)
Wisconsin
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Thanks all for imput. As Bob guessed the BF is 2850 lbs unloaded,so ~3100 with our stuff. The Towmax tires are ST225/75R15 with a D rating. So I'll go with 50 PSI, since my trailer is similar to Bob's, no Winter package accounts for the lesser weight. By the way Bob, I use Roger (Bob's trailers former owner) as my Bigfoot expert.
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Old 09-04-2009, 06:14 PM   #10
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Hard to beat Roger as the expert; he's owned more trailers than I could name!
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