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Is 2x 4700 Tiagra better than 3500 Sora for minimizing chain rub?

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Is 2x 4700 Tiagra better than 3500 Sora for minimizing chain rub?

Old 03-30-16, 07:20 AM
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ph0rk
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Is 2x 4700 Tiagra better than 3500 Sora for minimizing chain rub?

I know, I know - cross chaining is the devil. The Sora 3500 group I have (well. FD, RD, and STis, the cassette is sram and the crankset is FSA) rubs something terrible, the two largest cogs in the big ring and the two smallest in the little chainring. I've fiddled with the limit screws and that is as good as it gets - unless I want chain rub at the other end of the cassette. I have checked and the rub is always the FD itself. No trim in the shifters.

So, evils of cross chaining aside - would a new Tiagra groupset (well, STis, FD, RD, chain, casette, crankset) rub this badly?
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Old 03-30-16, 10:33 AM
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Originally Posted by ph0rk View Post
So, evils of cross chaining aside - would a new Tiagra groupset (well, STis, FD, RD, chain, casette, crankset) rub this badly?
4700 would run a little better - especially up front. Do 3500 STIs have a trim function (~a half shift of the FD)?
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Old 03-30-16, 10:58 AM
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I've cured chain rub of chain and FD cage contact by having a friction shift lever

and simply move the lever to re center the cage after a rear (or front) shift.


So, evils of cross chaining aside - would a new Tiagra groupset (well, STis, FD, RD, chain, casette, crankset) rub this badly?

Other than reality can your dream be fulfilled?

With STI the engineers had the Idea that avoiding those cross chain combinations the cage should not scape .

avoid those combinations. & the fix is not requiring a parts change.

do a gear chart and learn the ratio sequence of the combinations [it requires counting tooth numbers] ..

Last edited by fietsbob; 03-30-16 at 11:08 AM.
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Old 03-30-16, 12:57 PM
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Sure, but on another bike that is SRAM 2x10 there is no rub in any gear. With all the sand and mud and crap this bike collects cross chaining isn't the biggest concern with respect to drivetrain life, I wouldn't think. Sora 3500 has no trim for the FD that I can figure out how to use - it is either little or big, no in between.

I can even decide which end of the cassette I want rub at with the limit screws - it is annoying I can't just be rub free across the whole cassette like my other bike - I'd settle for full range of cassette with big ring but I can't even get that with the stock FD. I tend to "live" right around the point where the small ring gets some rub, and shifting back and forth on the FD is a PITA - enough that I've considered shifting the rub on the big ring so it is my topmost gears (50x11 doesn't get used much, if at all). For a commuter bike it is annoying enough I'd consider changing up the group. Both rings look aligned pretty close to the middle of the cassette, too.
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Old 03-30-16, 01:11 PM
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Originally Posted by ph0rk View Post
I can even decide which end of the cassette I want rub at with the limit screws
You shouldn't attempt to adjust the limit screws to make cross-chain rubbing go away; that's not what the limit screws are for.

Are you certain you have the FD mounted properly, rotated so that the outer cage plate is parallel with the ring? Sometimes though, having the cage toe in or out a tiny bit can help.

You can always replace just the shifters to a higher end model that allows for trimming; no need to replace the entire drivetrain, unless you just ant an excuse to upgrade everything.
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Old 03-30-16, 01:58 PM
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the trim shift should take out most of the chain rub issue or you could change to a 10 speed chain it is slightly narrower and will allow a bit more cross chaining before it rubs?
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Old 03-30-16, 03:57 PM
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Aren't limit screws to set the maximum inward and outward range of the FD? As it currently sits, the limit screws are adjusted because of chain rub, not because of shifting - that is, limit screws set where shifting is smoothest and no further creates massive chain rub. In fact, when I bought the bike the upper range limit screw was out so much to avoid rub (I assume) I could shift the chain right off the big ring. At stands now, they are set for good shifting and then tweaked to minimize chain rub. This thing will rub in 50x11 and still snap up to the big ring just fine.

Originally Posted by techsensei View Post
Are you certain you have the FD mounted properly, rotated so that the outer cage plate is parallel with the ring?
No, I didn't mount it - but I'll check it out.

I should add that for the short term I am perfectly capable of shifting around it. It just annoys me every once and awhile - all the more given that I know it isn't a necessary part of FD function (at least in general - I think it might be with this FD and this chain).
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Old 03-30-16, 04:07 PM
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Originally Posted by ph0rk View Post
Aren't limit screws to set the maximum inward and outward range of the FD?
Yes, but the way you described it above, it sounded like you were adjusting the limit screws to get rid of cross-chaining noise. When you do that, it almost always result in poor shifting performance.
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Old 03-30-16, 04:45 PM
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Originally Posted by ph0rk View Post
I know, I know - cross chaining is the devil. The Sora 3500 group I have (well. FD, RD, and STis, the cassette is sram and the crankset is FSA) rubs something terrible, the two largest cogs in the big ring and the two smallest in the little chainring. I've fiddled with the limit screws and that is as good as it gets - unless I want chain rub at the other end of the cassette. I have checked and the rub is always the FD itself. No trim in the shifters.

So, evils of cross chaining aside - would a new Tiagra groupset (well, STis, FD, RD, chain, casette, crankset) rub this badly?
4700 is 10-speed, 3500 is 9. Are you planning a full upgrade?

Frankly I've had no problem eliminating chain rub with 3500, except for small-small. And half the time, that's the chain rubbing on the inside of the big ring, for which there is no cure that won't screw something else up. That's your sacrificial combination. Don't use it, it makes the chain flop around anyway. 4700 won't cure that.

Stop blindly twiddling limit screws and take it to a bike shop. Then ask the mechanic to show you how trim is supposed to work. Or, if you insist on doing it yourself, read the shift adjustment section of this book: https://www.amazon.com/Park-Tool-BBB-...bicycle+repair

Last edited by oldbobcat; 03-30-16 at 04:49 PM.
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Old 03-31-16, 08:31 AM
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Originally Posted by techsensei View Post
Yes, but the way you described it above, it sounded like you were adjusting the limit screws to get rid of cross-chaining noise. When you do that, it almost always result in poor shifting performance.

Fair enough - I was prioritizing shifting first and then seeing if I could ameliorate some of the rub - and the answer was not with that FD on that bike with that chainline.


Originally Posted by oldbobcat View Post
4700 is 10-speed, 3500 is 9. Are you planning a full upgrade?
At some point probably - or, if I were to do it I'd replace pretty much the entire group minus brakes.


Originally Posted by oldbobcat View Post
Frankly I've had no problem eliminating chain rub with 3500, except for small-small. And half the time, that's the chain rubbing on the inside of the big ring, for which there is no cure that won't screw something else up. That's your sacrificial combination. Don't use it, it makes the chain flop around anyway. 4700 won't cure that.
I still get chainrub from Big ring to two biggest cogs, and a hint of it on the third biggest cog. If I only had chanrub on small/small I'd live with it (well, I am living with it, but I'd be less annoyed), but I can't use the bottom/biggest two or three cogs on the big chainring, either.

Originally Posted by oldbobcat View Post
Stop blindly twiddling limit screws and take it to a bike shop. Then ask the mechanic to show you how trim is supposed to work. Or, if you insist on doing it yourself, read the shift adjustment section of this book: Park Tool BBB-3: Big Blue Book Bicycle Repair and Maintenance Guide: Amazon.com: Books
Edit: oh, and I have a copy of this, but it isn't terribly helpful about this issue

It isn't blind, and I think you're missing my point. My point was - if there were any reduction in chain rub to be had by adjusting the limit screws I have already claimed it, and it isn't enough. When it was new the limit screws were set wide enough to allow it to shift off the big ring and I had to fix that.

If you think I should be able to eliminate chainrub on the big ring with 3500, that's news. I haven't seen anyone else claim that - was it a Sora crankset, too? In terms of chainline, which rear cog was the big ring most closely in line with? In my case it appears to be between the 4th and 5th smallest cogs - close to the middle of the cassette.

I'd really prefer to fix it myself (to the extent it can be fixed). The local mechanics don't seem too enthusiastic about diagnosing minor things like this unless I show up when they're pretty dead. And, I usually have to spend the time to explain that it isn't a loose seat post, etc. Wrong time of year for that sort of stuff, I suppose, and trucking the bike out of town isn't happening - I'm car light.


Edit: scratch most of that - I was aware of the extra half click on the big ring but never noticed it on the small ring. With the FD adjusted and using trim I can avoid rub in all but small/small - though the limit screws did need to move to get there.

Last edited by ph0rk; 03-31-16 at 01:36 PM.
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Old 03-31-16, 07:10 PM
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OK, here's my protocol for front derailleur tuning. It's relevant for all current Shimano 8-10-speed road systems. Older systems differ in feel, clearances, and lack of trim in lower models. And 11-speed is a totally different animal.

First, align the derailleur correctly. The outer plate should be parallel to the chain rings and 1-2 mm above the large one. This is straight out of the Shimano tech docs.

Second, shift to big in back, small in front. Adjust the low limit screw (on the front derailleur, of course) so the cage barely clears the chain when the chain has tension on it. Loosen the cable if the cable isn't letting you do this. While you're looking at limit screws here, loosen the high limit screw a turn to give yourself some wiggle room.

Third, loosen the front inline adjuster an pull excess cable slack through the front derailleur pinch bolt. Don't pull the cable drum tight, a bit of slack is good.

Fourth, shift the rear derailleur to the smallest cog.

Now try a front derailleur shift. If it overshifts, replace the chain, tighten the limit screw a little, and try again. This time, don't pull the lever all the way, just far enough so it clicks. If it undershifts, shift back down, tighten the cable with the adjuster, and try again.

When it stays on the big ring, observe the position of the cage relative to the chain. It should clear the chain by about 1 mm. Adjust cable tension to affect this.

When you have the right cable tension, tighten the high limit screw so it lightly hits the bumper on the derailleur cage.

Try some practice shifts. If you're overshifting, loosen cable and tighten limit screw. If you're undershifting, tighten cable and loosen limit screw. Try some shifts with chain in other positions on the cassette. Satisfy yourself that you can hit the big ring from cogs 2-9 in the back.

Now we work on rub. There are two trim half-click positions on a 2-speed Sora front shifter. Low trim is a half-upshift from low, and high trim is a half-upshift from high. Shift to big-big and see if high trim can eliminate the rub. If it doesn't move the derailleur or it skips over into low, the cable is too tight against the limit screw. Release some cable tension or loosen the high limit screw, whichever seems more appropriate. Try again. Repeat until it all works.

Likewise, low trim will allow you to crosschain from the small ring to cogs 6-8 or 9 in the back. Generally, you can't adjust for this.

If you can get it right, remind yourself that any monkey that can follow directions can adjust a rear derailleur, but it takes finesse and judgement to get the front working just right.
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