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Old 06-08-2010, 08:22 AM   #31
Bill
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ShrimpBurrito posted
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... And the tires run fairly cool. No more than luke warm on a 85-degree day....
Dave -

Based on my experience with 15" Marathons (thanks, Bobby), you will find cool tires to be the normal situation. And you will enjoy the feeling of confidence you get each time you touch them. You've made a good move.

Careful, though. Don't panic, as I did, when one of the 15" tires felt quite a bit warmer than the other (not hot, but WARMER)! Turned out that the tire on the sunny side of the TM feels quite a bit warmer than the tire on the shady side. I've noted this several times since, and each time I have to calm my racing pulse.

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Old 06-08-2010, 10:24 AM   #32
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Dave,

Would you mind measuring the OD on your new 15" tires. I am installing a lift kit on my TM and I think that I will have to move my axle forward a bit (even after a 2.5" lift). I was thinking that I might move it 1" but I'm not sure that will be necessary to go that far. I currently have less than 1/4" clearance between my right tire and the frame member behind the tire. I'm actually surprised that the tire doesn't touch the frame at highway speeds.

Maybe wmtire already has that measurement. I thought that someone had posted them at one time but I can't find it.
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Old 06-08-2010, 11:34 AM   #33
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Originally Posted by harveyrv View Post

Maybe wmtire already has that measurement. I thought that someone had posted them at one time but I can't find it.
I don't have a measurement, but there is a formula that we use to get a real close approximation.

Say for example you have a metric sized tire of 225/75R15. The first number (225) is the section width. The second number (75) is the aspect ratio and the last number (15) is the rim diameter.

Here is the formula

(Section Width X Aspect ratio X 2) divided by 2540, then add rim diameter= approx tire diameter

(225 X 75 X 2) =33750

33750 divided by 2540 = 13.287

13.287 + 15 = 28.287 inches is approximate tire diameter.

You multiply the section width and aspect ratio by two, to give you the height of the two (or top and bottom) sidewalls of the tire.

You divide this result by 2540 because the tire size section width to begin with was in millimeters (225 millimeters). There are 25.40 mm to an inch, so we are converting it all over to inches at that stage and moving our decimal place (which we need to do to properly add it it to the wheel diameter which is given in inches). Technically, the aspect ratio is a percentage of the section width (or 75 % in our example). It's easier to just use a whole number and use 2540 in the conversion part. (instead of .75 and 25.40)

Now you take this converted number, which is the height in inches of the two sidewalls, and add it to the rim diameter (or hole in the middle of the tire).

You now have the approximate diameter of the tire in inches. It should work well enough to figure out your clearances, etc.
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Old 06-08-2010, 12:05 PM   #34
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Originally Posted by wmtire View Post
I don't have a measurement, but there is a formula that we use to get a real close approximation.

Say for example you have a metric sized tire of 225/75R15. The first number (225) is the section width. The second number (75) is the aspect ratio and the last number (15) is the rim diameter.

Here is the formula

(Section Width X Aspect ratio X 2) divided by 2540, then add rim diameter= approx tire diameter

(225 X 75 X 2) =33750

33750 divided by 2540 = 13.287

13.287 + 15 = 28.287 inches is approximate tire diameter.

You multiply the section width and aspect ratio by two, to give you the height of the two (or top and bottom) sidewalls of the tire.

You divide this result by 2540 because the tire size section width to begin with was in millimeters (225 millimeters). There are 25.40 mm to an inch, so we are converting it all over to inches at that stage and moving our decimal place (which we need to do to properly add it it to the wheel diameter which is given in inches). Technically, the aspect ratio is a percentage of the section width (or 75 % in our example). It's easier to just use a whole number and use 2540 in the conversion part. (instead of .75 and 25.40)

Now you take this converted number, which is the height in inches of the two sidewalls, and add it to the rim diameter (or hole in the middle of the tire).

You now have the approximate diameter of the tire in inches. It should work well enough to figure out your clearances, etc.
Thank you very much Bobby....I knew that you would have the "Proper" answer.
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Old 06-08-2010, 06:23 PM   #35
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If I were to convert to 15 inch wheels, but install a low profile tire that so that the overall tire diameter is the same, what would I gain? I would think that the air volume would decrease, therefore making the tire run hotter.

I also have only 1/4 inch clearance as I back the TM into the garage.

Letting air out is not an option because I park it against a wall.
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Old 06-08-2010, 08:15 PM   #36
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"My TM tracks very slightly to the right due to the factory welding the axle about an inch or so (IIRC) further back on one side vs. the other. Could that contribute to failure, or would that just result in uneven wear, similar to a car out of alignment?"

I would think this would have alot to do with your problem.I do question how you know its an inch off and how you measured it. The reason I ask is that I have built several single axle and tandem axle flatbed trailers. The way you measure is go to a point on the axle closest the to wheel and measure to the center of the ball hitch. I usually "eyeball" the ball hitch center and tape some string and let it drop with a fishing weight(plumb bob) tied on before it hits the ground. Then have someone hold the tape to the outer most common point on each side of the axle, measure to the string. I am good with a 1/4" difference. You cannot go from same side frame to axle measurements, think of the trailer as a triangle as thats what you are pulling, just a box mounted on top of the "triangle"
I have never used torsion axles, just leaf spring setups. I have never looked under my TM closely at the axle to be honest. Surely they are not welded in place, and are bolted in. The torsion axles mounts should be slotted to allow for adjustment. I cant say for sure, but a 1" difference would create wear and heat I would think.
Also when trailer is in storage are the tires covered? I know I have run into tire problems with a trailer at work that is not used much, but when loaded to near capacity I am having tires blowout that are 2-3 yrs old and these a 19.5 tire with less the 20k on them.
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