For my '05 T-bird I wanted a replacement spare that is closer to the
OEM regular tire size of
P235/50R17 (26.25" OD and 9.25" wide on 7.5" rims) than the original
Maxxis T185/60R17 temporary spare (25.74" OD and 7.28" wide on a 5" spare rim). The largest tire I found that just fit in the trunk only when mounted on the 5" spare rim is a P205/55R17 (25.88" OD and 8.07" wide, which is a bit wide for the 5" spare rim but it works without the high 60 psi required for the temporary spare). I purchased a Federal Formoza FD2 P205/55ZR17 from SimpleTire.com for about $90 shipped. It should be good for at least another 12 years.