Thank you so much for all the suggestions and ideas!! I’m as confused as heck now.. LOL…
Seems like the XT micro spline hub with its 12-speed drivetrain is the major sticking point. Perhaps if I swapped my drivetrain to an HG hub, running 9, 10, or 11 speed might do the trick, but i still have to deal with the 148mm spacing.
Thanks again, for all your expert input! This is going to be quite a learning process for me.
We will let you know how it goes-- it's a learning process for us, too. I was considering a drivetrain swap as well, someday might do that, though now I'm not sure I will need to.
As we consider the chainline issue for the TSDZ2B, which is mechanically better than the previous Tongshen, but has the crank limitations
@EMGX identifies (and that Pedal and I knew we'd encounter as well) the issues are really only evident in 1st, 2nd, and (only vaguely) 3rd gear, and that is mainly a problem for moderate-to-long steep climbs. In this one specific situation on the Marin, it's a particularly important problem to solve, because this particular motor feels like it's 60-75nm of torque, (meaning not that powerful) under those conditions, though I like the torque sensor generally. A lot.
I think we automatically think in terms of a 34t chainring or less, but consider a typical configuration:
34t chainring + 42t low gear @ cadence of 70 = 5.6 MPH, which is totally workable for extended moderate-to-steep climbs.
However, sticking with the stock Tongshen 42t chainring option , which keeps the chainring as close to the bottom bracket as possible:
42t chainring + 51t low gear @ cadence of 70 = 5.7 MPH, which is basically the same!
Hopefully, removing one (or two) gears from the center cluster, where the individual cogs are replaceable, will accomplish this (with the necessary offset.)
@PedalUma do you think that we could actually remove TWO (non-consecutive) sprockets? It all depends on how each of the three cluster elements are attached to each other, but we're pretty confident we can at least remove one, which should give us an 8+ mm offset. On paper, this should put first gear, that now-critical 51t, about where 2nd gear used to be: Totally usable, still some friction, hopefully *might* reduce friction and clatter a bit more.
The only other issue is this weird issue with perceived effort: 42t+51t and 34t+42t may be the same ratios on paper, but many cyclists report that faced with these two options, the combination with the smaller chainring just
feels like it's easier or more efficient. Is this some hidden physics or engineering thing, or an issue with familiarity, where it's just a change in technique that's required? I think part of it is or might be familiarity, but that's the thing:
You really don't know until you try it. There's no reliable way to game out all the variables-- including the torque sensor on the TSDZ2B, which I mostly really like because it's so efficient and it does have grunt for those brief nasty sections.
(Also, this is a 29'er, so YMMV in terms of the numbers.)
I haven't stood on the pedals since I was a teen, but have been doing that with my TSDZ2B on hills. Mainly to show I can still do it, Then I read hat that kind of stress can break the torque sensor. Bummer.
Doing this recreationally and indiscriminately for bravado, yeah, that's probably not great for the hardware, but-- doing it strategically for brief and brutal segments in granny gear, I expect, would be less stress on the motor, you're asking less of it. But the motor can really deliver in that situation, feels like an eMTB motor.
Anyway, the Marin Build (I'm still zeroing in on a name) kicks ass around town, and is very usable in the Hollywood Hills, even before changing anything. However, the changes will hopefully make it more comfortable, and quieter in the Hills, and getting that 51t online should mean we can go steeper than that, like the Verdugos.
