Front shifters - how much cable do they shift?

[Colin MacDonald]

My daily commute bike started life as a drop-bar tourer with downtube
shifters. I recently converted it to flat bars with trigger shifters.

Pre-conversion, the downtube shifters (friction, rather than indexed)
could move the derailleur just about far enough to cover the triple
crankset. They needed an extra nudge to get onto the big ring, but
that was fine.

Post-conversion, the front shifter (Shimano Alivio triple, indexed)
can roughly span the big and middle chainring across the full range.
This is tolerable because I never use the small chainring on this bike
anyway, but it means a double-shift to get from middle-to-large or
back again.

My guess, therefore, is that downtube shifters move more cable from
one extreme to the other than trigger shifters. Is this right?

Colin

 

[landotter]

On Feb 15, 8:18 am, Colin MacDonald <[email protected]> wrote:

> My guess, therefore, is that downtube shifters move more cable from
> one extreme to the other than trigger shifters. Is this right?

That's my experience with old friction shifters--they had tolerance
for sloppy cable tension, so could pull more cable. This became
unnecessary with indexed systems. That said, if you like friction
front shifting, it's not too hard to find a flat bar friction shifter.
Best of both worlds.

 

[inahurry]

On Feb 15, 7:18 am, Colin MacDonald <[email protected]> wrote:
> My daily commute bike started life as a drop-bar tourer with downtube
> shifters.  I recently converted it to flat bars with trigger shifters.
>
> Pre-conversion, the downtube shifters (friction, rather than indexed)
> could move the derailleur just about far enough to cover the triple
> crankset.  They needed an extra nudge to get onto the big ring, but
> that was fine.
>
> Post-conversion, the front shifter (Shimano Alivio triple, indexed)
> can roughly span the big and middle chainring across the full range.
> This is tolerable because I never use the small chainring on this bike
> anyway, but it means a double-shift to get from middle-to-large or
> back again.
>
> My guess, therefore, is that downtube shifters move more cable from
> one extreme to the other than trigger shifters.  Is this right?
>
> Colin

Colin,

The indexed front shifters are very good at shifting if you have the
correct crankset and bottom bracket to go with them.
If you are still running the original cranks the shifting will be less
than satifactory.
You need to find a mountain type crankset and bottom bracket, road
will not work with mountain shifters and vise versa.
Try and find an LX crankset and bottom bracket and you will never look
back.
Remember the correct bottom bracket is determined by frame and the
cranks you are purchasing.

Inahurry

 

[Colin MacDonald]

On 15 Feb, 18:30, inahurry <[email protected]> wrote:
> On Feb 15, 7:18 am, Colin MacDonald <[email protected]> wrote:
>
>
>
> > My daily commute bike started life as a drop-bar tourer with downtube
> > shifters. I recently converted it to flat bars with trigger shifters.
>
> > Pre-conversion, the downtube shifters (friction, rather than indexed)
> > could move the derailleur just about far enough to cover the triple
> > crankset. They needed an extra nudge to get onto the big ring, but
> > that was fine.
>
> > Post-conversion, the front shifter (Shimano Alivio triple, indexed)
> > can roughly span the big and middle chainring across the full range.
> > This is tolerable because I never use the small chainring on this bike
> > anyway, but it means a double-shift to get from middle-to-large or
> > back again.
>
> > My guess, therefore, is that downtube shifters move more cable from
> > one extreme to the other than trigger shifters. Is this right?
>
> > Colin
>
> Colin,
>
> The indexed front shifters are very good at shifting if you have the
> correct crankset and bottom bracket to go with them.
> If you are still running the original cranks the shifting will be less
> than satifactory.
> You need to find a mountain type crankset and bottom bracket, road
> will not work with mountain shifters and vise versa.
> Try and find an LX crankset and bottom bracket and you will never look
> back.
> Remember the correct bottom bracket is determined by frame and the
> cranks you are purchasing.
>
> Inahurry

The bike has a Dotek 46-36-26 crankset fitted, which I think is a
mountain bike crankset, and I think it should work fine with the new
shifters. At least I hope so, because I'm not about to change it. My
suspicion is that the front derailleur is a roadie, and just doesn't
move far enough for a given amount of cable pull. Possibly it was
chosen to suit the downtube shifters when I upgraded the crankset some
years ago, but just doesn't have enough swing to work with indexed
shifters.

Colin

 

[meb]

On 15 Feb, 18:30, inahurry <[email protected]> wrote:
> On Feb 15, 7:18 am, Colin MacDonald <[email protected]> wrote:
>
>
>
> > My daily commute bike started life as a drop-bar tourer with downtube
> > shifters. I recently converted it to flat bars with trigger shifters.
>
> > Pre-conversion, the downtube shifters (friction, rather than indexed)
> > could move the derailleur just about far enough to cover the triple
> > crankset. They needed an extra nudge to get onto the big ring, but
> > that was fine.
>
> > Post-conversion, the front shifter (Shimano Alivio triple, indexed)
> > can roughly span the big and middle chainring across the full range.
> > This is tolerable because I never use the small chainring on this bike
> > anyway, but it means a double-shift to get from middle-to-large or
> > back again.
>
> > My guess, therefore, is that downtube shifters move more cable from
> > one extreme to the other than trigger shifters. Is this right?
>
> > Colin
>
> Colin,
>
> The indexed front shifters are very good at shifting if you have the
> correct crankset and bottom bracket to go with them.
> If you are still running the original cranks the shifting will be less
> than satifactory.
> You need to find a mountain type crankset and bottom bracket, road
> will not work with mountain shifters and vise versa.
> Try and find an LX crankset and bottom bracket and you will never look
> back.
> Remember the correct bottom bracket is determined by frame and the
> cranks you are purchasing.
>
> Inahurry

The bike has a Dotek 46-36-26 crankset fitted, which I think is a
mountain bike crankset, and I think it should work fine with the new
shifters. At least I hope so, because I'm not about to change it. My
suspicion is that the front derailleur is a roadie, and just doesn't
move far enough for a given amount of cable pull. Possibly it was
chosen to suit the downtube shifters when I upgraded the crankset some
years ago, but just doesn't have enough swing to work with indexed
shifters.

Colin

As you've correctly deduced, the problem is not in cranks. The front cable pull ratio is different for road vs. mountain. Most likely a road deraileur is fitted to go with the downtube shifters. Matching road shifter with road fder or moutain shifter with mountain fder would be the solution-either way.

Alternatively, if someone knows what the two rates are, it would be possible to add inline something to compensate for the difference in pull rate.