Help, Im Fishtailing (and other first trip encounters) - Page 3 - Fiberglass RV


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Old 09-06-2012, 06:20 AM   #29
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Name: Jesse
Trailer: 1984 Scamp 13'
Maryland
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Quote:
Originally Posted by cpaharley2008
I have noticed that sometimes the tire manufacturer recommends one PSI level and the car maker, another set of PSI levels. The car company wants a soft ride normally and for example my Jeep states on door jamb 30 psi but the tire states 45 psi. When towing I use 45 and I leave it that way the rest of the time. It rides a little harder but it make life a little simpler. So check both places.
Tire manufacturers do NOT list a recommended pressure. They list the MAXIMUM pressure that the tire can handle. Car companies choose a pressure that suits the weight that is on each axle.
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Old 09-06-2012, 06:24 AM   #30
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Quote:
Originally Posted by Dennis Clinton
Per the Scamp web site, for a 13' trailer the top of the ball should be about 18" above the ground. As far as your tires, there are several threads here about tire pressure. Personally, I think 20# is way too soft and that will cause some sway(and possibly overheat the tires). I always go with the tire manufacturers recommendation-listed on the tire.
As far as hitch height, don't forget that older 13 foot Scamps sit much lower than new ones.

The Scamp 13s tow MUCH better with the proper pressure in the tires. Both the tire manufacturers and Scamp recommend a pressure which corresponds to the weight on the axle. There is a chart that shows how much pressure you should use depending on the weight.
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Old 09-06-2012, 06:34 AM   #31
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I may have missed this info, Jimbo... How fast we're you driving when you experienced sway?

The previous owners of my Scamp gave me lots of (bad) advice on how to tow. They had the tires at MAX pressure and packed up the Scamp so that it had about a 300 pound tongue weight. About 15 miles down the road, I redistributed weight and lowered the pressure to 20 pounds and it towed like a dream. It did not sway, but it bounced and pushed around the TV. Now I keep the tongue weight at about 130 pounds and the tires at 20 pounds. The tires will NOT run hot or wear out prematurely at the PROPER pressure for the WEIGHT of the trailer.
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Old 09-06-2012, 12:49 PM   #32
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Thanks again everyone. Lowering the tire pressure definitely helped smooth the towing. It vibrated soooooo much at 40 psi that the
Fire extinguisher broke its strap and some of the molding in the edge of the cabinets rattled off

Bob thanks for the tip on Arrow. I'll give them a call. McBrew with the adjustable hitch lower it towed PERFECTLY at ALL SPEEDS --with the fixed hitch and tongue a little higher it would sway even at 60
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Old 09-06-2012, 12:51 PM   #33
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Before I changed my axle, wheels and tires the trailer was at the maximum weight limit for the 13" tires. I was forced to use the maximum pressure listed on the tire to achieve the listed capacity. Now with the 185R14 Kumho 857's I have about 500 pounds reserve capacity per side, and I can use less air in the tires if desired for ride or tire wear control. Too little air causes the edges of the tread to wear prematurely, less fuel enonomy, and can amplify a sway condition caused by other problems. Too much air causes the centers of the tires to wear prematurely, hard ride, more weight carrying, and better fuel economy. The correct pressure will yield the best combination of all those things.
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Old 09-06-2012, 02:35 PM   #34
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Quote:
Originally Posted by Thee Jimbo View Post
Brand spanking new tires.
Are they ST- (special trailer) or P- (passenger car) rated tires?
I ask because my Trillium came with brand spankin' new P (passenger car) tires and it swayed badly until on the advice of my RV guy I replaced them with ST tires. Apparently this is a pretty common problem...

ST's have much stiffer sidewalls than P-rated tires, and flabby sidewalls is a recipe for sway on a towable.

Also, Scamp recommends bias-ply tires, but allows for radials IF they're ST-rated. (source: http://www.scamptrailers.com/Portals...nersManual.pdf
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Old 09-06-2012, 03:07 PM   #35
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Definitely ST "trailer" tires. radial not bias. Towed perfectly 1000+ miles. "swayed" the last portion of the trip only .
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Old 09-06-2012, 03:19 PM   #36
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Quote:
Originally Posted by Thee Jimbo View Post
Definitely ST "trailer" tires. radial not bias. Towed perfectly 1000+ miles. "swayed" the last portion of the trip only .
Well, if they're ST's, they're probably rated for 50 pounds of pressure and should be run at or near that for best performance. Extreme underinflation (e.g., 20 lbs) in any tubeless tire is just asking for separation from the rim, and in a trailer tire it only increases the flabbiness that aggravates sway conditions.

The main causes of trailer sway are:

#1: Tongue weight too low. Should be 10-15% of trailer weight, the more the better. "Too heavy" will not induce sway.
#2: Wrong tires and/or wrong tire pressure.
#3: Speeds in excess of 60 mph, especially on downhill grades.
#4: Short wheelbase tow vehicle and/or load-carrying extensions on the trailer bumper (These affect center of gravity)
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Old 09-07-2012, 07:22 AM   #37
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Quote:
Originally Posted by Francesca Knowles
Well, if they're ST's, they're probably rated for 50 pounds of pressure and should be run at or near that for best performance. Extreme underinflation (e.g., 20 lbs) in any tubeless tire is just asking for separation from the rim, and in a trailer tire it only increases the flabbiness that aggravates sway conditions.
Not true. Please review what the tire manufacturers and trailer manufacturers publish on this subject.

20 PSI is PROPER inflation for certain trailer loads.
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Old 09-07-2012, 08:50 AM   #38
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Perhaps tire manufacturer's should also list a minimum pressure on their tires, regardless of load. I find it interesting that one manufacturer of an item which has it's own limits can be changed by another manufacturer who utilizes that product in their product. I was always under the impression to keep tires at their maximum, regardless of how or what it it is being used on. To under inflate a tire perhaps on sand is one thing but how would an individual reduce the inflation based upon the weight of the trailer? That would encompass having it weighed before each use. Does Scamp really suggest 20 psi in their literature?
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Old 09-07-2012, 09:56 AM   #39
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Originally Posted by mcbrew View Post
Not true. Please review what the tire manufacturers and trailer manufacturers publish on this subject.

20 PSI is PROPER inflation for certain trailer loads.
Actually, Francesca's post is quite true.

I have pulled literally 100's of different trailers, big and small, and have never seen a recommended pressure anywhere as low as 20 lbs. I am curious as to where you have seen it recommended by either a tire, or trailer, manufacturer to go this low with a tire rated for 50 psi.
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Old 09-07-2012, 10:35 AM   #40
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Name: Jesse
Trailer: 1984 Scamp 13'
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Quote:
Originally Posted by cpaharley2008
Perhaps tire manufacturer's should also list a minimum pressure on their tires, regardless of load. I find it interesting that one manufacturer of an item which has it's own limits can be changed by another manufacturer who utilizes that product in their product. I was always under the impression to keep tires at their maximum, regardless of how or what it it is being used on. To under inflate a tire perhaps on sand is one thing but how would an individual reduce the inflation based upon the weight of the trailer? That would encompass having it weighed before each use. Does Scamp really suggest 20 psi in their literature?
It is exactly the same on cars. The tire has a maximum pressure, which is the maximum safe pressure for the tire, not the optimal pressure for the job at hand.

I have a CO2 tank that has imprinted on it 2700 PSI MAX. However, it never gets filled to 2700 PSI. This is the maximum safe pressure, not the working pressure. My beer keg says MAX 130 PSI on the side. However, the proper dispensing pressure is 12 PSI.

The tire manufacturer does NOT print the RECOMMENDED pressure on the tire. They cannot, since they don't know how the tire is going to be used. The manufacturer of the vehicle or trailer (or the operator, in the case of many trailers) is responsible for setting the proper operating pressure based n the load n the tire.

MAXIMUM desk not always equal OPTIMAL. Less than the MAXIMUM pressure does not necessarily mean under inflated, just as taking an elevator to any floor other than the top floor is not undertransportation.
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Old 09-07-2012, 10:36 AM   #41
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Name: Jesse
Trailer: 1984 Scamp 13'
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Quote:
Originally Posted by Jim Bennett
Actually, Francesca's post is quite true.

I have pulled literally 100's of different trailers, big and small, and have never seen a recommended pressure anywhere as low as 20 lbs. I am curious as to where you have seen it recommended by either a tire, or trailer, manufacturer to go this low with a tire rated for 50 psi.
Two places: one on each side of my Scamp (manufacturer's sticker) and also in the Goodyear documentation for ST tires.



My Scamp 13's tires are the top row... Same as the original ones that it came with. The loads listed a for EACH tire, not the total axle weight. So you can see that 20 PSI is the proper inflation so long as there is not more than 795 pounds per tire.
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Old 09-07-2012, 12:48 PM   #42
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Hmmm...

Can it be that I've once again proven the wisdom of Josh Billings' famous saying:
"It ain't the things you don't know that gets you in to trouble- it's the things you know for certain that just ain't so."

That "inflate-to-the-max" rule has been in my head for simply EVER...and it's beginning to look to me as if I've been...dare I say it?... WRONG.

I distinctly hear the ripping sound of a Hole Being Torn in The Fabric of My Universe.

Mind you, I'm not quite ready to throw in the towel, especially since reducing the pressure on my present tires may not be wise since I've been running them at 50 for several years.

They're probably as stretched out as the "size 5" jeans I keep cramming my size 10 self into.

BUT
I'm just about due for new trailer tires, and when I get them I'm going try the lower pressure. That is, IF my trusted Tire Guy at Les Schwab concurs...

Thanks, I think!
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