I'm from the US, but always wanted to call my trunk a boot. That said, here is my question. I want to know if I can fit a full size spare where my crappy little donut is stowed. I have a 2002 C5 with the BBS RC wheels with 245 35 17 zr tires. I recently had a blow out on a trip to Palm Springs and learned the hard way the importance of having a full sized spare. The blowout happened on New Year's Eve. No shops were open that day or New Year's Day. On Sunday i tried to find a shop that had my tires, but nobody had them in stock. I did not want to drive home with a donut. I broke down and had to get four new tires.

When I put the donut on, I tossed the full size in the trunk and it didn't seem like it fit where the donut did. I believe there was some foam that could be removed that might have made a difference.

Anybody have a definite answer? Thanks a million.

 

I have a definite answer for a C4 with original 15 inch tires:
a full-size 15 inch spare fits perfectly, with plenty room left on the sides (the original "scissor" jack is mounted on one side) - more than a palm width on each side. However, in between the tire and the "front-to-back" walls I can hardly insert my hand perpendicularly (fingers pointing downward).
I would assume a full-size 17 inch wheel would hardly fit in my C4's "boot". There's no foam to remove from the "walls" in my crappy C4.

As far as I can see, the 2002s came in two flavors: 16 and 17 inch. If yours came with 17 inch, then you should definitely be able to fit a full-size 17 inch wheel in there.
If it came with 16 inch, then probably you may have hard time to do so.

 

My A6 came with a full size rim and spare in the boot. Running 235/4x-17 tires. Can't remember the profile right now but these are oem tires and rims.

 

My 2004 A6 came with a full-size 17" spare...

 

I believe it is a requirement (not sure who requires) that an OEM full size tire will fit in the spare tire well in the boot.