I know a few people have dumped their spare wheels to fit a big sub and reckon they're OK with puncture foam, but today I had to use mine. A big split-pin went in through the tread and out through the sidewall, causing a bit of rim damage on its way. When I tried the foam stuff, the exit hole was so big that nothing sealed and I had to rely on a (fortunately unused and inflated) j-spec 13 year old space-saver. And I was in France... I drove a good hundred mile home at 48mph, but without that space-saver, I'd still be in France, probably in a bar drowning my sorrows, waiting for a tyre dealer to get a 275/35x18 for me.