Question about double shifters
 

What is it about front chainring configurations that makes a double front shifter work with 50/39/30 teeth chainrings but not a std 52/42/30?

I recently installed microshift 9 speed shifters knowing that I was buying the double shifters because the triple specific model wasn't available however the actual specs on microshifts website and all the reviews of the product say that they do shift doubles or triples but specifically it's listed as the 50/39/30 combo. My mechanic rigged mine up to work with the 52/42/30 but its far from perfect. In looking up the gear combos I see that the 50/39/30 would still give me a nice range of gears and take very little of the top end. Besides, at 235lbs, i'm never spinning out the top gears on the big ring unless i'm going down a pretty massive hill. I have an opportunity to the 50/39 tooth chainrings for pretty short money so it seems like a good move to make. I really don't want to go to a compact double because again, at 235, the granny gears come in very handy.

First, 52-42-30 is no longer the standard, most new triples have a 39 middle ring.
Whichever works better is dependent on the derailleur geometry, not the shifter.
Front derailleurs are designed to work best with a particular set of chainrings and chain width. Any departure from the design may reduce the deraileur's performance. The differences are in the rail depths and cage width.
A triple front shifter needs to have click stops (detents) that are compatible with the crankset. This does NOT mean that there must be two stops for a double or three steps for a triple. It simply means that there needs to be stops that will work. Shimano road triple shifters have 4 main stops and usually a trim stop for the smallest chainring. I am not familiar with your particular shifters.

If you drop the indexing criteria and learn to use a friction shifter,
even if just for the front derailleur,
then you can mix and match parts more readily.

On my Road bike, I fitted a 'Campag race triple', came as a 50, 40,30 .. swapped out the 30 for a 24.

and have a pair of friction Bar end shifters, Its fine.
the main shift controller is in the saddle, runs off :beer:

this is a flat bar to drop bar conversion. I realize I can pick up a leftside sora triple shifter for cheap that will solve my problems but I like the hand layout of the microshift model (soras can only downshift from the hoods). If I have to put a sora shifter on the left side it's not the end of the world but I'd like consistency. I don't really see how I could go to a friction based option.

As for the shifters i'm using, a lot of people aren't familiar with microshift www.microshift.biz if you look at the info for the 9 speed shifters you will see what i mean. I'm trying to understand what it is about the chain tooth size that would make these double shifters work with smaller chainrings but not larger. I totally understand what al1943 is saying about how the number of clicks doesn't really matter it's whether or not they move the derailer to the right place but the reviews of microshifts shifters consistently talk about the great versatility because they were both double adn triple compatible but now it seems like that isn't entirely true.

What is your front derailleur? Are you using the same FD that was on the bike previously when it had the flat bar? I ask this because I'm not aware of a FD that is compatible with both flat bar indexed shifters and road shifters; they pull different amounts of cable.

What is the front derailleur, the FD geometry may be the compatibility problem?

no, I swapped out the flat bar derailer because as you have said, it was a MTB and pulled differently. i'm using a Tiagra triple FD

Maybe it's the derailleur. Maybe your old FD accomodated the 40T middle ring, and the new one doesn't. I think I'm having a similar experience; I had to replace a 105 triple FD from '03 with a new Ultegra triple when I got my frame replaced; fatter seat tube. '03-vintage bike came with a 52-40-30. When I built up on the new frame, and set the height of the der according to the little guide sticker, the inner plate hits the teeth of the 40T chainring. I didn't know until reading this thread that 39 is the new "standard" for the middle. For now, I've just raised the derailleur up on the tube about 2mm; it's outside the "range" according to the guide sticker, but it shifts alright. Is that what the shop did to make yours work?

I'm not totally sure what he did to make it work other than he added a barrel adjuster. I guess i'm still confused on how the size of the rings impacts things. I envision a FD simply moving side to side and guiding the chain to the next sprocket, I didn't realize there is more to it than that. I need to look at it up close I suppose. i guess what i'm interested in is why Microshift rates the SHIFTERS as being able to handle 50/39/30 as opposed to saying a particular Front Deraileur handles it.

As of now, sometimes I struggle to get it down into the small ring. It doesn't always want to go there from the middle ring, but I can get it all the way down there from the big ring no problem. it's more than functional for now and I do a majority of my riding in the middle ring anyways. I usually hit the small ring for the bigger hills and the big ring only when I'm going down hills though I sometimes go to it when I'm cruising on th eflats. here in nyc, there is so much stop and go riding so there aren't a lot of long flat areas where I have the need for the big ring.

Triple front derailleurs are designed to work with a specified minimum difference between the large and middle rings; the height of the inner plate of the FD cage will vary according to what this specified difference is.

Example: Shimano's 6603 FD (Ultegra) is technically designed to work with a 6603 triple crankset with 52/39/30 rings. When the chain is shifted onto the large ring, the outer plate of the cage will be at the optimal distance from the large chainring's teeth, while the inner plate will just clear the middle ring.

Using this same FD with chainrings with a lesser difference between large and middle rings can present an issue. For instance, Shimano's 5603 (105) triple crankset has 50/39/30 rings; the difference is only 11t, compared to the 13t difference the FD is designed for. If you install the 6603 FD so that the outer plate of the cage is the "correct" distance above the large ring, the inner plate of the cage will contact the middle ring, preventing the shift. To counter this, you'd need to raise the FD's position on the seat tube so that the inner plate clears the middle ring on the upshift. The problem now is that the FD may be so high that you can't get decent upshifts, or you risk dropping the chain when you do.

I looked at the microshift site and have no idea why they specified a particular shifter to work with a particular chainring combination. The shifter pulls the cable a certain amount, causing the FD to move across the chainrings. A shifter needs to be compatible with a crankset in regards to the number of chainrings; the size of the chainrings is a compatibility issue with the FD.

This is exactly what I described above. 6603 FD, but 30/40/52, but since that's only 12t, the inner plate contacted the middle ring just as you describe. I would call them the "outer" and "inner" plates, though, so as not to cause confusion with the "front" and "back" of the bike.

It may be that my bike is shifting fine by raising the derailleur because the difference is only one tooth, but the OP's middle ring is a full three teeth above the FD's design spec. This would require raising the FD on the seat tube a LOT more (I reckon 6-ish mm), which likely compromises shifting performance.

Yeah, I think that's what caused the initial confusion, making the shifter the topic of the thread. But the OP also reports having replaced the FD.

Thanks for the correction, madpogue. When I was typing my post, the wording felt *odd*. No wonder...I was using the wrong terminology! (I've edited my above post).

I reread your post #8 and see that I did closely describe what you've experienced. FWIW, I actually did install a FD6603 on my FC5603 50/39/30 crankset; that's why I chose that scenario for my post. The cage is mounted a few millimeters higher than ideal; however, it has worked well. Shifting is excellent, I've never dropped the chain, and I've never had to touch the adjustment in the ~7k miles with this setup. Maybe I just got lucky. I don't think I would have had the same experience had there been a difference of one more tooth, though.

I don't believe Shimano ever offered a 40 tooth middle ring. With the exception of D-A, Shimano triples had 42 middle rings before 10-speeds became standard and now most have 39 middles. Campy has produced some triples with 40 middles.

EEK, you are correct. I dunno where I got the 40T notion from; just checked it and indeed, it's a 30-42-52. Which really has me wondering now why it still shifts alright. Sorry about all the misleading posts above. Hmm, found an old little-used Shimano SG 40T middle ring in a parts box; must be way old-school, as it has no pins or ramps. Probably won't work worth poo in replacement of the 42.