you can do 19's on a e36, its not hard.
18's are super easy to fit, but remember 235/40/18 is too big.
say no to shitty Chinese tires. (there are OK ones, though)
I run a canadian HID kit company, if you have any questions about hid kits in canada or would like to check out our products please contact me here: http://absolutehid.ca
Hot: 2001 Estoril M Roadster
ZCP 19's michelin supersports, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt ZCP 19's michelin supersports, deoranged, dechromed, led tails, ZHP knob, UUC SS v3, GROM, OEM 18's w310's,
Fun: 2006 YZF-R6, black