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Chainline & Q-factor Questions

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Chainline & Q-factor Questions

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Old 06-20-10, 07:01 PM
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rothenfield1
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Chainline & Q-factor Questions

I'm not that inexperienced, I've built some nice bikes. Well, at least I think so. But, this was the first time I'd ever heard of the Q-factor after posting a thread about building a modern touring bike. It seems to have more to do with the riders body type and riding preference than anything else. I've always been more concerned about the chainline when trying to match BB, crank, & cassette. I'm looking to build a Soma Saga with a Sugino XD500T 48/36/24t and 12-32 9 spd cassette. Why should it matter if I can fit a 110 BB instead of a 130 for better 'tread'? Shouldn't it matter more that the centerline between the 2 lines up?
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Old 06-20-10, 07:18 PM
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contemporary chains are really flexible, so perfect chainlines are kinda bunk, IMHO. I mean, its only perfect in a few gears, so screw it. That said, the sugino isnt exactly a low Q crank so.... what does it really matter? run the shortest bb your frame can clear and it will be OK. and really, a 130 mm wide bb? you mean a 113?
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Old 06-20-10, 10:03 PM
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Originally Posted by XO1 View Post
contemporary chains are really flexible, so perfect chainlines are kinda bunk, IMHO. I mean, its only perfect in a few gears, so screw it. That said, the sugino isnt exactly a low Q crank so.... what does it really matter? run the shortest bb your frame can clear and it will be OK. and really, a 130 mm wide bb? you mean a 113?
Sorry! Typo. Of course I meant 113.
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Old 06-21-10, 03:24 AM
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Anatomically speaking it takes all kinds, there are even pedal axle extenders(knee savers) that some people like. Aerodynamically though, narrow BBs/cranks are apparently preferable.
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Old 06-21-10, 05:51 AM
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Originally Posted by rothenfield1 View Post
I'm not that inexperienced, I've built some nice bikes. Well, at least I think so. But, this was the first time I'd ever heard of the Q-factor after posting a thread about building a modern touring bike. It seems to have more to do with the riders body type and riding preference than anything else. I've always been more concerned about the chainline when trying to match BB, crank, & cassette. I'm looking to build a Soma Saga with a Sugino XD500T 48/36/24t and 12-32 9 spd cassette. Why should it matter if I can fit a 110 BB instead of a 130 for better 'tread'? Shouldn't it matter more that the centerline between the 2 lines up?

You likely won't notice a difference between a 110mm and 113mm BB as far as Q factor goes. 165mm(or so) vs. 162mm. Either it works for you or it doesn't it. If it's too wide, there are few choices any narrower at the moment. Velo Orange is coming up with some old school cranks, one of which the triple Q will be in mid to upper 140's for the triple.... like the old Sugino AT triple.

If you want the lowest Q with the XD crank, use the 110mm BB and a 1 or 2mm driveside spacer inside the BB cup. The XD is spec'd with a 47.5mm chainline w/113mm BB. You can get a slightly tight chainline by using the 110 BB and spacer ...... as long as the rings and bolts clear the stays. This won't make a big difference in your shifting though, in fact I doubt you'd be able to tell a difference.
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