I'm new to cycling and my wife purchased a gmc Denali 700c a year ago for my birthday. I just started riding it trying to lose weight. I have about 11 sessions under my belt with around 150 miles. I'm having issues throwing chains off my crankset. Everything is up to par no bent or missing teeth on the crank any suggestions on what to do from here? Thanks for any advice! I'm 6'4" 270lbs