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Old 01-16-2008, 11:25 AM   #1
saltamonte
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Default Tire Size Upgrade Etc.

Today I have my unit in a wheel and axle shop in Deep South Texas. I'm changing from 14 to 15 inch tires, so once this is done I'll make a posting of the success or failure of this exercise.

I don't expect a problem with tire clearance, as others have done this successfully. I was concerned about the bigger tire hitting the skirt, but it seems I'll be okay here as well. I'm going for the load bearing capability and overall better performance with the 15 inch tires. I've noticed numerous postings about tire failures and want to avoid that malady at all cost. I'll be traveling in Mexico and as we all know the roads there are often very poor.

I'm waiting for a call from the shop owner to let me know what brand tires are available, as I told him I wanted Prometer or anything other than Marathon. He told me that Brands have little meaning to him, as different manufactures will slap this name or that on a tire. He personally uses Marathons (not on a TM) and has put thousands of miles on them without problem.

I told him I'll go with the 15 inch Marathons if there is a long wait for anything else. He further mentioned that most all of the small trailer tires had blow out problems a few years ago, but this has now been sorted out.

Furthermore, I'm going with load range D, as load range E (10 ply) would be overkill and the recommened tire pressure with these would likely beat the unit up with a hard ride.

This is uncharted territory for me, so I'll have to see how things work out before making further comments. I see that many other owners have the same unit as mine and have had little trouble with the tire size upgrade, so I'm optimistic about the outcome. I'll post later with my overall experience, as it likely will be helpful to others considering the same modification.

Bill has been a great source of information for this and other TM related issues and I want to publicly thank him for his knowledge and support. Also, I'm very grateful for the postings of others and the TM Forum generally, as its provided me with a wealth of information that may have helped me avoid future problems on the road.

Dan

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Old 01-17-2008, 03:11 PM   #2
rickst29
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If you're concerned about bad "road" (ahem!) conditions down there, you might want to invest in a TPMS (Tire Pressure Monitor System). Catch any punctures and sudden pressure loss before huge damage occurs.

On my 2619, which we load very heavily, the correct pressure for the tire loading is usually less than 50 PSI. (In fact, the Goodyear Table recommendion usually works out to less than 45 PSI.) So although the class-D 15" tires are capable of 65 PSI, running rock-hard like that tends to shake the TM and contents more than you'll like.

It's also a bit of a safety issue, the contact patch with the ground is to small.

And I'll SWAG that maybe it's a bit of a tire issue too: Marathons are made to run with a certain amount of flex in the sidewalls, and driving gazillions of miles on "bad" roads with no flex and high pressure might not be good for the tires. Maybe WmTire can chime in-- does this SWAG make sense or am I blowing smoke (about the tires themselves)?

In any case, though, you're not gonna want 65 PSI for the two reasons I listed above. (Except maybe when crusing fast on smooth freeways.)
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Old 01-18-2008, 07:00 AM   #3
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Wonder why the TrailManor factory doesn't offer 15" tires as a factory option? Does anyone know if there is a compelling reason not to do so? Would be nice to enjoy the benefits and safety of traveling with our 3326K without being concerned about being over loaded. As it is, we travel near the maximum load capacity and that is with an empty water tank. Do very much enjoy our 3326K though. It is one great travel trailer.
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Old 01-18-2008, 07:44 AM   #4
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Quote:
Originally Posted by Dixielou View Post
Wonder why the TrailManor factory doesn't offer 15" tires as a factory option? Does anyone know if there is a compelling reason not to do so? Would be nice to enjoy the benefits and safety of traveling with our 3326K without being concerned about being over loaded. As it is, we travel near the maximum load capacity and that is with an empty water tank.
Dixielou,

Since the larger TMs have 2 axles, you have four 14" tires in the 3326k to distribute your load, up to about 4900 lbs. max. load capacity on your unit, with ~4400 lbs. on your TM axles (~4900 lbs. GVWR minus ~500 lbs. tongue weight). So that would leave you about 1100 lbs. per tire, well under the 1870 lb. per tire rating of the C rated 14" tires. Yes, it would still be better if they used 15" tires, but I would think the 3326 probably has the best "cushion" factor per tire than any other TM model, mainly because you are distributing the weight between tandem axles.

I guess my main concern is if you lost tire pressure in 1 tire, then the other tire on that is over its rated capacity....that could be a potential problem. The TMPS that rickst29 mentions above could help with that problem if a tire goes down slowly, or even if you aren't aware of a blow-out. I have the Doran system, and it is extra peace of mind during travel.

Chap
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Old 01-18-2008, 10:12 PM   #5
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Dan,
I certainly wish you success and I am very interested in your results. But I have to say that I will be surprised if the 15 inch tires and wheels give you the necessary clearance on a '07 2720sl with the 22.5 degree axle. As I noted in another post, we have the same model and our clearance (from the top of the wheel to the wheel well) is only TWO INCHES with the 14 inch wheels. I don't know who is telling you that the 15 inch tires will work unless they tell you that you should also have a lift kit installed. I also contacted Dexter and verified that we do have the 22.5 degree axle by using the axle numbers. Dexter also responded that a minimum 3 inches of clearance is required. I have also heard that the TM factory has changed to the 45 degree axle after using the 22.5 degree axle for only the '07's. What this suggests to me is that the factory did not engineer the '07 2720sl properly and did not discover that the 22.5 degree axle did not provide adequate clearance until sometime after manufacture. Please --- if the trailer has only two inches of clearance when equipped with little more than the factory options --- then we do have a problem. We have a problem even if we do nothing --- even if we hold onto the 14 inch wheels. I know that assumptions can be dangerous and I'm trying to see the whole picture. So --- before I express my concerns to the factory --- I hope to hear from you. I also want everyone to know that I think very highly of all of the folks at the factory who have assisted me this past year. I'm not trying to be a hardcase. If, however, there is an engineering problem --- and TM did not follow Dexter's axle guidelines when using even the 14 inch tires --- then I expect the factory to provide a solution for the '07 2720sl folks. I don't care how nice some of the folks at the factory are to work with. I don't think that it should be my responsibility to correct engineering and safety issues. I believe that the factory should then provide a lift kit and bear the cost of its installation. If what I have shared is true and if there is an engineering issue --- then TM should perhaps announce a recall and correct the defect for everyone who is affected. I'm not sure how this post will be viewed. It may be pulled because it casts a bit of a shadow on TM. I will be the one of the first to write a glowing recant if I am off-base on this. But this is a forum for opinions, ideas, and sometimes --- speculation. I am only searching for the truth and an answer. Dan, please post your results.
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Old 01-19-2008, 07:58 AM   #6
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Dan, apparently the 22.5 degree axles go back further than the 07s. After several of the posts over the last couple of days, it appears that my 2003 has the 22.5 degree axle, and I think Bill posted that his 2006 has it also. I don't remember if I checked the clearance before I added the lift kit, but I will check out the present clearance when the weather gets a little better. I imagine that my caculated figures (pre lift kit and 15 tires) will be close to that what yours are now.

Chap
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Old 01-19-2008, 10:07 AM   #7
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Eric (and others who are worried about tire clearance) -

I understand that you are upset. But there is a solution that doesn't involve re-engineering, or a lift kit, or a new axle, or anger. We discussed it some years ago, so I'm not surprised that you didn't see it. It works like this.

If you take off the wheel well cover on the side of your TM, you will see that there is plenty of clearance ahead of and behind the tire. The question is whether there is enough clearance between the top of the tire and the wheel well liner. If not, it should be pretty simple to raise the liner. It is not a structural part of the trailer in any sense - it is just a piece of molded plastic.

The wheel well liners are simply screwed to the floor inside the TM, and easily accessbile from inside the kitchen cabinets. So unscrew the liners from the floor, screw a piece of 1X1 hardwood to the floor where the liner used to go, and screw the liner back down on top of this lip. Bingo, you've gained an inch in tire clearance.

Though I haven't done it (haven't had to), I think that it really is that simple. When you are done, you will probably have to add a screw at the top of the wheel well cover, to hold it against the outside surface of the TM sidewall. And you may have to do some caulking where the liner used to meet the sidewall of the camper. But I don't think it is a big deal.

Bill
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Old 01-19-2008, 02:46 PM   #8
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BINGO.....Bill to the rescue!!! Probably a lot simpler than adding a lift kit.

Chap
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Old 01-19-2008, 05:00 PM   #9
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Bill, I appreciate your solution. So, between my full-time job and my weekend volunteer work, and sometime before or after I write my monthly, $300 check for our '07 trailer ---I should get the trailer out of the garage, set it up in the street, remove my fender wells, go to lumber yard for hardwood, and make the necessary repairs for another factory decision. I'm sorry to wax sarcastic but it sure seems that the factory gets more than its fair share of grace. In kindness and with the best of intentions you said, "fix it yourself". I will undoubtedly follow your advise and do just that.
Sometime after a long day and late into the night --- I'll fix it myself. I've already fixed quite a few factory Oops. I've held my center but I've still let my feelings be known. It would sure be nice if the factory decision-makers could share my experience in all those late-night repair episodes. It would be nice if they gave up their warms beds to work beside me. This would be accountability that I would welcome. There is a gift in all of this. I just haven't found it yet. Eric
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Old 01-20-2008, 05:15 AM   #10
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Hay Eric be carfull, Bill will start to delete all of you posts, as he does most of mine.
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