Forget spare parts, in my opinion, if you're really carrying all the necessary tools to work on a Jeep AS WELL AS the fluids YOU NEED and simply can't MacGyver or make out of thin air, there's no way you have enough room to carry a 40" spare inside your Jeep. I carry just what I need and in the most compact form possible and at least for me, there would be no way I could do it. Likewise, if you're actually playing on the kind of terrain that requires 40's, you're kidding yourself if you think you won't ever get a flat or that you could just go back to your trailer and get it if needed.
At only 3 miles in length, a trail like Devil's Canyon is one I would consider to be short but it is one that will give a JK on 40's a hard time. If you break or have a flat in it, you're working on it right there and there's no having some turn around let alone having them wheel all the way back over everything you just came over, just to get your 40" spare back at your trailer and then wheel it all the way back to you. Sure, you might be able to walk the 5 miles to the closest place you could have parked your trailer and then carried it back but it would be in triple digit heat and all the while, you'd be "that guy" blocking the trail for everyone else.
A lot of the trails out in Johnson Valley are like this as well as out in Florence Junction. If you only play up in the mountains, I would say there are parts of Fordyce that are like this and then there's always Carnage Canyon. Whatever benefit you think you'll see by not having to carry a 125 lbs. spare will be a moot point once you're in need of it. If nothing else, for everyone else's sake, please don't be "that guy" on the trail.
