I came on to find out something about spare wheel sizes for the XK & spotted this thread. I was the Engineer who introduced foam to the 1999 DB7 V12 as a cost reduction & weight saving. To test it, I drove over a piece of 4x2 timber with 3 six inch nails in it. I then reversed back over the same wood leaving 6 holes in the front nearside tyre. I filled the 18 inch tyre with Holts tyre weld. After driving around for a few meters the tyre self inflates. I then drove from Bloxham (Banbury) wto Bruntingthorpe (Leics) & drove around & around the track for about an hour at silly speeds. Bored, i then started doing J-turns whcih puts a fair amount of stress on the front tyres. After about 3 hours of messing around on the track, I came back to base. In conclusion, after around 100 miles road driving, 100 miles track racing & lots of J turns, the tyre remained fully inflated. Be careful who you listen to about tyre weld. its !Removed! good. Look for research on actual failure, rather than desktop experts who speculate on failure. I know of zero cases of failure personally. After we added it to the Aston range, Jaguar (then a sister company) followed suit along with many others. I think we copied Mercedes, I don't recall. But on Saturday I will drive London-Bucharest in an XK probably & I have no concerns about a spare! 1600 mile drive in one sitting.
