Ok, the PO of my 1982 300D swapped the old alloy 14" bundt cakes for some chrome 15" flatface rims off of a late W107 or W126, but, he left the original spare tire in. Since the spare tire does not have bolts, and you have to use the bolts from the flat tire on the spare in case of a flat, will the bolts on the 15" rims work on the 14" rims? Or do I need to go find a cheap alloy flatface 15" rim for the spare?
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

which I might not have seen, and the spare is a bundt cake aluminum rim rather than a steelie, you should be just fine with the same bolts. What you need to do is take one of your bolts and check how far it projects from the mounting face (back or inside) of the spare: it should be about 16 to 19 mm (11/16 to 3/4 inch). If it should happen to be significantly less than that, which is unlikely unless you've got steel wheel bolts, you may have too short a length of bolt from the tip of the threads to the beginning of the taper for safe load bearing. If the projection length is significantly longer than that, you will be at great risk for having it tear up your parking brake mechanism if you have to put the spare on the rear. But chances are your bolts are quite acceptable -- just check to make sure.

I once had fantasies about creating a custom look by using those long headed bolts that were OE on the flatface wheels on bundt cake rims, but then I decided it wouldn't really be in good taste, and the extra unsprung weight wasn't worth it either.