Pending a test ride i'm decided on a new streetbob. Now, it's actually a little while away due to the bank being a scrooge. In the mean time, i'm planning a change of bars for my current ride... I want 18" apes. Now, I know there is a clearance (bars->tank) design rule... (can only be of a certain distance) but, does this prevent a roadworthy? and what is the actual clearance amount?