I was wondering what most people do for spare tires? I did do a search and found some good info...confirming the use of tubes and such. But some clubs require the use of spare tires and here in the North East with limited open space sometimes a club event can get you into otherwise "off limit" areas. If I run 36/12.5 SX's I will run a 34/9.5 spare fully aired up and of course carry tire plugs, tubes, and a sewing kit to sew up a gash. Buuuut, if I run a 38/12.5 SX, which I am most likely going to run, could I still get away with a 34/9.5 spare fully aired up and air down the remaining tires? I do have Detroits lockers in both axles so I realize I need to keep tire heights almost equal. I am trying to keep the spare tire diameter down and a 34/9.5 I think would work well and not block rear visibility hanging off the carrier too much. Thanks for any input! John

You could keep your smaller spare, but only use it on the front with that hub unlocked. That might mean changing 2 tires if you ruin a rear, that would suck on the trail. My advice is run the same spare as the rest of the tires. One time I had one rear tire about 8 pds lower than the other and my detroit did not like it at all. Made awful noises.

-Jeremy

We just finished throwing my spare in the tub yesterday. I have a Tuffy box that was in the back. We cut out the bottom of the box and welded it higher in the box to form a shelf. Then bolted it in the tub with enough clearence to get my 35X12.5 MTR out and in. It works great for us. We saved a lot of weight by getting rid of the swing out and cutting down on the amount of tools that was carried.

I'm getting into this delemma right now john...I just ordered my 38" TSL's this week, and didnt bother buying a 5th since I wont be on the trail for a little while (ie save some money) and I ahvent figured out where I'm putting it yet.

I fabbed a tire carrier that is capable of handling the beast, but it mounts such a tire high enough as to not effect departure, and all ow tow jerry cans to be mounted beneath it. (angles the tire forward a bit)
This compromises visibility on the trial...not soi much a wheeling problem, it a spotter, or "spectator behind me problem.
Almost run over a couple of people with this set up.

So I am shitcanning the tire carrier I think...just going to put the spare inboard.
I'm gonna run a fullsize and just deal with it.

A buddy (Charly on here) is mounting his spare (when he gets one) standing up behind the driver.
This is a good idea I think, and I am seriously thinking about hijacking it for my own purposes.

Reason being...I am moving my stock 20 gallon CJ tank up some into the tub at some point...this will take up even more "tool and spare part" area.

Its a conundrum.

MJ

Its not so much the height that should be kept equal but the circumference. Airing down a tire isn't going to appreciably change the circumference (maybe a quarter inch at most) so the bigger tire will still travel further than the smaller spare for each revolution. It will work in a pinch if you have an open diff but lockers don't really like it too much.

Here are the figures...roughly:
34" tire = 106 inch circumference
36" tire = 113 inches
38" tire = 119 inches

So a 38 inch tall tire will travel about 119 inches per revolution while that small 34" spare is only going to go about 106 inches. May not seem like much but it adds up quickly.

-Jeff

Uh, if the diameter of a tire changes so does its circumference. Circumference = Diameter * Pie. Change one change the other. Although you are mostly right. A fully aired up tire has approximately the same unloaded ( off vehicle ) diameter as a aired down one. The rubber only spreads so much.


Ben

All very good ideas, I will have to see what I end up with as far as space in the tub (bed) of my bobbed CJ8, I know I have some extra room from you CJ7 guys but only like 10 inches.
That is what I was thinking air down my running tires and keep the spare fully inflated to be about equal to each other. That is only in a pinch if the tubes and etc. don't work.....I will be beadlocked. Thanks all for your input and some very good points too! John

That Pi * Diameter formula assumes you are still dealing with a circle. As we all know, airing down the tire will elongate the footprint of the tire, thus making it not round anymore. You still have the same circumference, it is just in a different shape.

Unless you air down enough to have folds in the tread, the circumference will remain mostly a constant, give or take a tiny bit of stretch.

-Jeff