Since I usually ride early, I find that bagels are too heavy but I will get up and be on the road bike within a half hour, not really enough time to digest much. If I ride the mtb, maybe 20 min longer til on the bike, still not enough to really digest anything heavy (bagel). I have been into the clif bars lately (wonder why) and if I ride for an hour, I eat half before the ride and half after, still probably overkill though. If I know I am riding 1.5 hours I might eat the whole bar first. If I ride 2 hours, full bar before and maybe another at 2 hours, depending on the intensity of the ride.
Also note that this is what I am doing right now. In the spring/summer/fall (when I am in better shape) I usually eat nothing before my rides.