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  1. #1
    FOG
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    What is so great about a centered chainline?

    I have been thinking about buying a new road bike, many of which have 53/39 cranks, and making the crank a triple. Assuming the chainwheel clears the frame, and that I can get a front derailleur to shift close to the frame, why can't I leave the old bottom bracket on, accepting that the chainline on the inner chainwheel will not be straight if it goes to one of the outer sprockets, because I wouldn't want to use the inner wheel except for the shortest gears anyway? Then the other two chainwheels would be closer to center, and the majority of riding would be smoother. BTW- I realize the rear derailleur issues this brings.

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    Senior Member Inoplanetyanin's Avatar
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    I didn't understand what you meant... and what the problem was.

    If a chainring is on the same surface, i.e. parallel to the rear ring (gear) then it is a perfect configuration beacause chain will not rub the sides of the links against side of tooth......
    Rear deurailler is suppose to keep front and read chainrings as parallel as possible...

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    The Red Lantern Rev.Chuck's Avatar
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    The issue is with(mostly) middle chainring issues, shifting to small chain ring when backpedaling and the chain is on larger cogs and the chain rubbing against the big ring in smaller cogs
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    FOG
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    Originally posted by Rev.Chuck
    The issue is with(mostly) middle chainring issues, shifting to small chain ring when backpedaling and the chain is on larger cogs and the chain rubbing against the big ring in smaller cogs
    Why would a chain with the middle and outer chainrings in exactly the same place they were on a double rub more when I put a third inner ring? The outer two rings should ride as well as before, and the inner ring is only for the big cogs, so it would not be closer to a line with the big cogs anyway. If I were to mount a triple according to convention what would happen is the center of the middle chain ring would be centered on the middle cog, where in a double the gap between the outer and what would be the middle in a triple is centered on the middle cog. It seems like all the chainrings would be in better positions.

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    hello roadfix's Avatar
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    Mr. Fog,

    Sometimes, you will find yourself in the middle chainring and accessing the entire cog, from top to bottom. Idealy, it would be nice to line up the middle ring to the center of the rear cluster.
    On the other hand, if a good majority of your riding will be on the two big rings, why even bother having a granny? Maybe a larger rear cog instead??
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    FOG
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    Originally posted by George
    Mr. Fog,

    Sometimes, you will find yourself in the middle chainring and accessing the entire cog, from top to bottom. Idealy, it would be nice to line up the middle ring to the center of the rear cluster.
    On the other hand, if a good majority of your riding will be on the two big rings, why even bother having a granny? Maybe a larger rear cog instead??
    the lrger rear cog makes lots of sense to me, but I could buy a "triplizer and a new front derailleur for lesss than a rear derailleur and cassette. Question then would be whter the rear derailleur could handle it and whehter I had to change bottom bracket. It obviously is making a lot more sense to buy exactly what I want in the new bike, but just fumbling for alternatives which yield a good gear system. 39 front 23 rear just won't cut it. Another option which I have been thinking about is to buy a muntain bike triple and take off the inner ring. 44/32 front 11/25 or better yet, 11/27, rear might work. On the other hand I guess I should just wait for a bike configured the way I want it.

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    FOG
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    Maybe I should take typing lessons too.

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    The Red Lantern Rev.Chuck's Avatar
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    The chain rings are not allways in the same position, a double crank does not have a place to put a small ring it requires a different crank. I can't say for certian, about yours, because I am not standing there looking at what you have, but I would be willing to bet money that I have done more double/triple conversions than you and often there are issues like what I posted earlier. If you do this conversion without changing the BB and it works for you, great. Often even changing cranks triple to triple, like on a mountian bike will cause a change in chainline.
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    Mr. Fog,

    Unless you plan on doing lotsa climbing, your MTB crank & rear cog combo seems awfully low FOR A ROAD BIKE and only gives you about 106 gear inches at the top end. Exactly what type of riding do you plan on doing with this bike?
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    I use a Stronglight 80 chainset on my 2 hack bikes. This has a very small bolt circle and can take rings from 28 upwards. It works as a single, double or triple.
    I originally used it as a 36/48 double. I switched to a 28/38/48 triple, and changed to a wider BB to give a better chainline. On my flatland town bike, I use just the 36 ring. I dont have any high gears, but never go fast on it. A friend of mine uses one as a 28/38 double.
    The point is that std factory gearing is not neccessarily the right gearing for you, and ther are plenty of ways to gear the bike to your needs.

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    The deal is smooth quiet shifting and being able to get the most from your drive trane. The center of your cassette should align with the center of you crankset, this will allow equal misalignment on both sides of center as you shift up and down when on the middle ring, you bike will be much more quiet and exreriance less wear as you ride. If you are going with a tripple crankset, go with the proper bottom bracket.
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    Mr. Cellophane RainmanP's Avatar
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    There is more to the issue than you realize. You physically cannot put a triple crankset on a bottom bracket sized for a double crank. The length of the spindle for a double is shorter than a triple. Spindles are sized so that the inner chainring barely clears the chain stay. If you put a triple crank on a shorter spindle bb, the little chainring will be jammed into the chainstay. So to go triple you need a bb with a longer spindle. Bottom brackets are not that expensive so this is not a big expense item. You would also need a front der designed for a triple because a double probably does not have enough range of motion. A front der is inexpensive also. Oops, you also need a triple front shifter. So there is a lot more to the whole thing than just a centered chainline. Ask your LBS what they would charge to upgrade the bike. They may even have one set up already or can get one with a triple for only a little more than the double.
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    The best method to determine what works as far as chainline is to simply try it. It is not possible to exactly determine ahead time exactly what will happen with any particular change. Having acceptable chainline simply means having acceptable shifting. Many bikes are off either way (front rings too far out or in) and yet still shift for their riders. With the newer 10 speed bikes with the shorter chainstays, it is often impossible to have every gear combination useable.

    As you alreay own the bb, simply install the triple and see if it clears the frame. If the front derailleur will get the chain down there, it may be useable. Front derailleurs do have limits, however, on how for inward they will move.


    See also Chainline

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    FOG
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    I think there is a misunderstanding here. I do not already own the bike, I am trying to figure out what would work. I would be happiest if I could find a good double with a wide range, but such setups seem rare. If I have to sacrifice gears I would prefer to sacrifice gears at the high end, not the low. But the root question here remains. that question is: what are the adverse effects of non-centered chainlines, especially when adding a third ring? I realize there are clearance and derailleur issues. There are lots of threads focusing on those- here the question is limited to chainline.

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    You get excess wear on the chain, and sometimes on the teeth.

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    Mr. Cellophane RainmanP's Avatar
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    I am really not trying to be smart, but I am not sure what more you want. When it gets down to it the chain line on a multi-gear bike is seldom "straight". For each chainring there is exactly one cog in back that will produce a "straight" chain line. Every other gear combination will be off line to some extent. On a fixed gear bike or singlespeed chainline is more important. It must be very close to straight or the chain will jump off. On a multi-gear bike the der is helping keep the chain in line with the chosen rear cog so chain line becomes less important.

    There are a couple of more subtle issues. With the chain on the big ring (outside) of a double crankset you want to avoid being on the large cog (inside) in back. If you are on the big ring or a triple the chain is even farther out so you want to avoid using the big ring with the largest and second largest cogs. But even these caveats can be violated briefly when useful.

    In my opinion, for what you are describing chain line is the LEAST important issue. You can't put a triple crank OR a triplizer on a short spindle bottom bracket.

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    The Red Lantern Rev.Chuck's Avatar
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    If you have not purchased the bike yet, then look into bikes that have triples allready. There are nice bikes from Specialized(steel & alluminum), Giant (alluminum & ally with composite stays), Bianchi(steel & alluminum) and others.
    Other issues of getting a double and swapping to triple include needing a longer cage rear der and a front shifter that is for a triple(Some are double only and some are double/triple)
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  18. #18
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    Mr. Fog,

    Aside from excess noise and wear on your chain, cogs, and chainrings.......as long as you're able to shift smoothly on ALL GEAR COMBINATIONS, your chainline issue is really irrelavant here. Chainline is important when you're talking about track & fixed gear bikes. Unlike track drivetrain components, multiple shift rings, cogs, and chains are designed & machined so they can be driven a bit off-centered from a slight angle. Thank you!
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    feros ferio John E's Avatar
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    Originally posted by George
    Unless you plan on doing lotsa climbing, your MTB crank & rear cog combo seems awfully low FOR A ROAD BIKE and only gives you about 106 gear inches at the top end.
    I find my current road bike top gears of 94, 100, and 104 inches perfectly adequate. Modern road bikes have absurdly tall top gears for nonracers. In the 1970s, Peugeot PX-10s and other high-end racing bikes commonly had 52/14=100-inch top gears.


    On most frames I have seen, one can obtain a near-optimal chainline by placing the inner chainring within about 2mm of the chainstay. As the Rainman noted, if a bike has the right spindle length for a double, it will probably need a longer spindle for a triple, to maintain this clearance.
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  20. #20
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    Mr. John E,

    I absolutely agree with you about tall gears on current road bikes. I really don't even remember the last time I had a chain over my 12 cog. Therefore, come to think of it, about 100 inches does seem quite adequate for the average rider. Thank you!
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  21. #21
    DEADBEEF khuon's Avatar
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    I think I understand what FOG is getting at. Since FOG views the granny in the triple as a last-ditch emergency-only position, it doesn't matter that shifting into and out of it will be pretty and smooth. However most people will acknowledge that by going from a double to a triple with the "correct" middle-to-middle alignment, one decreases shifting smoothness throughout the entire range. FOG doesn't want to give up the smoothness of shifting across the entire range but would rather suffer with having the pain be placed when in the inner chainring and also admits that shifting of the rear would be limited to probably the larger two or three cogs anyways when dropped in the granny. I kind of like this idea. If one could get the granny to clear the chainstay then go for it. Another idea might be to try using an adjustable BB so you could play with the chainline a little more.
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  22. #22
    hello roadfix's Avatar
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    Mr. Fog,

    After all these postings, I understand what you ideally want. It would be nice and simple if one can easily add a granny to an existing double chainring setup without altering its chainline or anything else provided it clears the chainstay and that the front derailleur pulls in far enough. It sure makes good sense because one would only use the granny with the inner large cogs anyway. I wish life is as simple as that.... that's why of all the bikes I currently own, only one is equipped with a derailleur. I think I will tinker with my bike tonight over some Mozart, wine & brie....... Yeah!
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  23. #23
    FOG
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    I solved the problem pro tempore by buying a couple of lemonds with triples, one 55cm tourmalet equipped with rsx, the other a 57 cm Buenos aires equipped with rsx/105 mixture. I haven't got the BA in my possession yet but the tourmalet feels light, and looks like a good choice. After a bit of cycling with my son and daughter we'll sort out who rides what, and then maybe go for another round, but with four road bikes with STI triples, and two more with XT (48/38/28) triples (but downtube shifters and ultegra 6 speed cassettes)we should be good for a while., yet another with downtube indexed shifters and a road double.

    I was looking to capitalize on closeouts of some nice ultegra/105 doubles, but I think it will be a while, at least a year, before it is time to go shopping for bikes again. Now on the BA we might want to talk upgrade.........naah, not yet

  24. #24
    FOG
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    BTW- I did the conversions to triples on the two older bikes some time ago, and the only problem I have had is in keeping the wheels true, which had little to do with the actual conversion, and more to do with the wheels I was using.

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