Most of the other bloggers here are either racers or triathletes. Because I haven't seen any other long-distance riders writing articles, it may be helpful to explain a bit about the sport.

Centuries (and variations such as double centuries, metric, half, double metric) are organized rides of a certain distance. Most of the double centuries I ride have time limits as well. Most of these will post the finish times for each rider, and some don't. You either finish in the allotted time or you don't. This type of setup tends to attract  the kind of people who like the camaraderie of riding long distances without the pressure to win, place, or show. True, there are people who try to finish first, but most people are out for the adventure and for the experience of finishing 200 miles in a day. Most double centuries are supported events which means that there is a company that’s hosting it, you pay them money, and they provide food, water, mechanics, and SAG support along the way. You could also arrange to have them transport some gear to a checkpoint late in the ride – this bag drop might contain lights, thermal gear, etc.

In brevets, the distances range from 200K to 1200K, have strict time limits for reaching the checkpoints, and the burden is on the rider to provide or find sufficient water, fueling, etc. Any mechanical problems are yours to fix. You can go off course to get food, take a nap, buy a new wheel, etc. but you have to get back on course at the same place. Brevets are similar to double in that brevets have check points where you have to sign in within a certain time frame. If the checkpoint closes before you get there, your ride is over. Even if it’s 3:00AM in the middle of the desert. You’re DNF’ed.

If most riders aren’t trying to finish in the top three, but rather trying to finish, why then, would PowerCranks be helpful? Here are a few good reasons:

1) Double usually have an early start and a late start. The early start is for people who think they need a full 18 hours to finish a ride. These people usually leave at 4:00AM. The late start is for people who think they need 16 hours or less. If you’re an early starter (like I was all last year) you need to pack a headlight for the 2 hours you’re going to ride in darkness. You can’t hand that light off to anyone at daybreak so you have to carry it the whole ride. This extra weight can be a nuisance when you’re climbing 10000 feet in the summer heat. Late starters also probably get a better night sleep and maybe a light breakfast. Not so with early starters.

2) Inefficiency can last only so long. Before I started using PowerCranks, I’m sure that I was using my quads for about 90% of the power while pedaling. After several hours, my quads get overloaded, and performance drops off. The doubles I did last year had gentle rollers or downhills for the last 30-50 miles, so I never had to find out what it was like to climb big hills with legs that were this close to failure.
 
3) Safety. In the Easter Sierra Double, I stopped at the last checkpoint a little bit before sunset, and the finish line was about 35 miles away. All I had to do was share a highway with pickups pulling boats, with semis, with farm equipment. Given the choice, it’s better to get to the last check point sooner and to spend as little time as possible riding on a highway at night. The way to do that is to go faster throughout the day and have enough energy to sustain that speed until the finish.

4) Comfort. If you're out on a course for 17 hours, it might be in the 50s when you leave at 4:00AM and it might get into the 100s when you're riding through the desert at 2:00PM. This means that you have to carry extra thermal gear throughout the ride. If you have the power and speed to leave later, there's a lot of gear that you don't need to haul around.

All of this is to say that there are lots of reasons for needing extra speed and power, even if you’re not a racer or triathlete.