Help! Scavaging parts from another bike

I have a shimano "mountain bike" derailer on my road tourer and it works
fine. The parts you may have trouble interchanging are those that are
dependent on the frame's geometry, such as rims, hubs, headset, BB,
stem, seatpost, and cranks.

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Comments and opinions compliments of,
"Your Friendly Neighborhood Wheelman"

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Quoted message said:

Ok, I have an old road bike and and newer mtn bike that my
Sister-in-law left. Here is the question, assuming that the gearing
works - I konw that the difference between Mtn bikes and road bike
gears are a lot, can I take derailur (sp) off the mtn bike with
handlebar shifters and put it on a road bike with downtube shifters?
Right now the road bike is an 12 speed and the mtn bike is a 21 speed.
I would probably just want to change the back derailur for now and if
the gears work, take them, OR find another used road bike, with 21
speeds and take the gears of that.

Thoughts?

Make sure that the chain sizes are the same.

A 12 speed road bike probably has a 1/2" pitch chain that may be wider
than the MTB deraileur is designed to handle.

Most MTBs from the last 10 years use index shifting and the are a number
of different flavors of these setups.

So the answer is maybe?

Chas.

Quoted message said:

Ok, I have an old road bike and and newer mtn bike that my
Sister-in-law left. Here is the question, assuming that the gearing
works - I konw that the difference between Mtn bikes and road bike
gears are a lot, can I take derailur (sp) off the mtn bike with
handlebar shifters and put it on a road bike with downtube shifters?
Right now the road bike is an 12 speed and the mtn bike is a 21 speed.
I would probably just want to change the back derailur for now and if
the gears work, take them, OR find another used road bike, with 21
speeds and take the gears of that.

You can get it to work, but might take some trial and error. Reading
relevent articles on Sheldon's site will help a great deal. This will
work best with friction shifting. Make sure the chain is clean, and
not badly worn (take it off the bike, measure it,clean it). I hope
your MTB has Shimano stuff on it -- if it is a really low end bike with
weird parts, it might be more difficult.

Mainly, I wonder what you are trying to accomplish. There might be a
better way to get there. But, probably not as much fun.

Regards,
Larry

* * Chas said:

Quoted message said:

Make sure that the chain sizes are the same.

A 12 speed road bike probably has a 1/2" pitch chain that may be wider
than the MTB deraileur is designed to handle.

Most MTBs from the last 10 years use index shifting and the are a number
of different flavors of these setups.

So the answer is maybe?

Chas.

The statement above about chain pitch is incorrect:

Every 6 speed or 5 speed rear freewwheel that I have seen works well
with a chain designed for 3/32" cogs. Such a chain is advertised as a
"3/32 chain", as opposed to one of the newer narrow chains for 7-10
speed frewheels / cogsets. This refers to the width of the teeth the
chain is made for.

Note: I cheat and use cheap, 3/32 " chains on 7 speed freewheels /
cogsets, even though they are supposed to take narrow, 7/8 spd chains.

Excerpt from the Harris Cyclery / Sheldon Brown Website Glossary:

http://sheldonbrown.com/gloss_p.html#pitch

PITCH: "The pitch of a chain is the distance between adjacent drive
rollers. All modern bicycles use 1/2" pitch. Some older chains,
especially those used on track bicycles used 1" pitch chain (see skip
link and block chain.) For a while, Shimano experimented with a 10 mm
pitch for track use, but it never caught on.
Sometimes people mistakenly refer to "track pitch" vs. "road pitch"
when they are really referring to the wider (1/8"😉 sprockets used on
single-speed bicycles, instead of the 3/32" thick sprockets used on
derailer-equipped bicycles.

(End website Excerpt)

Regards,
Pat Smith