tony R said:Hello all,
the situation is this. The middle ring on my commuting bike's chainset is wearing out. It's a
cheap chainset and the rings are not removable (as far as I can tell). I had always planned with
this bike to replace bits as they wore out (and where possible) with the old but good and
serviceable bits off my old tourer and buy nice shiny new bits for the tourer. This seems like my
first opportunity. My first question:- will the fact that the chainset is coming off a bike with
rear spacing of 127mm and going on one with spacing of 135mm. make any difference at all to the
feasability of this plan? I'm assuming I'd stick to the same length bottom bracket as recommended
for the chainset so wouldn't the chainline alter and does this matter?
Chain angle would indeed alter. There's a chance a longer bottom bracket than the recommeneded
standard would be required to make it acceptable. I'm sorry I can't be any more specific than that.
The question should be worth reposing to rec.bicycles.tech.
Chainline with derailleur gears is not an exact science because chainline is always compromised as
it can only be perfect in one gear (generally supposed to be middle ring to middle sprocket - but
doesn't strictly have to be). What gear combinations you prefer, plus more subtle factors like chain
stay length, make a difference to how well transmission works. For instance, if bottom bracket did
turn out to be on the short side for the hub, chainline from middle ring to smaller rear sprockets
would be poorer but middle ring to larger sprockets would be better. In fact, there is often
excessive friction when using these particular gears on road bikes with triples and 130mm hubs. So
it's silver cloudy roundabouts and swings and linings... or something like that :-) The very top and
bottom gears are likely to be ok, anyway, but there will be a more limited number of "good" gears
from both inner & outer rings if the chainline was "off". I think this is less important than what
effect it has on the middle ring (because that's what is usually used for most of the time).
Quoted message said:My other question concerns the new chainset. I'm sorely tempted to browse the TA range. They seem
to have two new ones - Carmina and Vega. I can't seem to find out much about them except one's
black and one's not. Anyone know anything more substantial such as are either suitable for a
strictly on-road tourer?
Sorry I don't know much about those models but I don't see why any chainset or ring sizes you like
wouldn't be good on a tourer if the bottom bracket and front mech were suitable. Dawes are even
fitting compact Shimano MTB chainsets to some of their tourers.
~PB
