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sirrus elite chainline problem

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sirrus elite chainline problem

Old 10-06-11, 07:55 AM
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pothound
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sirrus elite chainline problem

i purchased a new sirrus elite bike for my wife, who is 5 foot 2 inches tall. the bike is 47cm in size. the bike is out of warranty now. its been more than a yr. i couldn't get specialized or the bike shop to modify the chainline. i need to repair it myself. the chainline is way off. the crank is too far out. it is a deore 28/38/48 crankset with 118mm bottom bracket. any help would be appreciated.
thank you pothound
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Old 10-06-11, 08:09 AM
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Pix?
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Old 10-06-11, 08:30 AM
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Whern you say the chainline is too far out, do you mean as compared to the centerline of the cassette (middle ring should line up with middle of cassette, or slightly outboard of there), or do you mean there's excess clearance between the chainrings and chainstay?

Cassette alignment is more important, but chainstay clearance determines minimum chainline offset. Assuming that it is too far outboard the fix depends on the crank and BB. Newer cranks with spindle fixed to the right crank and slipped through the bearings use spacers on either side of the bearings to set chainline, switch one from the right to the left to move the crank in.

With older cranks where the spindle is part of the bottom bracket, the chainline is set by the spindle length, so the only way to modify it is to buy a new BB.

Before you do anything reconfirm your conclusion that the chainline is too far out, since that isn't common on new bikes with the original setup.
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Old 10-06-11, 08:42 AM
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Is the current chainline actually causing shifting problems or is it just "not right" visually? Unless it's a real problem, leave it alone.
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Old 10-06-11, 08:55 AM
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Originally Posted by HillRider View Post
Is the current chainline actually causing shifting problems or is it just "not right" visually? Unless it's a real problem, leave it alone.
100%.

The first rule of wrenching is "if it ain't broke, don't fix it". I extend that to mean that nothing is a problem unless it causes problems.

If the bike works, shifts OK and rides OK leave it alone and enjoy it.
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Old 10-06-11, 10:01 AM
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the crankset is sticking out way to far causing a shifting problem in the middle chainring in the lower cassette cogs. i was thinking of a tiagra road crankset and matching bottom bracket if it would help. what is your opinion? i appreciate your replies. pothound
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Old 10-06-11, 10:04 AM
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can i modify the rear wheel so the cassette is out further?
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Old 10-06-11, 10:10 AM
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I can't advise without knowing particulars, especially the current chainline.

Measure by either of these two methods

Measure from the tip of the outer chainring's tooth to the side of the downtube, add 1/2 the downtube diameter, then subtract the distance to the center of the chainrings, either to the middle ring of a triple or to the middle of the gap between doubles.

Lay a straight edge on a secant against the face of the outer ring, and carry the line back to the cassette. Compensate for the distance from the outer face to the middle of the chainrings and see where it lines up. Should be at the middle of the cassette or slightly outboard. BTW- use the edge of the straight edge, not the flat surface because most aren't truly flat or flex can cause a poor measurement.
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Old 10-06-11, 10:12 AM
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Originally Posted by pothound View Post
can i modify the rear wheel so the cassette is out further?
pothound
No, normally the cassette is carried as far outboard on the hub as possible while allowing chain clearance between the last sprocket and dropout.

You're putting the cart before the horse. Stop trying to fix it, until you make the measurements to know exactly what you're trying to fix. Then you can consider the options.
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Old 10-06-11, 11:30 AM
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One of the first things I would check is to make sure the bottom bracket is screwed set the whole way in on the drive side.
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Old 10-06-11, 07:32 PM
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using my crude method, i came up with 48-49mm center of seat tube to middle chainring. the crankset is deore fc-r443 triple. the cassette is 9 speed. a strait chainline right now is middle chainring to #8 cog.
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Old 10-06-11, 08:19 PM
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Originally Posted by pothound View Post
using my crude method, i came up with 48-49mm center of seat tube to middle chainring. the crankset is deore fc-r443 triple. the cassette is 9 speed. a strait chainline right now is middle chainring to #8 cog.
pothound
your chainline is just about spot on. (refer to the table here). So there's no need to tinker with the crank. Now since you say the chainline is too far out, I assume that the #8 is the second outermost. That's kind of strange based on the chainline being on target.

Assuming your measurements are accurate, it would seem to indicate that the frame is misaligned and the rear triangle is to the left of center. Don't panic yet, because it could be something else, but at this stage I suggest you let a knowledgeable mechanic have a look.

If you want to try one more measurement before seeing a pro, loop a piece of string around the headtube and bring it back to both dropouts. Pull it tight and trap it under the QR skewer. Measure from the string to the seat tube. Both sides should match.
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Old 10-08-11, 06:23 AM
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as an experiment, i took all the garbage off. [crankset, front derailleur, and bottom bracket] i installed a 105 front derailleur, a 110mm square taper bottom bracket, [un54] and a sugino xd600 crankset. it improved the chainline. i did expect more improvement than this. it doesn't compare to my other bikes. i did have trouble adjusting the 105 derailleur to the lx shifters. are they compatible? what do you think? pothound
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Old 10-08-11, 06:52 AM
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Originally Posted by pothound View Post
i did have trouble adjusting the 105 derailleur to the lx shifters. are they compatible? what do you think? pothound
No, they are not. Shimano's road front derailleurs like your 105 are not compatible with MTB shifters like your LX as the cable pull amounts don't match.

Rear derailleurs are a different story as Shimano's road and MTB rear derailleurs and shifters are cross compatible with the sole exception of the newest 10-speed MTB components.

Your chain line "problems" seem very strange considering the original chainline was very close to ideal when you reported the values at FBinNY's request.
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Old 10-08-11, 09:21 AM
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when i built my touring bike, i used sugino xd600 crankset, 105 front derailleur, and xt shifters. it works fine. if i should use a different derailleur, what would you recommend? back to chainline, the sirrus came with 130mm rear wheel. my touring bike wheel is 135mm. it will fit. will this improve the chainline? if it will, i will build a rear wheel with an xt hub. any comments? maybe i should remeasure the chainline. thank you pothound.
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