Front derailleur for compact chainset - any suggestions?

[Velorum59]

Has anyone experience of fitting front derailleurs for sub-compact chainsets on traditional road bikes?

I have fitted a Spa Super Compact TS2 chainset to my 1981 Mercian Rally GT.

34/24 chainrings which I find perfect for the very hilly local conditions.

I'm still using the original Suntour front changer (with friction downtube changers) and although it works OK there is a significant gap between it and the largest ring.

I have been told that there are MTB/Gravel Bike changers with shorter cages that may be a better fit.

Any recommendations?

Thanks!
Ian

 

[fossyant]

You'd usually drop the mech down either by adjusting where it sits on the braise on mount, or undo the mech's band and move it down.

But if you have a braise on mount, I doubt you'll be able to drop the mech enough to sit close to the chain rings as it will have been made before sub compacts came on the market. If it works, then it works.

 

[T4tomo]

I might be missing something, but cant you just slide the Suntour mech down the seat tube a bit?

 

[fossyant]

Other option is but a vintage MTB front mech !

 

[fossyant]

I'm guessing the cage doesn't follow the circumference of the ring very well as it's working with a much smaller ring than it was designed for.

 

[Velorum59]

I might be missing something, but cant you just slide the Suntour mech down the seat tube a bit?

Its down as far as it will go - but still a large gap between it and the largest chainwheel at the top!

 

[Velorum59]

I'm guessing the cage doesn't follow the circumference of the ring very well as it's working with a much smaller ring than it was designed for.

Exactly - these vintage changers were made to fit 50t+ chainwheels.

 

[fossyant]

Best bet is a vintage MTB front mech, especially a polished allot one if you want to keep the 'period' of the bike. They are designed for 42 - 46 rings.

 

[mickle]

I bought a NOS Suntour XC Pro recently for my tourer recently. Designed for Suntour MicroDrive which was immediately copied by Shi**no and marketed as Compact Drive. This was the moment that BCDs moved from 110mm to 94mm and from 48/46t outer rings to 42t. So any mid-nineties onwards mountain bike triple from the three (or four depending on how you count) Shi**no, Suntour, SRAM/SACHS will suit. Obvs pay attention to band size and whether top or bottom pull.

If you must have a *new* one i understand that Microshift currently make a few to fit modern 'alt' compact doubles, but good luck sourcing one. Spa Cycles aught to.

 

[Velorum59]

Thanks folks! I have a much better idea of what I need now. Will talk to Spa - I have always found them very helpful.

 

[fossyant]

Spa and SJS are something else...

 

[Velorum59]

Spa suggested trying a Shimano Claris triple changer.

This resulted in an even bigger gap than the original Suntour shifter - nearly 2 inches!

I found a Microshift Marvo 2x9 on the Bikeparts website so have ordered that.

 

[Velorum59]

Whilst waiting for the Microshift I thought that I would try a Shimano Altus FD-M315

Its looking promising - way less gap

 

[Velorum59]

The Shimano Altus didnt work out at all! The cable run is convoluted and stiff in bottom pull mode - I suspect top pull would be fine though. Try as I might I simply could not get clean changes from this and stop it from throwing the chain off the largest chainwheel. I suspect that some of this is due to the stiffness and imprecision of the cable pull. I spent hours yesterday out on the road adjusting the pull and fine tuning the actual position of the derailleur body with no success. I guess that its simply just not suited to this particular set up.

The Microshift Marvo 2x9 is another story!

Lovely clean cable run and required very little fiddling about with to achieve crisp changes.

It doesnt look like the most robust thing in the world due to the number of plastic components but at £20 Im not complaining. Im tempted to buy another just to keep as a spare in case the supply of these dies up!