Auto/Truck tires on 13 ft. Scamp?

[Garret Walther]

I am changing to 14 in. wheels on my 2002 13 ft. Scamp. Using aluminum 6 in width. Trying to find tires that are similar to original 24 in. diameter. But trailer tires are not available in that diameter. Wondering if I could go with an auto or truck tire? Looks like 195/70 is close with 24.8 in. diameter. Does radial or bias matter?

[evan]

Garret, trailer tires are a totally different animal. I don't know if car/truck tires are recommended. I heard they cause weird handling? You might try searching online for a trailer tire size for your wheel. I would also like to use a bigger tire after lifting my Scamp.

[Benny K]

Howdy, most people on this site are against using auto "P" tires on trailers.....I use auto tires on both my 13' and 17' Bolers and haven`t had a problem with sway or or other handling characteristics with either.....I don`t use sway control devices or WD hitches......I run tongue weights that are about 15% or more of my trailer weights....a term used on this site is "wallering".....if that term is what I think it is, I`ve never had my trailers handle like hogs in a mud hole......they both track true....even the 13' during evasive maneuvers to miss pot holes, etc.....I have read a number of posts on this site about people using ST trailer tires having to replace them after having blow out and tire disintergration problems on the road.....I tow at legal highway speeds and sometimes a bit over and when passing on 2 lane roads a lot over......am very satisfied with my tires....both my Bolers when built had bias ply auto tires recommended.....I realize times and technologies have changed since then......I also run my tires at max cold tire pressures as per my sidewall specs.......so the ball is your court...good luck....Benny

[Gina D.]

I am no tire expert, other than to say it pains me to buy them (I just bought a set of tires for the Element that cost me more than I paid for my first car!)

My trailer came with auto tires that were in very good condition. Almost brand new, even tho they had been sitting for awhile.

I put larger trailer tires on before a long trip as a precaution because the New Old stock tires on it had been sitting so long. (Went from 75 to 80s, I think, I'd have to look) I did notice right away that the trailer "Boing" that was predominat with the auto tires on was significantly reduced when the new tires went on. I suspect this is related to the stiffer sidewalls on trailer tires.

Anyway, they were not a huge difference in price, about 5 bucks each, so I am glad I did it.

[Brian B-P]

Various other FiberglassRV members and information from several tire company and tire retailer web sites have identified the one factor which I would be careful to consider in using a passenger-service tire in trailer service: the "P" type tire capacity must be reduced by 10% to get the capacity in trailer service.

In the original sizes used by most trailer manufacturers the tire are very heavily loaded by modern automotive standards. Since the capacity of a tire is fundamentally limited by size and pressure, they often must be run at more than the typical 35 PSI of automotive tires to have sufficient capacity - that makes it hard to find a suitable passenger-type tire in many cases. Basically, if the trailer tire has adequate capacity in load range B, then it only needs 35 PSI and passenger tire might work; if a higher load range is needed, then 50 PSI (load range C) or 65 PSI (load range D) is called for.

Although I know I'll get some flack for saying this, I can't believe that there is any meaningful difference between a specific trailer tire ([b]Special Trailer, designations starting with "ST") and any commercial or light truck tire (Light Truck designations start with LT). I think the only reason ST tires exist is that there are no LT tires in the small sizes used by small utility and travel trailers. It cannot be coincidence that once you get larger than the largest ST tires (e.g. ST235/80R16 in a Goodyear Marathon), your're into LT size territory. All of the largest commerical and RV trailers use LT tires - or commercial vehicle tires. When an LT tire is used on a trailer, its capacity does not need to be rated lower (as a P tire does).

In the end, to replace an ST185/80R13 tire (about 24" diameter) there will be no LT tire available (too small for LT), all ST tires will be 75-series or 80-series (so on a 14" wheel they will be too tall), and you are left with P tires if you want to match diameter.

Capacity in passenger car tires, and now in LT tires, is given as a load index. If you need to support (for example) 1600 lb on the trailer axle, that's 800 lb per tire (before accounting for that 10%) which happens to match a load index of "77". I used Goodyear's search tool for 195/70-14, and found that in this size P-type tires are typically load index 90, which looks like lots to me. A tire with a higher speed rating (that's the letter after the load index) will likely have stiffer sidewalls for better control.

For comparison, the T@B trailer is equipped from the factory with low-profile Fulda passenger car tires. If it's good enough for the Europeans, and for the Thor division selling these trailers in North America, then perhaps the magic ST designation is not required.

This subject came up at the end of the recent topic [b]Blue boler pix. Lance is also using 14" passenger car tires, but hasn't shared with us yet the specific size or type. I'll repeat here my opinion regarding radials versus bias-ply from that thread:

There's certainly nothing wrong with radial tires, for just about any application. The most common recommendation I have seen in this forum is for the Goodyear Marathon, which is available only as a radial.

By the way, Goodyear overhauled their website within the last week or so, and old links will probably no longer work).

[b]Correction and edit: Andy spotted that I incorrectly omitted a reference to the very common use of commerical vehicle tires (not just the LT type) on larger trailers - I corrected this with an addition to the text above.

[Loren G. Hedahl]

The only type tires I've read about having a lot of blow out problems are the ST rated tires. This has been documented on this forum and the Casita forum.

I have wondered why this has been so. Probably it is because they have such stiff sidewalls that people compare the sidewall bulge with that of their tow vehicle having P metrics and figure the pressure is good to go.

What would I do if I could start up with a clean slate? --- i.e., I came home and someone had relieved me of tires and wheels on my diesel Jimmy and Scamp, and the insurance company was anxious to indulge me?

I would purchase eight wheels and tires all the same that would fit the Jimmy to my liking and modify the Scamp brake drum to fit.

[Pete Dumbleton]

I think the reasons why we hear so much about ST blowouts are twofold; first, the vast majority of us are using STs in the first place, and second, the tradeoff for sidewall stiffness is a lower top speed. Unfortunately, many of us tend to tow at close to that max speed and if everything isn't right with the ST tires, they will be more likely to blow.

There's also the fact that trailer tires tend to hit more curbs, etc., so any kind of tire on a TT will tend to suffer more damage than the tires on the tow vehicle.

Personally, if I couldn't find STs in the size I wanted, I would look to LTs rather than P radials. I've had my experience with P radials on a trailer and wouldn't do it again.

Folks on other groups who tow big trailers find they can reduce sway by swapping out their truck's rear P radials for LTs if so equipped.

I don't thing it makes much difference if STs are bias ply or radial, so long as both tires are the same.L

Late Addition: Here's a timely thread on tires from another group:

RV.NET - Towing Forum

[Jim C.]

Has anybody thought of using intertubes inside of ST tires? I had a 25 foot Terry that I bought in 1983 with bias ply tubeless truck tires and tubes in them with the valvestem holes reamed. I lived in the trailer in various campsites and trailer parks until 1996. As far as I know, all four tires are still carrying a heavy load and the trailer is parked nearby (someone local bought it). I have recently purchased an 85 Uhaul which I am going through and I will be replacing all three tires and have been thinking about doing the same thing with the tubes. Any comments would be appreciated.
Thanks, Jim and Leslie

[Donna D.]

I would purchase eight wheels and tires all the same that would fit the Jimmy to my liking and modify the Scamp brake drum to fit.

That's exactly what I did...figuring I'd only need one spare and could use it on tug or trailer. Didn't work out as planned The setback on the wheel blew that idea out of the water. I needed a totally different setback to clear the disc brake caliper on the front of the tug. That made the setback too great to get the tire on the axle and clear the wheel well on the trailer. Sigh. Oh well, at least the wheels "match." I ended up buying Marathons for the trailer anyway.

[Brian B-P]

I think the reasons why we hear so much about ST blowouts are twofold; first, the vast majority of us are using STs in the first place, and second, the tradeoff for sidewall stiffness is a lower top speed. Unfortunately, many of us tend to tow at close to that max speed and if everything isn't right with the ST tires, they will be more likely to blow...

I don't know about the idea that sidewall stiffness reduces top speed (since the stiffest passenger car tires are those with the highest speed ratings), but ST tires are not normally rated for high sustained speeds.

From Goodyear's Marathon Special Trailer Applications - General Information:

Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is necessary to increase the cold inflation pressures by 10 psi above the recommended pressure for the load.
o Do not exceed the maximum pressure for the wheel.
o If the maximum pressure for the wheel prohibits the increase of air pressure, then the
maximum speed must be restricted to 65 mph.
o The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the
maximum load of the tire.

Since people are unlikely to inflate tires to greater than the maximum shown on the sidewall, they will potentially have underinflated tires for high speed.

Passenger and LT tires also have speed-dependent load ratings. I have seen tires with dual load index values, one without a speed rating and the other (lower value) with a rating - pick your speed and you can see the resulting load at the same maximum inflation pressure.

[Garret Walther]

Garret here. Update on my question about tires. I decided to go with an automotive tire, BF Goodrich TA. Size: 195-70 R 14. Similar diameter (24 in. ) to the 13 in. Scamp original tires.
I hope they work out. Thanks for all your suggestions/comments/opinions. They were all helpful.

[Andy Earthman]

"All large commerical and RV trailers use LT tires. When an LT tire is used on a trailer, its capacity does not need to be rated lower (as a P tire does)."



Im pretty sure that ALL trailers do not use LT tires. And that TAB does use ST tires.

You should be a little more careful what you state as fact. Some people will take it as fact. When it is not the case.

http://www.haulmark.com/cgi-bin/shopper.ex...lates/list.html

[Brian B-P]

"All large commerical and RV trailers use LT tires. When an LT tire is used on a trailer, its capacity does not need to be rated lower (as a P tire does)."
Im pretty sure that ALL trailers do not use LT tires. And that TAB does use ST tires.

You should be a little more careful what you state as fact. Some people will take it as fact. When it is not the case.

http://www.haulmark.com/cgi-bin/shopper.ex...lates/list.html

Sorry, that should have been [b]commercial or LT tires. I certainly missed the obvious one there - thanks for catching that, Andy. My intent was to indicate that they were trailers, and did not use ST tires; that is, not all trailers need to use ST tires.

The T@Bs I saw, walked through, and closely examined on a dealer's lot last year in British Columbia (near Kelowna) certainly did not have ST tires on them; they may have alternatives or have changed their practices.