fd question / compatability / education

[onsight512]

So...I'm building up my first bike and am learning a lot as I go along (!).

I need to get a fd. The frame is a Kogswell PR and requires a fd with a 28.6mm clamp and bottom pull. The rd is a Shimano XT and so I figure an XT up front, but after looking at Shimano's website, I'm a bit bewildered.

The crankset is a Sugino XD2 (triple, 46,36,24). Cassette is an XT 9-speed (11-34).

Would someone be so kind as to line me out with which XT fds would suit?

many thanks,
Chris

[eddief]

1. these days 28.6 fd can be hard to find, but most 31.8 ones will include shims for 28.6.

2. Many would say that if your are using integrated road shifters, then you should use a road fd, not a mountain (xt) one. Supposedly the pull ratio is slightly different between road and mountain fds.

What kinda shifters are you using?

[onsight512]

What kinda shifters are you using?



Suntour bar ends.

[eddief]

so my bet is any fd will work, but bar ends not my specialty.

[Peter P.]

The Suntour shifters are not meant to provide indexed shifting so you'll be operating in the friction mode.

In that case, ANY rear derailleur will work. The cable pull ratios between the two brands, Suntour and Shimano, will likely not match. That may lead to either lots of over-shifting to complete a shift or undershifting which is like very sensitive shift levers.

If at all possible, I'd recommend keeping the shifters and derailleurs in the same brand family.

Also, since it sounds like you're going the "Rivendell" route with your parts picks, you might want to try contacting them (http://www.rivbike.com/) for suggestions. Grant Petersen and company are usually pretty helpful and I'm sure they won't get angry if you didn't buy the parts from them, but at least buy SOMETHING if they help you.

[kramnnim]

So are you looking for an FD or an RD, the post is unclear. I'd go with an XT old enough to come as a 28.6 rather than a newer one with shims... You'd select top swing vs bottom swing based on the location the bottle cage mounts...

[onsight512]

Yes, I'm planning on friction shifting with the Suntours. Assuming that, does it matter that the fd is Shimano? I'd think not, but like I said, I'm new to most of this.

And thanks for the info about the bottle cage locations & fd (kramnnim). I hadn't realized that had anything to do with it, but looking at the bike, it makes perfect sense.


more thanks,
Chris

[m_sasso]

I would look at the Shimano CX70 Front Derailleur and as to the reasons why look here: http://www.rivbike.com/product-p/d14.htm

[onsight512]

I would look at the Shimano CX70 Front Derailleur and as to the reasons why look here: http://www.rivbike.com/product-p/d14.htm

Please pardon my ignorance, but what do they mean with this:

"Designed to only work for double cranks but we've also gotten it to work good on some weird half step set ups. The minimal inner cage plate doesn't hit the middle half step chainring like a typical triple derailer cage does"

I'm running a triple.

[kramnnim]

Half step is some weird thing that you don't need to worry about since your chainrings are a more standard ratio.

You don't need a Suntour FD, Shimano will be fine.

[m_sasso]

Please excuse posting you another link however Sheldon Brown describes it more comprehensible then I ever could here: http://www.sheldonbrown.com/gear-theory.html#halfstep

[Peter P.]

Please pardon my ignorance, but what do they mean with this:

"Designed to only work for double cranks but we've also gotten it to work good on some weird half step set ups. The minimal inner cage plate doesn't hit the middle half step chainring like a typical triple derailer cage does"

I'm running a triple.

"Half Step" means the difference between the middle and large chainrings is very small, usually less than 7 teeth. Technically, it means a shift of the front derailleur from say, middle to large ring, is half as much of an increase/decrease in gearing as would a change of one cog in back.

Some front derailleurs shift better or worse with such minimal differences between chainrings due to the shapes of the inner and out cage plates. The 10T differences on your SD crank don't pose that problem.

[onsight512]

If the specs for a fd say that 'Top Gear Teeth 42T', does that mean that's the maximum capacity, for the big ring, for that fd?

for example: http://bike.shimano.com/content/sac-bike/en/home/mtb1/shifting---braking/front-derailleurs/fd-m781-d.html