Sscarich said:Hi
I have been doing my winter training on a late 80's mountain bike with a triple
chainring. I have had sore knees; I suspect it is either the 181mm length or
the high Q-factor.
181 is an odd length for cranks. Are you measuring them in order to get
that number, or reading it off the cranks themselves? If the former, make
sure you measure center-to-center. 180mm is a long crank arm, even for
mountain bikes. It all depends on your preferences and size, of course.
175mm is more or less standard for mountain bikes, and for "average" size
men, 170mm is standard for road bikes. But your purpose is winter
training for road riding; probably the same length as your road bike is
preferable.
I am not convinced that q-factor is all that important. I prefer the
newer "compact" cranks that have a bit of bend outward at the pedal, or,
perhaps, are displaced inward at the spindle. They tend to have wider
q-factor, but for me that is no big deal, and getting the spindle end out
of the way of my bony ankles is a big deal.
Quoted message said:I have
decided to intstall a road double, to replace the current MTB triple. My
question is:
Is there going to be an inherent chainline problem, due to the new,
narrower BB/Crank setup? It seems obvious that this will be a problem,
but I just wanted some quick feedback, before I take on the project.
Should not be that big a deal. You may want to get a different bottom
bracket to improve things, but whether or not you want longer or shorter
depends on the type of cranks involved. You might want to go 2 to
5mm wider than the recommended size, since the cassette is further out
from the centerline on a mountain bike. That will increase the
q-factor, of course. But it should work OK in any event. Especially with
the long chainstays of your old mountain bike, the shifting should be fine.
Oh, check to see how the front derailleur works with the road cranks.
Mountain-bike derailleurs are made for smaller rings than road bikes have.
It's usually OK to use a road derailleur with mountain cranks, since the
larger circle of the derailleur will not lead to interference (I use
this), but the other way around may cause trouble. If you use Shimano
indexing, prepare for hassles there if you swap derailleurs, because most
Shimano mountain bike derailleurs require more cable pull per shift than
their road versions. Rear is OK, but someone decided otherwise for the
front.
--
David L. Johnson
__o | "What am I on? I'm on my bike, six hours a day, busting my ass.
_`\(,_ | What are you on?" --Lance Armstrong
(_)/ (_) |
