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Thread: Drivetrain Mods

  1. #1
    Member ciriarte's Avatar
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    Drivetrain Mods

    After much research and handwringing, I've pulled the trigger on a Bike Friday Pocket Sport purchase. With a top gear-inch of around 87", I can see a drivetrain mod in our near future.

    The BF/PS comes with a 30-42-52 front triple and an 11-28 rear 8-sp cassette. From what I can gather, a swap to a rear 9-26 Capreo would involve a new rear hub, new derailleur and new shifter. The other option is to get a bigger chainring (I've heard of some folks bumping up to a 60-tooth!), but that might involve a new front derailleur. But, I might want to get longer cranks anyway.

    Has anyone gone through this already? Any advice/observations?

    Chris

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    My very early Pocket Rocket (1994) uses 46-60 front chain rings and a 11-28 rear cassette with 451 wheels and with that you end up with a top of 109 gear inches. My wife's 2006 Pocket Crusoe uses a triple up front with a 52-42-30 and a 9-26 Capreo with 406 wheels which gives a top of 104 gear inches. If she had ordered 451 wheels it would of had a top gear inches of 115 gear inches. She chose the 406 wheels because it is easier to find tires for it. Roger

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    Senior Member kamtsa's Avatar
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    Are you buying new Pocket Sport? If so, why not to order it with the gear range you want? It should be less expensive then moding it.

    Kam

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    Member ciriarte's Avatar
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    I find it's cheaper -- and more fun -- to do it yourself!

    Chris

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    Senior Member kamtsa's Avatar
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    Quote Originally Posted by ciriarte View Post
    I find it's cheaper -- and more fun -- to do it yourself!

    Chris
    I can't argue with the fun part ;-)

    Kam

  6. #6
    Senior Member oddball's Avatar
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    Capreo hub is probably your best option. The hub you will need for sure as it the only on that will take a 9 or 10 tooth cog.
    You could try a Schlumpf Speed Drive internally geared bottom bracket. http://www.schlumpf.ch/antriebe_engl.htm However that would probably require a LBS experienced with it to install it as you may need a special tool and I am not sure it would work on a BF.

  7. #7
    Member ciriarte's Avatar
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    Quote Originally Posted by oddball View Post
    Capreo hub is probably your best option. The hub you will need for sure as it the only on that will take a 9 or 10 tooth cog.
    You could try a Schlumpf Speed Drive internally geared bottom bracket. http://www.schlumpf.ch/antriebe_engl.htm However that would probably require a LBS experienced with it to install it as you may need a special tool and I am not sure it would work on a BF.
    Intriguing! I've heard of the Hammertrax (sp?), but not the Schlumpf cranks. Are they readily available in the States?

    Chris

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    Senior Member kamtsa's Avatar
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    Have you considered SRAM Dual Drive?

    It can give you 20 - 110 gear inches and will eliminate the front derailleur which complicates the fold with BF method of folding.

    I have it on my NWT and am very happy with it.

    Kam

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    Senior Member oddball's Avatar
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    LBS's that specialize in small wheel bikes like folders and recumbents usually have access to the Schlumpf bottom bracket drives. They're not cheap though. I believe you are looking at around $500US. I've seen at least one Moulton with one and several 'bent trikes with them. Greenspeed offers them as an option on their trikes. The major difference between this and the few other geared BB's is that there are no cables, you shift it by hitting a large button in the middle of the cranks with your heel.
    If you want to be silly about it you can mount triple chainrings on a Sclumpf combine it with a SRAM dual drive and have 162 gears.

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    Quote Originally Posted by ciriarte View Post
    Intriguing! I've heard of the Hammertrax (sp?), but not the Schlumpf cranks. Are they readily available in the States?

    Chris
    I have a couple of new Schlumpf Speed Drives left .. PM me if interested.

  11. #11
    Member ciriarte's Avatar
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    Quote Originally Posted by kamtsa View Post
    Have you considered SRAM Dual Drive?

    It can give you 20 - 110 gear inches and will eliminate the front derailleur which complicates the fold with BF method of folding.

    I have it on my NWT and am very happy with it.

    Kam
    Ah! Good idea ... I hadn't thought of that. I just ran a gear calulator, and with a 48-tooth chainring, a SRAM D/D and stock cassette will give me a 23-to-110 gear inch range!

    Chris

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    I think one thing that often can be easier with more specialized bikes is modifying your riding style a little, 87 gear in on those 406's 52/11 at 120rpms is 32mph.. How often you need to pedal that fast?
    The 80/20 (or 90/10 or 95/5) rule is valuable with these types of bikes.

  13. #13
    Member ciriarte's Avatar
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    Quote Originally Posted by JimBeans83 View Post
    I think one thing that often can be easier with more specialized bikes is modifying your riding style a little, 87 gear in on those 406's 52/11 at 120rpms is 32mph.. How often you need to pedal that fast?
    The 80/20 (or 90/10 or 95/5) rule is valuable with these types of bikes.
    That thought had occurred to me as well, which is part of the reason I ordered the bike completely stock vs. having any drivetrain mods made to it before I put some miles on it.

    I just got done doing a metric century on my full-size road bike. It's a 20-speed with 11-27 cassette and 34/50 crank, so 17th gear is roughly equal to the Pocket's top gear. It's conceivable that I may be happy with the gearing as is ...I'll see when it gets here!

    Chris

  14. #14
    Senior Member kamtsa's Avatar
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    Quote Originally Posted by ciriarte View Post
    Ah! Good idea ... I hadn't thought of that. I just ran a gear calulator, and with a 48-tooth chainring, a SRAM D/D and stock cassette will give me a 23-to-110 gear inch range!

    Chris
    The 3x9 DualDrive has a range of about 550%, so with 23" at the bottom you should bet about 120" at the top.

    When I climb very steeps hills (at least by my standard) I sometimes wish to have even a lower gear so I plan to try a smaller chainwheel (40T compared to the existing 46T) to get a range of 17 - 92".

    Kam

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