The Viper 9 is just the right size and format for mountain biking, for me anyway. It holds what it needs to hold and can take more in the area between the main compartment and outer pocket if you need to drag rain gear along. The water bladder was big for a smallish pack. That's important for those of us who ride the Southwest in summer. But, the pack could only put up with so much abuse. After 4 years of bashing and crashing and sewing-up damage, I sent it to Osprey for a little professional attention. They must have had a good laugh when they saw it, because they decided to just send me a new one. OK, that's a Mother of a warranty. I would not expect that from any business. The pack didn't fail; it died a gallant death in the face of hostile forces. Let's see, who am I going to for my next pack?