Front Derailleur to manage jump 22>38t unpinned

[sarniacycle]

Evening all

I have a 1x10 set-up on my touring bike. The front ring (38t, unramped & unpinned) is middle mounted on a mountain triple and I'm happy with this 99.5% of the time. But I also have a 22t granny for really loaded touring and use some old double front derailleur pulled by a downtube shifter to shift down and up (a hit and miss process, you can imagine, but I use it so rarely it doesn't bother me.) Now I have a little time to tweak things, I'd like to improve my chances.

Does any particular front derailleur stand out in people's experience as being especially effective at managing the jump from 22t to 38t, unramped and unpinned? I'm imagining a triple FD for starters any clues about particular models? Indexing is not an issue, would need to be 31.8 band on.

Many thanks

Adam

[Nebulous]

Shimano FD M615 is designed for 22-36T double. That could work.

http://www.retrobike.co.uk/forum/viewto ... 9&t=408616

Bit of fettling needed perhaps. But at £7, worth a shot.

NB I have no affiliation to this item.

[Mick F]

22 to 38
What's the difference in radii?

Let's say 22t is 11" circumference = 3.5" diameter = 1.75" radius.
Let's say 38t is 19" circumference = 6" diameter = 3" radius.
3" - 1.75" = 1.25"

I had a 36/53 chainset for years. Stronglight 99 and unramped and unpinned. Just plain chainrings. Still have them!
36t = 2.8" radius
53t = 4.2" radius

Difference is 1.4" and it worked fine.

[Brucey]

difference in radius happens to be very close to 2mm per tooth, so 16T is 32mm difference in radius (*).

IME the downshift will be dominated by the fit of the chain on the teeth of the 36T ring, and the lack of any shift gates in the ring. The former can be more important than the latter; if the downshift is reluctant to go the first thing I'd do is to check the exact width of the tooth and compare it with the tooth width for a derailleur setup using the same chain. As little as 0.1mm can make a difference here; the chain will be noticeably reluctant to shift if it is even slightly snug on the teeth, so a chain that 'fits well' is not the best chain for shifting; it actually needs to be laterally sloppy for the best shifting. You can make shift gates by truncating a tooth, at two points on the chainring.

The chain only won't 'land' on the small chainring if the spacing is wrong. If this turns out to be a problem (with the chain falling too far to the left) you can fit a jump stop.

Upshifts will be dominated by the (lack of) ramps on the chainring, the tooth height on the big ring, and the FD profile. If you can use a FD meant for a 16T interval then great, but if it is a triple FD then it won't have the correct curvature to the outer side plate. However unless you can get a double mech meant for a ~38T to 40T big ring then this will be the case. IIRC there are some MTB doubles which are about like that, so (if I was going to get another mech at all) I'd just get one of those (for matching chain width), even if it was meant for 14T interval or something like that; a slightly larger tooth interval than specified is no problem on a double.

Since the shift quality will be dominated by the big ring, if the shifting is poor I'd probably just get a middle ring for a triple and use that. The exact type of FD is likely to be far less important than the chainring.

(*) circumference per tooth / (2x Pi) = 12.7mm/(2 x Pi) = 2.021mm

cheers

[sarniacycle]

Thanks Jan, Mick and Brucey for your time - this is all really helpful and I've learned quite a bit to boot. Cheers! Adam

[Tigerbiten]

How are you going to shift it ??

If it is to be only once in a blue moon and you fit some form of friction lever then you can use any front derailleur that works.
That's how my 55/38 front double is setup.
But if you use some form of indexing shifter then you'll probably need to match the derailleur to the lever so you have the correct matching cable pull between the two parts.
This may limit you on exactly what derailleur works with what lever, road and MTB parts may not work well together.

Luck ...........

[peterh11]

Shifting on a double front with a friction lever is quite easy with a bit of practice, if you take care to set the high and low stops right. For a number of years I used a Suntour “Edge” double front derailleur with a Shimano friction lever and once set up right it worked well with 12, 16, and even 20 tooth difference over the years. This was with a 2x8 and at the end 28/44 chainrings with no modern pins or ramps. I could just go from one stop to the other and only needed to trim if close to small/small or big/big.

Another data point for you.

PeterH

[nsew]

Evening all

I have a 1x10 set-up on my touring bike. The front ring (38t, unramped & unpinned) is middle mounted on a mountain triple and I'm happy with this 99.5% of the time. But I also have a 22t granny for really loaded touring and use some old double front derailleur pulled by a downtube shifter to shift down and up (a hit and miss process, you can imagine, but I use it so rarely it doesn't bother me.) Now I have a little time to tweak things, I'd like to improve my chances.

Does any particular front derailleur stand out in people's experience as being especially effective at managing the jump from 22t to 38t, unramped and unpinned? I'm imagining a triple FD for starters any clues about particular models? Indexing is not an issue, would need to be 31.8 band on.

Many thanks

Adam

Shimano FD-CX70 (Ultegra level) will handle that comfortably. I use with 24-39-42 7spd. Judging from reviews it’s a derailleur that shifts a broad range of tricky combinations with ease. Here’s a good video https://youtu.be/hRJK6cBO-zY

[sarniacycle]

Thanks peterh11 and nsew - more good tips here. I've got a new (old) front derailleur on order and will see how that first.

Thanks all, all good for the time being.

[TheBomber]

+1 for the CX70 mech. Amazed at how well it moves my 10sp chain on an old Stronglight 28-42 double chainset sans ramps, pins or gates. Operated by a road STI lever.