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Old 01-25-2008, 07:42 AM   #1
grakin
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Default Tire inflation - Goodyear Marathons

I was reading: this document and was trying to make sense of it.

It says:

==
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
==

Does this mean that I can put 60 psi into my 14 inch Marathons, if the metal wheel can handle it? If I can, will the metal wheel handle it?

I hate towing faster than 65 MPH, but in this area of the country it's a bit risky to go that slow sometimes, and would like the extra margin.
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Old 01-25-2008, 08:25 AM   #2
Bill
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Joel -

I don't think anybody knows exactly what this statement means. We had a long discussion about it a couple years ago, with lots of ideas but no conclusions. I've even talked to the TM factory to get their take on it, and they are mystified. Part of the problem comes from the fact that, if you rummage around the Goodyear site some more, you will find that same statement somewhere else, with slightly different wording. As I recall, the different wording suggests that if you nudge up the tire inflation to get more speed rating, the load-carrying capacity is actually reduced. The statement is not quantified, so I don't know what to do with it.

As far as the wheel is concerned, I recall that when I switched to 15-inch wheels/tires, all the info was stamped inside the body of the wheel - in other words, you can't read it unless you take the tire off. But that is apparently not universal practice. As it happens, I have a spare TM wheel with no tire on it (the one I have been tryng to give away on the Parts and Accessories forum). This is an original 14-inch factory wheel. The stamping here is on the outside back surface, and it says "DOT T14X6.0 10 04 MAX 1870 LBS JCA KOREA". No reference to pressure, unless wmtire can make something out the JCA code.

Sorry not to be more help.

Bill
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Old 01-25-2008, 06:21 PM   #3
wmtire
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Quote:
Originally Posted by Bill View Post
it says "DOT T14X6.0 10 04 MAX 1870 LBS JCA KOREA".

I looked at the requirements that a rim manufacturer is supposed to adhere to. I didn't find anything that states that they HAVE to put the air pressure and/or load designation on them, although some do. I guess that would make it too easy if they all did. I would safely assume that whatever air pressure the above trailer (ST) tire takes to carry 1870 pounds (or 50 psi according to Goodyears own spec charts) is also the maximum air pressure this particular rim is rated for also.

http://www.goodyear.com/rv/tirecare/...iontables.html

Even if the rim is capable of more air pressure, it still won't carry more weight. If you err on the side of caution, and keep your maximum tire air pressure in line with the maximum weight of the wheel, then you should always be safe on both counts..... especially if you don't know exactly what air pressure the rim is rated for.

If they manufactured the rim in accordance with the DOT regulation, then the "JCA" on Bill's wheel is most likely the company who made it in October of 2004. Sorry, I couldn't be of more help either.

Here is the reg referenced for our engineering or more useless trivia members:

12.2 RIM MARKING REQUIREMENTS (S5.2)
Rims must be marked with the following information in lettering not less than 3 millimeters in height, and impressed or embossed to a depth or height of not less than 0.125 millimeters. Items A through C must appear on the weather side of the rim.

A. A designation which indicates the source of rims's published nominal dimensions, as follows:

T - The Tire and Rim Association
E - The European Tyre and Rim Technical Organisation
J - Japan Automobile Tire Manufacturers Association, Inc.
D - Deutche Industrie Norm
B - British Standards Institution
S - Scandinavian Tire and Rim Organization
A - The Tyre and Rim Association of Australia
N - Independent listed with NHTSA

B. Rim Size Designation.

EXAMPLE: 20 x 5.50 or 20 x 5.5

C. The Symbol DOT. Manufacturer's certification that rim complies with all applicable FMVSS.

D. Manufacturer's Name, Trademark, or Symbol.

E. The month, day, and year or the month and year of manufacture, expressed either numerically or by use of a symbol.

EXAMPLE:
January 4, 1999 may be expressed as any of the following:
MO.-DAY-YEAR: 10499 (or) 104 (or) 99
99 104
MO.-YEAR: 199 (or) 1 (or) 99
99 1

Any manufacturer that elects to express the date of manufacture by means of a symbol shall notify NHTSA in writing.
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Old 01-25-2008, 07:11 PM   #4
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After eating a half bag of Funyuns, I have had time to reflect on what I previously posted. I really gave a "cover your hind end" answer.

In real world experience, we have several members who have upgraded their factory Trailmanor tires/wheels (which are just like Bill's original ones) to the Euro sized 195R14's and are running upwards to 65 psi in them. I haven't heard of any problems with this pressure/factory wheel combination.
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Old 01-26-2008, 12:06 PM   #5
grakin
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Okay, maybe I'll be another test point then - running the Goodyears at 60 PSI. We'll see how they hold up...so far, with around 10,000 miles on them, they are doing great, but i'm pretty careful about tire inflation (both trailer tires get checked at every gas stop).

EDIT: The 10,000 miles are at 50 psi
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Old 01-26-2008, 12:34 PM   #6
Virginia Deacon
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Default Speed Issue

Hi Joel!

You said, "I hate towing faster than 65 MPH, but in this area of the country it's a bit risky to go that slow sometimes, and would like the extra margin."

I've found that no matter how fast I travel, there's always someone who insists on traveling 10 mph faster. Two points here: (1) I simply don't tow our TrailManor over 65 mph; it's a matter of being in control of tow vehicle (4000 lbs) and TrailManor (3500 lbs) vs. being out-of-control. Also, I believe the speed rating for the TrailManor tires is 65 mph, and (2) I refuse to let another driver (including semis) "drive" my car, by their actions.

Remember, at 60 mph we are traveling 88 feet per second! That's not "slow."

Happy Camping! Spring will be here before we know it!
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Old 01-27-2008, 07:52 PM   #7
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In California the top trailer towing speed is 55MPH so when I tow here I try to keep it under 60. We've been to East Texas a couple of times, to the East coast and down the atlantic coast and up the pacific coast into Oregon. All with the original Goodyear Marathons. I keep them inflated to 60PSI cold and check them each day we travel before leaving. The only flat I've had was in the trailer storage area at home and it turned out to be a torn valve stem. The curb side tire has a little more irregular wear than the street side tire due to there be more irregularities in the highway pavement on the curb side. Also a little bit of "cupping" which my trailer guy says is due to bounce. The wheels have never been balanced and after being looked at by my trailer maintenance person and a tire shop, they both said they didn't think it was necessary and never do it. They did say if the wear on the curb side got noticebly worse we could swap the curb side tire to the street side or get into a rotation schedule with the spare.
so far I have no complaints about the tires.
Dan
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