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Discussion Starter #1
So I am planning on attending the West Coast Camp Commander (as long as the work gods cooperate). Since my last major 4X4 adventure I have added some mods, and as I am sure many of you can relate to, ran out of funds.

I was looking for a good way to mount a spare, still use my enclosed roof box, and tow my travel trailer. This did away with my thoughts of throwing the spare in a roof basket, or using a hitch mount spare tire carrier.

I measured the old stock tire mounted in the factory position under the rear and found it to be 29" in diameter. My brand new tires post-lift are 32". Since I am currently out of funds, and still in need of a great alternative form of transportation for a full sized spare, I came up with the thought that maybe, just maybe, 29" is close enough to full size for the purposes of a spare.

I haven't had a full time 4X4 before, so I am not sure how that kind of drive can be affected by a couple inch difference. I am sure someone out there is the type of person who likes math waaaaaaay more than I do (doesn't take much for that to happen) and will know something about how many rotations this difference becomes, how that affects the gearing, etc, etc. Those are just the potential things I could come up with, wouldn't suprise me if there are more.
 

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The Math

I'll let someone else tell you about the mechanical aspects, but here's the math.

But first, the stock tire is 29.5 inches so I'll use that length instead of 29".

Pi * diameter = circumference
Pi is approximately 3.14159

A 32 inch tire will travel 100.53 inches on the ground in one revolution.
A 29.5 inch tire will travel 92.68 inches on the ground in one revolution.

That's roughly an 8% difference.

I don't know if the differentials can handle that or not, but at most, I would only use it to limp back to get a flat repaired or buy a new full size tire.

Do you have QT II or QD II 4x4 system?

Edit to add: If you have QTII, I think you would be ok. I think they have open axle diff's and if so, then turn the traction control off. And keep it in HI range. Hopefully, more knowledgeable people will be along to post shortly and correct me if necessary.
 

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Here's another thought, if you had a problem on the trail, the 32" tire is pretty popular and I bet someone would loan you a spare until you get back to town to get a new one or repair.

Of course if it happened on the road, your on your own.

And if you have QDII with Electronic Limited Slip Diff's, I don't think I would do it. I bought a used 32 inch tire from Discount and had that for a spare for a few months. It cost about $45. Of course, that doesn't solve your stowing problem. I mounted my spare on the roof rack.
 

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In talking to a local transmission shop in town, he warned me against doing that. He said you will tear the drivetrain (especially the front diff) up rather quickly running mis-matched tires.

If you have a 2 wheel drive or if we had the ability to take the Commanders out of 4 wheel drive you could get by with it but since they are a full time four wheel drive and it electronically shifts torque around between the 4 wheels, you will run into issues.

I'm sure someone else will be along here that is more knowledgeable than I am but I figured I'd pass on what I've been told.
 

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I
Up to what size tire can the spare wheel well hold?
245/75/17 fits without a hitch receiver from personal experience. Any taller and you may have issues... with or without a hitch.
 

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Discussion Starter #7
Wheel hole

My 29" inch spare (might be a 29.5 tire as stated by GP, but actual tape measured diameter on my particular tire is 29" - worn maybe?) leaves only about 3/4" clearance on one side and about 1/2" clearance on another fitting into the underbelly recess. I looked at the items a larger tire would be rubbing and there is no such easy fix as a little grinding or bending either.
 

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Consider doing what I did...my 245/75 (about 31.5" I think) fits underneath with a hitch after deflating the tire a bit and slightly pushing it in around the hitch. It's not deformed enough to cause any damage to the tire, and when I need it, I'll inflate it with the $25 "Slime" portable air pump I purchased. Stormtrooper has fit a 265/70 in the stock spare location as well, although he trimmed the back of the hitch receiver as well. Good luck.
 

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Discussion Starter #9
I like this idea as well. Any Techies out there have any problems with this solution?
 

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Deflating a bigger spare is an excellent solution. You can even use some cinching ratchets to really squeeze it down if necessary.

For what it's worth, I personally have QDII and run with an undersized spare. I've had assurances from a Jeep engineer involved in designing the system that I'd be fine for limping off the trail like this until I could get my full-size rubber repaired. Not having a big ol' 5th tire saves me a lot of cash and room, not to mention I'm carrying less weight -- especially if getting a full-sizer means getting more steel in the form of carriers. Blech. Lighter is always better.

Besides, in my decades of Jeeping I have never had a flat on the trail. Nor can I recall ever having been with someone who did. One likes to be ready for a rainy day, of course, but not at much cost!
 

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I have stock 245 65 17's on the mine and they state the height at 29.5". Just crawled under it and there is 1" before it hits the back of the hitch and the muffler has a heat shield that could be coaxed back a bit to fit up to a 30.5" tire under there. Any tire larger would need some cutting donw to the hitch and bolts or as stated earlier deflation. When I go to the 265 70 17 on mine I will use the deflation method or as El Cid put it, use the current spare and limp to a close suitable place for repair.
 

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Consider doing what I did...my 245/75 (about 31.5" I think) fits underneath with a hitch after deflating the tire a bit and slightly pushing it in around the hitch. It's not deformed enough to cause any damage to the tire, and when I need it, I'll inflate it with the $25 "Slime" portable air pump I purchased. Stormtrooper has fit a 265/70 in the stock spare location as well, although he trimmed the back of the hitch receiver as well. Good luck.
I have stock 245 65 17's on the mine and they state the height at 29.5". Just crawled under it and there is 1" before it hits the back of the hitch and the muffler has a heat shield that could be coaxed back a bit to fit up to a 30.5" tire under there. Any tire larger would need some cutting donw to the hitch and bolts or as stated earlier deflation. When I go to the 265 70 17 on mine I will use the deflation method or as El Cid put it, use the current spare and limp to a close suitable place for repair.
So, call me stupid but I still do not fully understand what hitch component(s) do not fit with a larger spare tire.

Will the OEM hitch receiver by itself fit with a fully inflated 245/75/17 tire?

Do the hitch mounting bolts interfere and simply need to be shortened or is it the ball hitch interferes with the tire when installed?

Any pictures? I seem to have about 1/2" of clearance between my 245/75/17 SlientArmor spare and the cross member right now.

 

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Do you have a trailer hitch on the back of your XK? It's hard to tell by the picture.
 

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Do you have a trailer hitch on the back of your XK? It's hard to tell by the picture.
Not yet... wondering whether it will fit or not with my bigger tire tucked under the truck.

Did you upsize the spare with the OEM hitch? How does it fit?
 

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So, call me stupid but I still do not fully understand what hitch component(s) do not fit with a larger spare tire.

Do the hitch mounting bolts interfere and simply need to be shortened or is it the ball hitch interferes with the tire when installed?

The 4 mounting bolts as well as the square tube part of the receiver is what will cause the interference. By looking at mine, it appears that you could cut off the ends of the mounting bolts. Also, depending on the length of your ball mount (how far does it actually go into the receiver), it may be possible to cut off about an inch from the receiver tube. I have a Reese ball mount with a 3.25 inch drop, and I can not feel the end of it inside the receiver tube. So, in my case, it would be possible to cut some of it off, but I do not know if doing this would compromise the integrity of the receiver. Maybe someone can chime in on this.:eek:rangehat:
 

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As long as you cut the excess tube off after the weld it should not interfere with the integrity of the hitch as that section does not carry any load. Also just turning the bolts around and having the bolt head on the tire side should help. Well thats my take on it but I am no engineer.
 

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Does anyone have a success story with installing the OEM hitch with a 245/75/17 spare tire fully inflated? I am guessing the answer is no.
 

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I have the OEM hitch installed and am running a fully inflated P245/65r17 tire for a spare -- with at least .5" room all the way around it. Depends on the wear on your spare, then, but it should just barely fit.
 

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Just realized you were asking about a 75r17, whereas I was thinking you were asking about a 70r17. That might be stretching things without some physical adjustment of the surrounds.
 

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I don't think you're going to hear any success stories with this exact situation. The back of the receiver housing is about an inch or so too long and a fully inflated 245/75 will not wedge between it and the metal crossbar on the opposite side of the spare well. If you angle the tire so it clears the hitch first, you can get it to a point where it is unobtrusive for just daily city driving, but the lower end of the angled tire dangles down further than I'd be comfortable with for trails and such.

I've been running my setup deflated for a while now with no problems, other than the "Spare Low Pressure" warning in the EVIC. But, I had a flat a couple weeks ago, and I changed it out, inflated it with the portable compressor, and remounted in less than 20 mins...it's not a bad way to go if you can deal with the EVIC message. My thoughts...
 
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