Replacing 14" Marathons with 15" Marathons

Last weekend I had a blowout. I'm guessing the tires are from 2003 as I bought the TM used. It was a short two hour drive, without the flat, and changing the tire on the side of the freeway was no joy but better than in the middle of nowhere on the way to UT. While just finishing up someone honked as they went by. Another TM, the first I've seen.

So I've been debating on whether to buy another spare or go to 15s. To help me decide I did a bit of math.

2870 dry weight from memory but all are guesses
100 AC unit
50 awning
100 batteries and propane
200 water
100 food and personal items probably way low as just the bikes and rack were that much. I didn't take my generator either.

3420 total if my math is right. You could argue up or down on all of these but you get the idea.

Two 14" Load range C tires at 1870 each is 3740. Now say your tires are underinflated to 45psi which is 5psi or 10% under. We would expect the load capacity to decrease by 10% or 374 making only 3366. So it's not hard to go over the tire capacity and the margin for error is very slim.

I don't know how I can, in good conscience, rely on this setup and feel relaxed on a vacation. I think it's time to fix TM's oversight.

And another thing, my swing arms appear to contact the TM 2" lift blocks. That must reduce wheel travel and put more strain on the tires too when that arm slams to a stop. No wonder the tire gave out on that hot day traveling up the very bumpy LA 101.

Your math computations got me curious. When I looked up a 2720SL on the trailmanor website, the specs state it has a dry weight of 2865 lbs. What catches my eye is the spec that states it has an Approx Load Capacity of 1210 lbs. 2865 + 1210 = 4075, which is over the carrying capacity of the OE 14 inch tires. I'm confident that the Load Capacity spec pertains only to a parked/camping state, including people's weight inside, and wouldn't mean towing weight. Does anyone know for sure?

It seems that the ones who have went upwards to the 15's (that had the room for the taller tires) are doing well early on in the experiment. So are the ones who have upgraded to the Euro sized 14 inch Load Range D tires.

I also don't want to lose sight of Freedom's solution of using Bias Load Range D (I believe this is what he is using) tires. Bias tires have tougher sidewalls.

Whatever decision you make for replacement tires, I hope you will let us all know, so we can keep tabs. It will be several years down the road until we can really tell if these changes work better.

Thanks

[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

fwiw, my 2005 TM 2720 fully loaded with all the camping gear I own weighed 3380 pounds on the axle the one time I weighed it.

Besides base weight I had the following:
swing tongue
awning
over sink cabinet
microwave drawer
40 gallons fresh water
6 gallons water heater
charged toilet
free standing awning
8 camp chairs
3 camp tables
Honda 2000 generator
3 cases of bottled drinking water
an untold quantity of my favorite cold beverage
a well stocked bar
2 full propane tanks
dual group 24 batteries on the tongue
a well stocked assortment of canned food, just in case someone stops by
pots, pans, etc.
clothes for DW and I for a week
portable BBQ with bag of briquettes

I was trying to simulate a week long camping trip for DW and I, plus DD(26) and DS(24) plus their significant other.

Based on this one experiment, I believe that in order to exceed the documented capacity of the TM, you would have to be a rock collector.

I no longer weigh it, because I have no doubt it always weighs less than it did on this trip.

I did not weigh the tongue.

I do not use a WD hitch. The sag at my rear bumper of my truck is about 5/8 inch. The front bumper rises about 3/8 inch as I recall.

You can easily measure the weight on the tires. Measuring the weight on the axle is more difficult, because the weight of the axle and wheels is not on the axle.

[Bill]

Bobby wrote

What catches my eye is the spec that states it has an Approx Load Capacity of 1210 lbs. 2865 + 1210 = 4075, which is over the carrying capacity of the OE 14 inch tires.

Bobby -

I don't have any specific info, but the coincidence is too much to ignore. It looks to me like the spec on Load Capacity was obtained by working backward from the tire capacity, assuming that with a WDH, 10% of the dead weight of the trailer is carried by the hitch. In other words, if the total weight is 4075, but 10% (407 pounds) is carried by the hitch, then 3667 pounds is carried by the tires. This is remarkably close to the tires' rating of 3740 pounds.

Again, I have no specific information, so it is just my surmise. But it makes sense to me.

When in a campground, the load on the tires is less, since the tongue weight (14% of the total) comes down entirely on the ground, not the tires. There is no WDH to reflect some of the tongue weight back to the tires.

Bill

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.

Yep Bill, I actually did forget that. They say that's the second sign of old age. I can't remember what the first one is.

Ok I got a set of 15"x6" wheels rated at 2150 each. $36ea. Tires are Nanco ST225/75D bias with 4 sidwall plies and 6 tread. $63ea. Max load 2540 at 65psi. S seems to imply speed rating of 112mph. They fit with my 2" lift and have more room at the skirt than the 14" radials. Spare fits in rack no problem.

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.

I'll post pics in my gallery later. <Done but the before and after look the same really so I just posted a comparison.>

Originally Posted by larsdennert

Ok I got a set of 15"x6" wheels rated at 2150 each. $36ea. Tires are Nanco ST225/75D bias with 4 sidwall plies and 6 tread. $63ea. Max load 2540 at 65psi. S seems to imply speed rating of 112mph. They fit with my 2" lift and have more room at the skirt than the 14" radials. Spare fits in rack no problem.

I moved the lift spacers because the arms hit. You all may want to check that.

I'll post pics in my gallery later.

Larsdennert, if you are referring to the "S" on the 'ST" designation on your tire, it won't be a speed rating as in a passenger tire. ST means Special Trailer. This let's you know that the tire is designed for trailer use only, and not to use it on your vehicle. I haven't seen a trailer tire yet (but that doesn't mean that don't make one), that carries the specific ST designation, that is rated for anything over 65 mph. We kinda touched on that when we were talking about using LT or the Euro sized tires in other forums.

We have also been debating a point on using the maximum inflation for our upgraded ST tires, that should carry much more weight than the OE tires did. Well, I found an article from 2001 Camping Life Magazine that shows that the engineers from different manufacturers also differ on this as well. Some say always use the maximum air pressure, while others say use needed pressure to safely carry whatever load you have........which is the same thing we are discussing.

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

Please keep us informed of how the Nanco Bias Ply tires do for you.

Good point on the speed rating. That's confusing but I wasn't planning on doing 112 anyway LOL. I noticed too that I forgot to subtract the tongue weight on my post about overloading the 14s. That 300 lbs isn't caried by the TM tires.

Originally Posted by larsdennert

Good point on the speed rating. That's confusing

I agree, it's all becoming confusing about tires.....especially these Tire Pressure Monitoring Systems (TPMS) that every vehicle manufactured with a gvw under 10,000 lbs now has since September. We had a customer yesterday who had bought himself a new set of fancy schmancy (not sure if spelled correct) wheels for his new Ford pickup. The place where he bought these wheels, didn't put his sensors back onto these aftermarket wheels (which they wouldn't have fit anyway). He brings his vehicle into us, expecting us to be able to turn his now ever-illuminated dashboard tire pressure light off for him.

I inform him, even if I knew how to bypass it (which I don't), that it would be against the law. However, it's not against the law for the aftermarket wheels installer to not have to reuse his sensors. Now that's crazy......but true. You can legally do away with the sensors, but not bypass the system.

I advised him, of two options. He could carry all 4 of his original tire/wheels in the back of his truck, so they could transmit an OK to the onboard computer or place a piece of electrical tape over the dashboard light.

OK, enough ranting on my part, and really this doesn't even fit this forum topic. If an administrator wants to delete it, then that's OK.