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  1. #1
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    Question compact crank ratio?? gearing

    building a new bike with a 50/34 crank set. on my other bikes i use a 12/25 in the rear, with the normal 53/39 set up. a 12/25 will be way to much for where i live(with the compact), but does anyone know about what a 23 rear "feels" like with a 34? i know the 25 falls in between a 28/29 ratio......where does the 23 fall, comparing to the "normal cranks, thanks, m
    Last edited by kestrel03; 03-11-2005 at 03:59 AM.

  2. #2
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    simple fractions...

    23/34 x 39 = 26.38

    The above is the equivalent gear formula. I don't get why you'd bother with a compact if a 34/25 is "way to low". Does that means 39/25 isn't low enough, but a 34/23 will be "just right"? If you're building with shimano a 53/39 with a 12-27 would make more sense.

    With campy, you get left out if a 39/27 is the perfect low gear. It's either a 12-25, 13-26 or 13-29. You can make a 12-26 by substituting the 23-26 pair from a 13-26 into a 12-25, but that's a lot of expense just to gain 1 tooth.

  3. #3
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    Brings up a question.

    [QUOTE= I don't get why you'd bother with a compact if a 34/25 is "way to low".

    How many grams do compact cranks save? You have a smaller crank, chainrings and cassette, not to mention a shorter chain. All of the weight savings is moving, too.

    Disclaimer: This is my question and probably has nothing to do with the original poster.
    We have nothing to lube but our chains.

  4. #4
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    another weight weenie...

    It's difficult to quantify the exact weight difference since not many cranks come in identical models, one compact and the other standard. The chain would be about 5 grams lighter and the cogs might be 20 grams lighter, at most, assuming an 11-23 was used instead of a 12-25. Most users want lower gearing and make no change to the cassette.

    That samll weight saving sure won't win you a race, particularly if you consider the lost momentum that can occur from repeatedly making one more cog shift, every time the chainrings are shifted. The negative effect of additional cog shifting with a compact seems to be easily ignored by it's proponents.

    The fact the the parts are "moving" is extremely insignicant, IMO.

    Another topic that's never discussed is the effect of increased chain tension when using smaller rings and cogs. I got into a debate on another forum where a person claimed that increased chain tension reduced the life of the chain, hubs and BB. His claim was tha it was better to stay in the large chainring whenever possible, even if it meant using the big/big combo. He also claimed that chains should be "broken-in" by deliberately riding in an extreme chainline to "quiet them down". He is right that using smaller chairings increases the chain tension, but so far I've not seen any reduced life from using small rings. I would never use extreme chainlines, becasue it will reduce chain life.

    I often spend 1/3 of my riding time using a 28T ring going up mountains and my chain life has not been reduced when compared to the days when I rode flatter terrain. After 3000 miles, my chain shows very little wear.

  5. #5
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    thanks

    i am using campy, always wanted the 26, but not to give up the 12, live in the foothills of NC, lots of climbing and an hour away from MT Mitchel, 29 is to much for around here, but goto Mitchel, a dear. the compact and the 23 should work great for that trip now, and not lose to much here. thanks for the info. i do wish campy made a 12/27, btw. mark




    Quote Originally Posted by C-40
    23/34 x 39 = 26.38

    The above is the equivalent gear formula. I don't get why you'd bother with a compact if a 34/25 is "way to low". Does that means 39/25 isn't low enough, but a 34/23 will be "just right"? If you're building with shimano a 53/39 with a 12-27 would make more sense.

    With campy, you get left out if a 39/27 is the perfect low gear. It's either a 12-25, 13-26 or 13-29. You can make a 12-26 by substituting the 23-26 pair from a 13-26 into a 12-25, but that's a lot of expense just to gain 1 tooth.

  6. #6
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    I don't know, how about a 50/36 with the 12-25, shifting might be better, carbon cranks?

  7. #7
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    another vote for 50/36 with 12/25

    Quote Originally Posted by kestrel03
    building a new bike with a 50/34 crank set. on my other bikes i use a 12/25 in the rear, with the normal 53/39 set up. a 12/25 will be way to much for where i live(with the compact), but does anyone know about what a 23 rear "feels" like with a 34? i know the 25 falls in between a 28/29 ratio......where does the 23 fall, comparing to the "normal cranks, thanks, m

    seems like this combo will give you the low end you're looking for, but you'll have the advantage of not having to make the extra shifts on your cassette when you change chainrings - i.e. with the 50/34 you will often find yourself making two shifts in the rear for a smooth transition in cadence
    ________________________________
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  8. #8
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    Not me. I'm usually a fat guy on a steel bike.

    I was just speculating as to how much of the interest in compact cranks came from gram shaving. Imo much of the weight-weenie stuff is a competition for people with more money than talent. I really was joking the time I asked about how to attach a cleat directly to my foot to save the weight of the shoes, but folks answered explaining that it wasn't a good idea.
    We have nothing to lube but our chains.

  9. #9
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    I dont see what good a 50/36 does. Its still 14 tooth diff, just like 39/53. I went with a 50/34 and 11-23 so I can still have a good top end and a slightly smaller gear for climbing compared to 39/53 and 12-25. To me a 50/36 defeats the whole purpose of using the compact set-up.

  10. #10
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    carbon stella azzuras

    yeah i was thinking about the 36 also. thanks


    Quote Originally Posted by Al1943
    I don't know, how about a 50/36 with the 12-25, shifting might be better, carbon cranks?

  11. #11
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    Quote Originally Posted by jtompilot
    I dont see what good a 50/36 does. Its still 14 tooth diff, just like 39/53. I went with a 50/34 and 11-23 so I can still have a good top end and a slightly smaller gear for climbing compared to 39/53 and 12-25. To me a 50/36 defeats the whole purpose of using the compact set-up.
    With a 50/36 12-25 you would get closer ratios, fewer front shifts, smoother shifting, less chain rub. And most people won't need a 50-11 combination. But it all depends on where you ride and what you need. And there wouldn't be any problem having an extra ring, it would be easy to switch back and forth between a 34 and a 36.

    Al
    Last edited by Al1943; 03-11-2005 at 02:32 PM.

  12. #12
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    there is a difference..

    Everyone should ultimately choose the gearing that meets their needs. a 50/36 although a 14 tooth difference, is not the same percentage difference. Comapring all three, a 53/39 is a 36% difference, the 50/36 is a 39% difference and the 50/34 is a 47% difference. The 50/36 does not require the extra cog shift that many find so annoying with a 50/34.

    The 50/36 is the same as one cog lower at the low end, so it pretty much trades off some top end for some low end, if the cassette is not changed. A 36/25 is the same as a 39/27. As othere noted, you can't get a 27 from Campy, but this would provide the same gear ratio.

    If the cassette is changed from a 12-25 to an 11-23, then you get the same low end as a 39/25, but slightly more top gear, since a 50/11 is equivalent to a 53/11.66.

  13. #13
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    Quote Originally Posted by Al1943
    With a 50/36 12-25 you would get closer ratios, fewer front shifts, smoother shifting, less chain rub. And most people won't need a 50-11 combination. But it all depends on where you ride and what you need. And there wouldn't be any problem having an extra ring, it would be easy to switch back and forth between a 34 and a 36.

    Al
    How do you figure 12-25 is closer than 11-23.

    I do understand about the extra shift with with the 34/50. I guess you cant have your cake and eat it too.

  14. #14
    Rain Man
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    Thumbs down K103..Ditch the compact. It's the stupidest thing I've

    spent bike money on. Just a marketing ploy.

  15. #15
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    At some point shouldn't you just get a Triple?
    The 39 or 42 ring solves all these "what ring to be in" problems.
    Even a 30/23 is lower than the other options when you need it. (or 25 or 27)
    Your 30-42-53 shifts are crisp 12 or 11 tooth jumps up front.
    And you get the three front rings to spread the wear over!

  16. #16
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    Toast, I think your missing the purpose of compact. Its to give minor flexibility in gearing without having to use a tripple.

  17. #17
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    a better triple...

    IMO, the best road triple is 53/39/30 or 53/39/28, which produces the most uniform shifting. With the 53/39/30 a 2-cog shift is usually required at the transition between rings.

    The middle ring and biggest cog creates a too-extreme chainline and really shouldn't be used. If you have a 42 middle ring and a 12-25, then the lowest useable gear before resorting to the little ring is a 42/23, which is the same as a 39/21. Better to have a 39/23 available to mimimize the use of the little ring.

    I chose the 53/39/28 with a 12-25 for the mountains. My lowest three ratios are equivalent to a 39/29, 39/32 and 39/35. I can stay it the little ring up to a 28/15 if needed, which is equivalent to a 39/21. This pretty much handles all your serious seated climbing needs.

    If I chose to stand to use my legs differently, then I shift up to the 39 chainring and use something in the 19-23 range (whatever is 2-3 cogs higher). With the 28T little ring, the 28 to 39 is a 3-cog difference, so you can usually just shift ring and stand.
    Last edited by C-40; 03-12-2005 at 07:26 AM.

  18. #18
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    Quote Originally Posted by jtompilot
    How do you figure 12-25 is closer than 11-23.
    Yeah, I was talking about the 50/36 being closer than the 50/34. For most there would be more situations where you could use a 36 than a 34. The 50/36 12-25 drive train has more overlap than the 50/34 11/23 so fewer shifts on the front end.

  19. #19
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    Quote Originally Posted by jtompilot
    Toast, I think your missing the purpose of compact. Its to give minor flexibility in gearing without having to use a tripple.
    Hey pilot,

    I think I get it, but it reminds me of a hybrid. The worst of both worlds. All the shifting issues and gaps, but not quite all the gears.
    I bear the stigma and 200 grams, and never have any gear issues.

    -Toast

  20. #20
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    Thanks for the tripple info. If I ever move out to the mountains I'll remember that tripple gearing.

  21. #21
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    Ird

    For those looking for additional flexibility when designing their Campy based compact drivetrain, be aware that IRD has some solutions. They make both a 11-28 and a 12-28 10 speed cassette to fit Campy hubs. They are perhaps $20 less expensive than the Campy Chorus steel cassettes, but also 60 g or so heavier.

  22. #22
    j-dawg
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    With Ultegra?

    Hi C-40,

    Are you doing that setup with Ultegra perhaps? I've seen the 39 before but never the 28. Your riding sounds similar to mine. Mostly in the foothills/mountains. Most of the time I try to sit and spin my way up but there are times it's just too steep or you need to give the hammies a rest and stand for awhile.

    What mountains do you ride. I'm in Northern CO (FC/Loveland). Curious to hear about your rides.

    -j
    I may be fat but I'm slow.

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