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  1. #1
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    Captain crank length change?

    I'm trying to decide whether it is worth the money to switch my captain's cranks from 170mm to 175mm. I am 6-feet tall, 167lbs, with long legs. I am used to 175mm cranks on single bikes. I prefer a medium to high RPM on single bikes but tend to mash a bit more on the tandem because my stoker likes to pedal at low rpm.

    I think that the shorter cranks are reducing my pedaling efficiency, especially when pedaling at low RPM or when climbing hills. Is it just my imagination? It doesn't seem like 5mm could make all that much of a difference but I really think I can tell. Any opinions?


    Thanks!

  2. #2
    hors category TandemGeek's Avatar
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    Interestingly enough, I recently changed out the cranks on both road tandems going the other way. I'm 5'8" with about a 29" inseam and have always ridden with 170mm cranks on my single bikes... well back to the beginning of time (1970's).

    When we when shopping for tandems back in 1997 and knew zilch the spiel from the dealers and manufacturers was, longer-crank arms (175mm/170mm stoker), wider bars, and more upright. More upright went out the window pretty fast and a 2mm bump in handlebar width was all I could stand. However, the longer cranks didn't seem to bother me. In fact, we ended up putting 175mm/170mm cranks on the next five tandems. Moving between the track/fixed gear w/165mm, my road bikes with 170mm, and the tandems with 175mm cranks didn't take but about a few miles to adjust, but I wasn't logging long miles on anything but the tandem which saw 99% of my cycling time.

    After spending more time back on my single bikes and then moving to the tandem last fall I began to notice that I was really laboring to keep my cadence in the 90's on longish hard rides and by the end of the ride even keeping them in the 80's was tough. I attributed some of that to my declining fitness (something I still need to fix) and 10 years of aging (not much I can do about that) but also decided to experiment with 170mm cranks on the front of the tandem. After going back and forth a few times I really found the 170's to be much more familiar and easier to spin consistently thoughout the ride, regardless of distance.

    So, at least for me, I'm now of the mind that the cranks should be the same on single road and tandem bikes unless you feel you need to ****** your cadence by going longer or to bump it up by going shorter.
    Last edited by TandemGeek; 06-15-07 at 09:02 AM.

  3. #3
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    Quote Originally Posted by TandemGeek
    So, at least for me, I'm now of the mind that the cranks should be the same on single road and tandem bikes unless you feel you need to ****** your cadence by going longer or to bump it up by going shorter.
    Thanks, that sounds like sound advice. It's surprising that 5mm in crank length is noticeable but I think I can tell a difference... it's good to know that other folks notice the difference too. I plan on getting some longer cranks. And I do need to ****** my cadence... so per your advice I may even be happy with cranks longer than those on my single bike.

    If anyone is selling any used 175mm or longer captain's cranks for a square taper BB, please PM me. I do not have the cash to buy them new... and my tandem is a well-used late '80s steel Santana so I really don't feel compelled to buy new parts for it anyway.

    Thanks again for the help.

  4. #4
    shut up and ride
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    i would have a set if of 175s if i could find a set of 172.5s to match my singles... but i haven't seen any cheap ones especially as it seems that 172.5s are pretty rare for tandem cranks.

  5. #5
    Senior Member zonatandem's Avatar
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    Many folks don't notice difference in crank lengths.
    Saw one tandem with 175 front and 170 rear. However shop mechanic (?!) had mixed up the crossover tandem cranks . . . nobody riding it had noticed.
    Longest crank arm lenghts was custom built 220mm for a fellow that's 6'7". Had to utilize higher than normal BB setup.
    We've been using 170s front and rear for decades, even with a height impaired stoker (4' 10 3/4" tall).
    If your body/mind feels better with the switch, then do it!

  6. #6
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    Apparently a common fix for spinning captains is to put on longer cranks since the long cranks reduce rpms for a given amount of pedal travel. I went from 170's to 175's (on my single bike) and dropped from spinning 110+ rpm to about 80 rpms. I worked hard to bring back some of that pedal speed and now ride at perhaps 100 rpm comfortably. If you ride shorter cranks more regularly (i.e. you ride the single bike more) then moving to 175's should cause you to slow down just a touch.

    I'm close to TandemGeeks height and leg length and all normal rules would say 175's are too long. However I've not only ridden but also raced 175's successfully for about 5 years without any problems.

    For cranks with square taper BB, check out some of the online shops that link up to QBP (Quality Bicycle Products). There are relatively cheap Sugino cranks listed - approx retail is $34 for the left and $20 for the right crank. I only know of one (bikeman.com) but I'm sure there are others. Any LBS would be able to order the same cranks through QBP.

    hope this helps,
    cdr

  7. #7
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    We have a -5 mm cranklength for the captain and an identical for the stoker on our tandem. I (captain prefer shorter cranks I think because of the difference in pedals: ' clip-in' pedal (LOOK) on single bike and 'normal' pedals' on the tandem.

  8. #8
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    Quote Originally Posted by carpediemracing
    Apparently a common fix for spinning captains is to put on longer cranks since the long cranks reduce rpms for a given amount of pedal travel. I went from 170's to 175's (on my single bike) and dropped from spinning 110+ rpm to about 80 rpms. I worked hard to bring back some of that pedal speed and now ride at perhaps 100 rpm comfortably. If you ride shorter cranks more regularly (i.e. you ride the single bike more) then moving to 175's should cause you to slow down just a touch.

    I'm close to TandemGeeks height and leg length and all normal rules would say 175's are too long. However I've not only ridden but also raced 175's successfully for about 5 years without any problems.

    For cranks with square taper BB, check out some of the online shops that link up to QBP (Quality Bicycle Products). There are relatively cheap Sugino cranks listed - approx retail is $34 for the left and $20 for the right crank. I only know of one (bikeman.com) but I'm sure there are others. Any LBS would be able to order the same cranks through QBP.

    hope this helps,
    cdr
    Thank you very much for your help. I didn't know that longer captain's cranks were used to lower effective RPM for the stoker. I'll check QBP out.

    Since I'm used to 175 on single bikes, I may try to get 180mm cranks for the tandem... it would be a significant change for me, but I'm sure my stoker would appreciate the lower RPMs and that's what matters.

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