Replacing 14" Marathons with 15" Marathons - Page 7

fourteener · 07-30-2012, 07:48 AM

Well it is a success, I upgraded my 2007 2720 TM to the 15" tires & rims this weekend! We leave on an extended weekend trip this weekend. Hopefully when I get back I can synopsize the project with specs and pricing. I actually was able to complete everything in a long afternoon (approx 8 hrs).
Thanks for everyone's helpful guidance!

I've decided to make time to outline the upgrade, simply to help everyone with the specifications. Please note that you may be able to find a better or cheaper option, but after reading this long sting, this is what I decided to go with. See attached word document, and please note that I kept one of the 14" tire & wheels to serve as my spare (maybe next year's upgrade

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4Rajas · 07-31-2012, 01:52 PM

Thanks for your post! In the process of upgrading the 14" tires on my 2007 2720 to 225 75 R15's as well. Could you please confirm based on your experience:

1. Do you need to open the trailer to replace the tire to get easier access? Does it matter?
2. Did you try the spare tire holder in terms of it fitting the newer tire? Seen some posts where modifications were required.
3. What was the final clearance between the tire and sideskirt? I have over 3" above the tire for travel and with 2+" on the outside more than enough in theory.

**ShrimpBurrito** · 07-31-2012, 02:51 PM

Fourteener - great chart. I'm sure lots of folks will find that useful. And I am sure you did yourself a great service by making the jump to the 15" wheels. Did you happen to use at least a Grade 5 bolt for the lift kit? I am nearly certain TM supplies at least that, and maybe even Grade 8 (I can't remember), for the bolts that come with the lift kit.

Dave

07-31-2012, 06:26 PM

It appears that you did not replace the spare unless I missed something. Unless you already have 15" spare ( doesn't sound like it) you are going to be limited in how far/fast you travel if you have a flat.

fourteener · 08-01-2012, 09:56 AM

Quote:

Originally Posted by rumbleweed

It appears that you did not replace the spare unless I missed something. Unless you already have 15" spare ( doesn't sound like it) you are going to be limited in how far/fast you travel if you have a flat.

I did not replace the spare (this year anyway), even my 14" spare is tight, so I'm possitive when I go to make that upgrade I will need to modify the spare rack, but there are many great post on the mod. I've been told the 14" will be sufficient to get me to the next town that is enought to fix/replace a tire (sort of like the small donuts most cars are equiped with in the trunk).

I built the lift kit myself, as the TM factory couldn't locate any bolts and this would have caused a delay in the project that I didn't find acceptable. I had an existing 1-1/2"X12" aluminum block (factory lift) and I simply stacked a 2"X2"X18" heavy wall steel block on top of the existing. This brought my total lift to approx 3-1/2". This gave the top of the tire right at 3-1/2" of clearance with the trailer resting on it (as I wanted a minimum of 3" as directed from the above post). I was able to find Grade 8 5/8" fine thread bolts (exactly what TM orginally used) except they are now 5" long.

I would highly recommend having the trailer open for this modification, it will simply make the whole process easier. I had to, as I replaced the wheel wells also (as they were both damaged from past 14" blow-outs).

**Bill** · 08-02-2012, 08:49 AM

Quote:

Originally Posted by fourteener

I've been told the 14" will be sufficient to get me to the next town that is enought to fix/replace a tire (sort of like the small donuts most cars are equiped with in the trunk).

The 14-inch spare should be good for more than limp-home. It should be good for anything that the TM factory intended you to do with the original 14-inch tires - after all, it is exactly the same TM with exactly the same tire.

The reason you converted to 15-inch tires is that the 14-inchers were marginal for regular use, of course. But the conversion doesn't make them any more marginal.

Of course if you have a flat on a 15-inch tire and put the spare on in its place, you no longer have a spare. So just based on that alone, I wouldn't drive hundreds of miles. But the spare ahould be good for it, assuming it is properly inflated and not over aged.

On a TM, the two wheels are independent, meaning that the tires are not mounted on a common axle shaft. So the fact that they won't rotate at the same speed shouldn't cause any problems. And I don't think that the small side-to-side height difference (about 1/2 inch) will cause any problems, although I suppose over a long haul it might cause a bit of edge wear. WMTire may have better advice, which I will be glad to see.

Use care when travelling without a "spare" spare - but not fear.

Bill

fourteener · 03-24-2014, 10:21 PM

I just did some quick math that I just had to share, if this doesn't sell 15" tires, I don't know what will.

This is based on Goodyear Marathons:
14" are 26.1" diameter which is 81.95" circumference (or 6.83')
15" are 27.1" diameter which is 85.09" circumference (or 7.09')

Which doesn't look like a huge difference, but let's convert the difference to a single mile (5,280').

This means the 14" tire rotates 773.1 revolutions/mile,
And the 15" tire rotates 744.7 revolutions/mile.

That means the 15" tire makes 28.4 less revolution for every mile, or 2,840 less revolution/100 miles, and 2,840 less revolutions on my bearings! This would equate to a lot less heat build-up on the bearings also.

Yep, I'm so glad I made this modification!!!