Top pull front derailleur for 2x (46/30)

Nics

New member
Hi everyone,

I am looking for the right derailleur for the following setup:

I have a 2x gravel crankset with 46/30 chainrings. The standard GRX and Road front derailleur for this setup are of the down pull type. But I would like a top pull front derailleur instead because I want to utilize the space between rear tire and seat tube for small but heavy luggage items on bicycle tours. If there's a cable going down from the front derailleur to the bottom bracket the space is a lot smaller than it already is.

Because I have a flat bar handlebar I could use front derailleurs with pull ratios made for mountain bike or road bike shifters.

I'm not sure what the best (good functionality, light) option is. The Shimano Cyclocross specific cx70 front derailleur? Are there mountain bike front derailleurs made for 2x and do they work with my chainring sizes? I am aware of the Problem Solvers pulley solution but that defeats the purpose because it eliminates the space between seat tube and tire even more than the cable going down to the bottom bracket.

Maybe a down pulll front derailleur would also work (especially if it is a braze on model) if the cable is running far enough to the front and/or to the side. I don't have a clear picture of where the cable is actually running.

And a somewhat separate question: do top pull front derailleurs work just as smoothly and precisely as down pull front derailleurs?
 
Hi everyone,

I am looking for the right derailleur for the following setup:

I have a 2x gravel crankset with 46/30 chainrings. The standard GRX and Road front derailleur for this setup are of the down pull type. But I would like a top pull front derailleur instead because I want to utilize the space between rear tire and seat tube for small but heavy luggage items on bicycle tours. If there's a cable going down from the front derailleur to the bottom bracket the space is a lot smaller than it already is.

Because I have a flat bar handlebar I could use front derailleurs with pull ratios made for mountain bike or road bike shifters.

I'm not sure what the best (good functionality, light) option is. The Shimano Cyclocross specific cx70 front derailleur? Are there mountain bike front derailleurs made for 2x and do they work with my chainring sizes? I am aware of the Problem Solvers pulley solution but that defeats the purpose because it eliminates the space between seat tube and tire even more than the cable going down to the bottom bracket.

Maybe a down pulll front derailleur would also work (especially if it is a braze on model) if the cable is running far enough to the front and/or to the side. I don't have a clear picture of where the cable is actually running.

And a somewhat separate question: do top pull front derailleurs work just as smoothly and precisely as down pull front derailleurs?

Hi Nics,

You could use a Shimano cyclocross top-pull FD (with a matching shifter) FD-CX70-F-T. Note that this derailleur uses the "old" style shifters, so it won't work with the new 11-speed Shimano road shifters (nor with the 10-speed Tiagra 4700), and it's not a perfect match for MTB shifters (it can work OK-ish, but not ideally). So, for the best shifting, you would need to use either a friction shifter, or a 9 (or fewer) speed road shifter (like Sora, Claris, etc.) - or the old 10-speed ones like 105 5600, 105 5700, Ultegra 6700, etc.

MTB FDs for doubles are not designed for chainrings larger than 42 teeth (if even that many). So they would not work perfectly well with the 30-46 cranks.

In terms of performance, top or bottom routing doesn't seem to make any difference I could notice. Both are good in and of themselves (other factors matter more - like your luggage clearance problem).

Regarding the cable routing question, you might be able to see that in my video about friction shifters, in the section where I talk about down-tube shifters (the link should start it at 7:50 where that's visible and where I'm explaining it):


Relja
 
Hi Nics,

You could use a Shimano cyclocross top-pull FD (with a matching shifter) FD-CX70-F-T. Note that this derailleur uses the "old" style shifters, so it won't work with the new 11-speed Shimano road shifters (nor with the 10-speed Tiagra 4700), and it's not a perfect match for MTB shifters (it can work OK-ish, but not ideally). So, for the best shifting, you would need to use either a friction shifter, or a 9 (or fewer) speed road shifter (like Sora, Claris, etc.) - or the old 10-speed ones like 105 5600, 105 5700, Ultegra 6700, etc.

MTB FDs for doubles are not designed for chainrings larger than 42 teeth (if even that many). So they would not work perfectly well with the 30-46 cranks.

In terms of performance, top or bottom routing doesn't seem to make any difference I could notice. Both are good in and of themselves (other factors matter more - like your luggage clearance problem).

Regarding the cable routing question, you might be able to see that in my video about friction shifters, in the section where I talk about down-tube shifters (the link should start it at 7:50 where that's visible and where I'm explaining it):


Relja
Hey Relja,

what a nice coincidence that you published that video today. I found it very helpful.

Are flat bar thumb friction shifters the only option or is there a flat bar option in the following two categories that you mentioned? "9 (or fewer) speed road shifter (like Sora, Claris, etc.) - or the old 10-speed ones like 105 5600, 105 5700, Ultegra 6700, etc."

The SHIMANO CX70 FD you mentioned is 10 speed. Does that work with my 11 speed drivetrain (mainly the chain)?

Nics
 
Hey Relja,

what a nice coincidence that you published that video today. I found it very helpful.

Are flat bar thumb friction shifters the only option or is there a flat bar option in the following two categories that you mentioned? "9 (or fewer) speed road shifter (like Sora, Claris, etc.) - or the old 10-speed ones like 105 5600, 105 5700, Ultegra 6700, etc."

The SHIMANO CX70 FD you mentioned is 10 speed. Does that work with my 11 speed drivetrain (mainly the chain)?

Nics

A 10-speed FD should work fine with an 11-speed chain.

For shifters, Shimano makes flat bar road-compatible Shifters (if memory serves me, Claris and Sora are made with the flatbar shifter variant - I'd have to Google for details).
Microshift is another company that makes various Shimano-compatible shifters (along with decent friction shifters).

If you are going with 2x11 speeds, then you might need to get unmatched shifters for the front and the rear, because Shimano's 11-speed front road shifters are designed for their new road FD cable pull (those are designed to require a lot more cable pulled for a shift compared to Shimano's older road FDs and their MTB FDs).

Edit - my brain still works OK: :)

Relja
 
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Will a 43.5mm chainline front derailleur like the one you mentioned at the beginning of your first reply (FD-CX70-F-T) work with a 46mm chainline crankset?
And doesn't that also depend on the direct mount brace of the frame?
To make the this front derailleur perfectly compatible with the 46 mm chain line crankset I mentioned, would it not be sufficient to have a direct mount derailleur brace welded to the frame that is designed for a gravel / 46 mm front chain line?
 
Will a 43.5mm chainline front derailleur like the one you mentioned at the beginning of your first reply (FD-CX70-F-T) work with a 46mm chainline crankset?
And doesn't that also depend on the direct mount brace of the frame?
To make the this front derailleur perfectly compatible with the 46 mm chain line crankset I mentioned, would it not be sufficient to have a direct mount derailleur brace welded to the frame that is designed for a gravel / 46 mm front chain line?

Good question - will the FD be able to swing far enough out?

My old FD swings no problems to a 47.9 mm chainline (with some room to spare) - the calculation and the bike are shown in this video:


Will the new CX-style FD be able to move by the about 3 mm further out than its stated optimal chainline? I don't know before I try it.

Relja
 
Good question - will the FD be able to swing far enough out?

My old FD swings no problems to a 47.9 mm chainline (with some room to spare) - the calculation and the bike are shown in this video:


Will the new CX-style FD be able to move by the about 3 mm further out than its stated optimal chainline? I don't know before I try it.

Relja
Is your derailleur in the video a Shimano road (43.5mm chainline) FD?

And do you know whether the brace that holds a direct mount (braze on) FD must be specific to the chainline of the road derailleur?
Are those braze on brackets always at the same distance to the frame center or does it vary depending on the chainline of the FD?

My thinking is that I could weld on a FD braze on bracket that is ~2mm further outward than usual. Then the chainline of FD would again match the crankset chainline again (almost) perfectly.
 
Is your derailleur in the video a Shimano road (43.5mm chainline) FD?

And do you know whether the brace that holds a direct mount (braze on) FD must be specific to the chainline of the road derailleur?
Are those braze on brackets always at the same distance to the frame center or does it vary depending on the chainline of the FD?

My thinking is that I could weld on a FD braze on bracket that is ~2mm further outward. Then the chainline of FD would again match the crankset chainline again (almost) perfectly.

That is an old road FD. I'm not 100% sure, but I think it was from the 126 mm hub era and relatively narrow chainlines. I'd have to take a look at the model and try to google the specs to confirm.

Of course, that doesn't guarantee that the newer Shimano FDs are built with the same movement range (haven't got that CX model at hand to check and compare).

If your frame has round tubes (not oval), you could use a FD with a clamp, or get a clamp separtely (to mount a FD without a clamp). No need to complicate with welding a hanger. Clamp also gives you more up-down movement range, if you wish to play with different front chainring sizes.

I don't know enough about frame-building standards to say how far out the braze-on mount should be from the bike's centre-line (not from the tube, because tube diameters differ, and the chainline is measured from the bike's longitudinal centre-line). I suppose that could be measured on bikes with the brazed-on mount. Welding a hanger too far out could limit choices if you decide to use smaller-chainline cranks or go with a triple crank (the FD's movement towards the frame is also limited, of course).

Relja
 
That is an old road FD. I'm not 100% sure, but I think it was from the 126 mm hub era and relatively narrow chainlines. I'd have to take a look at the model and try to google the specs to confirm.

Of course, that doesn't guarantee that the newer Shimano FDs are built with the same movement range (haven't got that CX model at hand to check and compare).

If your frame has round tubes (not oval), you could use a FD with a clamp, or get a clamp separtely (to mount a FD without a clamp). No need to complicate with welding a hanger. Clamp also gives you more up-down movement range, if you wish to play with different front chainring sizes.

I don't know enough about frame-building standards to say how far out the braze-on mount should be from the bike's centre-line (not from the tube, because tube diameters differ, and the chainline is measured from the bike's longitudinal centre-line). I suppose that could be measured on bikes with the brazed-on mount. Welding a hanger too far out could limit choices if you decide to use smaller-chainline cranks or go with a triple crank (the FD's movement towards the frame is also limited, of course).

Relja
Good idea with the bolt on clamp option. I guess that was I can control the perfect chainline by putting some spacer material (tin can or similar) between the clamp and the frame.
 
Good idea with the bolt on clamp option. I guess that was I can control the perfect chainline by putting some spacer material (tin can or similar) between the clamp and the frame.

Good thinking. Yes. :)

If your seat tube is 28.6 mm diameter, you could use a clamp made for 31.8 mm and add a shim (some clamps come with the shim, and you can source those separately - or improvise one).

If your seat tube is 31.8 mm diameter, you could try to find a 34.9 mm diameter shim and a matching spacer.

Not sure if there are any options for such improvisation if your tube is 34.9 mm though.

Relja
 
There is also a version of the same FD with an integrated clamp (it seems): https://bike.shimano.com/en-EU/prod...d-onroad-hydraulic-diskbrake/FD-CX70-B-T.html

I think I prefer that because it's lighter and probably cheaper than a braze on FD + after market clamp on bracket and I can still put something between clamp and tube even though my tube is 34.9 but with a longer screw maybe I can get 1mm out of it.

The other option would be the braze on version because there I can vary the distance from the tube center a s I want.

I will have to think about it.
 
I think I do favor the braze on version because there I can make the FD chainline match the crankset chainline perfectly, it's lightweight, cheap, and if I do decide to run a "normal" road down pull front derailleur there's always a Shimano road option with a 43.5 mm chain line. This works because I will not run a normal road crank set with a 43.5 mm chain line. Not having a clamp around the seat post also is beneficial (simplifying production) for the box I want to put behind the seat tube. The only disadvantage I see is that the tube gets a bit weakened through the extra welding heat of the braze on bracket but it's not a high stress area.
 
There is also a version of the same FD with an integrated clamp (it seems): https://bike.shimano.com/en-EU/prod...d-onroad-hydraulic-diskbrake/FD-CX70-B-T.html

I think I prefer that because it's lighter and probably cheaper than a braze on FD + after market clamp on bracket and I can still put something between clamp and tube even though my tube is 34.9 but with a longer screw maybe I can get 1mm out of it.

The other option would be the braze on version because there I can vary the distance from the tube center a s I want.

I will have to think about it.

A note, just to be on the safe side:
In practice, adding "only" 1 mm may not be very easy.
The clamp is designed to be a pretty tight fit.
You might need to do some filing of the clamp's end (it's usually a 90-degree finish, and that angle might "hit" the seat-tube if you add 1 mm of spacers even on only one side).

Of course, this is not relevant if you decide to go with the brazed on mount (which has its pros, as you've noted).

Relja
 
Update:

Just checked my FD model. It is the old 105, model FD-1050 VIA.
Late 80s, 8-speed (probably - may someone correct me if I'm wrong), 43.5 mm designed chainline.
 

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