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Old 03-28-07, 10:33 AM   #1
Riles
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What else to consider changing to a double chainring

Hi,

I am upgrading my crank set & will go to 2 chain rings, instead of 3 I currently have - I never use the small one.

I just want to know if this means also chaning :

1) the STI levers to suit double ?
2)changing the front Derailleur ?
3)I guess rear derailleur I can use a short cage if I want to ?

Thanks !
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Old 03-28-07, 10:41 AM   #2
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You're actually downgrading 3-->2

1) Depends on what STI levers you have
2) most likely yes
3) most likely yes.
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Old 03-28-07, 10:44 AM   #3
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STI levers and derailers will be fine switching from triple to double - they'll have more capacity than they need for a double, but will work fine with a double. (I've got a double front and rear derailers that I'll trade you though, since I don't have an STI-compatible triple FD and would like one, along with another long-cage road rear der.)

If you're using the same crank and just removing the small chainring, another thing you'll want is a shorter bottom bracket spindle, to put the crank closer to the bike for chainline purposes.

edit: shakeNbake is wrong about compatibility. Triple-compatible STI levers will always work with double cranks, and the same is true for front and rear derailers. You'll just have more capacity than you need, so your drivetrain will weigh slightly more than necessary (but not enough to worry about).
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Old 03-28-07, 10:47 AM   #4
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Add a new bottom bracket of the correct width to your list. And new cables and housings, while you're at it.

And you had better swap out the rear derailleur or it will be painfully obvious that you used to have a triple.
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Old 03-28-07, 10:54 AM   #5
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Good upgrade, but your only absolute need is the shorter spindle. The RD for style points.
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Old 03-28-07, 12:39 PM   #6
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Quote:
Originally Posted by Riles
Hi,

I am upgrading my crank set & will go to 2 chain rings, instead of 3 I currently have - I never use the small one.

I just want to know if this means also chaning :

1) the STI levers to suit double ?
2)changing the front Derailleur ?
3)I guess rear derailleur I can use a short cage if I want to ?
You definitely don't need to change the STIs or the rear derailer. You could use a short cage rear derailer, but there's no benefit to switching.

Most likely you will need a new bottom bracket to get proper chainlne.

See: http://sheldonbrown.com/bbsize

Try it with the present front derailer, it will most likely work just fine.

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Old 03-28-07, 01:24 PM   #7
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I've gone from a triple to a double on a bike. You have to readjust the limits on the front derailleur. Otherwise, I was able to use the triple shifter and derailleur minus the third shift. If you go with a 10 speed double, you don't have to worry about the spindle length.
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Old 03-28-07, 10:32 PM   #8
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Quote:
Originally Posted by Falkon
If you go with a 10 speed double, you don't have to worry about the spindle length.
Well, you won't need to worry about spindle length because you'll have just bought a new bottom bracket along with your new crank. Which is about what we all meant by "worry about your bb spindle, too."
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Old 03-28-07, 11:05 PM   #9
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That's what I'm saying.
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Old 04-08-07, 08:14 PM   #10
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I just did this switch (Ultegra 6503 -> some NOS 6500 cranks I had picked up cheap and are in a length more appropriate for my legs.).

The front derailluer may have to be moved if your big chainring is different; you will have to change the FD UL and LL settings and adjust the indexing. With the triple front brifter, you have trim positions between the L and H settings to accomodate some amount of cross-chaining. The chainline will be a few mm further out than ideal; this may cause rubbing of the chain on the FD cage, especially when in the largest cog. You can tune all/most of that out with the LL screw. The most extreme cross-chaining combos may not work as well but I at least don't use them much anyway.

It is not the "optimal" setup, but unless someone is paying you to ride, it may not matter. A short cage RD and FD designed for a double might provide crisper shifting, and a replacement BB will take care of the chainline. In my case, the BB has one season on it so I am not in a hurry to replace it unless I later opt for a compact and do cranks and BB at once. The RD has under one season of use, so I'm less likely to replace it unless I stumble onto a bargain.
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Old 04-08-07, 08:55 PM   #11
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I also just did this switch. New BB and crankset,move fdr and readjusted limit screws on fdr, check chain length and ride.
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Old 04-09-07, 07:37 AM   #12
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I'm still a newbie, and still running the triple (Tiagra, OEM on the bike). If one doesn't replace the FD, RD, bracket, and cranks all at once (to get the advantage of shorter chainpath and narrower BB), what are the advantages of simply having 2 chainwheels vs. 3? It seems one wouldn't realize the advantages that are typically purported of using the double. I've heard some claim that a double is a simpler setup and that the chain can skip the middle wheel on a triple, but to me that's something that a reasonably competent bike owner (even I) can tune out.

Is this just one of those things that people do because the "big kids" do it, or is there still an advantage to be gained from changing part of the kit and not all of it? So far, I'm using the granny gear less and less as I get stronger. However, I've been thinking that when I do upgrade, I'd rather get a set of larger chainwheels so that my ratios are overall a bit higher, pushing me to using the middle chainwheel most of the time instead of the largest while keeping the triple (ie, make my granny gear slightly less granny).

For what it's worth, it is at least reasonably hilly where I ride, so I like the overall range of gear ratios I have and the spacing between ratios. I also like the overlap in gear ratios between chainwheels, so I don't have to constantly switch between chainwheels. I'm also thinking that even if I did upgrade, a 3x9 setup sounds like a lot less of a pain in the ass than a 2x10 from what I've been reading, which sounds finicky as hell with very little engineering tolerance.

Thoughts?
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Old 04-09-07, 08:25 AM   #13
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Y'all are giving him answers as if you knew what group he's talking about. Lots of words that could be wrong.
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Old 04-09-07, 10:11 AM   #14
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Quote:
Originally Posted by Mr. Underbridge
I'm still a newbie, and still running the triple (Tiagra, OEM on the bike). If one doesn't replace the FD, RD, bracket, and cranks all at once (to get the advantage of shorter chainpath and narrower BB), what are the advantages of simply having 2 chainwheels vs. 3?
It's a teeny bit lighter, and has a slighly simpler shift pattern.

Quote:
Originally Posted by Mr. Underbridge
Is this just one of those things that people do because the "big kids" do it,
Bingo!

Quote:
Originally Posted by Mr. Underbridge
So far, I'm using the granny gear less and less as I get stronger. However, I've been thinking that when I do upgrade, I'd rather get a set of larger chainwheels so that my ratios are overall a bit higher, pushing me to using the middle chainwheel most of the time instead of the largest while keeping the triple (ie, make my granny gear slightly less granny).

For what it's worth, it is at least reasonably hilly where I ride, so I like the overall range of gear ratios I have and the spacing between ratios. I also like the overlap in gear ratios between chainwheels, so I don't have to constantly switch between chainwheels.
If it ain't broke, don't "fix" it!

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Old 04-09-07, 10:35 AM   #15
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Quote:
Originally Posted by Sheldon Brown
Sheldon "Odd Numbers Of Chainrings Are Best" Brown


Sheldon, I like the way you leave the door open for single speeds and fixies here... Not that I'm into that mindset, but I know you are.
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Old 04-09-07, 11:43 AM   #16
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Originally Posted by L D
Sheldon, I like the way you leave the door open for single speeds and fixies here... Not that I'm into that mindset, but I know you are.
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Originally Posted by Sheldon Brown
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There, fixed it for you
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Old 04-10-07, 05:29 AM   #17
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Quote:
Originally Posted by Mr. Underbridge

...

Is this just one of those things that people do because the "big kids" do it, or is there still an advantage to be gained from changing part of the kit and not all of it?

...

Thoughts?
Well, a couple thoughts here -

Removing the granny might allow ~1cm to fit a crankset on a shorter-than-necessary BB you don't want to or can't replace easily.

Someone I know enjoys dropping the granny in order to "force" themselves to work a little harder. Granted, they could just gear down to a reasonably low sprocket in the rear, but it removes one temptation, I guess.

As for me: I never use mine, but it _is_ nice to have flexibility. Maybe one day I'll need it, and who cares about a little bit of extra weight, anyway!?
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