I've just recently bought a new trek 4300 with disc brakes and ive been riding the crap out of it. I realized that one of my gears started falling and i looked and one of them was bent so i hammered it straight, but the same problem kept happening so i decided to buy a new crankest. Since i am fairly new to this sport i don't know what brand and model i should buy please help, thanks in advance. Like i said for a downhill mountain bike and biker.