question is why ...... go with a 160 mm regular one...... otherwise your braze ons for the disc caliper dont work... which is the bigger question all together , do you have a fork with disc brake braze ons.. and a hub for a disc brake rotor ?
Formula used to make a rear 140 mm rotor, which fits on Int Standard REAR braze ons with the Formula caliper.
In any way your 140 mm rotor wont work as there is no brake which uses a 140 mm up front,,,, ie. there is no fork manufacturer who welds the caliper mounts on the fork in that measurement ( it doesnt work as the caliper would be inside the fork leg )
I got an 06 downtube and the guy over there recommended a 140 so im lookin for a 140. Just tryin to feel what the best option is. If you say 160 what brand and model would you recommend? I got a velocity thracian front 20" wheel compatable for disc.
just make sure you have the disc brake braze on on the frame and on the fork ... thery will be Int Standard and than get a Avid Mechanical brake, as it seems that people have the least problems with them, although hydraulic brakes are better in the modulation ( not power, but feel and control )