What kind of tires? - Fiberglass RV


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Old 05-19-2003, 09:59 AM   #1
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What kind of tires?

Hi Everyone.

I just picked up a 96 13 ft Scamp in great shape. The original tires show some wear and checking so I want to replace them. Do I need a trailer tire? Will automobile tires work? The RV shop where I bought the rig inflated the tires to 50 psi. Is this correct? Seems kind of high to me.

Any and all tire guidance is welcome!



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Old 05-19-2003, 10:16 AM   #2
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Hi Gerry
I beleive that some of these FG RVs came with car tires.I know the Bolers did.If you can afford it go to Trailer tires.As for air my unit has air posted at 32lbs.Hope this helps.Other folks will chime in with there ideas.



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Old 05-19-2003, 05:21 PM   #3
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Hi Gerry ... I agree! It sounds like it's time to replace the tires.

What you want to look for are special "ST" trailers ... in your tire size, of course ... but a trailer tire should be branded "ST"... as in ST205-75-14.

When you back or turn a trailer sharply, there is incredible sidewall forces at play ... ST tires have reinforced sidewalls to withstand these pressures ... car tires don't.

Don't take my word for it. Put two fingers on your table, simulating the two trailer tires, then back your "trailer" into a sharp turn, simulating backing into a campsite. One finger will roll in a long arc ... but one finger will slide sideways, as you make your turn. This sideways, twisting force is why you need ST tires.

You can buy them at Walmart or most tire stores.



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Old 05-19-2003, 08:39 PM   #4
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Trailer Tires

For trailer tires 50 lbs is correct. It will say on your sidewall
of your tire about max pressure. ST's are the way to go - with load
range C if possible. I think load range C is 6 or 8 ply rating.
Much stronger since they take quite a beating as has been pointed
out.

Thanks...



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Old 05-20-2003, 09:10 PM   #5
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Howdy, I use car tires on my 13 ft. Boler and have no problems at all with handling, etc. There was quite a controversy about this on another website and I called a tire store in Winnipeg that sells only tires and was told that car tires were fine for my application and anyone trying to sell me trailer tires was just doing it to sell me trailer tires. We also used to use a flat deck car trailer to car shows in Minneapolis, Ohio and the Dakotas and also ran it on LT truck tires at maximum pressure without a problem. Also I believe that only time that you would have high side loads on trailer tires is when you have tandem axles, then they scrub when turning while backing up but on a single axle trailer I`ve never noticed any tire scrubbing. Even on a 90 degree jack knife the inner tire just pivots while the outer one rolls. Maybe if using an anti sway and not loosening it off when backing. If scrubbing was such a problem then you should run trailer tires on the front of your car because when you turn your front wheels they always scrub. Also run my tires on the Boler at 36 psi. Benny



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Old 05-21-2003, 04:58 AM   #6
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Benny is right there has been alot of controversy over car vs trailer tires. But trailer tires were made for trailers and have thicker side walls for a reason.

For our Trill there is a difference in price of about $20 per pair. For that small difference in price why would anyone bother putting car tires on a trailer?

Nancy



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Old 05-21-2003, 05:20 AM   #7
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What kind of tires?

We had a blowout on the 401 (a very entertaining experience!) just outside of Kitchener on a Sunday, and our choice of places to go for replacements was limited. Wound up at Canadian Tire, and bought a pair of radial (car) tires. They worked OK, but because of the tire profile, our Casita's bottom was a full inch closer to the ground! Not good when the trailer has minimal clearance to begin with! We quickly bought a pair of trailer tires when we got home.



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Old 05-21-2003, 05:24 AM   #8
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I'm a supporter of ST tires as well. Regular tires (tires with sizes starting with 'P') are not designed to run heavily loaded all their life. That's pretty much a description of our trailer tire's usage. 'ST' tires are designed for long(er) life at full loads. If you can fit a large enough 'P' tire on your trailer, then you might be OK.

Do you know exactly how much your trailer weighs while loaded for a trip? You'd need to know that before choosing a 'P' tire size. A 'P' tire shouldn't be loaded to more than 88% of it's maximum load capacity (per Tire & Rim Assn.) By the time you select an over-sized 'P' tire, you've pretty much lost any cost save.

The ST tire size specified for my trailer seems like the best choice for me.

Everybody gets to do pretty much what they want. Industry guidelines are there to protect the most people the way most of them use their tires most of the time, mostly;). You can do everything right and still have a flat, or other tire issue. I surmise that it's about doing what you can to reasonably reduce risks. (Hey, don't tug on Superman's cape, don't spit into the wind, etc.) Whatever makes you comfortable.



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Old 05-21-2003, 09:29 AM   #9
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Wow, ask a 'simple' question...

It seems to me that due to the relatively light weight of the 13 ft trailer, the difference between a car tire and a trailer tire would not really be noticed. The 13 ft standard trailer is what, about 1200 pounds dry (The manual with the 1996 says 950..yeah, right), and 1400 - 1600 pounds loaded. But, for the relatively small price difference, I think I'll go with trailer tires.

Thanks for the info.



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Old 05-21-2003, 06:44 PM   #10
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Trailer vs Car Tires

Hi folks!:wave

I admit I am no expert (it has been 30 years since I sold/installed tires), but I thought I read somewhere that the rubber used in trailer tires is formulated to withstand UV better than car tires. This would make sense, since the tires on trailers typically don't wear out the tread surface, they break down. This, along with the reinforced sidewalls would drive me to only put a trailer tire on my Casita. But then again, I live in the desert, where UV is a real problem.

UV in the northern latitudes, as well as areas of the country that don't have 320+ sunny days a year like we do, may not be such a problem. It is up to the individual to research both the requirements for his/her situation and the products that fill those requirements.

I guess my instructor was correct... you CAN apply systems engineering practices to nearly any situation.



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Old 05-21-2003, 10:25 PM   #11
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Hi again...Well if I was running a heavier trailer I may consider ST tires but for my purposes the car tires are ideal and I think that the trailer rides somewhat smoother. As I mentioned on the the other web site, a lot of the folks pulling fishing boats over the the crushed rock roads are running car tires because they seem to repel sharp stone penetration and repel bruising better than the ST tires. But whatever suits your fancy.....Benny



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Old 05-22-2003, 06:32 AM   #12
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>>they seem to repel sharp stone penetration and repel bruising better than the ST

Benny, I respectfully disagree with you. I've been around boating all my life. If your boat is bigger than a dingy, you need to put ST trailer tires on the boat trailer.

Walk around any marina and look at the trailers of large sailboats or speed boats. If you find a trailer running on car tires, ask the owner why he's not using ST trailer tires, 99 out of 100 will say "I didn't know there was such a thing as trailer tires!!"

And I really don't know how to react to your "sharp stone" comment ... other than to say I'm glad you used the word "seem" because your statement certainly is not true.

Listen, no sense beating this to death.

If you want to run on car tires, run on car tires. I, however, have always ... and will always ... run on ST trailer tires ... which are designed for use on trailers.

ST tires are not some conspiracy cooked up by the tire companies to get you to part with an extra $10 or $20 ... but if you choose to believe that, then, ok.



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Old 05-22-2003, 05:36 PM   #13
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What Brand?

What brand of tires? I hear a lot of bad things about Carlisle tires. I've not heard anything bad about any other brand of trailer tires.

My Scamp 16 has the Goodyear trailer tires it had installed by Scamp.

-- Dan Meyer



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Old 05-22-2003, 09:14 PM   #14
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Hi, Dan. Do a google search for Goodyear Trailer Tire Failure.

You'll find that Carlisles aren't the only tires that have had problems. There's at least one other rv forum where the Goodyears were discussed a year or two ago.

BTW, my '99 Casita also has Goodyears... :wink



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Old 05-22-2003, 10:38 PM   #15
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Hi Charles, My son and his friends all use 16 ft. aluminum boats and about 3 years ago they switched to car tires because of grief with ST tires and since then, no more problems. They usually go to a lake that requires a run of about 40-50 miles on crushed granite and it`s deadly on tires. But like you said ...use what you wish...And I am quite happy with car tires on my little egg and see no need to change as I don`t need tires yet...and let me assure you that price is not a question..... Happy trailering....Benny



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Old 05-23-2003, 05:37 AM   #16
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Hi Dan!

Carlisle had a bad run of tires a couple of years ago. Lots of folks had problems.

For whatever reason ... maybe blind luck, I've never had a blow-out with Carlisles ... and am using them to this day.

I think the important thing to remember, is that no matter what brand of tire or how bad a blow out, no one has reported losing control of their tow-vehicle/trailer combo following a blow-out. All have been able to safely stop.

I take comfort in that "real world" experience that shows that our little fiberglass wonders continue to track well and stay under control, even with the most severe blow out.



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Old 05-23-2003, 05:42 AM   #17
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Mary's correct in that Goodyear also had a bad run of RV tires a while back. I've even heard of folks having problems with Michelins.

Now, I'm not pointing fingers, and I'm not saying that tire companies don't occasionally produce a batch of bad tires ... but I also think that there are so many other variables that enter into RV tire problems.

Overloading, under-inflation, scrubbing, bouncing over curbs (I can't tell you how many curbs I've hit ... I'd be embarassed).

I also rarely run for long distances in extremely hot weather. When it gets hot, I head for the mountains or Canada.

And I'll be the first to admit that I'm not as diligent at checking the tire pressure as I probably should be ... as a result, I usually find I'm running a bit under-inflated.

In fact, a couple of trailers ago, I actually was running under-inflated, even when I filled the tires, because I mistakening thought the correct PSI was about 5 pounds less than it actually should be.



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Old 05-23-2003, 04:18 PM   #18
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A few years back, I had need to replace a set of ST tires on the road and they only had P radials in my size -- What a difference! With the P's on my Jayco 16', the whole rig waddled and swayed down the road -- I could even feel the difference just stepping into the trailer. I put ST's on the trailer and moved the P's to the truck and all was well again.

The bottom line is that the ST's are built with stiffer sidewalls, so they don't flex from side to side as much as P's, but the tradeoff is that by not roll-flexing as much, they don't get the better mileage that P's do on an automobile. LT's also have much stiffer sidewalls and the folks pulling the big rigs can feel the sway difference when they put LTs on their trucks.

Pete and Rats



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Old 05-25-2003, 01:25 PM   #19
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tires

Hi every one ..
i think i was the one that starded that post on the other site. i got a lot of answers back.it was very interesting.i was going to buy them that week.but as of yet i haven't lol.now i just got done of reading all of these post n learn something new about tires. i have price the trailer tires n was surprise to find out that fore a pair of radio trailer
put on the rims n balances is only $61.00 that's fore 13"185 we are just gettin at our 13' 74 boler now.so i m in no hurry for the tires.ho ya learning something new.. to make sure that they are st's what does st stand fore. n why st's what's the different...thank you
golden bunny



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Old 05-25-2003, 02:41 PM   #20
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WHOOP! WHOOP! GEEK ALERT!

The following chart compares load carrying capacity for the same size tire. It compares a P-metric, ST-metric and a P-metric tire de-rated for use on a trailer. Those of us with ST tires usually have a 'C' load range tire, which has a maximum pressure of 50 psi.

The Tire & Rim Assn. states that a P-metric tire should be de-rated, that is that the load it carries at any given pressure should be reduced 10% when used on a truck application. That's the line below the solid line on the graph. It also states that a P-metric tire shouldn't normally be used at greater than 88% of it's maximum load. That would be a line 2% below the lower dotted line.

What does this mean? The most a normal P-metric tire that has been properly de-rated can carry (at 35 psi) is about 1300 pounds. At 35 pounds, the ST tire can carry over 1400 pounds. However, the 'C' load range ST tire can carry up to 1750 pounds at it's maximum pressure of 50 psi.

What else does this mean? The formulas used to calculate the carcass strength of a tire are basically those used for steam boilers. If you think about it for a moment, you'll realize that the more pressure a vessel (tire or boiler) has to hold in, the stronger the carcass has to be. A ST tire has a stronger carcass than the same size P tire.

All this assumes a properly built and maintained tire. Also note that tires don't heal. Treat them badly once, and that's life that's gone forever.

I don't give advice. I can only tell you what works for me. I'm a tire engineer for an auto company and I can't and don't speak for them. Everyone probably knows someone who's abused tires and gotten away with it, and someone else who did everything right and still had a problem.

I'm just offering this up as a little information about P-metric and ST-metric tires.

<img src=http://www.fiberglassrv.com/board/uploads/3ed123daa9c28tires.JPG/>

Please DON'T pet the geek. Although normally harmless, he is exciteable. Resume your normal activites.



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