I've recently started mountain biking. Went out and purchased a $100 Mongoose XR-75 at Wall-mart to go trail riding with my brother in law, who is always new to the sport. The tail we've been riding has a ton of roots which seem to beat beating up our bikes. Is it even worth buying upgrades for my frame? And if I did get upgrades how would I know what parts work for my bike? For instance this Altus M310 7/8-speed Rear Der Silver(Got torn off the bike in my last outing).