Sizing an exhaust system?

[ProdigyCustoms]

I run 1 3/4 Hookers on my street racer. It is pretty slamed in the front, motor is lowered in the frame more then 1 inch (to help prevent wheelies). Even so, I still can go through parking lots, tall speed bumps may scuff a bit, but it is OK. Shorties will hurt you more then you can imagine. One thing to do with long tubes, and I need to do it myself, is get ride of the header flange and band clamp it, that will give you a extra 1/2 to 3/4 inch clearance.