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Old 08-01-08, 05:28 AM   #1
aesmith
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Shimano 105 ST-5600 STIs on a double crankset

Hi,

Quick question. The 105 STI is the same for either double or triple cranksets. So three main positions for outer, middle and inner ring.

The instructions suggest that on a double you should be using the two inner positions. However they caution that pushing the levers too far (towards the non-existent outer ring) could break the STI.

Any reason not to use the two outer positions instead, with the innermost left unused? Instead of danger or breaking the expensive lever, all that would happen is the cable falls slack if the lever's moved too far.

Ta in advance, Tony S
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Old 08-01-08, 05:44 AM   #2
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You "may" not get the proper trim function for a double if you do it this way.
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Old 08-01-08, 12:19 PM   #3
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Originally Posted by aesmith View Post
Hi,

Quick question. The 105 STI is the same for either double or triple cranksets. So three main positions for outer, middle and inner ring.
Sorry but that's not correct. Shimano road shifters for triples have four (4) main positions. The small ring position is with all of the cable out of the shifter. The second and third positions are used when on the middle chainring, the third position can also be used to trim the big ring. The fourth position is for the big ring. Most Shimano road triple shifters also have an additional trim position for the smallest ring.
For a double I would release all of the cable from the shifter, remove all slack and attach the cable to the derailleur, same as with a triple.
But if you really want to try using the third and fourth positions for the double I think it can be done. Make sure the cable end is seated in the shifter. Reel in the cable as far as the shifter will take it. Release the cable one stop with the smaller shifter, this will put it in the third position. Then attach the cable to the derailleur with no slack. Adjust the tension as needed with the barrel adjuster. I've never tried this so I can't really recommend it.

Al

Last edited by Al1943; 08-01-08 at 12:30 PM.
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Old 08-02-08, 01:39 AM   #4
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I maybe didn't express myself that well. What I meant was it supports three chainwheel positions, I wasn't accounting for the trim positions. Shimano documentation is ambiguous - some suggests there's trim only on the middle chainwheel giving four positions in total, some suggests you can trim on all three (giving six positions).

Maybe I just need to try it and see. The only disadvantage (other than possible trim) is that the cable adjustment process will be different and maybe more difficult.
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Old 08-02-08, 01:54 AM   #5
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I have the Shimano 105 ST-5600 levers. The left/front shifter has 6 positions: Chainring/wheel 1, trim 1, chainring 2, trim 2, chainring 3, trim 3.

For a double crank, you're supposed to use the first 4 positions. But I think the chainrings are all spaced evenly, so I don't see how using the last 4 positions wouldn't work. Though it may be more difficult to set up and, as you mentioned, you'll have a slack cable if you ever over-downshift.

However, if you used the first 4 positions, I imagine it would take so much force to break the lever when overshifting--much more than what you'd expect when shifting--that you'd realize you're already in the outer chainring before it broke.
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Old 08-03-08, 12:14 PM   #6
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However, if you used the first 4 positions, I imagine it would take so much force to break the lever when overshifting--much more than what you'd expect when shifting--that you'd realize you're already in the outer chainring before it broke.
The reason I asked originally, I've recently seen a couple of posts on this board where people have broken these types of shifters in exactly that way, and Shimano go to the trouble of specifically warning that its easy to do. One example here ...

Shimano 105 Shifter problem

I've had a few rides on the bike using the "last four" positions, and it does seem to work OK. From fully slack one full movement of the large lever does nothing but take out the slack. The next 1/2 click trims, or the next full movement shifts onto the outer ring. Once shifted you can go back 1/2 click on the small lever for trim. Actually as set up I don't even need to trim the the gears I "ought" to be using. It was a bit of a fiddle getting the cable tension right, but I think I'll bear with it for a bit.

I don't want to break one of those STIs, they're just about the most expensive part of the bike.

Tony S
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