The compact chainring front mech issues thread
- Thread starter nobrakes
- Start date
dtseng
Well-Known Member
Seriously, field lacing bike wheels is no big deal. I did it quite often. All you need is that red spoke tool.
I'm sure you're one of very few who feel this way. I've built a few wheels and with more practice sure I would improve. I don't travel with bike but I'd hate to think I had to relace and true two wheels upon arrival before I could ride. Not critisizing but impressed. I would have to find a different way.
Seth Cooper
Well-Known Member
So you are in the process of building a ti v20? Or you want to start? Are those pics of a ti boom and chain stay?
paco1961
Zen MBB Master
Just solved my S40 FD problem. In frustration I pulled off my Shimano 105 (5700) compact double, replaced it w my Ultegra (6800) compact double, set up the Sram yaw f derailleur and . . . Voila! The dang thing works. I have no explanation at all. Exact same specs except for weight and color . . . Guess my Lynskey frame is getting sold w the 105 crankset!
This is a real challenge and more and more people are asking for smaller rings - but with" stock" parts (The hanger is a stock part right out of the road bike catalog) you cannot have it both ways. The newer FD mount on the next run of stays (a ways out and I still need to get through the current ones so please don't flood the email) is in the works. We had to have a custom hanger made that is longer than anything else out there, as we couldn't just move the current one down a shorter stalk as then people who run QXL's or bigger rings would be out of space.
With the market going to all wide doubles and even to 1x setups we are trying this next round to accommodate as wide a possible range as is realistic.
With the market going to all wide doubles and even to 1x setups we are trying this next round to accommodate as wide a possible range as is realistic.
paco1961
Zen MBB Master
I can't imagine designing a frame these days to accommodate everything out there . . . or even try to get close! The fact that one can start with two cranksets identical in all reported measurements . . . and have one be a disaster and the other work just fine shows how much of a train wreck it can be! Tweak on CB masters!
dtseng
Well-Known Member
The detailed calculation is as follows:
The chainring diameter in mm is d = 12.75xN/pi, the radius r(50) = 101.5 mm, r(53) = 107.6 mm. Road bike FD mounting hole to lower edge of outer blade is 36 mm. The length of braze-on slot is 16 mm. Therefore, if the center of the slot is 145 mm to the center of BB, there is plenty of room to accommodate chain rings from 50-tooth to more than 53-tooth. (For even smaller chain rings such as 48, reduce the distance to 140 mm). I would suggest that braze-on slot 20 mm, slot center to BB center 143 mm, that would accommodate wide variety of chain rings and front derailleurs.
The chainring diameter in mm is d = 12.75xN/pi, the radius r(50) = 101.5 mm, r(53) = 107.6 mm. Road bike FD mounting hole to lower edge of outer blade is 36 mm. The length of braze-on slot is 16 mm. Therefore, if the center of the slot is 145 mm to the center of BB, there is plenty of room to accommodate chain rings from 50-tooth to more than 53-tooth. (For even smaller chain rings such as 48, reduce the distance to 140 mm). I would suggest that braze-on slot 20 mm, slot center to BB center 143 mm, that would accommodate wide variety of chain rings and front derailleurs.
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William Morris
Member
Has anyone used a Shimano or Microsoft triple front derailleur on a S40 ? I have a 48x38x28 crankset that I'd like to use. Are the FD issues exclusive to SRAM?
super slim
Zen MBB Master
I have a FSA Gossamer Expo triple with 53,39,25, Qrings, with external bearings, on a Silvio V1.0 Chain stay clamp on BB, and on a Silvio S30 Chain stay clamp on BB External bearings with lots of filing on the inside of the chainring and the right clamp to keep the same chain line as the V1.0.
Both with Shimano Ultegra ST6703 shifters and no problems with either!
Both with Shimano Ultegra ST6703 shifters and no problems with either!
William Morris
Member
Thanks for the feedback. My concern is that with a 48 tooth large ring the FD will be mounted too far from the cage. The Tiaga & 105 triple FD are optimized for a 50 tooth large ring, just like a compact double that so many people are having problems with.
nobrakes
Well-Known Member
After a couple more weeks trying to ride with the force 22 FD I've had it. I spoke to Robert and there are chainstays coming with longer braze on mounts, but in the meantime I've just ordered an Sram Rival 10 speed front mech which has 2 mounting positions instead of the central one on the force 22. Here's hoping it will work better - will report back when I've tried it.
I am glad to hear that the front derailleur stalk is being redesigned. On my Silvio 1.5 there are three problems with the front derailleur stalk . I am posting this in the hope that the new front derailleur stalk will have fixed all three issues.
1: The hanger is too short for compact chainrings.
2: The front derailleur is positioned in the wrong place and at the wrong angle .
This is the real problem with the front derailleur stalk as it prevents the work around solutions from working .
I got a Sugino adapter from Robert Holler which positioned the derailleur in the right place, but the angle of the derailleur is wrong and the chain touches the back of the derailleur in most of the gears on the large chainring. I was trying to load a photo to illustrate this , but failed.
Now that I have identified this, I have found that the chain will touch the back of the derailleur if I select large & large. 50 x 32
3:The derailleur is positioned too far inboard so there is not enough adjustment on the derailleur to position it correctly.
I have worked around this by putting a washer under one side of the derailleur stalk base which tilts the derailleur stalk over and allows enough derailleur adjustment.
1: The hanger is too short for compact chainrings.
2: The front derailleur is positioned in the wrong place and at the wrong angle .
This is the real problem with the front derailleur stalk as it prevents the work around solutions from working .
I got a Sugino adapter from Robert Holler which positioned the derailleur in the right place, but the angle of the derailleur is wrong and the chain touches the back of the derailleur in most of the gears on the large chainring. I was trying to load a photo to illustrate this , but failed.
Now that I have identified this, I have found that the chain will touch the back of the derailleur if I select large & large. 50 x 32
3:The derailleur is positioned too far inboard so there is not enough adjustment on the derailleur to position it correctly.
I have worked around this by putting a washer under one side of the derailleur stalk base which tilts the derailleur stalk over and allows enough derailleur adjustment.
nobrakes
Well-Known Member
I took the force 22 FD off today and got the Rival 10 speed one on instead. Haven’t had a chance to test ride yet but initial results are promising. I have spent literally 10 minutes setting it up and it is functioning pretty well. I’m sure it will be better once I get time to fettle it.
I added the wedge shim from the Rotor kit as the chain was catching on the top of the FD when I shifted due to the angle of the derailleur.
The trick with compacts appears to be to get a front mech with 2 mounting holes rather than one - you’ll see from the pic how close it is now because you can mount it in the furthest hole to get it that little bit closer.
Will report back more after a test ride.
I added the wedge shim from the Rotor kit as the chain was catching on the top of the FD when I shifted due to the angle of the derailleur.
The trick with compacts appears to be to get a front mech with 2 mounting holes rather than one - you’ll see from the pic how close it is now because you can mount it in the furthest hole to get it that little bit closer.
Will report back more after a test ride.
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dtseng
Well-Known Member
I am sure that would work. In a more ideal situation, the stalk should be angled in such a way so that the shifting of the chain should be initiated near the tail section of the FD blade/cage (i.e., a bit farther away from the engaging chain ring tooth). The front derailleurs are designed for road bike geometry. Perhaps they should make FD specifically for Cruzbike. Please refer to Auto CAD drawing in post #28, the stalk angle should be 65 .
How fast the shifting from 34 to 50-tooth ring depends on two factors: 1. as mentioned earlier, if the chain is pushed a bit farther away from the engaging tooth of the small ring, the chain can be flexed more easily toward the large ring; 2. on the inner surface of Shimano 50-tooth ring, there are 4 equally spaced studs (let's call them chain catchers), these studs would catch the edge of the chain and push it on the large chain ring tooth. FSA and RaceFace (pix below) also have 4 studs but not equally spaced.
How fast the shifting from 34 to 50-tooth ring depends on two factors: 1. as mentioned earlier, if the chain is pushed a bit farther away from the engaging tooth of the small ring, the chain can be flexed more easily toward the large ring; 2. on the inner surface of Shimano 50-tooth ring, there are 4 equally spaced studs (let's call them chain catchers), these studs would catch the edge of the chain and push it on the large chain ring tooth. FSA and RaceFace (pix below) also have 4 studs but not equally spaced.
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nobrakes
Well-Known Member
I've done around 100 miles on the V since changing the FD now - the chain hasn't been dropped once. It's not perfect shifting in terms of instantaneous shift up but it's good enough for now. I haven't really had a chance to fettle due to other commitments so I've just ridden it 'as-is' with a quick setup in the garage. I'm hoping I can improve on the crispness of the upshift with a bit more work. The chain is rubbing on the FD cage a little in the biggest two cogs when on the big ring, so a bit more adjustment needed. However, this is a viable solution if you are struggling with a compact - make sure you get an FD with 2 mount holes instead of one.
Is your previous FD issue that the chain occasionally falls off going from 34 to 50? I have a 50/34 with Rival 22 FD and have encountered that problem sometimes. I realized that I have to shift crisply and ease back on my leg force for the chain to shift up to 50. Of course that doesn't work too well if I am riding on the street and trying to speed up, and the chain falls off at the most inopportune time.
I am contemplating getting a chainring guard so that at least the chain doesn't fall on the crank arm. Do you think that could work?
https://www.amazon.com/Driveline-Gu...526062940&sr=8-2&keywords=driveline+chainring
paco1961
Zen MBB Master
Chain guard may help but I have not used that specific model.
I have Sram Force FD; 50-34 and yes, the problem I have encountered is the chain jumping off the outside of the big ring. I have mostly worked out that problem though not completely. The trick seems to be to play quite a bit with the outer limit screw. Do the basic Sram Yaw derailleur set up (that can be a little tricky but there are plenty of good YouTube videos - particularly the Art's Cyclery video). When you are done with that you will likely find that the chain can jump off the big ring, especially if you shift quickly or with inadequate pedal pressure. The last step is to work the outer limit screw in and out no more than 1/8 turn, maybe even less, at a time. You want it to set where on shift, you almost can't get the brifter to click as required. 1/8 - 1/16 of a turn too little/much and the chain jumps. that much too far in the other direction and the shift won't catch. Even with that I have to be careful on my shifts to the large ring. The shifting trick seems to be moderate (but not too much) force on the pedal as you shift until the chain slips into the chainring teeth, then continue the shift until it clicks in place. If you shift to quickly, the chain slides right by the teeth on the slight overshift that is designed into the Sram derailleur.
Now that I have this all worked out I only occasionally drop the chain . . . usually when I'm waiving and smiling at some pretty young woman or a TV camera! Karma has no sense of humor!
I have Sram Force FD; 50-34 and yes, the problem I have encountered is the chain jumping off the outside of the big ring. I have mostly worked out that problem though not completely. The trick seems to be to play quite a bit with the outer limit screw. Do the basic Sram Yaw derailleur set up (that can be a little tricky but there are plenty of good YouTube videos - particularly the Art's Cyclery video). When you are done with that you will likely find that the chain can jump off the big ring, especially if you shift quickly or with inadequate pedal pressure. The last step is to work the outer limit screw in and out no more than 1/8 turn, maybe even less, at a time. You want it to set where on shift, you almost can't get the brifter to click as required. 1/8 - 1/16 of a turn too little/much and the chain jumps. that much too far in the other direction and the shift won't catch. Even with that I have to be careful on my shifts to the large ring. The shifting trick seems to be moderate (but not too much) force on the pedal as you shift until the chain slips into the chainring teeth, then continue the shift until it clicks in place. If you shift to quickly, the chain slides right by the teeth on the slight overshift that is designed into the Sram derailleur.
Now that I have this all worked out I only occasionally drop the chain . . . usually when I'm waiving and smiling at some pretty young woman or a TV camera! Karma has no sense of humor!
