Another Tire Question - Page 4 - Fiberglass RV


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Old 01-16-2013, 01:23 PM   #43
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Well, actually, 33,000 miles...

As to the original tires, again they were well within the trailer's weight. According to Goodyear's Marathon Trailer Tire inflation tables, at 50 PSI the tire rating is 1820 lbs, or 3640 lbs for the axle, well over the axle rating & even further over the typical axle weight of an Escape 17B (mine is 2800 lbs loaded).

The Maxxis table shows the same values for the 205/75/15 tire. I have no problem going with the "C" rated tire, however they are difficult to find in that size. As I noted before, I will probably be purchasing the "D" rated tire & run it at the appropriate pressure for my rims.

The unusual wear I mentioned in my original post is not all that visible in the pictures - the outside edge wear is down beyond the tread on the section of the tire opposite the wheel weights but fairly even across the tire 180s around the tire. In any case, I suspect there is enough outside wear that I will have the alignment checked, providing I can find someone who knows how to do it.
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Old 01-16-2013, 01:33 PM   #44
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Red face

Quote:
Originally Posted by Brian B-P View Post
The unnecessarily higher-rated tire is heavier, probably more expensive, less compliant (and therefore has less traction), and may build more sidewall heat due to resistance to flexing.
Got no dog in the overspec fight but I could not help but notice this statement. Brian, is it really the case that a stiff sidewall can generate and retain greater heat than a more flexible sidewall? This seems to me to run counter to the universal experience of flexing everything from muscles to steel. It seems to me that elastic deformation [bend/stretch] creates heat at the molecular level and that the greater the deformation (stretch and bend) the greater the amount of heat created. You seem to be saying that resistance to deformation creates heat. I think that must be what's happening right now in my cranium

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Old 01-16-2013, 02:16 PM   #45
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According to my understanding, yours is the correct assessment, Jack...flexing creates heat, and flabbier tires flex more.

But an overspec'd tire isn't going to flex any less than an adequately spec'd tire that's properly inflated for the load.


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Old 01-16-2013, 02:40 PM   #46
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Quote:
Originally Posted by rabbit View Post
Got no dog in the overspec fight but I could not help but notice this statement. Brian, is it really the case that a stiff sidewall can generate and retain greater heat than a more flexible sidewall? This seems to me to run counter to the universal experience of flexing everything from muscles to steel. It seems to me that elastic deformation [bend/stretch] creates heat at the molecular level and that the greater the deformation (stretch and bend) the greater the amount of heat created. You seem to be saying that resistance to deformation creates heat. I think that must be what's happening right now in my cranium

jack
The answer, of course, is "it depends!"

I'm making generalizations here, but the tire deflects in two ways. Primarily in the "hoop" direction from round to flat in the contact are and then round again. The other way is in the sidewall.

Within a subset of tires, ST's for example there is generally little difference in the deflected radius acheivable with changes in sidewall reinforcement. (heavy with the generalizations here since you CAN change the deflection with certain reinforcements)

So, if you have basically the same deflection, the thicker, stiffer tire will run hotter. The load formulas were basically designed such that all similar tires, all ST tires say, have the same percent deflection at their rated load and inflation. A given size "C" tire at 50 psi carrys the same load as the same size "D" tire at 50 psi. They will both have about the same deflection at the same rated load and pressure and thus, If the "D" tire has more "stuff" in the sidewall it will have more losses (exhibited by heat and/or rolling resistance). Heat in and of itself is not bad...Too much is.

Like everything about a tire, there's a a bazillion variables that effect the tire. Generalizations are just that and a passive-agressive can pick out exceptions. I don't know if I've even added to the discussion. These tire discussions are largely doomed anyhow.
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Old 01-16-2013, 03:10 PM   #47
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Yep, that clears it up. Steve, we "passive-aggressives" prefer to think of our activity as a sort of cavalry probe at a point of potential weakness in the line of argument. Often the weakness is in our heads. I have to run away now.

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Old 01-16-2013, 04:23 PM   #48
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I wasn't thinking of you when I wrote the passive aggressive comment. Yours was a good question/comment and one I've fielded from my bosses in the past so I've sorted through it before.
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Old 01-16-2013, 04:46 PM   #49
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Well, if you're saying that there's anything passive about my aggression, I double-dog dare you to come over here and say that!

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Old 01-16-2013, 05:07 PM   #50
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Originally Posted by rabbit View Post
Yep, that clears it up. Steve, we "passive-aggressives" prefer to think of our activity as a sort of cavalry probe at a point of potential weakness in the line of argument. Often the weakness is in our heads. I have to run away now.
jack
Please dont! I love reading your prose!
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Old 01-16-2013, 05:19 PM   #51
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These tire discussions are largely doomed anyhow.
Tires tend to fall into the same realm as discussions on safe towing practises, wax or floor polish, generators or solar, using Sway Bars, best type of tow vehicle and fresh to the list this week using Weight Distribution Hitches.
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Old 01-16-2013, 05:22 PM   #52
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and the list goes on...
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Old 01-16-2013, 05:23 PM   #53
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HHHmmm,
I wonder if all these discussions are contributing to the climate issue we are experiencing, last year being the warmest on record.
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Old 01-16-2013, 05:47 PM   #54
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Thanks Carol. I'll tell the infinite monkeys to keep up the good work.
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Old 01-16-2013, 09:43 PM   #55
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Steve provided the same answer that I would to Jack's (reasonable) question about stiffer sidewalls running hotter, although he stated it perhaps more eloquently and certainly more authoritatively than I would have. Thanks, Steve.

Quote:
Originally Posted by baron100 View Post
Most of us have single axle trailers. A failure of either tire could result in a catastrophic accident. Replacing a tire at the side of the road by itself presents significant risk to the owner while changing the tire. Think I-405 in Seattle at rush hour.

The single most important safety decision we make as trailer owners is in tire selection. The travel and boat trailer forums are replete with pictures of mangled tires and damage to trailers from tire failures. Often owners report multiple failures.

...
Buy the best tire you can put on your trailer...
All of this logic applies equally well to the front tires of the tug - you don't want one of those to fail! Does anyone use the very best tire sold for their tug, and do they choose tires with much higher rated capacity than the axle rating, and much higher even than the manufacturer's original equipment?

Even if someone does want to use the "best" tire, this is not the same as the tire with the highest rated load capacity.

If trailer tire failures are routinely caused by under inflation and overloading, as is commonly asserted in this forum and by tire manufacturers and retailers, then the solution is obviously to use the right size of tire, properly inflated... just as we do on our tugs.

Quote:
Originally Posted by baron100 View Post
An extra two plies of tire construction affords him additional protection in the form of reduced risk of tire penetration from a foreign object (a leading cause of failure after under inflation) and is a tire of much greater strength.
Ply ratings do not describe the actual number of plies of tire reinforcement. They are scheme invented many years ago to relate the now antiquated non-belted bias ply tires (think 1930's) to standard load ranges: the "ply rating" indicated that the tire had capacity similar to a traditional tire with that many layers of fabric in the carcass.

For instance:
2-ply rating (typical max inflation pressure 24 psi) = Load Range A
4-ply rating (typical max inflation pressure 35 psi) = Load Range B (= passenger car Standard Load or SL)
6-ply rating (typical max inflation pressure 50 psi) = Load Range C (= passenger car Extra Load or XL)
8-ply rating (typical max inflation pressure 65 psi) = Load Range D
10-ply rating (typical max inflation pressure 80 psi) = Load Range E

In practice, modern tires have many fewer plies, especially in the sidewall. Standard Load car tires typically have a single sidewall ply, I have had Extra Load tires with 2-ply sidewalls, and my motorhome's stock Michelin XRV 235/80R22.5 Load Range G tires have one-ply sidewalls, albeit one layer of thick steel cord (small tires commonly have polyester sidewall plies). Even the tread doesn't have the number of belt layers under it that were once used.

A LR-D trailer tire does not have two more plies than LR-C, and may not have any more plies... but read the sidewall if you're curious.

Applications which require greater sidewall damage resistance (such as off-road truck designs) routinely add more protective rubber, rather than more reinforcing cord layers. That might be handy for incompetent trailer pullers, who bounce the trailer tires off a lot of curbs.

Quote:
Originally Posted by baron100 View Post
Consider one other point. Many trailer manufactures scrimp on the axles they chose. A loaded Casita SD (and many other brands) trailer is very close to the max 3,500 lb rating the Dexter axle provides, leaving minimal margin. It is reasonable to assume that the additive tension resulting from the axles stressed to the maximum causes additional stress on the tires.
I don't understand the term "additive tension". If this is meant to refer to higher shock loads due to suspension bottoming, then it makes sense that additional tire load capacity is needed... but are these trailers really routinely hammering the compression travel limit?
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Old 01-16-2013, 10:31 PM   #56
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Quote:
Originally Posted by Jon Vermilye View Post
Well, actually, 33,000 miles...

As to the original tires, again they were well within the trailer's weight. According to Goodyear's Marathon Trailer Tire inflation tables, at 50 PSI the tire rating is 1820 lbs, or 3640 lbs for the axle, well over the axle rating & even further over the typical axle weight of an Escape 17B (mine is 2800 lbs loaded).

The Maxxis table shows the same values for the 205/75/15 tire. I have no problem going with the "C" rated tire, however they are difficult to find in that size. As I noted before, I will probably be purchasing the "D" rated tire & run it at the appropriate pressure for my rims.

The unusual wear I mentioned in my original post is not all that visible in the pictures - the outside edge wear is down beyond the tread on the section of the tire opposite the wheel weights but fairly even across the tire 180s around the tire. In any case, I suspect there is enough outside wear that I will have the alignment checked, providing I can find someone who knows how to do it.
Hi: Jon Vermilye...I still remember being shocked at having my 69 Dodge Van aligned. It took 2 guys to do it. One to hold the long iron bar against the axle and the other guy to swing the sledge hammer.
Alf S. North shore of Lake Erie
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