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Old 09-05-2015, 09:07 AM   #941
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If you have different diameter tires on a vehicle, it should not be driven very far or fast. It will be like walking with one short leg (or long one). On a trailer, since the axles are close together one smaller tire will cause the tire next to it to carry a lot more weight. And when towing, stability is very important, and with one smaller tire you'll have reduced stability.

But when we bought our second set of Michelin 16" tires, I did not change the spare. Maybe in a few years, or with a cheaper 16" tire. Since it is hard to wear out trailer tires before they age out, an identical spare and wheel are a poor investment. On a car or truck, tire need to be rotated frequently and I rotate the spare in with the others, thus getting more wear out of the tires. Trailer tires need rotation far less frequently. If I had thought this out originally, I would have bought a cheap steel 16" wheel and a cheap spare the same size as the Michelins—I would have saved $150 or so.

Gene

Gene, I'm not sure what size tires you have or the size of the spare but I bet you could get a good deal on a worn out 16" tire taken off an SUV or similar that was maybe only 4 years old. If it was thoroughly inspected to confirm no damage that could be a low cost alternative for the spare tire.

Do you carry the spare on rear bumper or under the TT? If not under the TT you can extend the life of the spare if you use a white cover.
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Old 09-05-2015, 09:38 AM   #942
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I ordered five of the SenDel T03-66655T aluminum wheels and one galvanized steel SenDel S62-66655TG wheel for the spare. The fifth aluminum wheel is in storage as a battle spare.I figure having a spare, Murphy will not let me damage a wheel.
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Old 09-05-2015, 10:51 AM   #943
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Tireman, the spare is kept either in the garage or back of the pickup, so it gets no sun. But it was rotated around the trailer over 5 years. The sidewalls started to show sidewall cracks before we started traveling this summer, so I replaced four of the five. Michelin gave me a price reduction on new tires. The original 5 had about 35,000 miles on them and the tread was very good. I picked the one with the fewest cracks for the spare.

The Tundra came with 4 full sized tires (18" I think) and a spare that was smaller on a steel wheel. Ironically the spare was a better quality tire (Michelin) than the tires mounted on the truck—Goodrich. The Goodrichs rode badly and wore fast. That spare is now 8 years old and I lower it sometimes to check the air and condition of the tire—looks fine and never has been used.

Maybe I'm counting on the Michelin spares to last longer than the average tire and that Michelins rarely get flats. I can fix a flat on the road if I have to. Maybe I'm just too cheap to buy new or nearly new spares, maybe I'm too lazy to deal with it.

But Tireman, I have a question for you—what do you think of my theory that one smaller tire promotes instability, especially when on a trailer, plus that the proper sized tire on a tandem axle carries too much weight then?

Gene
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Old 09-05-2015, 02:30 PM   #944
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Once the date of manufacture code is 5 years old, the tire should not be used for anything. As soon as a tire is manufactured the casing begins to decay internally. It has been determined that at 5 years from the date of manufacture, the decay to the casing approaches catastophic failure. I have had blowouts on an 8-year old Michelin on a motorhome (before I knew about the 5-year rule) and on a 5-year old tire for the toad. While it is true that environmental damage from sun does occur, the decay to the casing takes place no matter where and how the tire is stored. So while you are blithely motoring along a thinking that you tires are good and that the 6 or 8 year old spare will do in a pinch, you may find that your old spare fails within minutes of your mounting it.

Be safe, not sorry.
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Old 09-05-2015, 04:36 PM   #945
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Michelin says their tires last 8 years, maybe yours was a bit older. With a high mileage truck, we keep it in the county except when we tow, so an old spare isn't such a big deal. On the road, I can fix a tire because I keep a tire repair kit and a compressor with us. Sure tires can fail anytime, and more likely when older.

On the other hand, a tire never used may decay faster because all the chemicals that keep it happy slowly flow downward under the truck (the trailer spare gets moved in and out of the truck and rolled around the garage. I have been lax at moving the trailer every few months during the winter to keep the chemicals moving back to what was the top and then is the bottom. My guess is that is what caused the trailer tires to start sidewall cracks sooner than I expected.

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Old 09-06-2015, 09:29 AM   #946
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Tireman, the spare is kept either in the garage or back of the pickup, so it gets no sun. But it was rotated around the trailer over 5 years. The sidewalls started to show sidewall cracks before we started traveling this summer, so I replaced four of the five. Michelin gave me a price reduction on new tires. The original 5 had about 35,000 miles on them and the tread was very good. I picked the one with the fewest cracks for the spare.

The Tundra came with 4 full sized tires (18" I think) and a spare that was smaller on a steel wheel. Ironically the spare was a better quality tire (Michelin) than the tires mounted on the truck—Goodrich. The Goodrichs rode badly and wore fast. That spare is now 8 years old and I lower it sometimes to check the air and condition of the tire—looks fine and never has been used.

Maybe I'm counting on the Michelin spares to last longer than the average tire and that Michelins rarely get flats. I can fix a flat on the road if I have to. Maybe I'm just too cheap to buy new or nearly new spares, maybe I'm too lazy to deal with it.

But Tireman, I have a question for you—what do you think of my theory that one smaller tire promotes instability, especially when on a trailer, plus that the proper sized tire on a tandem axle carries too much weight then?

Gene
two separate questions
My suggestion to get a newer worn out tire for a spare for the RV was aimed at saving you some $$ rather than buying another new RV tire. I would shop for a tire of the same size as on your RV. I see used tires offered for $25 or less.

The spare on the truck was selected to provide satisfactory temporary service if you get a flat on a "ground" tire on the truck so in this case different size is something that vehicle engineers evaluated so would not worry about. Does it say "Temporary" on it or is it just a smaller size than the ground tires?
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Old 09-06-2015, 09:39 AM   #947
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Once the date of manufacture code is 5 years old, the tire should not be used for anything. As soon as a tire is manufactured the casing begins to decay internally. It has been determined that at 5 years from the date of manufacture, the decay to the casing approaches catastophic failure. I have had blowouts on an 8-year old Michelin on a motorhome (before I knew about the 5-year rule) and on a 5-year old tire for the toad. While it is true that environmental damage from sun does occur, the decay to the casing takes place no matter where and how the tire is stored. So while you are blithely motoring along a thinking that you tires are good and that the 6 or 8 year old spare will do in a pinch, you may find that your old spare fails within minutes of your mounting it.

Be safe, not sorry.
Sorry I don't know of any "rule" that says tires should not be used on anything if they are 5 years from date of manufacture. Many tire warranties start on application date so may already be a year or more "old" at that point.
I have seen in print from Michelin a 10 year "rule" if you want to word it that strongly.

Use on a trailer is much different than use on a motorized vehicle so the suggested age limit is shorter on trailers than motorized vehicles. I suggest you Google "Interply Shear RV tire" to learn the science behind tire structure failure.

"Blowouts" are usually what people incorrectly call Run Low Flex Failure. You might read THIS thread to learn more about blowouts.

Yes rubber does age all the time but the RATE is dramatically affected by how a tire is stored with temperature being a major factor.
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Old 09-06-2015, 12:32 PM   #948
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Thanks for the answers Tireman. Your next post is interesting to me where you say "suggested age limit is shorter on trailers than on motorized vehicles". I would think the opposite since they are neither drive nor steering tires and seem to me to have less stress on them, but having Googled the description of "Interply Shear RV tire" I get what you are saying (seems you are everywhere). And the info there is a good reason to keep inflation at max psi for the particular tire. I don't quite get the part about tandem axles, but maybe need to think about it longer—seems like it would apply to MH's and large trucks with tandem axles close to one another too.

Another reason could be because most of the time trailer tires are not used and non-used tires age faster? And if temperature is a major factor, will tires age slower in a colder climate like Colorado?

Gene
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Old 09-06-2015, 05:40 PM   #949
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Tireman9 -

The 8-year old tire that failed was an inside rear tire on a 1994 AS LY diesel pusher. When the tire blew it took out part of the side of the motorhome. This was when I learned (I was at the International at Bozeman MT) that the rule-of-thumb was to retire a tire from use when it reached 5 years from the date code. At that time I bought all 7 new tires. Two years later the toad I was pulling behind it had a tire blow while in tow - that tire was 5 years old (from the date code).

With the AS trailer I now have, I started with all 5 new ST tires (date coded in 2011). Within 3 years I had 2 tread separations and a blow out. I have upgraded to 16-inch wheels and Michelin LTX225/75R16(E) tires with the Dill TPMS system. I no longer have any issues with my running gear.

I realize that you are very knowledgeable about tires, but as the guy who footed the bill for repairs and replacements, absent a full lab and the scientific knowledge to measure the true condition of any particular tire, wishing to avail myself a very healthy margin of safety, I'll stick with my rule of thumb. The last blowout on my AS trailer cost a mere $1,000 to repair, more than a set of new tires.
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Old 09-06-2015, 05:59 PM   #950
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I Googled Interplay Shear RV tire and found a site called rvtiresafety; no surprise. So the tires are under much greater stresses when there a multiple axles. Does this impact the use of LT tires? While LT tires can handle the "static" load can they handle this turning shear? I thought that ST tires had larger poly cords for these loads that are not in LT tires.
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Old 09-07-2015, 07:44 AM   #951
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Tandem Axles

Quote:
Originally Posted by Gene View Post
Thanks for the answers Tireman. Your next post is interesting to me where you say "suggested age limit is shorter on trailers than on motorized vehicles". I would think the opposite since they are neither drive nor steering tires and seem to me to have less stress on them, but having Googled the description of "Interply Shear RV tire" I get what you are saying (seems you are everywhere). And the info there is a good reason to keep inflation at max psi for the particular tire. I don't quite get the part about tandem axles, but maybe need to think about it longer—seems like it would apply to MH's and large trucks with tandem axles close to one another too.

Another reason could be because most of the time trailer tires are not used and non-used tires age faster? And if temperature is a major factor, will tires age slower in a colder climate like Colorado?

Gene
The reason tandem axles are significant in increasing the shear forces on trailer tires is that whenever turning any corner or even just rounding a curve the tires on a trailer are "dragged" around the curve as the center of rotation is not the center of the turn radius. Two axle motorized vehicles always have all tires rotating around center lines that do point to the center of the turn. Cars and pick-ups etc even have something called "ackerman" built into the front suspension & steering such that the two tires each point to the center of the turn and are not parallel. You can Google "Ackerman steering" for something I didn't write about.

Not having the tires rotate about the center of the turn increases the shear forces by about 24% above what one would see on a motorhome.
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Old 09-07-2015, 07:52 AM   #952
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I Googled Interplay Shear RV tire and found a site called rvtiresafety; no surprise. So the tires are under much greater stresses when there a multiple axles. Does this impact the use of LT tires? While LT tires can handle the "static" load can they handle this turning shear? I thought that ST tires had larger poly cords for these loads that are not in LT tires.
The stresses we are talking about are in the belts not the body. P or ST or LT it makes no difference to the physics.
It does seem that the various construction features that allow LT tires to have higher speed ratings also may be the major contributing factor as to why they seem to be able to handle the Interply Shear better than ST type tires which are mostly designed to 65 mph speed rating.

Another reason LT tires may perform better is that identical physical sized LT tires carry lower load than ST when inflated to the same psi so this gives a greater margin. So there are really at least 2 reasons for LT tires to perform better in trailer application.
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Old 09-07-2015, 08:53 AM   #953
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Tireman9,


Thank you again for your helpful guidance.

So if one goes to 16" LT with the proper rims you get the same if not better safety characteristics of the 15" ST and:

-comparable if not better static load support (safety)
-comparable if not better handling of the interply shear among the belts (safety)
-Michelin (quality)

Will the sidewalls of the LT also meet the stress demands from a trailer caused by tracking battles in multiaxle configurations and sharp turning if properly inflated?

Regards
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Old 09-07-2015, 11:14 AM   #954
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Tireman, thanks again. I've noticed front tires turn differently, never knew why. One of the reasons ST tires were created in the 1970's, as I understand it, was that the relatively new radials had weak sidewalls, people didn't want bias ply tires anymore because radials were better in most ways and so a radial with a stronger sidewall was development for trailer use.

But, the ST's available are just not very good tires except perhaps for someone who travels very little and whose ST's age out before they have more than a few thousand miles on them—why spend twice (or more) as much for a good quality LT? For the rest of us, a different answer though. The Michelin Rib tire may be a better solution than the LTX because the Rib has steel cord in the sidewall. The Rib is designed for delivery trucks used in town and is made to be recapped one or more times, but may be a good choice for trailers. Hope I got that right.

Gene
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Old 09-07-2015, 01:22 PM   #955
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I just re-read the last few postings and must add a qualifier to my last posting. I should have said:

"So to summarize the comments by the knowledgeable tire people (NOT myself), if one goes to 16" LT with the proper rims......"
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Old 12-17-2016, 06:12 PM   #956
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