Surf Side Tire Pressure - Fiberglass RV


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Old 07-27-2015, 02:45 PM   #1
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Surf Side Tire Pressure

The factory label puts tire pressure at 20 lbs.Tire size now is 175/80R 13 tire size on factory label is 65x13 bias ply , I imagine , since it was made in 1975 . Gross trailer weight is 1600 lbs. I have not hauled very far about 500 miles with tires @ 20 lbs. and tire wear is not apparent and it seemed to ride nicely , however it still seems to me to be a very low pressure . Hope someone can re-assure me to continue at 20 lbs. or any other thoughts on the subject?
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Old 07-27-2015, 03:38 PM   #2
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Bob, try looking at page 9 of this link where Goodyear indicates the relation between load and proper inflation pressure for various sizes of ST tires.

http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf

Using their chart, you can establish the proper pressures for different loading conditions.

The load rating is per each tire, so 1,600 lbs equates to 800 per tire. An ST175/80R13 is rated for 795 lbs at 20 psi, so it looks like you are right about where you want to be.
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Old 07-28-2015, 09:58 AM   #3
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Thanks for the info Mike , that re-assures me .
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Old 07-28-2015, 10:46 AM   #4
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You're welcome. To clarify, the tires should be run at a pressure that corresponds to the actual loaded weight. For my part, I have been taking the stated dry weight of my trailer on faith and sort of guessing at how much gear we typically add to that when loaded for travel. I really need to get to a scale and validate the lies I have been telling myself.
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Old 07-28-2015, 10:58 AM   #5
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Tires have changed a fair bit since the Surfside was made. I would keep the pressure at the maximum recommended by the tire manufacturer for better performance, and longer life.
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Old 07-28-2015, 11:19 AM   #6
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Another education opportunity:

As Civilguy wrote, your best bet is to find the load/inflation chart for your size of tires. And to get the actual loaded weight on an accurate scale.

But, without that data, two simple checks you can do without a tire pressure gauge. First, look at the tires as they sit on a hard surface. Is there a noticeable bulge in the sidewalls? there should be just a small bulge. If there is no bulge, you have too much air pressure.
Second, with the small bulge, go and drive at highway speeds for an hour or so. Stop, get out, and feel the tires. If you can hold your hand on the sidewalls, if just slightly warm (and not from the sun) you are good to go.
A third test: does the trailer bounce too much on the cracks and dips in the pavement? ....too much air pressure. Let some out.
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Old 07-28-2015, 01:40 PM   #7
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The original tire size was probably 6.50-13, not 65-13. I expect you "fat-fingered" the size so no problems.

Lacking an actual weight I'd inflate the tire to an adequate pressure to carry the GAWR/2 plus perhaps 10% to allow for side to side variation. this of course assumes the trailer hasn't been badly overloaded.

Inflating to the maximum sidewall pressure is ok so long as you've already established that the tire is capable of carrying the axle GAWR to begin with.

Lacking knowledge of what the trailer GAWR is, it's all a crap shoot.

I was with Wayne on his first recommendation, less so on his second.
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Old 07-28-2015, 03:09 PM   #8
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Quote:
Originally Posted by Bob in Mb View Post
The factory label puts tire pressure at 20 lbs.Tire size now is 175/80R 13 tire size on factory label is 65x13 bias ply , I imagine , since it was made in 1975 . Gross trailer weight is 1600 lbs. I have not hauled very far about 500 miles with tires @ 20 lbs. and tire wear is not apparent and it seemed to ride nicely , however it still seems to me to be a very low pressure . Hope someone can re-assure me to continue at 20 lbs. or any other thoughts on the subject?

Point 1, Check the age of the tires, Tire wear is NOT an indicator of trailer tire condition. Age of the tires is a better indication 5 to 6 years is about all you can expect and anything over 10 year old tires you're looking a nice little blow out.

Point 2. Trailer should always be inflated to the max COLD pressure molded into the side wall. Those charts are for minimum pressure vs weight, NOT recommended pressure vs weight.
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Old 07-28-2015, 04:26 PM   #9
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Quote:
Originally Posted by Byron Kinnaman View Post
Point 1, Check the age of the tires, Tire wear is NOT an indicator of trailer tire condition. Age of the tires is a better indication 5 to 6 years is about all you can expect and anything over 10 year old tires you're looking a nice little blow out.

Point 2. Trailer should always be inflated to the max COLD pressure molded into the side wall. Those charts are for minimum pressure vs weight, NOT recommended pressure vs weight.
I strongly agree that tire age is a very serious issue. Some tires fail catastrophically when they get too old. Based on what I have read on the subject, I would concur with the 5 to 6 service years Byron notes. Due to the typically limited use they get, RV tires often need replacement due to age, not tread wear.

I am not sure I agree with or perhaps I don't understand the second point. My vehicles all have manufacturer-recommended inflation pressures for half and full load operation. These recommended pressures are all well below the maximum cold pressures on the tire sidewalls.

I would think that trailer tires would, like vehicles, be subject to premature wear in the center of the tread if operated at high pressure / low loading. The Goodyear publication that I linked above seems to support this view.

"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load. (See load inflation charts on pages 9–11.)"

As noted, some trailer tires may never even see substantial tread wear before they get too old to operate. However, I would think a "softer" ride on a lower inflation would benefit the trailer's suspension and the contents, until that day we send the tires on to that great tire-pile in the sky.

I'm interested to learn more.
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Old 07-28-2015, 04:38 PM   #10
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Goodyear also notes:

"What you should know about tire load and inflation.
The recommended maximum inflation pressures for your tires are indicated on the certification label or in your owner’s manual. Because RVs can be loaded with many different configurations, the load on each tire will vary.
For this reason, actual air pressure required should be determined based on the actual load on each individual tire.
Inflation pressure should be adjusted to handle the tire carrying the heaviest load, and all tires on the axle should be adjusted to this pressure.
Each manufacturer provides load and inflation tables specific to its products to help you determine the correct tire inflation pressure for your vehicle’s loading."
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Old 07-28-2015, 05:54 PM   #11
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Quote:
Originally Posted by Byron Kinnaman View Post
Point 1, Check the age of the tires, Tire wear is NOT an indicator of trailer tire condition. Age of the tires is a better indication 5 to 6 years is about all you can expect and anything over 10 year old tires you're looking a nice little blow out.

Point 2. Trailer should always be inflated to the max COLD pressure molded into the side wall. Those charts are for minimum pressure vs weight, NOT recommended pressure vs weight.
Other than if no visible damage, I would go at least 7 years with tire replacement. In line with what you are saying though.

Regarding tire pressure you are correct. My Goodyear Marathon ST tires are rated for 65 mph at the recommended pressure from the charts, and if you have room to increase the pressure by 10 psi without exceeding max pressure, they are rated at 75 mph.

The manager at the tire shop I use for all my vehicles, recommends both beginning to monitor at 7 years, and always keep to maximum pressure for performance and tire life.

While it is the minimum allowable pressure in the charts provided, I am not one for maintaining minimums, and much prefer a larger safety margin. But, it comes down to what we believe to be true, and what we are comfortable. with.
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Old 07-28-2015, 06:21 PM   #12
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Jim, I'm comfortable with finding a tire pressure that I'm comfortable with. It's that pesky search for the truth that gets me so befuddled all the time. Maybe I need to quit doing that!
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Old 07-28-2015, 07:45 PM   #13
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Originally Posted by Civilguy View Post

I am not sure I agree with or perhaps I don't understand the second point. My vehicles all have manufacturer-recommended inflation pressures for half and full load operation. These recommended pressures are all well below the maximum cold pressures on the tire sidewalls.

I would think that trailer tires would, like vehicles, be subject to premature wear in the center of the tread if operated at high pressure / low loading. The Goodyear publication that I linked above seems to support this view.

"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load. (See load inflation charts on pages 9–11.)"

As noted, some trailer tires may never even see substantial tread wear before they get too old to operate. However, I would think a "softer" ride on a lower inflation would benefit the trailer's suspension and the contents, until that day we send the tires on to that great tire-pile in the sky.

I'm interested to learn more.
I think you will find that most of us with small fiberglass trailers with 13" ST tires need to inflate to max due to the real world loaded weights of the trailers & the relatively low capacity of many of the 13" ST tires.

I know due to having had the trailer weighed and each wheel weight recorded separately more than once (Thank You Frederick) that I have one side of the trailer that is heavier than the other and due trailers design no way to fix that. As such I inflate both tires to max in order to accommodate the one heavy side. Even when inflated to max there is still a noticeable bulge in the tire.
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Old 07-28-2015, 07:48 PM   #14
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Quote:
Originally Posted by Bob in Mb View Post
The factory label puts tire pressure at 20 lbs.Tire size now is 175/80R 13 tire size on factory label is 65x13 bias ply , I imagine , since it was made in 1975 . Gross trailer weight is 1600 lbs. I have not hauled very far about 500 miles with tires @ 20 lbs. and tire wear is not apparent and it seemed to ride nicely , however it still seems to me to be a very low pressure . Hope someone can re-assure me to continue at 20 lbs. or any other thoughts on the subject?
Bob I am with the others forget the old factory label on the trailer and go with what the tire manufacture recommends.

I have seen some old Scamps with tire inflation labels stuck on the sides above the wheel as well. I know if I was to follow that label and inflate to the number suggested my trailer would look like I was running flat! LOL
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