I'm a roadie, and am pretty fast on the pavement. I've been racing road for a year, and have moved up to Cat4 without much of a problem. Anyways, my buddies who race MTBs provided me a bike to race on ealier this summer, and I ended up pulling faster times then most of them, and that was the first time on a MTB in 7 years. So they've been bugging me to buy a MTB and race. So 3 weeks ago I finally broke down and bought a MTB. A heavy (almost 29lbs) 29er rigid SS. Doing a little riding here and there (I still do more road riding) I have been able to pull times at trails around here about the same as some of my buddies who race and place in sport class. I rode with a buddy who does well in beginner class yesterday, and was dropping him left and right without even pushing it much. He said that I could probably beat him by 5 minutes on this 5x minute trail.
Anyways, there is a race next weekend, and the three classes I am considering racing are beginner, sport or SS. In this series, you can run SS in any class. My buddies are telling me that if I race beginner, I will easily win by 5+ minutes. Since there is only one SS class, they tell me that class ends up being one of the fastest since you have so many different skill levels in the one category. So that kinda leaves me to race either sport or beginner. What do you guys think?