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Old 04-14-2015, 11:19 AM   #85
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I would like some tire help

I believe the only design for a Michelin LTX is a P rated tire in the 15 inch. Yes I de-rated it, and am plenty covered. Still my question of mileage is unanswered. Is there more rolling resistance because they only handle 50 psi ?


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Old 04-14-2015, 12:18 PM   #86
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I run the 15" p XL Michelins. I cannot answer the mileage question because that is all I have run on this trailer in the 9 years I have been pulling it. With my 2500 diesel I doubt the tire rolling resistance makes much of a difference in fuel use. But the question does interest me because I also have pulled my 32' with ST tires at 65psi and got better milage than I sometimes get with the 25'. The trip was on relatively flat ground (Fl to Ohio and back) and I am not sure what to attribute the difference to. On the diesel truck such things as the quality of the fuel you get and the wind speed and direction do make a difference
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Old 04-14-2015, 02:05 PM   #87
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In my opinion, wind resistance affects fuel mileage more than the tire type or inflation pressure (assuming tires are not under-inflated).

After switching to LT tires, we towed our Bambi on one 2,000 mile, all-Interstate highway, quick trip at 75 mph; and we got 10-11 mpg with our 2008 Tundra CrewMax and 2005 19' Bambi. On several other trips (same route), we have driven 55-60 mph and gotten 13.5-14 mpg.

Needless to say, we no longer cruise at 75 mph; as, for us, this results in a 15% decrease in fuel mileage.

Of course, besides saving fuel, towing at a slower speed has other safety advantages, besides making the trip more enjoyable.
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Old 04-14-2015, 03:13 PM   #88
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In my opinion, wind resistance affects fuel mileage more than the tire type or inflation pressure (assuming tires are not under-inflated).

After switching to LT tires, we towed our Bambi on one 2,000 mile, all-Interstate highway, quick trip at 75 mph; and we got 10-11 mpg with our 2008 Tundra CrewMax and 2005 19' Bambi. On several other trips (same route), we have driven 55-60 mph and gotten 13.5-14 mpg.

Needless to say, we no longer cruise at 75 mph; as, for us, this results in a 15% decrease in fuel mileage.

Of course, besides saving fuel, towing at a slower speed has other safety advantages, besides making the trip more enjoyable.
No opinion needed....it is a fact.
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Old 04-15-2015, 09:35 AM   #89
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I believe the only design for a Michelin LTX is a P rated tire in the 15 inch. Yes I de-rated it, and am plenty covered. Still my question of mileage is unanswered. Is there more rolling resistance because they only handle 50 psi ?
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Sorry but a LOT more involved than juut inflation pressure.

While it is true that with any given tire increasing inflation will improve fuel economy there are limits and the improvement % drops as the inflation gets higher.

BUT There can be a greater difference between two tire designs and especially between P type and LT type such that it is possible to get better mpg with a P type at lower pressure than an LT at higher pressure.

There is no easy to measure other than a tire test lab. You could hire an independent lab to do a comparison but you would need to provide two new tires and pay a few thousand dollars to have the test run.

I can provide appropriate contact but I would budget at least $5k for basic test.
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Old 04-15-2015, 10:36 AM   #90
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I'm combining these 2 posts to answer them in one post.

First, I think there are several reasons why LT appear not to do that.

1) In every instance I have observed, the replacement LT tire size has gone up - and that equates to an increase in load carrying capacity. The rated load is specific to the type of service and the way ST tires and LT tires are rated is different (with the ST tire being rated at a higher load for the same dimensions)

2) ST tires are built by oh, I call them 3rd tier tire manufacturers (with 2 exceptions). I am sure these guys aren't at the cutting edge of tire technology and I wonder what these guy's LT tires would do. I never find out the answer to that question.

3) Then there is the issue of failure rate. If the actual failure rate is on the order of 10% (probably high), then there is a very large population of people (90%) who will never perceive a problem.

Put another way, if a person were to replace 4 tires, of which one was a failure, with 4 new ones, the odds are they will not experience a second failure. Of course, that person will have difficulty understanding that and will insist that any change they made was the difference.

Now, I am NOT saying that ST tires are equivalent or better than LT tires. I am saying there is a lot going on here and it can be difficult to sort this all out. I am merely pointing out what I perceive to be differences.

- AND -

One of the keys in trying to sort out this complex situation is pressure buildup. Pressure buildup is a way of determining if the load carrying capacity is adequate.

So if the pressure buildup for an ST tire (or any tire for that matter) exceeds 15%, then a failure is likely and it would be due to overload/underinflation/excessive speed and not the manufacturer's design or a defect or the type of tire (ST vs LT).
1. Many many people that went up a load range on ST tires had them fail for no reason.....

2. If you have to check hot pressure to see if the tire is ok when you bought correct load range tires I wouldn't buy them. Being around semi trucks for years I have never seen or heard mechanics or drivers talking about checking hot pressure to see if the tire is correct for their truck.

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Old 04-15-2015, 12:08 PM   #91
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Sometimes people become too trapped within academic details while discounting the intrinsic value of practical experience.

I used to be that way to some degree.... But I got past it.


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Old 04-15-2015, 12:48 PM   #92
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2. If you have to check hot pressure to see if the tire is ok when you bought correct load range tires I wouldn't buy them. Being around semi trucks for years I have never seen or heard mechanics or drivers talking about checking hot pressure to see if the tire is correct for their truck.
That may be and I would bet most of the semi-trucks are running tires that were sized and inflated to what was recommended by design.

Most of the tire discussions on this forum are about changing tire sizes/types and altering inflation pressures from OEM specs. Usually to get more load capacity on the same load in the hopes of longer service life without a sudden end to that service life.

Sooooo if playing with different tire pressures and/or tires sizes/types, one may need to check pressures when in service (hot) to determine if the rise in pressure is inline with good service life. Not to make an adjustment in pressure when hot, just as a measurement of what is happening inside the tire. As I understand it, a better indicator than using an IR gun or as truckers sometimes use a thump stick. Which would be far less accurrate on much smaller trailer or TV tires.

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Old 04-15-2015, 12:53 PM   #93
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Imho, the manufactures when designating a cold inflation pressure expect that the pressure will increase as the tire warms. Therefore the expectation of increased hot pressure would be built into the cold inflation recommendation, and the increase in pressure will be within the margin of tire design.

This is obvious to most people right?


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Old 04-15-2015, 01:10 PM   #94
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I would like some tire help

How about another bit of practicum?

If the center of the tread wears faster than the edges, it may be that the tire is over inflated for the load.

If the edges wear before center of the tread it may be that the tire is being run under inflated or is insufficient for the load carried.

Most of the time a tire that is grossly under-inflated under a load will look under inflated and/or will feel warmer to the touch after a good drive than its companions.

Knots, bulges, and sidewall irregularities (even small ones) mean that the tire has internal damage and it will fail in continued use. Don't waste your time trying to milk a few more miles out of it.

A tire is serviceable to 2/32" tread on trailers and drive axles and serviceable to 4/32" tread on steer axles.

I seldom let them get very close to this in drive and trailer positions and NEVER anywhere near 4/32" in steer positions.

Look at your tires when you stop and put a hand on them. Learn what a tire that has been run flat looks like, observe and be proactive, and time spent on the side of the road dealing with a "tire emergency" can be greatly mitigated.


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Old 04-15-2015, 11:29 PM   #95
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Sorry but a LOT more involved than juut inflation pressure.

There is no easy to measure other than a tire test lab. You could hire an independent lab to do a comparison but you would need to provide two new tires and pay a few thousand dollars to have the test run.

I can provide appropriate contact but I would budget at least $5k for basic test.
Naahh! I was just curious. I figured if I could save fuel choosing one tire over another, that would sway my decision. The Michelin LTX 235/75/15 is $118.00 and the Yokohama RY215 is $176.00. I may as well go with the cheaper tried and true Michelin. I don't think I am gaining anything by spending more money.
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Old 04-16-2015, 07:31 AM   #96
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1. Many many people that went up a load range on ST tires had them fail for no reason.....
First, some tires fail due to unidentified road hazards - and I always wonder how many of reported failures fall into that category.

Second, without knowing what loads and speeds the tires were subjected to, we can't really say if the increase in load range was enough. It's possible it wasn't.

Lastly, I've heard folks going up in load range and not using more inflation pressure, so in effect, they haven't gone up in load range at all.

There is a lot going on here and there just isn't enough information to assure that all the boxes have been checked off. So be careful making that assertion.

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.........
2. If you have to check hot pressure to see if the tire is ok when you bought correct load range tires I wouldn't buy them. Being around semi trucks for years I have never seen or heard mechanics or drivers talking about checking hot pressure to see if the tire is correct for their truck.

Over-the-road trucks have a wealth of experience selecting tire size, Load Range, and inflation pressure. (Put another way, selecting load carrying capacity). Not only do they have to comply with load limits, but the trucks are checked periodically. (Ever see those weigh stations?) They have a pretty good handle on this.

Further, when they do check, they generally have a tire rep who handles all of this for them - and one of the things they do check is pressure build-up. Needless to say, once a truck has been checked it doesn't need to be checked again. Plus a fleet has so many of the same truck (make and model) that checking all of them is a waste of time. Only a few need to be checked to verify the situation.

But what we have with trailers is a largely unverified mess - many trailers have been identified as having overloaded tires. So as a precaution, I recommend measuring pressure build up. It is quick and easy and gives a lot of useful information with little expenditure of effort.
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Old 04-16-2015, 07:36 AM   #97
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Mustang, are both those tires p rated?
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Old 04-16-2015, 08:11 AM   #98
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I would like some tire help

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Mustang, are both those tires p rated?

The the Yokohama RY215 is not p rated. It is a load range D, 65 psi, LT tire. According to their site it is recommended for trailer use. It is about an inch narrower and an inch taller than a ST 225/75/15.

Also I believe it is an 8 ply instead of a 6 ply tire. Thought it might work well for people with triple axel 34s

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