I've been wanting to get a 12 bar for a while now. If it's your first time really stunting 50's, I'd probably take off the bar until you learn that brake pretty well. Before I got it down, I'd have to jump off the back to keep from loosing the wheelie and would scrape the fender a bit. If you hit the bar when doing that, it's gonna grab and be a major bitch to try and save. But I don't have a 12 bar so I don't know, but I do know I was scraping the shit out of the fender before "cover the rear brake" wasn't just a saying.
Can you do anything with those rear pegs? They're hard as shit to wheelie on.
