Hello all, I'm new to the forum, I found it on google, and honestly I know I'm probably going to get flamed for my post. But I have recently bought a bike, and I have been having some problems with it. I can honestly say this is the first serious bike I've ever bought, and probably don't know what I've gotten into. I am 6'4" 212lbs, and I have a 26" mongoose mountain bike, but I just kind of ride it anywhere. I have noticed some slipping of the gears when I try to accelerate. If I try to stand and pedal the gears almost always slip. It's very annoying, and becoming dangerous, because I usually ride to the gym which is several miles of busy road away. I haven't gone to the bike shop yet, because I honestly don't have the time. I honestly don't know much about bikes, but I'm trying to learn. It's not really a passion for me, I just want to ride to be more healthy, and maybe have some fun. Anyway if anyone can help I would gladly accept it.