There has been some discussin about fitting larger than stock tars into the factory tar tubs. Well, I'm here ta tell ya, it can be done!
If you look at the two front bolts that the tub swings down on, you will notice that they are threaded into the frame, with a "lock-nut" arrangement. Loosen the two bolts, leaving at least three-four threads sticking out on the other side of the frame. There are holes next to the bolts, so you can stick yer finger in them to tell how much is left. After you loosen the bolts, loosen the nut on the bolt, and tighten it up to the frame, to lock the bolt down.
The rear bolt that holds the rear part of the tub will screw out, too. There is(or should be) a roll pin in the end of it, to keep it from coming all the way out. Loosen this bolt all the way, put yer fatter than stock tar in the tub, and hook the rear bolt back up to the tub, and tighten it down as normal.
My car came wid G-70R15 tars, and the metric equivalent is a 225-70R15. It don't fit in da tub without lowering the tub some, but it do fit. The tub will now sit about 1"-1 1/2" lower, so you have to be careful of steep driveways and such, but you should be careful of that anyway!!
If anyone needs, I can go scoot under my car and take a pic to show what I mean... Adams' Apple38872.8755787037

Soooo....do that mean it makes sense, or it is totally non-unnerstandable (or, are you the goober that's gonna make me go crawl under my car for a pic? )
Is that snot dry?Adams' Apple38872.7610648148

What about a 255-60R15? That will make it fit also?

Dang....always somebody wid a problem!!
I don't know aboot one that big, Dwain. Try it and see if it will work for a truck tar!!
If not, I gots some balin war!!!
You could always let the air out of it. It would fit then. I'll have a small compressor on the trip.

 I was just thinking the same thing. Let the air out and pump it back up if needed. So... a 15X8 rim will fit without lowering the tub?

Dude....15x8 is the stock size. Why you gotta be such a troublemaker?
btw...you got that thang runnin yet?

Well.. if thats the stock size, letting the air out of the tire should make it fit, no?

Joel, just how much extra room would you say is in there after your low-
rider rear rolling stock restructuring?

Enough, say, to maybe/perhaps/hopefully squeeze in a 17" wheel and
deflated tire somewhere along the lines of a 245/45?

Having a totally empty spare tire carrier under the car now (and no new
wheels/tires to try stuffing in it yet!), I'm fantasizing about the
possibilities, without the benefit of any real-world evidence to base them
on. Somehow I think a cold bucket of reality is going to wake and shake
me from the dream, but it's nice while it's lasting...

Ted, I don't think a 17" rim would fit in there, unless your tire only had a 1" sidewall!!
The tubs were made to adjust for the tire sizes common for the period There were no 16-17-18" rims back then. The most common tire change was to a wider(60-50 series) tire, not taller and wider.
The reason for this info was to let ya'll know that you can adjust the tubs down a bit to fit in a metric/stock replacement sized tire, which for most of us, is a 225-70R15. Even then, the 225 is a bit taller overall than the G-70R15. If you got some other sized tire, I can only say, "Try it, and see!"
If you have a '78 up car, the tubs are different, anyway. They used a "space-saver" spare, and the tubs were designed to be used with either the smaller spare, or the normal road tires.