Fitting a bb for a given crank is to me, like doing plumbing in your house. It's ever a custom job as no two spaces are ever the same. Likewise, same with frames, not only varying from brand to brand and model to model, but even a given model. Just because a given object is marked with branding(I can't help but think how ranchers brand their cattle), doesn't mean they are exactly the same. Nothing is ever the same, twice ! Ever !
That said, I keep on hand Shimano/Tange-like cartrdiges from 107 to 118 at hand, and lots of cup spacers, from .5mm to 2mm, for chainline tuning.(Placed between the driveside shell and the lip of the cup). You can't do that with cup and cones, for those that aren't familiar with them. Cartrdiges are complete units, non-adjustable. The non-driveside cup is there for support only, so it can be moved laterally, given it has no lip of course. What does it matter how far or near the chainrings are from the frame ? That's a legit question for non-mechanics ! Too near and the rings would rub against the frame, too far and the front derailleur wouldn't be able to reach the outer ring. So in betweeen is room for much negotiation. In theory, the middle of the cranks chanrings, be it 1,2 or 3, is supposed to match the middle of the number of rear cassette/freewheel cogs. That's a good starting point, but it's not a must, especially if the rider knows what rings and cogs they ride mostly in, or want access to. So it's okay to have the chainline a little to the inside or outside of middle in that case. Again, assuming one does not know anything about bikes, with 2 or 3 rings, it's not necessary to be able to shift into every cassette cog from every ring. With a single ring you have no choice, and while in the smallest or largest cog of the cassette is can get noisy from the friction of the angles, as long as the chain stays put it's not the end of the world. With a 3 ring setup it's not necessary or a good thing to be able to ride in every cog. I myself have never used more than 3 cogs in the tiny 24/26t ring, otherwise it's back on the middle ring. The middle can generally be used for all cogs, though the ends may be iffy, depending on the setup. In the outer ring generally all but one ot two of the largest cogs. Again, that depends on the setup of a given bike ! Think of "custom/DIY" work as "local", pertaining to your locale, your home, your bike, and "you" ! In regards to BB's, do inquire the specs of a given unit as some are offset(one side extends further than the other), some are equidistant. For example a Tange/Shimano 107 and 110/11 have the same driveside length, the difference is all the non-driveside. If you buy a frame alone and it comes with BB installed, surely you're not obliged to use it ! Same with the Kalloy seatpost. Keep them as parts if they aren't if want/need something else. On Saturday, February 1, 2025 at 8:31:01 PM UTC-5 [email protected] wrote: > John, to suggest an answer to your question --- What I have done in the > past is to initially mount the crankset up with what ever BB I happen to > have at hand, then check the chainline and add or subtract the distance it > is off from my desired CL. Assuming a symmetrical BB spindle, the needed > width = +/- value x 2 + the test spindle width. (As a rough reference the > distance between cogs on a cassette is close to 4mm). > > Steve in AVL > > On Friday, January 31, 2025 at 10:17:13 PM UTC-5 brendonoid wrote: > >> The real fun with square taper cranksets is that depending on its >> previous usage/owners they can not give you advertised chainline no matter >> how good your research is. >> Some people really like to bottom out that taper! >> > -- 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 [email protected]. To view this discussion visit https://groups.google.com/d/msgid/rbw-owners-bunch/65b8f271-7d89-4afa-b7ce-2fede166eb76n%40googlegroups.com.
