tire pressure for a 13' 20lb max? - Fiberglass RV
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Old 12-16-2016, 08:57 AM   #1
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tire pressure for a 13' 20lb max?

What are tires on an older 13 foot to be inflated to? The original decal on my wheel well says 20lbs Max in red. The new 13" tires say they can be inflated up to 50ftlbs.
Being the older Scamps usually weigh only 950lbs is 20-30lbs tire pressure ideal? If 40-50lbs is advised today is that due to Scamps built today being much heavier with all the customer's needed luxuries and gadgetry?
I know my little Geo Metro uses the same 13" tires as the Scamp and it calls for 32ftlb tire pressure and I know the Metro weighs more than 950lbs.
I'm sure too great tire pressure can be rough on the axle and frame when you hit a pot hole. A softer tire pressure will absorb more bumps and protect better in theory. I know when I pumped up the metro tires to 45ftlbs I got a little better mileage but any bump I hit was rough on the chassis. What tire pressure do you use on your older lightweight 13'?
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Old 12-16-2016, 09:31 AM   #2
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I would inflate then to near 50 lbs.
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Old 12-16-2016, 09:45 AM   #3
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I would weigh your Scamp loaded for camping. I expect 1400-1500 pounds and would inflate to 45-50 pounds. The axle, not the tires, is meant to cushion the ride. Underinflation can contribute to sway.
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Old 12-16-2016, 10:54 AM   #4
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Why did Scamp put 20lb max on the wheel well back then? Where the tires different? Wouldn't a lower pressure be better in the winter for gripping slippery roads? Thank you
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Old 12-16-2016, 11:09 AM   #5
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Here we go again!

NO, you do NOT need 50 psi. That is only for if the tire is carrying the max load.
Looking at a Load/Inflation chart: If you have 175/80R13 tires.
20 psi can carry 795 lb per tire or 1590 lb per axle
25 psi = 905 and 1890
30 psi = 1000 and 2000
35 psi = 1100 and 2200 lb and this is the max for "B" rating tires
40 psi = 1190 and 2380
50 psi = 1360 and 2720 lb, the man for "C" rating tires

You must weigh the trailer as loaded for travel; and set the pressure accordingly.
50 psi will give you a harsh ride, a lot of bouncing. And the tires are more susceptible to damage from sharp edges, rocks, etc.
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Old 12-16-2016, 11:32 AM   #6
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Quote:
Originally Posted by Wayne Collins View Post
NO, you do NOT need 50 psi. That is only for if the tire is carrying the max load.
Looking at a Load/Inflation chart: If you have 175/80R13 tires.
20 psi can carry 795 lb per tire or 1590 lb per axle
25 psi = 905 and 1890
30 psi = 1000 and 2000
35 psi = 1100 and 2200 lb and this is the max for "B" rating tires
40 psi = 1190 and 2380
50 psi = 1360 and 2720 lb, the man for "C" rating tires

You must weigh the trailer as loaded for travel; and set the pressure accordingly.
50 psi will give you a harsh ride, a lot of bouncing. And the tires are more susceptible to damage from sharp edges, rocks, etc.
No, you don't need to use 50 lbs, you can go as low as the minimum pressures you listed, BUT you will get better performance from the tires with increased pressure. ST tires are meant to be have a firm sidewall and the more pressure the better to achieve this. A softer side will promote some wear. Passenger tires on the other hand are thing walled, and require flexure to perform better.

50 lbs will not give a harsh ride, and in fact could be a lot less so, as there will be less 'bounce' in the tire, and will allow the suspension to do it's thing.

Another thing with having a pressure at least 10 lbs over minimum, is that some tires will allow an increased speed rating of 10 mph.

Ask just about any tire shop or trailer manufacturer, and they will tell you to fill trailer tires to maximum pressure for better performance. I daily pull a trailer of one sort or another, as I have for many years, and would not ever consider using a pressure lower than somewhere near max.
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Old 12-16-2016, 11:38 AM   #7
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Yep, Here we go again is right.
Jon and Wayne represent the two extremes that show up every time this topic comes up. I tend to go in between. I agree more with Wayne, but add a little more pressure to protect the sidewalls. Even though you'll see even people you'd expect to be knowledgeable say go with the max on the tire wall, I think the load/inflation charts are the definitive guides. I see no benefit from pounding your trailer and everything in it with over-stiff tires.
I currently run at 55 PSI on tires rated at 80 PSI max. The axle weight on my trailer loaded for travel is 3100 lb as measured on a CAT scale.
Where folks often run into trouble is running the tires for too long. My rule there is 20,000 miles or three years, whichever comes first. And don't buy tires more than a year old.

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Old 12-16-2016, 11:39 AM   #8
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tire pressure for a 13' 20lb max?

I've been using 50psi on my Escape 13 (estimated total loaded weight ~2000lb). I've hauled it about 40,000km (24,000mi) with zero tire wear.
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Old 12-16-2016, 12:35 PM   #9
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Quote:
Originally Posted by hiker22 View Post
What are tires on an older 13 foot to be inflated to? The original decal on my wheel well says 20lbs Max in red. The new 13" tires say they can be inflated up to 50ftlbs.
Being the older Scamps usually weigh only 950lbs is 20-30lbs tire pressure ideal? If 40-50lbs is advised today is that due to Scamps built today being much heavier with all the customer's needed luxuries and gadgetry?
I know my little Geo Metro uses the same 13" tires as the Scamp and it calls for 32ftlb tire pressure and I know the Metro weighs more than 950lbs.
I'm sure too great tire pressure can be rough on the axle and frame when you hit a pot hole. A softer tire pressure will absorb more bumps and protect better in theory. I know when I pumped up the metro tires to 45ftlbs I got a little better mileage but any bump I hit was rough on the chassis. What tire pressure do you use on your older lightweight 13'?
To answer your question. The tires were considerably different then today. You'll get a lot of answers lower than maximum sidewall pressure, the pressure that listed on the sidewall. However, some of us have spoken with the tire manufacturers and they will tell you inflate to max in cool of the morning. I've been doing this for 11 years and almost 100,000 miles.
Some of the shade tree mechanics will tell you otherwise. If want an example of what happens when you tire pressure too low look the Ford Explorer tire problems deaths caused by low tire pressure.
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Old 12-16-2016, 01:14 PM   #10
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The information on the decal applied to the tires that were on the Scamp forty years ago.
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Old 12-16-2016, 01:41 PM   #11
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You will get a variety of answers here on this topic, but your best bet is to Google 'ST tires max pressure'. This is of course assuming that you are using ST (Special Trailer) tires, which most of us do. I think you will find that ST tires, regardless of load, should be inflated to the max pressure as indicated on the sidewall.

ST tires are built differently from automotive tires and are designed to run at the max pressure.

The max load is listed on the sidewall and is calculated based on the max pressure, which I believe has led some to assume that 'less load-less pressure'. This may be so for other tires, but not STs.

My guess is that the assumption is on experience with car tires. On many vehicles,the pressures for the front and rear are different, using the same tire on both. It may also be recommended to increase pressure when carrying heavy loads. All of this however is based on the design of the tires and their intended use on automobiles
and light trucks. If you are using automotive tires on your trailer, you may want to adjust the tire pressure based on scaled weight.

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Old 12-16-2016, 01:41 PM   #12
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If you subscribe to the load-based inflation schedule, you would do well to weigh each tire separately, or at least add a margin to allow for uneven side-to-side loading. Some models are prone to be heavy on one side.

I doubt you could tell the difference in ride quality between 35psi and 50psi. But you can sure tell a difference when a torsion axle is at the end of its lifespan.
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Old 12-16-2016, 07:22 PM   #13
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I'd be more inclined to the actual weight of the camper. I know most Americans are weak. They want more luxury.
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Old 12-17-2016, 01:11 AM   #14
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The facts are: Hiker said the Scamp tires are the same as his Geo Metro tires. This may mean size and not design. Scamp has a specific tire pressure chart. Load/inflation charts for tires are clear about load vs pressure. These charts are more valuable than personal opinions used for giving advice.

We don't know from the available information if Hiker is using radial or bias tires or even if he's using ST tires. The original Scamp pressure recommendations are probably based on ST bias tires. The Geo Metro tires are most likely radial tires with a standard load rating. It is clear that softer tires will be less jarring on sharp bumps. Softer tires have better tracking on rough surfaces and better traction on icy roads, but may sway more at speed.

We don't know the brand, design, age, total load, intended travel speed, weather or surface quality of the road. But somehow, some of us seem to know that other's advice is incorrect.

Higher inflation pressure reduces drag for better mileage and reduces heat buildup. Tire failures from under-inflation are caused by excessive heat. But we don't know the weather conditions, the brand of tire, the design of the tire, the reputation of that particular model and brand, or the intended travel speed, etc.

So, quoting statistics and discounting opposite views, based on some generality or brand failure in the past, that is not related, is not very helpful.

Simply using the exact tire the trailer was designed for and following the manufacturer's recommendation, seems reasonable. Or getting a more modern radial tire and following the manufacturer's weight/pressure chart seems like a very good idea. But expecting a person to follow a bunch of different opinions, based on assumptions that are not known, or assumptions pulled out of a hat to build a case, or assumptions based on failures of a different kind, seems silly. No, it seems irresponsible if it might lead to an expensive failure for someone honestly seeking help.

Best advice I can think of (and I'm not claiming I have the absolute best answer): Get new, high quality tires designed to carry more than the intended load. Inflate them according to the manufacturer's recommendation for the weight being carried. Monitor them carefully at first to be sure the trailer is stable and they are not heating up. Adjust the pressure if needed to improve all of this (icy road skating, heat on hot highways, excessive bouncing on bumps). Then check them often enough to spot any problems. Forget about wear. Trailer tires will probably time out before wearing out. And here is the controversial one, which really only counts for heavier trailers: Use radial LT tires.

My advice to myself is to try to base my advice on real data, actual equipment and real conditions.

Wayne said it best with "here we go again". His reference to an actual model of tire and an actual manufacturer load/inflation chart is the best and most common sense advice. Using the chart on the trailer is also very good, if the tires are the same exact size and design as original equipment. Most other advice reveals a personal bias that may not be useful or even safe.
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Old 12-17-2016, 01:23 AM   #15
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If you read this thread and Electrical Brakes for a 13..
you can only come to the conclusion that the OP isn't looking for advice.
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Old 12-17-2016, 05:55 AM   #16
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Quote:
Originally Posted by hiker22 View Post
What are tires on an older 13 foot to be inflated to? The original decal on my wheel well says 20lbs Max in red. The new 13" tires say they can be inflated up to 50ftlbs.
Being the older Scamps usually weigh only 950lbs is 20-30lbs tire pressure ideal? If 40-50lbs is advised today is that due to Scamps built today being much heavier with all the customer's needed luxuries and gadgetry?
I know my little Geo Metro uses the same 13" tires as the Scamp and it calls for 32ftlb tire pressure and I know the Metro weighs more than 950lbs.
I'm sure too great tire pressure can be rough on the axle and frame when you hit a pot hole. A softer tire pressure will absorb more bumps and protect better in theory. I know when I pumped up the metro tires to 45ftlbs I got a little better mileage but any bump I hit was rough on the chassis. What tire pressure do you use on your older lightweight 13'?
I've read all your posts and you've received many good answers. The sticker on your rig is MOOT, any tire from that time frame is long gone or is now nailed to a boat dock. From your replies you don't seem to agree with the answers you're getting from long time trailer members. RVing isn't rocket science, use the correct tire for your TT and follow the inflation numbers on the side wall. Comparing your Metro to a trailer is apples and oranges, again, a moot point. Is the Metro your tow vehicle? Byron told you to weigh your trailer, very good idea just so you know for sure as the number you quote is most likely way off in the real world. You also seem to be against brakes because of the weight. Got to say that's not the best decision for any TT. If you were to tow the same trailer with & without brakes you'd be surprised at the difference in stopping or in the possibility to control a bit of sway. Unlike a utility trailer with no brakes that gets used once in a while for mostly short trips, TT's go 100s of miles just to get to the destination. Just my opinion after 50 years of towing, many of over 50K#. I've always said brakes and tires were the most important items. No flats or blow outs for control and no matter how long it takes to get to speed I want to be able to stop it as soon as possible .
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Old 12-17-2016, 06:10 AM   #17
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Years ago I changed out the tires on my 79 Boler and told the fellow at the station I wanted Trailer tires....
To make a long story short...
He put on Passanger tires....
The tires always look low on air no matter what the PSI is due to the Passanger tire, as my understanding is, has a weaker side wall.
Haven't had any trouble with the tire to speak of but do have alot more sway and bounce then a stiffer tire or a "TT" would give I'm sure.
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Old 12-19-2016, 09:55 AM   #18
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Old trailer has sticker for old tire. Modern tires have manufacturers current information which is probably available online or from the tire store that carries them.

Tires have a load rating and a speed rating. Both stated and incorporated into the code on the tire. https://www.google.com/search?site=&...ad+a+tire+code+

There are differences between ST (special trailer) and auto or truck tires in how they are designed and desired characteristics. There are possibly some differences in the testing procedures based on intended use of tire. For example most US trailer tires will state max speed of 55 mph. Even though they may have a higher speed rating designation letter and in real world most are driving them at 60 mph or more without issue.

I would personally go with the manufacture recommendation on air pressure for the load and use I have for the tire. And would generally purchase tires intended for trailer use but a whole lot of folks have good results using truck or even passenger tires under their trailer. So I can't say it won't work.

Bottom line sticker saying 20# inflation is wrong for a modern tire, leave it only for it's retro aspect of being an old camper.
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Old 12-19-2016, 12:23 PM   #19
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I would imagine that all the rating stamped on the tire is to Cover thier own A-- in case there is an issue.
As said I am sure a 55MPH rating will go faster without any mishaps but if there is manufacturer is covered
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Old 12-19-2016, 12:24 PM   #20
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LOAD/INFLATION Tables

The problem is that load/inflation tables are not supplied with each tire.
You have to go to the manufacturer's catalog spec sheets, or the Tire And Rim Associations hand book to find them.
Regardless, you are not required to use the max pressure shown on the tires .... unless they are carrying the max load.
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