Originally Posted by
BlazingPedals
Coastdowns have been a mainstay of recumbents for years. The problems with them are, you have to normalize weight and there's always a difference of opinion on the validity of the details - what speed to start, do you measure acceleration, top speed, total roll-out, etc.
Yeah, I've seen lots of references to coast downs but the protocols used vary tremendously, as you've observed. That's one of the things I was interested in: if you do coast downs, what protocol do you use. A common protocol is to try to control entry speed and mass and then to do either terminal rollouts, terminal (i.e., maximum) speed, or speed at the end of a known distance. In my experiments, all of these have limited precision. BTW, for some coast down protocols you don't actually need to control entry speed or mass -- in fact, you can improve precision by altering them. If you want precision (and not everyone needs or wants it) then the key isn't controlling speed, it's getting a precise measurement of it.
Measuring power at the hub would seem to be more reliable, but few non-racers are willing to buy a PowerTap hub or similar equipment. (I know a few are, but they don't talk about it.)
A lot of recumbents have unusual drivetrains that make something like a Power Tap inappropriate. It's true a Power Tap makes things faster but one of the alternatives I've been playing with doesn't actually use the PT hub--it uses a wired PT head and the old harness just as a way to record speed. Something like a GPS that had a wheel pickup for speed (rather than relying on the satellite positioning for speed) would also work.
[Edit:] BTW, someone just pointed me to
this, which appeared today.