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Old 09-23-11, 06:17 PM   #1
robo
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SRAM Rival front shifting - expectations vs reality

This is my first experience setting up and using indexed front shifting on a road bike - the bike is equipped with SRAM Rival brifters and derailleurs, and an FSA Gossamer Cross (34-44) crank and chainrings.

The front derailleur is aligned according to the manual, and the limit screws are set correctly.

The problem is that when the chain is in the lower geared half of the rear sprocket, it is difficult to shift to the large chainring (this is a double). When in the higher geared half of the rear sprocket, shifting up to the large ring is generally fine. Shifting back down to the small chainring is fine.

I can shorten the front derailleur cable with the inline adjuster, but this seems to set the alignment such that in the large chainring position, the front derailleur is pressed worryingly hard against the limit screw and the 'trim' click doesn't actually move the front derailleur, just reduces the excessive tension in the cable.

I could take the limit screw out a bit, but this takes it beyond what is specified in the manual, and also allows the chain to fall off the outside in some circumstances...


My question is whether this is expected behavior (only being able to shift up on the front reliably when in the higher geared half of the rear sprocket). Obviously using the larger rear cogs with the larger chainring is not ideal (cross chaining), but on a double (my past experience is with triples and friction front shifting) should one not be able to shift up or down on the front regardless of rear derailleur position?
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Old 09-23-11, 08:54 PM   #2
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Are those chainring sizes correct? The Gossamer Cross cranksets I'm finding are 46/36, not 44/34. 44 is getting pretty small for a road derailler though it still should work. If you are using 44/34 rings, are they ramped and pinned or flat chainrings (Sugino or similar)?

You should not have any problem shifting into the big ring regardless of which cassette cog you are in assuming ramped and pinned rings. Check the height of the derailler cage relative to the big chainring. It shouldn't be more than 2-3mm higher than the big ring when in its outermost position. Also, try making smaller adjustments to the limit screw. The front derailler shouldn't go from not shifting to over shifting at the slightest tweak.
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Old 09-23-11, 09:36 PM   #3
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Just to eliminate the possibility that chainring phasing isn't a factor. Are those the original paired chainrings on the crank, or did you switch one or the other?

If they're not original, I'll go deeper into how phasing might a factor and how to deal with it if it is.
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Old 09-24-11, 10:00 PM   #4
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Sram road front shifting is very sensitive to two things - the quality of the rngs/crankset that it is shifting on and the stiffness of the front derailleur hanger that it is attached to.

1) Gossamer chainrings, anything not marked N-10 or S-10 latest gen chainrings will shift like crap.
2) The derailleur rotaton must be set precisely so that the inside of the outer derailleur cage is parallel to the chain in the large ring, small cog combo.
3) The derailleur low limit must be set by precisely incrementing the low limit from a non rub situation to a rub situaton. Then, only then can you set the cable tension, set the maximum cable tenson possible until you lose the trim click.
4) Derailleur high limit again, set by extremem soft pedalling and running it as far out as possible without chain drop.

If you've never setup finicky 10 speed front shifting before (i'm assuming it's 10 speed), be prepared for some time investment.

We've literally setup a million bikes with sram front shifting on road bikes and even on a fully 10 speed sram spec'ed drivetrain, performance wise they are all over the map compared to shimano 10.
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Old 09-27-11, 02:54 PM   #5
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Thanks (by the way, it is indeed a 36/46, not a 34/44.. typo on my part).

Anyhow, I'll try your suggestions operator. The chainrings are FSA (the ones that came with the Gossamer Cross crank), the chain is a KMC DX-10SC, and of course the derailleur is SRAM Rival - clamp on style, bottom pull, but with a pulley allowing top tube cable routing. And yes, it's 10 speed.

I guess all of this (including the extra convoluted cable routing) is adding up to the poor shifting. I tried adjusting the setup again, and it seems inconsistent to a degree that really has me puzzled. We went on a long ride the other day, and during parts of the ride, front shifting was fine (regardless of rear chain position), and during others, it was literally almost impossible to get the chain on the large ring except when on the smallest few sprockets.

It's frustrating - particularly since it's my girlfriend's new bike and she now thinks I'm a completely incompetent bike mechanic :not amused:

Oh well - if this doesn't help, she may need a bigger large ring anyhow - any suggestions for a replacement?

Last edited by robo; 09-27-11 at 02:57 PM.
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Old 09-27-11, 04:39 PM   #6
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Quote:
Originally Posted by robo View Post
Oh well - if this doesn't help, she may need a bigger large ring anyhow - any suggestions for a replacement?
I don't think FSA makes a specific 50T ring to work with a 36T inner but they do make a 50T for a 34T inner which should work decent enough: http://www.universalcycles.com/shopp...7&category=641

Keep in mind that the larger jump is only likely to decrease shifting performance. You might want to consider picking up a Shimano compact crank which are generally known to shift far better than FSA cranksets. You can pick up a Tiagra 4600 compact for only a little more than the cost of that FSA outer chainring: http://www.ribblecycles.co.uk/sp/roa...et/SHIMCHAR465

Of course you'll need the matching bottom bracket too but that's pretty cheap too. You could then swap over the 36T ring from the FSA crank if your girlfriend prefers that to the 34T inner.
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Old 09-27-11, 07:47 PM   #7
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Quote:
Originally Posted by FBinNY View Post
Just to eliminate the possibility that chainring phasing isn't a factor. Are those the original paired chainrings on the crank, or did you switch one or the other?

If they're not original, I'll go deeper into how phasing might a factor and how to deal with it if it is.
School us on that. I bought a 36 tooth ring to replace the 34 of my 50-34. Is that what you are talking about?

After I got the 36 I found that SRAM does not recommend the 50-36 combination. Being hard-headed, I installed it anyway and it works real nice.
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Old 09-27-11, 08:37 PM   #8
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It isn't a question of the chainring size, but the orientation. When you have rings of different size you'll have areas where the teeth line up and areas where they don't. It's real easy to see this on a cassette.

On sprockets that don't have shift gates, the chain will move over when the alignment is such that the chain can be engaged on both simultaneously, something that happens a few times every revolution. But if you have a shift gate you want that favorably aligned position to happen at the shift gate.

When the phasing is bad on a downshift the chain will drop to the inner with the roller meeting the top of the teeth rather than the valley. When that happens you'll feel the crank advance a bit before the chain drops in. Upshifting is similar, you want the right part of the link to meet the pickup pin for the smoothest shift.

If you suspect that your chainrings aren't phased well, shift to the inner, then turning the crank slowly as you downshift and stop just as the chain first meets the smaller ring. Hold it in that half shifted position and see if the teeth line up. If not, you can rotate the inner and try one of the other four (on a 5-bolt mount) positions to find the one that lines up best.
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Old 09-27-11, 10:49 PM   #9
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Quote:
Originally Posted by joejack951 View Post
I don't think FSA makes a specific 50T ring to work with a 36T inner but they do make a 50T for a 34T inner which should work decent enough: http://www.universalcycles.com/shopp...7&category=641

Keep in mind that the larger jump is only likely to decrease shifting performance. You might want to consider picking up a Shimano compact crank which are generally known to shift far better than FSA cranksets. You can pick up a Tiagra 4600 compact for only a little more than the cost of that FSA outer chainring: http://www.ribblecycles.co.uk/sp/roa...et/SHIMCHAR465

Of course you'll need the matching bottom bracket too but that's pretty cheap too. You could then swap over the 36T ring from the FSA crank if your girlfriend prefers that to the 34T inner.
Thr rings you linkex are of the old non performing design. Op shoukd look for the n10 rings that are a bit more expensive and look like they are much stiffer.

I do agree that a 50/34 shimano is the best performing option.
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Old 09-21-12, 05:53 AM   #10
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Just wanted to post an update, as I just (!) solved the shifting issue, nearly a year later, without needing to replace parts. Basically, I'd tried all the adjustment tips given here, but nothing solved the problem. The front shifting would be perfectly adjusted, and then inexplicably, mid-ride, would be all out of adjustment... then an hour later, working perfectly. It made no sense. A couple bike shops looked at it and said everything was adjusted correctly, and there was no problem they could see. My gf just got used to intermittently not being able to shift on the front and stopped mentioning it - she just sometimes had to stop, get off, and manually push the chain from one chainring to another.

Then the other day while doing a routine lube and checkup on her bike I started to notice a creaking noise when the front derailleur cable. On further inspection it was coming from the cable pulley, which was a unit exactly like this: http://milewidesports.com/item//thor...u/lid=32966450

I removed the rear wheel, and unscrewed the pulley from the frame, and discovered that the pulley was on a bushing that was too tight - it could not turn easily and creaked as it turned.

I sanded out the nylon pulley so that it was a hair wider on the inside diameter, greased it, and reinstalled it, also without the cover:
(sorry about the filthy bike - it's covered in chalk dust)



Shifting has been perfect since then, for several hundred miles now!

Hope this helps someone else who might run into a similar issue.

Last edited by robo; 09-21-12 at 05:56 AM.
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Old 09-21-12, 06:57 AM   #11
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Hah. SRAM the red herring.

Hm, no sign of operator for six months...
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