My '87 Porsche 911 coupe came with an inflatable/collapsible spare tire. In addition to combining a heavy wheel with a heavy tire, you also need to carry an air compressor in the car at all times. As far as I know, my spare has never been inflated in the past 25 years and, if it were to be, I'm not sure that it would hold air or fully collapse into its original shape when subsequently deflated. Because the spare wheel fits snugly into a recess in the 22 gallon fuel tank, there's not really any room for a full size tire.
During one of my daily Craigslist searches, I found a nearly perfect 14x5.5 inch Fuchs wheel that was originally fitted to a 912. In addition to its beautiful condition, it's really light. My original plan was to flip it for a quick profit, but then I started to think about using it in place of the heavy collapsible spare that came with my car.
I started by confirming that the wheel would clear the front brakes on the car.
I measured the collapsible spare and it was approximately 20 inches across, with a small gap between it and the fuel tank. I wouldn't have room for anything bigger. I thought back to the small 14 inch temporary spare tires in my old Miata track cars. I found that a Miata spare is 19.5 inches across, when inflated on its 4 inch wide rim. I quickly acquired one in exchange for a twelve pack of Smithwicks.
I had to go to three tire shops before I could get someone to mount the tire onto the Porsche wheel. The first two shop said that it couldn't be done. I had to work my way down to progressively less skilled technicians until I found one who didn't know any better. The third shop mounted it with a new valve stem for a total cost of $4.
The tire is really stretched, but he was able to seat the bead and it holds air without leaking.
I didn't want to use the original steel hold-down on the beautiful forged aluminum wheel, so I dug through my big pile of Fuchs center caps, picked out the crappy one, drilled a hole through the center and sent it for a trip through the sand blaster. I also picked up a slightly longer metric bolt, along with one composite and one neoprene washer. The result was a precision fitted hold-down for my new light weight spare.
The new spare fits perfectly into the recess in the fuel tank and I can easily check to see that it's holding pressure.
The old steel wheel and collapsible spare weigh 34 pounds and the compressor added another 4.5 pounds. The new spare wheel and tire weigh 16 pounds, for a net savings of 22.5 pounds.