Front Shifting
drc
Posts: 3
Have just bought my first drop handle bar bike in 40 years - It's a Specialized Roubaix with Shimano 105s and a Compact crankset. Daft question - when I change up or down on the front derailleur - two clicks of the lever are needed - presumably this is correct.
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Comments
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Correct. The intermediate click is for trimming the front derailleur so that it doesn't rub the chain. The chain moves through a significant angle when moving up and down the entire 9- or 10-speed rear cassette, and that trim function allows you to use a larger portion of the rear gears from each chainring without causing chain rub.
Observe the front derailleur closely while clicking the shifter and you'll see what I mean.0 -
Thanks for the response will check this out - I suspect that it hasn't been set up particularly well .0
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Can i add a question to this?
When riding on the flat I can get into the lowest chainring on my triple no problem (i did this to test when i realised there was a problem, i'm not that slow!) However when riding up hills it's nearly impossible, it just doesn't want to drop down. I can only sometimes get it to drop down being in the lowest gear on the cassette.
I twisted the lower limit screw which improved it a little but it is still difficult. Is it just a case of turning the lower limit screw a bit more? Is it normal to be easier to shift on the flat than on a hill?0 -
mea00csf, yes, it is always harder to shift the chainring while going uphill (or anywhere where you are pedalling with a lot of force). If you look at your bike you'll see that the front derailleur shifts by bending the chain where it is under high tension from pedalling. The rear derailleur on the other hand bends the chain where it is returning to the cassette, and therefore under no pedalling tension. It follows that changing rear gears while pedalling hard is much easier than changing front gears. In fact, it is good practice to momentarily ease off the pedalling force (while still spinning the cranks of course) while changing front gears. This avoids strain (and wear) on the derailleur and cable while changing to a larger ring, and lowers the risk of the the chain being thrown off while changing to a smaller ring.
Still, even under a fair bit of pressure the front derailleur should shift to all chainrings. But simply opening up the lower limit screw will not improve things if cable tension is what is actually preventing the derailleur from moving inboard. And if you now reduce the cable tension to get the derailleur to shift properly, you may find that you have turned the lower limit screw too much, perhaps causing the chain to be thrown too far.
Ideally you want the lower limit screw, rather than cable tension, to determine the inboard position of the derailleur (because the screw gives a more definite and sharply defined position). The exact degree of cable slack while on the inboard limit should be determined by trial and error, observing how it affects shifting throughout the front rings, with the chain on various rear cogs. The amount of cable slack at the inboard position is also what determines the position of the derailleur in the middle (if you have one) and outer chainring, and therefore also the exact position of the trim positions available (if your front shifter has a trim feature).
A good overview of adjusting your front derailleur is available here, but to do a good job you'll need a bit of mechanical intuition or experience, and a lot of patience. The sad thing is, most bike shops including high-end bike shops do a terrible job of derailleur adjustment, so paying someone else to do it for you can't be advised unless you know for certain that that person will do a good job.0 -
Good explanantion DG
But if you can't get it set up properly as I don't seem able to, try shifting up at the rear - i.e. to a smaller cog - before shifting down at the front. Always seems to work as the front derailleur then has more to push on as the chainline is different.
It's counter-intuitive when you're desperate to shift down but you need only go a couple of cogs so the extra effort only lasts a few seconds. And it's better than getting off as you can't shift down.
Probably inidcates your better getting into the little chainring earlier too but I never remember0
