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You need some way to turn off the auto-zeroing, which AFAIK was the only difference between the normal P2M spider and the track one - the track one had auto-zeroing disabled, which you can't do with the normal one.
Isn't auto-zero a feature of the head unit, not the PM? Or does P2M do some re-calibration of itself independently of the head unit that you need to turn off for tark?
Howard-
Isn't auto-zero a feature of the head unit, not the PM? Or does P2M do some re-calibration of itself independently of the head unit that you need to turn off for tark?
Nope, it's a feature of the PM. You can use a head unit to trigger a zero calibration, but the auto-zero stuff is done by the PM itself. The conditions in which the PM will carry out an auto-zero are particular to each, and they'll do it themselves. For example, with a Powertap track hub you need to turn off auto-zeroing. You can do that with a Joule GPS cycle computer, and once you've changed that setting you can use any head unit you like - the autozeroing will stay switched off in the hub's firmware.
Brommers
The USE chainring means you can use road cranks on a track bike, but it doesn't solve the problem of the auto-zeroing giving bad calibration results on a fixed gear bike. You need some way to turn off the auto-zeroing, which AFAIK was the only difference between the normal P2M spider and the track one - the track one had auto-zeroing disabled, which you can't do with the normal one.
These days I believe it's SRM or nothing for track crank-based PMs.