Replacing 14" Marathons with 15" Marathons

[commodor47]

Originally Posted by wmtire

. . .

This article also reaffirms a lot of the conclusions we have came to from our forums, even about replacing the tires every 3-5 years regardless of tread.

http://www.discounttire.com/dtcs/inf...ionAnxiety.dos

Just finished reading that article. Great information . . . thanks for sharing.

Dick

Originally Posted by commodor47

Just finished reading that article. Great information . . . thanks for sharing.

Dick

You're welcome, Dick. The following excerpt from that article really stuck out with me.

"As an estimate, in about three years roughly one-third of a tire's strength is gone, just because of the normal process of aging," Fry claimed. "We believe three to five years is the projected life of normal trailer tires."

If this estimate is close to being true (and/or if the premise is factual), then the OE 14 inch tires that are already close to weight carrying capacity on our Trailmanors new, certainly don't have a third to spare as they age. Very interesting comment, and another reason to check the manufacture dates carefully.


EDIT: After really thinking hard about that comment, and I believe that it came from Goodyears guy, this might be something that Ed and the great people at Trailmanor should possibly look into when buying tires from Goodyear. I would think they would need a tire that has a 25 to 40% reserve margin for load. This should cover the tire from becoming overloaded due to the deteriorating as stated, and following their recommendation of replacing the tires every 3 years. Bill, and his engineer mind, can probably come up with the exact math.

Originally Posted by Bill

Lars and Bobby -

You have both mentioned total weight, but don't forget that something on the order of 14% of that weight is tongue weight, and comes down on the hitch, not the tires. But to confuse the issue a bit more, the weight distributing hitch (WDH) that almost all of us use pushes about 1/3 of that tongue weight back onto the TM tires. So in summary, the tires will end up carrying 90-91% of the total weight of the trailer. But not the total weight.

There is some margin, but I agree that it is pretty slim. By the way, according to the Goodyear web site, the 10% underinflation you describe does indeed decrease the load capacity - but not by 10%. Each tire goes from 1870 to 1790 pounds of capacity, so the total for the pair is reduced to 3580 pounds.

Lars, there have been a couple threads where TM owners have actually weighed their rigs, so you might consider those measurements as you estimate of the weight of your trailer. For example, I weighed mine and posted the result at

http://www.trailmanorowners.com/foru...ead.php?t=3144

There are other reports, too, and of course they all depend on the specific model and the way you pack.

Finally, I'm not sure what you mean when you say the "swing arms" contact the "lift blocks". Are the "swing arms" part of the axle, and the "lift blocks" mounted between the axle and the frame, in order to lift the TM body further off the ground? If so, I'm not sure how they could come into contact unless the lift blocks are too wide (wider than the frame rails) or installed off-center or crooked. Do you have a photo?

Bill

Somehow I missed reading a couple of posts. I think because only one gets emailed but there might be others...

Yes the stock TM lift blocks can stick out (too wide) and cause the swing arm where the brake and wheel is mounted to rub when the suspension is compressed. The holes in my blocks were big enough that I was able to loosen things up and slide them out of the way. Hopefully enough. I took a thin straight edge and estimated clearance and it's really close now. Maybe 1/32". The appliance side of the trailer had some serious material removed from the lift block and the weld seam where the stub axle is mounted in the swing arm. The blocks do mount between the axle and frame. They weren't crooked per se but are pretty wide and did stick out from where the other mounts were. The swing arm mounts to the cross tube axle by, what I assume is, a torsion bar in the cross tube.

There are a lot of potential variables in the weight calculation but all of them seem to come out to pretty slim margins. The load rating of 1200 lbs on the 2720 as someone pointed out must be rolling load and not standing. If it was standing load we'd have a big problem too. A 2720 can sleep six. 6 x 200lbs is already 1200lbs with none of the other mentioned items. When you are standing you have the jacks down too. A tire can take a very high static load anyway but put that load through a pot hole and it multiplies quickly which is what does a tire in. The 1870 per tire is the dynamic load the tire can handle. Interesting that reducing pressure by 10% doesn't reduce capacity by less than 5%. Must not be linear. How much load capacity does the tire have when it's 100% empty LOL? For sure the tire gets hotter so the amount of time it can carry that weight is reduced. I don't use a WDH as I have heavy duty springs and air springs in addition to those. I prefer to have the articulation available between the trailer and TV. The truck sits level with the TM attached. Seems like the extra load from the WDH could play a role under the right circumstance. I'm guessing that people with WDH's have a light weight TV and carry less "stuff" anyway. Ok long post...

Originally Posted by larsdennert

I moved the lift spacers because the arms hit. You all may want to check that. This issue has nothing to do with the tires.

After reading this post and another by larsdennert a week or so ago, I finally got under my TM to check for this. I appears that 1 side of my torque arm just barely touches the lift block under load/bounce....but I don't think enough on mine that I am going to move that lift block. But as larsnennert says.....you all might want to check that...it could cause a problem if it rubs bad.

I installed my lift kit myself, and didn't check for that......bad boy.

Larsdennert: Is your lift kit factory installed or a later addition??

Chap

It appears factory as it is painted the same color as the frame but I bought the TM used with it.

See the link below and make sure you download the Goodyear Service Bulletin pertaining to their Marathon tires. This may have been posted elsewhere, but thought folks ought to see it!!

Click on the link that says Goodyear Special Trailer Applications to download and read the memo.

http://www.tirerack.com/tires/tires....arathon+Radial

Instead of a flat spacer, what if you used a wedge shaped piece, mount it with the fat side toward the wheel edge and then mount your screws on the thin side hence forcing a bow? For wedges you could use pressure treated wood and epoxy them in place if you can't find metal ones.

I'm not sure who's post you are responding too but I certainly hope you are not referring to using wooden wedge shaped lift spacers. Wood is not strong enough by any means and wedge shaped would cause a bow in the axle (if you could actually get the fasteners tight enough to have things sit flush.) It would also cause a bad positive camber situation on the wheels which would probably overheat the tires in short order or if you're lucky just wear them out quickly. I must be not understanding your post...

larsdennert,

I hope fdxflyer is refering to Bill's fender skirt mod, instead of our lift kit posts.

Chap

[mjlaupp]

Originally Posted by Fdxflyer

Instead of a flat spacer, what if you used a wedge shaped piece, mount it with the fat side toward the wheel edge and then mount your screws on the thin side hence forcing a bow? For wedges you could use pressure treated wood and epoxy them in place if you can't find metal ones.

If you "force a bow" in the axle you will destroy the rubber torsion suspension built into the axle.

Repair will consist of replacing the axle.

Mike