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  1. #1
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    What is a compact crankset? Any performance difference?

    What is a compact crankset? Is there any advantages or disadvantages of using one?

  2. #2
    NeoRetroGrouch
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    Quote Originally Posted by Jared
    What is a compact crankset? Is there any advantages or disadvantages of using one?
    Traditional road cransets have bolt circle diameters of 130mm (Shimano) and 135mm (Campy) for the chainrings. This limits the size of the small ring down to 38 teeth. A compact has a smaller bolt diameter, usually 110mm, so that it can take a smaller ring.

    Do a search for tons on the advantages or disadvantages.

    My advise is always to determine what gear ratios YOU need and then install the set up that gives you the most convenient use of those ratios.

    TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  3. #3
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    The idea with a compact crank is to have a lower and/or closer gear ratio than the std. 53/39 rings.
    The disadvantage would be if you needed to shift rings often, and the advantage might be to have lower and closer gearing w/out needing a triple....The "gear-inch metric developement" calculator on the Campagnolo site is very useful in looking at different gear ratio combinations for your particular needs. Compact is 110 mm BCD (bolt circle diameter) for the chainrings as stated above..The usual std. rings that come with a compact crank are 34t and 50t, and sometimes 36t and 50t. FSA makes rings that will fit any 110 BCD crank in many sizes; one ratio that looked interesting is the 36t and 52t combo.
    There are now specially designed front derailleurs for the smaller arc rings and large (16t) jump from the 34t to the 50t. A search is a good idea to determine the compatibility of various components in a compact drivetrain.

  4. #4
    NeoRetroGrouch
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    Quote Originally Posted by twelvepercent
    The idea with a compact crank is to have a lower and/or closer gear ratio than the std. 53/39 rings.....
    How would a compact give you a closer gear ratio? - TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  5. #5
    blame me for missed rides
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    road "compact" is the same as the mountain "standard", i.e. 110mm BCD. road "compact" appeared just as mountain "standard" was phased out. i believe it's a marketing hype as well as to reuse the designs and manufacture processes that the crank makers already have.

  6. #6
    NeoRetroGrouch
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    Quote Originally Posted by weather
    road "compact" is the same as the mountain "standard", i.e. 110mm BCD. road "compact" appeared just as mountain "standard" was phased out. i believe it's a marketing hype as well as to reuse the designs and manufacture processes that the crank makers already have.
    I don't think that there were many mountain standard 110mm doubles which is what is generally meant by a compact road.

    Road compacts became popular (acceptable) because Tyler Hamilton used one after breaking his collar bone in the TdF. Before that, anything less than a 53 was only for wimps.

    TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  7. #7
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    not quite right...

    Compacts generally have wider spaced chainrings (like a 50/34), not closer. The idea is to lose slightly less than one cog on the top end and gain nearly two cogs worth of low end. The penalty is more cog shifting after every shift between the chainrings.

    Of course, you can select other combinations, like a 50/36 or 48/34 that just trade a top gear for a low gear and avoid the additional cog shifting.

    In some case, the same thing can be accomplished much more easily by purchaing a new cassette such as a 13-29.

  8. #8
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    True...wider gearing (spread) on rings .... Closer gearing on the cassette only in certain circumstances.....for example if an 11/23, or 11/21 is used; then you can have closer gearing(only while in one ring or the other) as compared to a 12/25 ,12/27, or 13/29.
    In the original marketing of the FSA compact, "closer gearing" was a mkt.ing claim; the advertisement involved an 11/23 cassette as compared to a larger cassette on the std. 53/39 crank. The reference to Tyler Hamilton winning something or other with the compact was used as marketing to start selling compact cranksets.
    Overall, closer gearing would depend on how often shifting rings is needed...somewhat inspecific on my part, but hopefully this discussion is helping Jared understand the compact crank option.
    Last edited by twelvepercent; 09-04-2005 at 10:12 AM. Reason: addendum

  9. #9
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    eventual end for a triple road group?

    so does it mean the compact cranks will kill off triple chain ring for road group use? As I see it - it is much cheaper, lighter, should shift better (two rings instead of three) and provides all the ratios you need for road use. Not true?

  10. #10
    NeoRetroGrouch
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    Quote Originally Posted by acid_rider
    so does it mean the compact cranks will kill off triple chain ring for road group use? As I see it - it is much cheaper, lighter, should shift better (two rings instead of three) and provides all the ratios you need for road use. Not true?
    Absolutely not true. It is mainly used a compromise for those not willing to use a triple. The triple, in combination with appropriate cassette, provides a wider range of gears and/or closer ratios. The compact has its place, but is not magic. - TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  11. #11
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    Yeah, but ...

    Quote Originally Posted by TurboTurtle
    Road compacts became popular (acceptable) because Tyler Hamilton used one after breaking his collar bone in the TdF. Before that, anything less than a 53 was only for wimps.
    Tyler Hamilton's TdF win may have been used to sell compact cranks, but he didn't use the same set up that is being sold as "compact". He did use a 110mm crank, but his chainring setup could best be described as "semi-compact" - he used 52/36 chainrings. The 52 gave a top end gear less than 2% smaller than a 53 would, so the real difference was that he had a slightly smaller small chainring than can be had on a 130mm crank (36 vs. the 38 minimum size on a 130mm crank).

    So Hamilton used slightly smaller than typical road chainrings, but hardly the same compact cranks that are being pushed so hard by the manufacturers.

  12. #12
    Call me a Fred
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    The main purpose of the compact double is to allow riders who wouldn't be caught dead with a triple to have the lower gear ratios that they need. It's more of an image item than a needed item.
    Mike

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  13. #13
    blame me for missed rides
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    Quote Originally Posted by TurboTurtle
    I don't think that there were many mountain standard 110mm doubles which is what is generally meant by a compact road.
    simply do not drill the 74BCD inner holes on the mountain triple. viola! 110mm doubles.

  14. #14
    NeoRetroGrouch
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    Quote Originally Posted by weather
    simply do not drill the 74BCD inner holes on the mountain triple. viola! 110mm doubles.
    What??? I don't think not drilling the holes is an option.

    The chainline is also different and you cannot move it in on many frames because the granny ring mounts (even if not drilled) will hit the chainstay.

    TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  15. #15
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    not true...

    A compact crank is no miracle. It only adds a small amount of extra low end, always sacrifices top end abd creates more cog shifting due to the wide spaced ring.

    A triple doew not sacrifice top end. A triple can add four additional lower ratios with the same cassette. It also avoids the extra cogs shifting, since the ring spacing is not increased.

  16. #16
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    Quote Originally Posted by TurboTurtle
    What??? I don't think not drilling the holes is an option.
    He was refering to the manufacturer. After the cranks pop out of the mold/die/forge (or whatever process the manufacturer uses to create the crank), they can either drill and tap the 74 mm bcd on the inside of the spider arms to make it a triple, or not drill it and leave it as a double.

    Quote Originally Posted by TurboTurtle
    The chainline is also different and you cannot move it in on many frames because the granny ring mounts (even if not drilled) will hit the chainstay.
    Chainline is usually adjusted with the BB length, not the crank. This document on the ISIS BB design shows how this is done:
    ISIS Bottom Bracket Standards . From section 4.1 of the document: "The 10mm difference between the 76 and 86 spindle is sufficient to allow one crankset to perform the function of either road double or road triple simply by adding a chainring and switching spindles."

    Likewise, for Shimano's Octalink, a single crankset can be used as a road double or road triple by switching between the 109.5 mm and 118.5 mm spindles.

    As said before, compact cranks are neither new nor magic.

  17. #17
    NeoRetroGrouch
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    "He was refering to the manufacturer. After the cranks pop out of the mold/die/forge (or whatever process the manufacturer uses to create the crank), they can either drill and tap the 74 mm bcd on the inside of the spider arms to make it a triple, or not drill it and leave it as a double."

    The pieces that stick out for the to be drilled and tapped would still be there.

    "Chainline is usually adjusted with the BB length, not the crank. This document on the ISIS BB design shows how this is done:
    ISIS Bottom Bracket Standards ."


    When you change the spindle length (or move the BB off center), you are moving the crankset sideways.

    "From section 4.1 of the document: "The 10mm difference between the 76 and 86 spindle is sufficient to allow one crankset to perform the function of either road double or road triple simply by adding a chainring and switching spindles.

    Likewise, for Shimano's Octalink, a single crankset can be used as a road double or road triple by switching between the 109.5 mm and 118.5 mm spindles.""


    Again, on most road frames the pieces that stick out will hit the frame when you move the triple crankset in (by changing the BB spindle length).

    "As said before, compact cranks are neither new nor magic."

    Here we agree. In the mid to late 90s Shimano made the RSX double and triple with 110mm BCD that I run on my CX bike. There are probably earlier example. Also, I believe that there are some actual XTR doubles. I don't know whether they were common or one-off for pro racers.

    TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  18. #18
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    interesting point....I always wondered how Tyler Hamilton could compete against the boys on a 50/34.

  19. #19
    blame me for missed rides
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    Quote Originally Posted by TurboTurtle
    The pieces that stick out for the to be drilled and tapped would still be there.
    it's a very simple process to smooth out those little stubs. would you rather redesign a crankset from scratch, or simply eliminate those stubs?

    When you change the spindle length (or move the BB off center), you are moving the crankset sideways.
    that's precisely how you adjust chainline.

    Again, on most road frames the pieces that stick out will hit the frame when you move the triple crankset in (by changing the BB spindle length).
    lol you gotta be kidding me. no they won't. try it with a mountain triple. i have.

  20. #20
    NeoRetroGrouch
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    "it's a very simple process to smooth out those little stubs. would you rather redesign a crankset from scratch, or simply eliminate those stubs?"

    Me or Shimano? It would be much cheaper for shimano to design a new crankset than to have to grind down the five pieces sticking out.

    "that's precisely how you adjust chainline."

    But you said you didn't move the crankset.

    "lol you gotta be kidding me. no they won't. try it with a mountain triple. i have."

    What frame, what BB and spindle length and what crankset?

    TF
    "Don't those guys know they're old?!!"
    Me, off the back, at my first 50+ road race.

  21. #21
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    Quote Originally Posted by TurboTurtle
    Me or Shimano?
    either you have problem reading english or i have problem writing it. i wrote, in my first post, "it's a marketing hype as well as to reuse the designs and manufacture processes that the crank makers already have."

    do you not understand who are "crank makers"? do you not understand who, the consumer or the manufacturer, would "reuse the designs and manufacture processes"?

    It would be much cheaper for shimano to design a new crankset than to have to grind down the five pieces sticking out.
    hmm...i wonder why those component makers bother to improve upon their existing models when it's "much cheaper" to design a new one from ground up.

    But you said you didn't move the crankset.
    where and when did i say it?

    What frame, what BB and spindle length and what crankset?
    frame: 2000 schwinn super sport GLX, 56cm, 68mm english BB shell
    BB: UN72, 68x107
    crankset: kooka (the later CNCed arms), 175m, silver, 110/74mm BCD.

    the stubs were no where near hitting the frame. in fact the crank arms would bottom out against BB shell before the stubs hit.

  22. #22
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    Quote Originally Posted by TurboTurtle
    The pieces that stick out for the to be drilled and tapped would still be there.
    Firstly, the stand-offs don't stick out that far; secondly they are at a smaller diameter, closer to the BB shell, where there is more clearance with the stays. In addition, many triple cranks don't actually use stand-offs, opting to use spacer between the chainring and crank instead (so there is nothing to sick out).

    Quote Originally Posted by TurboTurtle
    When you change the spindle length (or move the BB off center), you are moving the crankset sideways.
    Which is exactly as it should be. In general, you want to align the center of the chainrings with the center of the cassette. On a double, the center of the chainline is halfway between the to chainrings. When you bolt a third chainring onto the inside of the crank, the chainline should be aligned with the middle chainring (which was the inside of the chainring when it was just a double crank), so you have to shift the crank outward to compensate. In addition, shifting the crank outward gives additional clearance for the inner chainring, so that larger inner chainrings may be used if desired. This has how triple and double crank chainlines have always been aligned

    Quote Originally Posted by TurboTurtle
    Again, on most road frames the pieces that stick out will hit the frame when you move the triple crankset in (by changing the BB spindle length).
    Which "most road frames" are these? I presently am using Ritchey triple chainring as a "compact crank" on a road frame by removing the inner chainring and using a road length BB. The inner chainring stand-offs have plenty of clearance. I've even installed a MicroDrive triple crank (with all chainrings installed) on a road bike with a road length BB and had no clearance issues.

    Quote Originally Posted by TurboTurtle
    Also, I believe that there are some actual XTR doubles. I don't know whether they were common or one-off for pro racers.
    I don't believe that XTR cranks came standard as doubles, but as discussed above, they could be easily made into doubles by removing the inner chainring (and using a shorter BB to adjust the chainline). The use of a double crank for MTB racers was formalized in the Ritchey 2x9 system.

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