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-   -   Really confused about front derailers (https://www.bikeforums.net/bicycle-mechanics/1138119-really-confused-about-front-derailers.html)

Waltsmith 03-12-18 01:14 PM

Really confused about front derailers
 
OK, another project Iím working on is upgrading the gear set on a comfort bike. (I love to go on ďslow rollĒ rides with groups in the area, and prefer to ride my comfort bike to my Hybrid (or road) bike. The bike bike currently has a 3x8 set up. I have decided on going to a 9 speed very wide ratio cassette, a deore 9 speed long cage derailer, and deore shifter.

But I would like to upgrade the front derailer as well. Thinking deore or 105 but Iím really stuck on what ďtypeĒ of derailer I need. The current front derailer is a clamp on. The shifting cable comes from under the bottom bracket, but the wraps around part of the derailer to fasten in front. If you follow, the cable pulls down, but because it wraps around it is actually pulling up on the pivot. So I donít know what kind of derailer that makes it.

Iím sure Iím not wording this well, but I hope you understand what Iím asking.

One of the main reasons Iím doing this is so I donít have to use the small ring. Only once or twice I have to use the small ring per ride. But shifting from the small ring to the middle ring seldom works. Iíve played with it, and two different LBS have played with it. Shifts fine on the stand, almost wonít shift on the road. I donít know if a better derailed will help, but Iím thinking Iím going to good stuff in the back, why not try good stuff in the front?

Thanks!

Kontact 03-12-18 01:23 PM

What you're describing is largely a waste of money. There are all sorts of factors that go into front derailleur selection, including the chainwheel sizes. Whatever is wrong with your bike is unlikely to improve if you have the people that can't get your equipment to work properly swap to other parts. Find out why your bike doesn't work.

Iride01 03-12-18 01:30 PM

The attach method is one of two things, braze-on or clamp-on. Though you can get an adapter clamp that allows you to use a braze-on DR without actually having to braze it on.

All your cables are going to come up from below. Though some actually route the cable over the BB instead of under it. Whether the DR itself changes the direction of the cable before pulling it's own lever, who cares.

What you do care about is that for indexed shifting you get the appropriate shifter and derailleur matched. Obviously indexed 2 spd shifters won't work well with a 3 speed crank. You also have to worry about the amount of cable they pull to make a shift. Some DR's require more cable to be pulled to make a shift. So if mix and matching components it's something to find out. Also, you have to look at chain line. Ideally, the centerline of the front stack of gears when extended should hit at the center of the rear stack of gears. The further you are off from this, the more you might see issues with getting into the lowest or highest gear on the front or back.

As far as you current shifting issue, if this is the original equipment that the bike came with then you likely have some adustment issue or something is worn out. Going for better components might not do anything but wast money if something is out of alignment such as the Rear DR hanger, the front DR is not positioned at the correct height, or your chainline is off too much.

Retro Grouch 03-12-18 01:58 PM


Originally Posted by Waltsmith (Post 20218675)
One of the main reasons Iím doing this is so I donít have to use the small ring.

Have you thought about just not shifting into the small ring?

fietsbob 03-12-18 02:03 PM

a middle ring of a triple and a single chainring have a lot in common they're both in the center.

SkyDog75 03-12-18 09:11 PM


Originally Posted by Waltsmith (Post 20218675)
The (front derailleur) shifting cable comes from under the bottom bracket, but the wraps around part of the derailer to fasten in front. If you follow, the cable pulls down, but because it wraps around it is actually pulling up on the pivot. So I donít know what kind of derailer that makes it.

Sounds like you're describing a "dual pull" derailleur. Those are designed to work in bottom-pull setups like yours, where the cable comes up from the bottom bracket, or in top-pull setups where the front derailleur cable is routed along the top tube and down the seat tube to pull the derailleur linkage from above. The cable is routed/attached differently depending on the pull direction.


Originally Posted by Waltsmith (Post 20218675)
Thinking deore or 105 but Iím really stuck on what ďtypeĒ of derailer I need.

We've got some variables to narrow down...

What type of shifters are you going to use? Shimano road and mountain bike front derailleurs have traditionally used different pull ratios, so you'll generally want to match your shifter and derailleur. Use a road derailleur with a road shifter (e.g. Ultegra, 105, Tiagra, Sora) or a mountain derailleur with a mountain shifter (e.g. Deore, Altus, Acera, Alivio). Since doubles have seldom if ever been fitted to mountain bikes, you'll notice a dearth of double mountain bike shifters.

Clamp-on or braze-on? If you use a clamp-on derailleur, you may need to know the diameter of your seat tube so you can select a derailleur with the right clamp size (or shims).

What are your chainring sizes? The curvature of a derailleur's cage will ideally match the curvature of the outer chainring, so you'll notice that derailleur specifications note chainring sizes. Derailleurs are also rated for the maximum difference between chainring sizes. And triple-specific chainrings have sculpted cages to fit prescribed inner/middle/outer ring size combinations.

Or, putting all the minutiae aside... If you're not going to use your inner chainring but you're otherwise happy, you can use the front derailleur's low limit screw to prevent shifting into the small ring, effectively giving you a double.


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