[readingaloud]

I've been thinking, in my own slow and muddled way, about the power phase out issues that flecc so clearly explains, and it seems to me that there's a relatively simple way for manufacturers to deal with the problem.

To oversimplify:

In order to still be considered bicycles for regulatory purposes, bikes cannot offer power assist beyond about 25 kph, and they phase out the assist so that it begins to diminish at about 15 kph. Well and good.

The problem is that the only way the bike knows how fast it's going is by the cadence. The control system doesn't know what gear the bike is in, so it has to assume that the bike is in it's highest gear. That means that it's going to apply stricter limitations to lower gears.

Now, how high a gear should the bike have? If the very highest gear were one that would only go 25 kph when ridden at a reasonable cadence of 70, that would seem a pretty wimpy top gear. So they give you a top gear that yields a respectable (but still not very fast) 25 MILES per hour when ridden at a standard cadence.

But in order to do that, they need to start phasing out the power assist at a much lower cadence. Hence the fact that the phase out begins at a paltry 39 cadence.

Since the only thing the control system knows about the bike's speed is the cadence, it can easily be fooled by changing the sprocket.

Now, as flecc notes, this has a side benefit, at least as far as the manufacturer is concerned, in increasing the range of the bike. Since a cadence of 39 is uncomfortably slow for most cyclists, most of the time, they'll pedal a bit faster than that, and the bike will scale back the motor's contribution accordingly. In a way, the bike is doing automatically what flecc and others recommend for getting longer range out of the bike--turning down, or even off, the power assist except when you really need the help.

But, assuming there are some who would want (or even need) more help, and were willing to live with a shorter range, there would seem to be a much better solution. Why not give the controller better information about bike speed? If the controller "knew" what gear you were in, it could adjust the phase out schedule so that it observed the legal limits, but didn't begin the phase out as low as 39 except when you were in the highest gear. That would make it possible to climb hills better, cranking up to 70, or even 90, for greater efficiency without being penalized by the controller.

Now, this would require some kind of feedback device so that the controller knew what gear you were in, and it would still be possible to fool the system by changing the sprocket size.

So why not go further, and actually measure bike speed? A wireless cycle computer could become part of the standard configuration, and the speed information would be sent both to a display mounted on the bars and to the controller located wherever it is it's now located. It would no longer be possible to fool the controller by changing the sprocket. You could, I suppose, try to fool it by mounting bigger wheels, but that would be much more difficult, and much easier to detect.

Bike computers are so cheap, these days, that the cost increase would be negligible. And how many people buy such an expensive bike without spending a little bit extra for the computer anyway?

Could you fool the system by disabling the wheel sensor? Well, the system could be designed to revert to the present phase-out threshholds if it didn't get a signal. Could you fool it by spoofing the signal from the wheel sensor? Well, I suppose you could (or at least some folks could), but that's still a lot more difficult than simply changing out a sprocket.

The more I think about it, the sillier it seems to have the bike enforce some kind of speed limitation without giving it some way of knowing what the speed is. Surely, with all of the fancy technology that goes into bikes these days, this is a solvable problem!