More Marathon tire failures

[fcatwo]

Bill

Thanks for not being offended by my attempt at humor. Re your questions: TMO member Senorsedona is the only person I know of who actually replaced his 215s with 225s. He reported good results although I think he traded up soon after. I'm almost sure he had the lift kit.

I spent many hours researching the possibility of switching when I bought new tires a few months ago but finally decided to stay with the 215s -- primarily because we have had no tire problems in 25-30K miles and 5yrs of TM towing. I don't know why we've been so lucky but we do travel lighter than most and avoid hot weather. I don't know if it matters but we also use a 600lb WDH which may be a little easier on the TM tires. I pulled my wheels and took them in to have the new tires mounted and balanced and found that getting the 215s off and on without removing the skirts was borderline even though we have the lift kit. I suspect you'd have to remove the skirts with 225s.

mtnguy

It's not a big deal but I think the 225s are only 0.3 wider than the 215s and not 0.8 (8.8 vs 8.5). They are significantly taller however and the lift kit is probably mandatory for their us. For info: I recall that RMR asked the TM factory at one time about using 225 tires on their 3500lb axles and was told they had not tested that combination and could not recommend it. IMO Bill has thoroughly tested the 215s on the 3500lb axle and found them wanting so it's time for the factory to get with the program. I can't answer the question about any possible offset difference between the 14" and 15" 5X4&1/2 rims. I planned to take one of my 14s to Camping World and compare it to a 15 to make sure they are the same but never reached that point. I should mention the the 15" rims are only about $40.00 each and the 225 tires are only about $10.00 more than 215s -- so it's a $150.00 upgrade at tire change time or a $500.00 upgrade otherwise.

wmtire

Thanks for sharing your professional expertise. I'm sure you have other things to do but don't forget us. We have Bill and a couple of others who know electricity and electronics but you are the first tire professional I recall seeing here. I think we also have an engineer or two and even a metalurgist but they are cautious about their postings.

Originally Posted by fcatwo

Bill

mtnguy

It's not a big deal but I think the 225s are only 0.3 wider than the 215s and not 0.8 (8.8 vs 8.5). They are significantly taller however and the lift kit is probably mandatory for their us. For info: I recall that RMR asked the TM factory at one time about using 225 tires on their 3500lb axles and was told they had not tested that combination and could not recommend it. IMO Bill has thoroughly tested the 215s on the 3500lb axle and found them wanting so it's time for the factory to get with the program. I can't answer the question about any possible offset difference between the 215 and 225 5X4&1/2 wheels. I was going to take one of my 14s to Camping World and compare them to make sure they are the same before switching but never reached that point.

FCATWO, let me give you a tire conversion formula we use everyday, to tell the difference between heights for tires. On a metric size tire Ex:215/75 15, the 215 is the section width in millimeters(215 millimeters), the 75 is the aspect ratio(which is the height of one sidewall from the rim to tread, or easier to remember as a percentage, 75% in this case), the 15 is the rim diameter. Ok, let's convert it to inches and get the approx diameter of the tire.

section width X aspect ratio X 2 (you have to include both sidewalls from the center of the rim)=?

Take the result and divide it by 2540. This is how you convert it over to inches. They're are 25.40 mm to an inch. If we take out the decimal at the last step, it saves on the next one.

Take this result and add it back to whatever the rim diameter is. In this case 15. Everything before this had just gave us the measurements of the sidewall (x 2), now we need to add the diameter of the middle of the tire or rim. The rim is already in inches, so we don't do any conversions, just straight adding.

If I punched my calculator right, then I got a 215/75 15 tire is appro. 27.70 inches tall. If I want to know the width, all I do is divide 215 by 25.40. Remember I said there were 25.40 mm to an inch.

Another thing to remember in comparing the differences between 2 tires (circles) is overall diameter difference is half of what difference you get in lift. Say there is a 1 inch difference in total diameter for two tires. This works out to be a half inch from the center to the top and a half inch from the center to the bottom. To visualize this, stand a penny beside a quarter, and notice how much difference. Now place the center(the hub) of the penny on the center of the quarter. You see it's only half to the bottom and top. A 1 inch difference in tire diameter, gives you a half inch difference in total lift of the trailer.

Here it is again

section width X aspect ratio X 2
------------------------------- + rim diameter =appr diameter (height)
2540


I say approx. because different tire manufacturers calculate their section width and/or aspect ratio at different points. Supposedly, the section width is the distance between the two bulging sidewalls at loaded status, but different tires have more bulge than others when loaded. The above formula will give you accurate results if you use the same brand and model to compare with. It'll be close when comparing two different brands, but not as accurate.

After you practice with this a few times, you can do it quickly. Here it is as per example

215 X 75 X 2
------------- = 12.70 + 15 = 27.70 diameter
2540

I threw the tread on a Marathon last fall on my 04 3326 (dual axles). The tire was about new at TM manufacture, Sept '03. So it was 3 years old at the time of failure. It ripped out my grey and black plumbing in the deal. When I got home, I noted the other tire on the same side wasn't round. It was in the process of throwing tread also.

One problem with trailer tire failures is that unlike in a car, you don't get any "feeling" when the tire is going bad. The first indication is the blowout. For this reason, I suggest another check for tires whenever you do a pressure check: run your hands around the tire feeling for bumps or lumps. It turns out that your hands are quite good at detecting these. It could give you a warning several hundred miles before the blowout.

I also have another check for tires, looking for early indications of failure. I bought an infrared thermometer at Radio Shack and try to remember to take it along with me in the TV. Then, I walk around the rig at a rest stop or filling station and quickly check the temperature of the tires and axles of the TM and the TV. I am looking for an unusually hot tire which would indicate it has lost pressure. I am also looking for a locked brake or hot bearing on the TM. In spite of this, I had the two tire failures last fall. I am sure they were not due to low pressure. In fact, I caught the second tread separation on a tire that was properly inflated. By the way, the only high temperature I have seen was right after getting my wheels packed when I saw 179 degrees F on one axle. They normally run 130 F or less here in the Az summer. The bearing must have been set too tight. Next time I checked, it was normal and just like the other 3 axles.

I put Carlisle tires on and don't have enough miles on them to give much of a report at this time. The 3326 with two axles has a huge weight margin on the tires. My TM weighed 3900# loaded last summer with a tire rating of 4X1870=7480#.

Originally Posted by BobRederick

In spite of this, I had the two tire failures last fall. I am sure they were not due to low pressure. In fact, I caught the second tread separation on a tire that was properly inflated. .

Bob, we have done an unscientific, real world test on tires (usually not trailer tires though) that come into our shop with the tread separated, that will probably fly in the face of conventional wisdom. If they haven't lost air pressure, we measure it. The majority of separated tires aren't underinflated, but the opposite...they are overinflated, sometimes WAY overinflated. I see a lot of times that people will air a radial tire up visually and not use an air gauge. All radial tires have a "squat" to them, that most people think is underinflation. They air them up till the squat is gone, which is dangerously overinflated. When you overinflate a tire drastically, you basically pull the belts away from the rubber. The tire is made to flex, but usually in a certain direction, which isn't the direction you are pushing it with air pressure., which pulls the rubber away from the belts.

When a tire is way overinflated, there isn't an immediate noticeable result of separation, but the underlying damage is done nonetheless. Even if you correct the inflation, most likely the tire will come apart within 30-60 days in my experience. There will be other factors that contribute to this including use and temperature. When we catch a customers vehicle that is way overinflated, we give them our prediction on what is going to happen with their tires.....and we're usually correct.

There are 2 more considerations in inflating a tire to think about. Air, as with most gases, expands as it gets hot. When you drive greater distances and in hotter climates, the air pressure inside the tire will increase due to this expansion. If you know you are going to be in conditions that the tire will get hotter for extended lengths, it is a good idea to let a few pounds out before driving, to allow for the expansion. Tires technically have a built in reserve capacity for overinflation, but I see this exceeded due to air expansion and incorrect inflations. Always check your tire pressure before trips, when it is technically cold pressure, to get an accurate reading. Make adjustments from cold pressure, not hot expanded pressures (unless absolutely necessary).

Another thing is maximum air pressure on tires. Maximum air pressure listed on a tire doesn't necessary mean operating pressure. A tire is manufactured for a wide array of different applications and weights. A tire may run the maximum for one application but less for another. Most charts just show the maximum air pressure and corresponding load. Maximum air pressure means just that----the maximum that it is tested to safely operate under a certain weight condition. Recommended inflation for your application (in this case the trailmanor), is what the manufacturer recommends to safely and comfortably carry the load. Most of the time, it won't be the maximum.

Sometimes the manufacturer recommendation is incorrect, as time will tell. Remember the Firestone/Ford deal? A lot of it could have been avoided had everyone not used 26 psi as Ford recommended and Firestone agreed to at the time. They both learned and bought a lesson with other people's lives on that one.

It was also discovered that Ford spec'd the tire without a nylon cap at the edge of the tread belt. It saved them a whole $2 bucks a tire. Firestone is just as culpable, because they sold the tires without it. Hindsight being 20-20, they should have said no to Ford, but they didn't....and probably are more guilty in a way. Ford doesn't build tires, Firestone does.

[rickst29]

Originally Posted by wmtire

The majority of separated tires aren't underinflated, but the opposite...they are overinflated, sometimes WAY overinflated.....

Recommended inflation for your application (in this case the trailmanor), is what the manufacturer recommends to safely and comfortably carry the load. Most of the time, it won't be the maximum.

Sometimes the manufacturer recommendation is incorrect....

Yep! Our Trailmanor info says to inflate the tires to Goodyear's max PSI all the time, but if you want to run SAFELY, with a properly-sized contact patch, you should instead tune the PSI downwards when you're not fully loaded.

Bad advice from TM has a lot of owners doing the wrong thing, see for example http://www.trailmanorowners.com/foru...ead.php?t=5411 (posts #4 and #6 emphasizing TM's bad advice, my post #8 quoting Goodyear's "tuning" recommendations).
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Thanks for your fantastic posts and research-- and BTW, I really LOVE your sig.