Air Pressure Scamp / Scamp 13 - Page 2 - Fiberglass RV


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Old 09-08-2015, 09:45 AM   #15
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Name: Emily
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Originally Posted by Carol H View Post
My first guess as to why the car dealership and the tire store did not inflate to max pressure is they think the trailer weighs much less than it actually does.... a common misconception.

What year is the trailer? I see you purchased it in 2011 but I see it had a new axle 5 years ago which suggests this is an older trailer. How old are the wheels? What do they have stamped on them as to Max pressure. If they are the original wheels perhaps the worry is they are so old they are not rated for anything more than 40 PSI.
Carol, I'm sorry I wasn't very clear....The dealership and Discount Tire have only done the tires on our Toyota Highlander, the tow vehicle, both prior to our purchasing a Scamp and after. It's this vehicle that they won't fill tires higher PSI on - I thought it was interesting that even our primary vehicle runs on lower PSI than the tires are rated for.

As for the Scamp tires, the wheels are new as well. It's a 1982, purchased from an RV place in Hatch, NM, where they also sell on consignment. They were selling it for the previous owner, who did many, many mods himself. Many that we are still figuring out! The dealer replaced the wheels, tires and bearings for us prior to our purchasing it. I'll have to look at the wheel ratings. Good to know that bit of info!
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Old 09-08-2015, 09:49 AM   #16
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Name: Jim
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The OP's "inflate to 20PSI" sticker is for the original hard-azz bias ply tires that were OE in 1976. My 1983 Scamp 13 came with OE 13" radials, so has a sticker above each wheel calling for "inflate to 25PSI". It has new radials on it, but that pressure seems a tad low to me, so I run them at 27-28 cold.
The results so far (only 4-5K miles) are good tire wear, temps are very reasonable (warm to the touch), and ride quality seems good, since things don't move around much inside the trailer.

That's my experience, YMMV, etc...
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Old 09-08-2015, 10:23 AM   #17
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Quote:
Originally Posted by emij View Post
Carol, I'm sorry I wasn't very clear....The dealership and Discount Tire have only done the tires on our Toyota Highlander, the tow vehicle, both prior to our purchasing a Scamp and after. It's this vehicle that they won't fill tires higher PSI on - I thought it was interesting that even our primary vehicle runs on lower PSI than the tires are rated for.

As for the Scamp tires, the wheels are new as well. It's a 1982, purchased from an RV place in Hatch, NM, where they also sell on consignment. They were selling it for the previous owner, who did many, many mods himself. Many that we are still figuring out! The dealer replaced the wheels, tires and bearings for us prior to our purchasing it. I'll have to look at the wheel ratings. Good to know that bit of info!
About your TV's Tires & PSI: Discount/America's Tire is usually very careful about holding to manufacturers specifications. I see that your 2011 Toyota Highlander came with a difficult to find tire size (LE 245-55R19) and I don't know what the Toyota spec in the owners manual specifies for max inflation pressure (But I am sure that the Dealership and Discount Tire's computers both know that number). In this typical example for the original tire size the maximum pressure is 44 PSI, suggesting that the tires that you have are over rated for the vehicle.
Firestone Destination LE 2 245/55R19

In addition, there may also be a pressure limit for the rims that prevents inflating to 65 PSI.

All that said, the tires may function perfectly well at 38 PSI, based on the manufacturers inflation pressure/weight capacity charts, so it looks like there may well have been a good reason to not go above 38 PSI.
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Old 09-08-2015, 10:33 AM   #18
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Quote:
Originally Posted by Bob Miller View Post
About your TV's Tires & PSI: Discount/America's Tire is usually very careful about holding to manufacturers specifications. I see that your 2011 Toyota Highlander came with a difficult to find tire size (LE 245-55R19) and I don't know what the Toyota spec in the owners manual specifies for max inflation pressure (But I am sure that the Dealership and Discount Tire's computers both know that number). In this typical example for the original tire size the maximum pressure is 44 PSI, suggesting that the tires that you have are over rated for the vehicle.
Firestone Destination LE 2 245/55R19

In addition, there may also be a pressure limit for the rims that prevents inflating to 65 PSI.

All that said, the tires may function perfectly well at 38 PSI, based on the manufacturers inflation pressure/weight capacity charts, so it looks like there may well have been a good reason to not go above 38 PSI.
Thank you for taking time to look that up and make such a clear explanation regarding our Highlander. Honestly, my husband has asked and asked for explanations over the years (we bought the vehicle new) and no one has been able to clearly articulate just why they inflate them to where they do. My husband will be SO HAPPY to read this. It's also great info for when we begin the process of deciding what to get when it's time to buy the next set of tires. Thank you.
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Old 09-08-2015, 10:38 AM   #19
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Under inflating trailer tires is not a good thing to do. Yes, some people get away with, but is the fuss of under inflating worth the risk. I talked to a Carlisle distributor not a dealer, one step closer to the manufacture. It recommended that trailer tires always be inflated to the max side wall pressure. Autos, trucks, etc. the vehicle manufacture publishes recommend inflation points. Inflation on powered vehicles effects handling. Under inflation of trailer trailer tires results in more flex in the side wall thus creating more heat, which can result in melting the tire. Not a pretty sight. Two ways to learn about things, one is from people that have seen the results or experiencing the results yourself.
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Old 09-08-2015, 10:39 AM   #20
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Just looked up my tires (P175/70R13) and some similar sizes in the super-secret tire manufactures "Application of load-inflation tables" guidebook.
Note that the 10% derate takes the 26PSI Load Carrying Capacity (LCC) down to 810#, which is close to the street side weight of my light Scamp.
Note how the XL tire has normal LCC up through 35PSI, but continues to offer more LCC as pressure is increased above "standard" pressures.
When my scary Chi-comm tires age out (next year!), I'll upgrade to S. Korea sourced Kumho P155/80R13 and run them at 29-30PSI. The 155 fits the 4.5" rim much better, has lower resistance, and is a teeny bit taller for reduced wheel RPM.

Tire Size SL/ XL/ LL 26 29 32 35 38 41 (PSI)
P155/80R13 SL 838 882 926 959
P175/50R13 XL 672 705 739 783 805 827
P175/70R13 SL 893 948 992 1036
P175/80R13 SL 1025 1080 1135 1179
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Old 09-08-2015, 10:44 AM   #21
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As far as inflation charts those are minimum pressures for the weight. Also they are cold pressures. As is the sidewall pressure a cold pressure. When you run minimum pressure you any loss of air puts you under the minimum and possible blow out. Running at maximum give a lot of room.
It's a good idea that at every stop you put your hand on each of tires. If it's hot you need to do something.

One other thing about trailer tires, they are rated for 65 mph max.
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Old 09-08-2015, 11:04 AM   #22
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I'd suggest keeping the inflation of the tow vehicle's tires separate from the trailer's tires. There are many more performance issues with tow vehicle pressures that argue for keeping the manufacturer's inflations.
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Old 09-08-2015, 11:30 AM   #23
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I presume the "50 psi maximum" (that's exactly what it says on the Scamp label) is an upper limit designed to permit satisfactory tire performance at the trailer's maximum load. Oddly, I can't seem to locate a GVWR anywhere, but I do know that late model 13' Scamps use a 2200 pound axle.

Most on-the-road Scamps weigh less than that, total, some a lot less. While there is nothing wrong with running at maximum pressure regardless of load, if it produces an unacceptably harsh ride (and assuming the axle is not the problem), it makes sense to cautiously reduce tire pressure somewhat. The dangers of under-inflation are greater than over-inflation, so I'd recommend an incremental approach. It is always a good thing to know what your trailer really weighs.

Two things can cause the axle to be the problem. One is an aged-out axle. Since your axle is only 5 years old, that's not it. Another is a over-rated axle. Some people, in the mistaken belief that more is always better, will install a heavy-duty axle on a 13' egg. That would also make it ride like a buckboard. If there is a tag on your axle with a serial number, you should be able to determine through the manufacturer whether your axle is appropriately rated for your trailer.
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Old 09-08-2015, 11:45 AM   #24
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Quote:
Originally Posted by Jon in AZ View Post

Two things can cause the axle to be the problem. One is an aged-out axle. Since your axle is only 5 years old, that's not it. Another is a over-rated axle. Some people, in the mistaken belief that more is always better, will install a heavy-duty axle on a 13' egg. That would also make it ride like a buckboard. If there is a tag on your axle with a serial number, you should be able to determine through the manufacturer whether your axle is appropriately rated for your trailer.
Jon- Thanks for the suggestion of looking for a tag on the axle with serial number. The PO outfitted our Scamp to be completely off the grid, so it wouldn't surprise me at all, if he put on a heavy duty axle. At 35 PSI, it towed for 4000 miles like it wasn't even there. At 48 PSI for ten minutes, it was bouncy, bouncy.
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Old 09-08-2015, 11:57 AM   #25
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I queried the google and found this inflation info on Goodyear's website. Click here. Interesting reading.

Also, I found the attached handy Goodyear pdf table. My tires are in the first row and my Scamp's axle weight calls for 30 psi to keep the whole tread width on the pavement. I assumed the tire gurus at Goodyear factored in handling too, though some folks swear that higher inflation improves mileage and loosens rivets. And who knows, maybe engineers were not consulted and the marketing folks wrote and the legal department edited the web page. YMMV

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I try to keep my tires properly inflated, whatever that means since you cannot trust the internet. (I have a super secret number of psi that I mostly keep to.) Also I give them a look at every gas stop to make sure they are not flat, sometimes even going as far as feeling the rubber. This sophisticated hand test finds they are almost always warm in warmer weather and cool in cooler weather and fully inflated all the time. And perhaps taking it a bit over-the-top I check the pressure with a gauge before any trip. Decades of towing experience have taught me that tires roll more smoothly, last longer, and mileage is better with air inside. ;-)

Happy trails, John

Attached Files
File Type: pdf rv_inflation.pdf (86.7 KB, 6 views)
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Old 09-08-2015, 12:11 PM   #26
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Only Two Schools of thought ??

Only two schools of thought - Wow Zowee !

OK - I can understand immediately that the 25 lb sticker is most likely an original sticker and relates to bias belted tires .... Will probably leave it there - just for grins !

Think I will keep the tire pressure at 33 and check the tire temp at each stop along the route - about 400 miles - maybe 8 hrs +/- including stops. May adjust along the way / may not !

I towed it home from Ill a few yrs ago - using higher tire pressure with out incident - but it had nothing in it to bounce around . Since then it has been an occasional project trailer ( replaced the stove + refrig - Removed and re bedded all opening windows and roof vents in buytal (sp?) rubber ( except the smallest by the stove) , replaced and rewired the interior and exterior lights - and stopped the leaking front and rear windows - and put a PVC plank across the width of the back - removed the water tank (which is a pain anyway - to me at least - will use bottled water from local grocery ) .
Also abandoned the furnace and front mounted propane tanks - will use only the 1 lb cans ( since I intend only short term camping and walmarts ae ubiquitous !) Made an awning etc . Now to try it all out and find out where I went wrong and what else I need to acquire or fix - One is never done with a trailer or a boat .....

Many thanks for the discussion and the breadth of your knowledgeable opinions.

See you 'round the bend ,
Ken
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Old 09-08-2015, 12:22 PM   #27
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1] Install appropriate sized and rated tires.
2] Inflate your trailer tires to sidewall pressure.
3] Enjoy optimum tire life and safety.
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Old 09-08-2015, 12:27 PM   #28
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Quote:
Originally Posted by John Linck View Post
I queried the google and found this inflation info on Goodyear's website. Click here.

Also, this attached handy pdf table.

YMMV and such discussions can be as perilous as talking religion. Use care.

I try to keep my tires properly inflated, whatever that means.

John

I think there's a reading comprehension problem here. "TIRE LOAD LIMITS (LBS) AT VARIOUS COLD INFLATION PRESSURES (PSI)" What does that mean. To me it means that at weight and pressure limits posted in that chart are the threshold between safe and unsafe. If I miss on the weight I could be easily over the limit. I add extra clothes and some canned food when I was at the limit, those thing could put me over the limit. As with many things it's good to stay away from thresholds. In this case, tires should be inflated well above the limit, but not above the maximum side wall. Which would mean at side wall pressure when cold. (first thing in the morning before moving the trailer.)
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