Originally Posted by
mkatz
On the other end, for riding uphill I would like a lower gear. As some of the components listed for the GT appear not to be particularly upscale (e.g.
SRAM X5-A1 10speed derailleur), if compatible substitutes were available I'd be quite happy to purchase replacements to extend the lower end; of course, now I'm wondering how far I can extend the lower end (11 speed 9-36? 12 speed 9-42? Yes, this last thought might be kind of ridiculous
) Right now I'm perusing the Birdy "master thread" in an effort to gather thoughts about what upgrades/modifications might available. (I'm definitely compulsive that way.)
I have used the Sunrace 11-speed 9-36t cassette with a 45t chainwheel. This works, but I had to space the chainwheel out so the chainline was bad in lower gears. With 52t or bigger chainwheel this problem will be worse. With a 10-speed cassette it will be less bad since they extend less inwards than 11-speed mtb does. 11-speed road cassettes do not have this problem, but they don't come in 9-36t anyway,
AFAIK. If you can find an 11-36 road (not mtb) cassette, that would improve your low gears without harming chainline much.
42t cassettes will also make chain rub worse, so chainline must be made even worse to compensate. This is sadly a general problem with the Birdy design: It's not made for big cassettes and/or big chainwheels. I needed the range of a 9-36t, but the Sunrace hub broke and I found the replacement was likely to break too, so I went for the Alfine 11 IHG instead. That solves the chainline / chain rub issues, at the cost of more weight and money.