compatibility question: double FD on triple

[j.schwartz]

Greetings, 

Curious if the group thinks this on-sale Claris "double" front derailleur would work well with a Riv Silver 44/34/24 triple crankset on a Clem L?

https://www.rivbike.com/collections/garage-sales-parts/products/claris-double-front-derailleur

In my experience, cranksets with smaller large chainwheels don't always require a "triple" derailleur with such a big cage.

thank you

[Bill Lindsay]

You should call Riv and talk about it. Since they took that front derailleur off of a Clem, they should be able to tell you why they took it off. Was it because they were taking apart completes to sell frames? Or was it because that FD wasn’t working on Clem’s for some reason?

Bill Lindsay
El Cerrito Ca.

[Joe Bernard]

The answer is maybe. It doesn't work on the wider-Q triple I put on my Clem, but that Silver crank snugs everything up very close to the frame. So close in fact that I can't ride them with the stock BB, my feet kept missing the pedals!

[aeroperf]

The Claris FD-R2400 that came with the double Suguino XD2 on my Sam did not have enough throw when I took off the bashguard and added a third ring.

My rings were 46-36-26.  It was not an adjustment thing.  The 2400 was not physically able to move far enough.

The FD-R2000 lists the same 43.5 chainline as the 2400.  So I would say NO.

I would suggest going to a triple, like a Sora FD-R3030.

The chainline thing is interesting.  Chainrings are typically 5mm apart.  The chainline is the middle of the chainring set, measured in mm from the bike centerline.

For road bikes, Shimano spec, a double crankset has one ring at 41 and one ring at 46.  For triples, one ring is at 40, one at 45, and one at 50.

So the chainline for a double is at 43.5, and the shifter has to be able to bring the chain in to 41 and out to 46.  For a triple the chainline is at 45 and it has to bring it in to 40 and out to 50.

That's Shimano spec.  Rivs Silver cranks are installed with bottom brackets that move the chainline out to 47, probably because of the 135mm rear (MTB) spacing.

Now a Shimano road double derailleur would have to be able to move to about 52, plus some for adjustment, to the outside of a triple on a Riv.  They're just not designed for that.

[j.schwartz]

Thank you for this.

I have had luck pushing the limits but in this case, I'll just get a triple specific FD.

was tempted by the price on that Claris.

[Peter White]

That derailleur would do every shift except the shift from the 24 to the 34. To go from the 24 to the 34 you would have to go all the way to the 44 and then back down to the 34. To shift 44-34-24 cleanly, you need a derailleur that has a much lower inner plate.

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Peter White

[Conway Bennett]

I have a deore xt triple FD from my Sam that is not being used if you want to to buy it.

[aeroperf]

Also, speaking of chainlines, and Joe’s and Peter’s comments…

I have to clarify I’m talking about the Rivs that have a 135mm rear spacing (not, for instance, dedicated road bikes like Roadinis or Roadeos).

The Riv catalog for cranks specifies chainlines and bottom brackets.  So from their “Crank - Silver - Triple” they say:
“It’s compatible with JIS taper bottom brackets, which are most of them, and the chainline is about 47 with a 110mm Shimano BB, and 50mm with a 113. The Q-Factor with a 107mm BB is 154mm.”

To decompose this, JIS is Japanese Industrial Standard, which is generally used on square taper bottom brackets made in Asia, like Shimano, and really IS most of them.
They quote chainline with various widths of bottom bracket, measured across the width of the axle.  The BB that came on my Sam was 110, as was the BB that came on my Homer.  Somewhere (and don’t shoot me, I’m looking for the reference) I saw the chainline on the Sam listed as 47.5.
The 50mm note above is because the standard Shimano spec MTB chainline is 50mm.  So a 113mm bottom bracket would use a Shimano MTB front derailleur.
Finally, Q Factor is something Grant made up while working at Bridgestone.  It is the width between pedal attach points on a crank/BB system.  Supposedly, per Sheldon Brown, smaller is “ergonomically better” (which may be why they quote it for a 107mm bottom bracket).  https://en.wikipedia.org/wiki/Q_factor_(bicycles)
 
So, Joe, Q Factor may explain your missing the pedals - your personal geometry may need a bigger Quack Factor.

And as Peter says, you may need a bigger inner plate on the FD.  My 26-36-46 shifts just fine with a FD-R3030, but my Homer has 22-32-44 and I went with an M610 MTB front derailleur.  MTB derailleurs will not only go “out” farther (because of the 50mm chainline), but also have bigger inner plates for lifting the chain off smaller inner chainrings.

Probably more than anyone wanted to know.  But when I found out that my Sam was a road bike in the front and a mountain bike in the rear I had to do a little digging.

[Joe Bernard]

It is indeed true, my Quack Factor is high.

[James / Analog Cycles]

Best wide range triple for rings under 46t out there is the Shimano CX70, which Riv used to spec on completes.  It still works great.  Ultegra level, but technically designed for a CX bike.  You can get it lower than any road triple mech out there, and it will shift down to a 20t.  We've run it was a triple or a double set up, never any issues at all.  It can handle huge gear jumps, or normal ones.  We set up a bike with a 20-46t jump, and it shifted fine.  

-james / analog cycles