Front derailleur for close ratios

[Craig]

My old bike had an Exage FD with triple chainrings 28, 34, 40 (it's
very flat where I live). I recently got a new bike with Alivio FD and
22, 32, 42 chainrings. Moving the old chainrings to the new bike, the
Alivio derailleur won't shift cleanly because the geometry of the cage
is different - it has to be set higher than optimum for the big
chainring so that it clears the middle one. Clearly it's designed for
the bigger difference in sizes. I can't fit the old Exage one because
the seat post diameter is different.

What current FD would work well with these ratios? Or, if the answer
is None, what is the minimum acceptable difference in number of teeth?

And, when buying a new FD, how is the clamp width specified - diameter
or seat post, or circumference?

Thanks

 

[LAN Support]

My wife's bike with 24-34-40 chainrings is using a Record triple FD without
problem. I suspect that any FD intended for double chainrings would work,
it's just that I didn't have a double FD with a 34.9mm clamp. The Deore XT
FD that was installed with the original 26-36-48 chainrings wouldn't work
with the 24-34-40 chainrings as the inside of the cage fouled the middle
chainring unless the FD was raised about 1/2" above where it should be.

Nick

"Craig" <[email protected]> wrote in message
news:[email protected]...
> My old bike had an Exage FD with triple chainrings 28, 34, 40 (it's
> very flat where I live). I recently got a new bike with Alivio FD and
> 22, 32, 42 chainrings. Moving the old chainrings to the new bike, the
> Alivio derailleur won't shift cleanly because the geometry of the cage
> is different - it has to be set higher than optimum for the big
> chainring so that it clears the middle one. Clearly it's designed for
> the bigger difference in sizes. I can't fit the old Exage one because
> the seat post diameter is different.

 

[Russell Seaton]

I just set up my half step plus granny touring bike with a Shimano
Sora double front derailleur. Chainrings of 45-42-20. Shifts OK.
Cost was about $11.50 for the derailleur from Nashbar. Surprisingly
the derailleur is able to handle the 25 tooth difference on the front
without the chain dragging on the bottom of the cage when in the small
cogs in back.


[email protected] (Craig) wrote in message news:<[email protected]>...
> My old bike had an Exage FD with triple chainrings 28, 34, 40 (it's
> very flat where I live). I recently got a new bike with Alivio FD and
> 22, 32, 42 chainrings. Moving the old chainrings to the new bike, the
> Alivio derailleur won't shift cleanly because the geometry of the cage
> is different - it has to be set higher than optimum for the big
> chainring so that it clears the middle one. Clearly it's designed for
> the bigger difference in sizes. I can't fit the old Exage one because
> the seat post diameter is different.
>
> What current FD would work well with these ratios? Or, if the answer
> is None, what is the minimum acceptable difference in number of teeth?
>
> And, when buying a new FD, how is the clamp width specified - diameter
> or seat post, or circumference?
>
> Thanks