Whats the biggest tire you ever put on a 14 x5.5 rim

A 235-60-14 @ 25.1" tall has a minimum recommended rim width of 6.5".

A 225-60-14 @ 24.7" tall has a minimum recommended rim width of 6".

All other 60s require an even wider wheel.

Really.... No useable (height wise) 60 series tire would be safe (in my opinion) on a 5.5 rim.