John, If you’re already running the crank, it shifts to your satisfaction, and your stance (q-factor) is comfortable, then it’s not something you need to solve. But should you migrate the kit from your old frame to a new one that comes with a BB pre-installed, then you might want to anticipate if the new BB is a different spindle length, whether the chainstays might be more or less curved (thus affecting crank arm clearance which can be adjusted by BB length), and factors like that.
Some riders prefer a narrow stance, therefore shorter-than-average BB spindle length (but long enough to physically avoid rubbing/hitting the frame). If Riv’s supplying frames pre-installed with BB (and headset), and their BB and recommended front derailleur are both dimensioned optimally for a triple crank, but many of their buyers intend to run a double crank, then some portion of those riders might find that Riv’s default parts don’t match the rider’s picky (that includes me) setup prefs. Many others won’t notice or care to notice these nuances and as long as it works well enough, they’ll be happy. Each make/model crank’s recommended BB spindle length are published by the manufacturer/seller, or are very commonly tabulated by users in forums. There are online guides on measuring the chainline on your installed crank, and published chainline recommendations for different drivetrains (e.g. Shimano 9, 10, 11…). Again nothing to solve if you’re already running the kit and it’s to your satisfaction. On Thursday, January 30, 2025 at 9:05:37 PM UTC-7 John Rinker wrote: > After reading through these comments I realize that I lack the > understanding of how one would calculate the proper BB length for a > particular crank- say, an XT M737 triple on my Hunqapillar? I've got a 113 > on there now, but only because that's what came with the bike when it had > the Sugino XD triple. It seems to work just fine. > > At this point in my understanding, calculating such sounds like a mix of > esoterica and wizardry. > > Cheers, John > > On Monday, January 27, 2025 at 9:09:32 AM UTC-8 Bill Lindsay wrote: > >> Let's list all the cranks for which 113mm is the perfect length. I'll >> start: >> >> White Industries VBC 2x >> >> Bill Lindsay >> El Cerrito, CA >> >> On Monday, January 27, 2025 at 8:07:45 AM UTC-8 isp...@gmail.com wrote: >> >>> Well... the SpaCycles UC Double is based on a triple chainline, and >>> their website says you should be using a 119mm BB spindle. That's all fine, >>> but it's not a typical use case. >>> >>> I'm just pointing out to the community that for the majority, who are >>> using a double crank intended for a double chainline, that Riv's included >>> BB runs a wide of that chainline. And that BB doesn't even match Riv's >>> Silver-branded double let alone other typical double specs on the market. >>> That BB is only chosen to mate well with their "skeleton key" front >>> derailleur, which also doesn't seem optimized for typical double cranks >>> (nor theirs). >>> >>> Riv admits on their website that they're spec'ing as many Microshift >>> items as possible to gain favor with that vendor (to further encourage >>> their collab on a Silver-branded Microshift drivetrain). The BB spec is a >>> loopy business decision where the average user is getting a BB that won't >>> give optimum alignment, and the user can't request an alternative BB (i.e. >>> swap at no cost). I'm less concerned from a cost perspective (since the BBs >>> they sell are affordable), but it affects a person's build parts list and >>> timeline. It's a setup for surprising a lot of people with a mismatch. >> >> -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/rbw-owners-bunch/96674ae1-3c45-486b-bfbb-2df054297da5n%40googlegroups.com.
