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  1. #1
    Mr. Cellophane RainmanP's Avatar
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    John E's Chainrings

    John E,
    That is an interesting chainring combination, 48-45-34. May I ask how you arrived at it? What brand crank is it based on? What brand rings? BCDs? My old Bianchi has Bio Pace chainrings which I do not like. I am considering replacing them with round rings, possibly a little smaller than the 52-42 it now has.
    Regards,
    Raymond
    If it ain't broke, mess with it anyway!

  2. #2
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    The best replacement chainrings are made by Specialities TA. They are used by professional racing teams (like US Postal). TA make them for just about any cranks and any size, 8 or 9 speed compatable, with profilled teeth.

  3. #3
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    I have a similar setup on my touring bike. It is known as a half-step plus granny" combination, and used to be fairly common. My rings, as most touring bikes, are 110mm BCD, and are Sugino ans another brand. They are 5 arm cranks.
    Road bikes would also sometimes use a half-step setup, without a granny. Most modern road bikes are 130mm (Shimano standard), 135mm (Campagnolo standard), and some older bikes are 144mm.
    Je vais à vélo, donc je suis!

  4. #4
    Member SteveF's Avatar
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    Ray,

    D*Alex nailed it on the head -- it's a "half-step plus granny" setup, useful for getting small changes in ratio when you've got a relatively small number of cogs to use on the rear wheel. The small difference between the outer and middle chainrings are what give it away.

    Essentially, the chainrings are chosen so that a shift between the outer two gives a change in gearing that's half the difference between each rear shift (hence the name). Since this doesn't provide a very low bottom gear with a double-ring crankset, it's normally used with a triple to provide the ratios needed for hillclimbing.

    Advantage: with a 6-speed wide-ratio freewheel (eg 13-28 or 13-32) and a triple crankset, you can get about 15 distinct, usable ratios, most of them spaced about as closely as one might otherwise obtain with a "corncob" rear cluster, and still have a 1:1 or less bottom end for steep hills.

    Biggest disadvantage: Once you're out of the granny, moving sequentially through each individual ratio means that you're double-shifting (shifting front and rear simultaneously) every other shift. You're constantly seesawing back & forth between the middle and outer ring while you also shift the rear every other time. Depending on your bike setup, double-shifting can be clumsy -- downtube shifters work best for me on this setup, since you can work both levers with one hand.

    As you know, I recently "semi-modernized" my 1986 road bike. It used to be an 18-speed half-step-plus-granny setup, with 26-46-50 chainrings and a 13-28 freewheel. I "de-half-stepped" it to a 24-speed, with 26-36-48 chainrings (still using the original 110/74 BCD crankset and front derailer) and either a 12-23 or 13-27 cassette. I still have about 15 distinct and useful ratios, but careful selection of the cassette cogs gives me the close ratios I am used to, with a lot less shifting!
    SteveF
    -----------------
    Lugged Steel Rider

  5. #5
    feros ferio John E's Avatar
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    A bit more detail regarding my half-step-plus grannie system -- A 3-tooth drop in front (49-52, 47-50, 46-49, etc.) with a 2-tooth progression in back is traditional for close-ratio half-step gearing, because the ratio change in front, about 6 or 7 percent, is half the average percentage change in back, from 13 to 15 to 17 to 19, or from 14 to 16 to 18. I use a 110/74mm BCD mountain crank with a mix of SR and QBC rings from eBay. I like a top gear of about 48/13 or 52/14, i.e., 100 gear inches. In front, the 34-45 shift is the same drop as a 42-53, which any older-style derailleur, such as my Shimano 600, can handle easily. Interestingly, 34-48 is the same 14-tooth drop as today's road standard, 39-53, so my 34-45-48 / 13-23 combination does not tax the rear derailleur any worse than a 39-53 / 14-24 would.

    For the transportation or recreational cyclist, half-step gearing works out extremely well. I accelerate through the gears one cog (i.e., two ratios) at a time, then, as I reach cruising speed, I can fine-tune as needed by shifting between the 45 and 48 rings. For an extra-fast, extra-smooth start, I dump the chain onto the grannie before stopping (or while stopped, by lifting the rear wheel). As I start up, I spin up to about 100 rpm, make the 34-45 shift, then start working through the rear cogset as needed.

    Leaving out the two cross-chains and allowing for the convenient redundancy at 61 gear-inches, I get 15 good ratios out of 18 possible combinations:

    ___48__45___34

    13 99.7 93.5
    15 86.4 81.0 61.2
    17 76.2 71.5 54.0
    19 68.2 63.9 48.3
    21 61.7 57.9 43.7
    24 ____ 50.6 38.2

    (I have used 13-23 and 13-24 freewheels on this bike, but 45/23 does not interleave between 34/17 and 34/19 as neatly as 45/24 does.)
    Last edited by John E; 09-13-01 at 02:09 PM.

  6. #6
    Mr. Cellophane RainmanP's Avatar
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    Thanks for all the explanations! I see what you are saying. I guess my 14-25 (14-15-16-17-18-19-21-23-25) gives me small enough steps in the mid range where I normally ride. I can see how the setup would be useful on a 5 or 6. Something to keep in mind for the old Schwinn Voyageur I am fixing up. A couple of chainrings might be all the "upgrade" it needs.
    Regards,
    Raymond
    If it ain't broke, mess with it anyway!

  7. #7
    feros ferio John E's Avatar
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    Precisely, Rainman. A one-tooth change in cog size, corresponding to about a 4- to 7-percent ratio change, is a near-ideal ratio progression. In 1965, with a 5-speed freewheel and limited derailleur capacity, the best solution was to adopt a 2-tooth progression, and to fill in the gaps with half-step (e.g. 47-50 / 14-16-18-20-23) or Alpine/one-and-a-half-step gearing (e.g. 42-50 / 14-16-18-20-23). [Note that by swapping only the inner chainring, one can quickly change between half-step for level rides and 1.5-step for hill work, as I do on my 2-chainring road bikes.] With a 9-cog freehub, you can now obtain a decent range across the freewheel without leaving any gaps in the critical middle and high ranges, thereby eliminating the need for carefully-interlaced gear ratio progressions.

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    One reason why "old" bikes usually had only even numbers of teeth was that some riders still used "skip-tooth chains". In order to use one of these style chains, you had to grind down every other tooth, so odd #'s of teeth weren't encouraged.
    Je vais à vélo, donc je suis!

  9. #9
    Mr. Cellophane RainmanP's Avatar
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    John E, what size rings do you use on the 2-ring crank?

    Anyone, what would be the smallest inner chain ring that one could bolt onto a standard 130mm BCD double road crank? Are there adaptors to allow one to go smaller? It occurs to me that something like a 48-36 front with a 13-27 (9-speed) rear would handle just about anything I might encounter hillwise in my area, providing steps of mostly 6% or less over 15 usable combinations with a low of 36 inches. If a 36 with 130 BCD is available, does anyone know where? Perhaps MichaelW's friend at Highpath could provide one.
    Regards,
    Raymond
    If it ain't broke, mess with it anyway!

  10. #10
    feros ferio John E's Avatar
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    The minimum tooth count on a 130mm BCD spider is 38; on 135mm (Campy), 39. A 50-38 / 14-15-16-17-18-19-20-22-24 setup would cover my needs nicely. Omitting the two crosschain and the two next-to-crosschain combinations leaves 14 good ratios covering 43 to 96 gear-inches. Maybe I should spread the Bianchi from 126 to 130mm ...

    Most off-the-shelf road bikes have at least two ratios (e.g. 53/11 and 53/12) which are uselessly high for nonracers.

  11. #11
    Mr. Cellophane RainmanP's Avatar
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    I agree, John. I put a 14-15-16-17-18-19-21-23-25 on my commuter when I upgraded to 9 speed. I would have to be going downhill with a tailwind to get into 52-12 or 11.

    What Bianchi do you have?
    If it ain't broke, mess with it anyway!

  12. #12
    feros ferio John E's Avatar
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    I have a 1982 Bianchi road bike with a 99cm wheelbase, a Columbus TreTubi frame (Columbus SL main triangle, seamed CrMo forks and stays), and a fairly rare metallic brown/"charcoal" factory paint job. Components include Campy NR derailleurs, pedals, BB, headset, and brake calipers, Ofmega cranks and hubs, and TTT stem. I changed from the original 12-speed gearing (52-42 / 13-23) to 14 speeds (50-42 / 13-26), using a Sachs Aris freewheel. I rarely use the 26T grannie cog, but it is reassuring to know it's there for those inevitable 15- to 19-percent grades.

  13. #13
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    45 Chainring 130mm

    Quote Originally Posted by John E View Post
    A bit more detail regarding my half-step-plus grannie system -- A 3-tooth drop in front (49-52, 47-50, 46-49, etc.) with a 2-tooth progression in back is traditional for close-ratio half-step gearing, because the ratio change in front, about 6 or 7 percent, is half the average percentage change in back, from 13 to 15 to 17 to 19, or from 14 to 16 to 18. I use a 110/74mm BCD mountain crank with a mix of SR and QBC rings from eBay. I like a top gear of about 48/13 or 52/14, i.e., 100 gear inches. In front, the 34-45 shift is the same drop as a 42-53, which any older-style derailleur, such as my Shimano 600, can handle easily. Interestingly, 34-48 is the same 14-tooth drop as today's road standard, 39-53, so my 34-45-48 / 13-23 combination does not tax the rear derailleur any worse than a 39-53 / 14-24 would.

    For the transportation or recreational cyclist, half-step gearing works out extremely well. I accelerate through the gears one cog (i.e., two ratios) at a time, then, as I reach cruising speed, I can fine-tune as needed by shifting between the 45 and 48 rings. For an extra-fast, extra-smooth start, I dump the chain onto the grannie before stopping (or while stopped, by lifting the rear wheel). As I start up, I spin up to about 100 rpm, make the 34-45 shift, then start working through the rear cogset as needed.

    Leaving out the two cross-chains and allowing for the convenient redundancy at 61 gear-inches, I get 15 good ratios out of 18 possible combinations:

    ___48__45___34

    13 99.7 93.5
    15 86.4 81.0 61.2
    17 76.2 71.5 54.0
    19 68.2 63.9 48.3
    21 61.7 57.9 43.7
    24 ____ 50.6 38.2

    (I have used 13-23 and 13-24 freewheels on this bike, but 45/23 does not interleave between 34/17 and 34/19 as neatly as 45/24 does.)
    What is the brand of your 45? Where did you get it?
    Thanks,
    -- Legros

  14. #14
    headtube. zzyzx_xyzzy's Avatar
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    this thread is 8 years old!

    remarkably John E is still around, but you'll probably have better luck sending him a PM.

  15. #15
    Senior Member
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    Quote Originally Posted by zzyzx_xyzzy View Post
    this thread is 8 years old!

    remarkably John E is still around, but you'll probably have better luck sending him a PM.
    I think he's still a fan of half-step gearing, too...

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