So, my old SR BB spindle crapped out on my Schwinn World Sport. You can still get road spindles but has anyone ever tried popping in a 68mm cartridge BB for an MTB? Will going from a 42.5mm to a 50mm chainline cause problems?
Bottom Bracket Replacement
- Thread starter garage sale GT
- Start date
Are you referring to having a square taper crankset? It is. I am just worried about attaching the crankset further outboard. Also, won't the pedals be off center if the new bb is about as long as the old one but the chainline and hence the RH crankarm is 8mm further right? My old spindle was a 124.5mm. So unless you get a MTB crankset the pedals will both be offset 8mm to the right, correct? should I get one of the 127.5 BB-UN26's to compensate?gclark8 said:
The FD is currently capable of derailling the chain to the RH side with only half its movement used up.gclark8 said:
124.5 is my current length. I was assuming the taper was larger so as to place the rings out further on an MTB crank. I guess the crankset could be different, but then why is the chainline listed as a feature of the BB spindle?
Also, the current spindle is assymetric. The new one may have different offsets. There's 52mm in the middle, 35 on the left, and 38.5 on the right. Looking at Sheldon's chart, it seems spindles run the gamut from symmetrical to highly offset and are probably designed to work with certain cranksets in order to leave your feet equidistant from the Cl of the frame.
That's what the ol' gut says, but maybe I'll kick back for a day or two and work on my new Peugeot and see if someone knows where a 124.5mm BB-UN26 would put the chainline and the centerline of the pedals. Thanks for the reply.
I have clipless on there, so I can't just have my feet 8mm offset on the pedals.
It's a nice, hardly used Schwinn, btw. I want to keep it nice and ride it. 4130 main tubes, but I covered up the "Miami Vice" themed pink Schwinn logo because nobody remembers Don Johnson's Sonny Crockett and I don't want to become known as the CroMo ****.
I have clipless on there, so I can't just have my feet 8mm offset on the pedals.
It's a nice, hardly used Schwinn, btw. I want to keep it nice and ride it. 4130 main tubes, but I covered up the "Miami Vice" themed pink Schwinn logo because nobody remembers Don Johnson's Sonny Crockett and I don't want to become known as the CroMo ****.
I don't know where the chainline will be with the Shiimano BB-UN26 and your crankset ...garage sale GT said:
BUT FIRST (belatedly), are you sure the SR uses a Shimano square-taper and not a Campagnolo/Sugino square-taper?
If the SR uses the Campagnolo taper, then you should be looking at something closer to a Shimano 118mm cartridge BB since mounting a Campagnolo-compatible tapered crank on a Shimano spindle bumps it out a couple of millimeters (the "slope" of the taper is the same).
As far as the fiddling with the chainline & offset, this is easily handled by spec'ing a cartridge for a 73mm BB shell ... you will have 2.5mm of left-right if the symmetry is correct ... and 5mm if you need to run it longer on the non-driveside. You can use an 8-speed cassette spacer which is 4.5mm, I think ... or any older BB spacers that you may have it your toolbox.
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