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  1. #1
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    Crankarm length vs leg extension

    Our tandem has 170mm cranks for the stoker and should have 165mm. She says that her legs are at too much of an angle at the top of the stroke. The frame size is correct for her, as is saddle height and I cannot imagine that crankarms 5mm's shorter will make a noticeable difference, but I'm not sure. Any expert opinions. Oh yes, it's a Rock n Roll Burley, not that it makes any difference, except that finding 165mm Sugino Fuse 500 cranks is proving pretty difficult.

    Thanks all,
    rlong

  2. #2
    hors category TandemGeek's Avatar
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    I have no idea why 175/170 became the default for tandems... but it has. While most of us of short stature aren't sensitive to and/or adapt to the differences (e.g., yesterday I rode the tandem where I have 175's and my fixed gear today with has 165's and my road bikes have 170), there are certainly some cyclists who struggle with the differences. I guess I'm compelled to ask... Does her solo bike have 165mm cranks?

    Regardless, given her short stature the 165's are certainly not an unreasonable request. I'll have to see if some friends of ours who picked up a set of the 165mm Sugino's still have them; they recently upgraded to a full set of daVinci cranks... one of the few offered in 165mm. Unfortunately, at $585 the super lightweight, stiff, and jewelry-like daVinci cranks are not exactly a best-value. PeterWhiteCycles.com has also been a source for 165mm cranksets but, again, the TA Specialties that he offers are fairly expensive.

    However, you're sort of in luck in that FSA recently added 165mm cranks to their Gossamer MegaExo Tandem line. A full set of the pre-MegaExo sold for about $249. Any FSA dealer should be able to order them, although I'm not sure if you can buy just the rear set and you must also buy a MegaExo BB to go with them.

    Dang, I feel like I"m pimping all the time but... Co-Motion now offers the Gossamer MegaExo's on it's tandems and some friends recently took delivery of a Speedster Co-Pilot with 172.5 / 165 cranks... it's about time we had choices in this regard.
    Last edited by TandemGeek; 11-20-05 at 09:35 PM.

  3. #3
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    Quote Originally Posted by rlong
    I cannot imagine that crankarms 5mm's shorter will make a noticeable difference, but I'm not sure.
    My tandem had 175s front & rear. That 5mm difference in each crank made a difference to me -- it brought on knee pain that I hadn't had before, and that went away when I put 170s on.

    Also, note that if you are adjusting saddle height to the same full leg extension at the bottom of the stroke, going from 170mm to 165mm results in a 10mm relative lowering at the top of the stroke. (When you put the shorter cranks on, the seat needs to go up 5mm to accommodate the original leg extension at bottom, which, combined with the 5mm shorter "reach" of the crank at the top, makes a 10mm net change at the top.)

    Apparently, sensitivity to crank length varies a lot with the individual. I still have the 175s for the stoker. My daughter uses crank shorteners, but my adult stoker -- who's probably about an inch shorter than me -- can ride all day with the 175s, spin them upwards of 120rpm, and not blink an eye.

    -Greg

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    Quote Originally Posted by TandemGeek
    I have no idea why 175/170 became the default for tandems... but it has. While most of us of short stature aren't sensitive to and/or adapt to the differences (e.g., yesterday I rode the tandem where I have 175's and my fixed gear today with has 165's and my road bikes have 170), there are certainly some cyclists who struggle with the differences. I guess I'm compelled to ask... Does her solo bike have 165mm cranks?

    Regardless, given her short stature the 165's are certainly not an unreasonable request. I'll have to see if some friends of ours who picked up a set of the 165mm Sugino's still have them; they recently upgraded to a full set of daVinci cranks... one of the few offered in 165mm. Unfortunately, at $585 the super lightweight, stiff, and jewelry-like daVinci cranks are not exactly a best-value. PeterWhiteCycles.com has also been a source for 165mm cranksets but, again, the TA Specialties that he offers are fairly expensive.

    However, you're sort of in luck in that FSA recently added 165mm cranks to their Gossamer MegaExo Tandem line. A full set of the pre-MegaExo sold for about $249. Any FSA dealer should be able to order them, although I'm not sure if you can buy just the rear set and you must also buy a MegaExo BB to go with them.

    Dang, I feel like I"m pimping all the time but... Co-Motion now offers the Gossamer MegaExo's on it's tandems and some friends recently took delivery of a Speedster Co-Pilot with 172.5 / 165 cranks... it's about time we had choices in this regard.
    It's actually more than 165! I ran two different crankarm software programs for her and she needs 145mm cranks!! And I don't mind you're pimping one bit. After all, isn't that the purpose of the forum, to solve problems and engage as a community? Thanks for your help. Perhaps the child adaptors I saw somewhere yesterday in my search will work. They bolt on to existing cranks and offer three different lengths of bolt patterns. I would love to get the daVinci's that provide the same (three bolt patterns), but at $285.00, well I'll think about it, but I think I'd rather have the whole diVinci bike:-)

  5. #5
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    There's not a lot of difference between each size crank arm. ONe of my tandems has 170s, one has 175s; all my racing bikes are 175 now, but I've raced 177s, 172s, 170s and 175s. This should not be a theoretical concern. Buy some new ones and see what's what: they're cheap, and opinions don't count for much when it's a fit question.

  6. #6
    Banned. galen_52657's Avatar
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    If your stoker is short, she should use short crank arms. TA Specialties has off-the-shelf cranks for singles and tandems from 155 to 185 mm in length and can be purchased from Peter White:

    http://www.peterwhitecycles.com/carmina.asp

  7. #7
    hors category TandemGeek's Avatar
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    Quote Originally Posted by galen_52657
    TA Specialties has off-the-shelf cranks for singles and tandems from 155 to 185 mm in length and can be purchased from Peter White:
    Nice stuff too... I have a set of standard 110 BCD (aka, compact) TA Specialties Zepher cranks on my Erickson solo bike.

    However, it's best to call (603 478 0900) or Email (shipping@peterwhitecycles.com) to confirm what they have in stock. TA discontinued certain models and sizes of their tandem cranks and I'm not sure what the smallest sizes are anymore, noting that the Web site contains some disclaimers regarding availability. Don't forget to address your bottom bracket requirements as TA use ISO square taper axles as I'm not sure what they are using with your current cranks: original spec was ISIS w/TruVative cranks.

    Harkening back to anther thread, I do have to note that Linda White is fairly prompt in answering Emails that come in during the regular work week. Very nice folks who deal in only high quality components.

    Note: I have an Email in to our friends who had the Sugino 165 stoker cranks and will advise if they are still available.

  8. #8
    Senior Member zonatandem's Avatar
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    Roger Durham (Bullseye) used to (still does?) build custom length crank arms. About 10 years ago we had a fellow 6'7" that wanted a tandem for him and his 5'3" stoker . . . Ended up having Bullseye build a pair of 220mm custom crankarms for him on their custom 27x18" tandem.
    BTW stoker Kay at 4'10 3/4" tall (?) has ridden 170mm cranks for the past 200,000+ miles. Works fine for her, but may not work fine for all.

    Pedal on TWOgether!
    Rudy and Kay/zonatandem

  9. #9
    K&M
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    When we bought our Burley I had my LBS ask Burley if I could get a different length crank arm for my stoker. The answer was no. We then asked FSA if they would switch out the Burley provided cranks for cranks of the length we preferred. They also said no. I can understand that Burley only orders cranks in 175 & 170, but why FSA wouldn't let us have the length we wanted is harder for me to figure.

  10. #10
    hors category TandemGeek's Avatar
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    Quote Originally Posted by K&M
    ... but why FSA wouldn't let us have the length we wanted is harder for me to figure.
    ... did you offer to pay for them and they said no, or did FSA just not want to make them available?

    Seriously, it's really not FSA's problem or place to exchange Burley's OEM components. As for Burley, it is clear that they have gone to a more cost effective business model (for them) where customization and special orders are no longer part of their business plan.

    Now, this of course begs the question... what's you dealer's position here? Did you approach them for a swap out or a "good guy" dealer-cost on a set of replacement cranks? While your dealer is certainly not obligated to do so, some might consider going the extra mile under the premise of good-will and future referrals.

  11. #11
    Senior Member zonatandem's Avatar
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    To make a 'sale' dealer can do many things; the idea is to make that part of the deal *before* ordering the tandem, not 'after'. Burley and other manufacturers have to set limitations. They are not custom builders. Approach Co-Motion or some other builders, with a custom build idea and they'll say "yes" . . . but be prepared to pay an extra charge.

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    Thanks to all of you for your suggestions. As I told Mark, we are going to try a set of Race2 crank shorteners to get down to the necessary 150mm. We are really using this bike as a trial platform and I don't want to put too much money into it only to purchase something more permanent in a few months. I did find a new set of XTR linear brakes with travelers on Ebay, which together with Koolstop salmon pads and daVinci rear brake booster are a real improvement. Then there's the new stem, seats, stoker seatpost, pedals, cables, chainrings, cassette, computer, tires, my god, is there no end to this experiment :.)
    Long Live Long Rides

  13. #13
    hors category TandemGeek's Avatar
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    Quote Originally Posted by rlong
    ...we are going to try a set of Race 2 crank shorteners to get down to the necessary 150mm.
    While not wanting to add further confusion to your thought processes, bear in mind that crank shorteners have a potential downside that you need to be mindful of...

    Crank shorteners bolt-on to the outside of a standard crankarm and, as a result, increase the overall distance between the pedals and, therefore the cyclists feet, which can create more serious problems for an adult cyclist than cranks that too long.

    This particular dimension of bicycle fit is referred to as either "tread" (analogous to the natural distance that exists between a person's feet as they stand or walk) or the "Q-Factor". Children -- for whom crank shorteners are designed -- tend to have very flexible joints which aren't overly sensitive to the increased Q-factor associated with these bolt-on solutions. However, for adults Q-factor can be a major issue even with standard width cranks and the shorter their legs are, the more prounced any ill effects from an increase in Q-factor will be. Therefore, if you go the route of crank shorteners be very sensitive to any feedback from your wife relative to increased hip or knee discomfort.

    Just something to keep in mind.

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    K&M
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    I've bought a few bikes in my time and I've never before had anyone balk at giving me whatever crank length I preferred. It's not like one length is more expensive than another (at least not in my limited experience). I understand that Burley only keeps their standard sizes on hand, so obviously they couldn't switch them out. If my LBS carried FSA cranks, they would have been happy to switch them - but they don't. Obviously, FSA has no obligation to trade me for the size I want, but there are plenty of manufacturers who do that kind of thing all the time .... it's called customer service.

    None of this was a big deal to us, in fact it was our LBS that called FSA to inquire about an exchange. The LBS really wanted us to have things EXACTLY the way we preferred. We weren't all that picky.

    All this occured PRIOR to buying the bike and we bought the bike knowing (and not much caring) that the crank length wouldn't be perfect. We have been getting along fine on the bike just the way it is.

  15. #15
    hors category TandemGeek's Avatar
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    Quote Originally Posted by K&M
    We have been getting along fine on the bike just the way it is.
    Speaking of crankiness...

    If it's of any consolation, when we bought our first tandem back in '97 (all wide-eyed and bushy tailed), despite doing some homework with the sparse information available at that time, I was pretty much an easy target for all kinds of "tandem speak" that was designed to gloss over some of the nuances of tandem component selection, or the lack thereof. The list of compromises we accepted was about equal to the list of quick modifications I made (barcon to Sachs Ergo brifters, Araya to Mavic rims , LX to XT brakes with XTR pads, gawd awful tires to my beloved Vredesteins, etc...). Included in those compromises were the 175/170 cranks, noting that me at 68" tall with my 30" inseam and Debbie at 62" tall with her 29" inseam "should have" had shorter cranks. However, our dealer dutifully noted that for tandems, you really wanted a longer set of cranks, yada, yada, yada... which I suspected was bunk given what I knew about crank length but hey, they said the wider, higher bars were also necessary.

    To make a long story short, we decided to replace our first tandem 10 months after we bought it (too many things to fix and too many compromises) but never batted an eye when we spec'd the same 175/170 cranks. It really wasn't until 5 years later when we were then up to three tandems with 175/170 cranks, including our off-road rig that I really started to wonder if we shouldn't be riding on 172.5/165 or 170/165 cranks. Given the cost of replacement (all three being daVinci's NC'd cranksets) and lacking any evidence that suggests we are hampered by the 175/170s, I've decided that there's no need to fix what probably isn't broken. Moreover, I've made a point to not even test the waters with shorter cranks as the results could be tantamount to "tasting the forbidden fruit": but one of these days....

    Moral of the Story: Sometimes knowledge just gets in the way of progress. If it works, it works.
    Last edited by TandemGeek; 11-23-05 at 01:50 PM.

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    Quote Originally Posted by TandemGeek
    While not wanting to add further confusion to your thought processes, bear in mind that crank shorteners have a potential downside that you need to be mindful of...

    Crank shorteners bolt-on to the outside of a standard crankarm and, as a result, increase the overall distance between the pedals and, therefore the cyclists feet, which can create more serious problems for an adult cyclist than cranks that too long.

    This particular dimension of bicycle fit is referred to as either "tread" (analogous to the natural distance that exists between a person's feet as they stand or walk) or the "Q-Factor". Children -- for whom crank shorteners are designed -- tend to have very flexible joints which aren't overly sensitive to the increased Q-factor associated with these bolt-on solutions. However, for adults Q-factor can be a major issue even with standard width cranks and the shorter their legs are, the more prounced any ill effects from an increase in Q-factor will be. Therefore, if you go the route of crank shorteners be very sensitive to any feedback from your wife relative to increased hip or knee discomfort.

    Just something to keep in mind.
    Well, the crank shorteners aren't intended to be a permanent replacement for the correct cranks, but I had hoped they could be used for a while. Now I'm not so sure and will have to consult with someone, not sure who, about the Q-factor angle and how long it might take before we have a whole new can of worms opened. damn.

  17. #17
    hors category TandemGeek's Avatar
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    Quote Originally Posted by rlong
    Well, the crank shorteners aren't intended to be a permanent replacement for the correct cranks, but I had hoped they could be used for a while.
    I don't think the Q-factor issue precludes your experiment with the crank shorteners... again, it's not a foregone conclusion that your wife is sensitive to a given tread width. However, in the event that you put the shorteners on the bike and your wife was reporting some discomfort that didn't exist before it could be beneficial to know that the increased distance between the pedals could be the source, totally unrelated to the length of the cranks.

  18. #18
    Banned. galen_52657's Avatar
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    I think crank length boils down to two factors:

    1. Comfort
    2. Maximizing performance potential to the Nth*

    Only at the far ends of the size spectrum will comfort come into play and I would venture to guess more on the short-person-with-to-long-a-crank end of the size spectrum than the other way around.

    I am tall and I have ridden a bike with 165's and they did not feel 'uncomfortable' just tiny.

    I have been riding 180's for many years and am considering going longer. When I first switched from 170's to 177.5's then to 180's I noticed a difference and felt I performed better with the longer cranks, but it was not the type of earth-shattering change that would have jumped me from a mid-pack CAT-3 to a National-class cyclist.

  19. #19
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    Quote Originally Posted by TandemGeek
    I don't think the Q-factor issue precludes your experiment with the crank shorteners... again, it's not a foregone conclusion that your wife is sensitive to a given tread width. However, in the event that you put the shorteners on the bike and your wife was reporting some discomfort that didn't exist before it could be beneficial to know that the increased distance between the pedals could be the source, totally unrelated to the length of the cranks.
    No disagreement there! Susan is pretty sensitive to any change and we will certainly be looking for anything new (pain) that did not present prior to the shorteners. I checked the specs on the shorteners and they will add a minimum of 1/2" on each side. So, if 5mm in length results in appearant changes, it seems unlikely that such a change in Q-factor will go unnoticed. Did I mention that I have emails out to Peter White, diVinci, and Precision Cycles? DiVinci has remachined Shimano Deore cranks at 150mm for child stokers. However, they only have spiders on one side. I asked if they could put together a full set as the price is much more in line with what I'm seeking. A new Deore triple for single is $80.00 at Performance today, so that's encouraging.
    Last edited by rlong; 11-25-05 at 10:13 AM. Reason: word use change

  20. #20
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    Quote Originally Posted by galen_52657
    I think crank length boils down to two factors:

    1. Comfort
    2. Maximizing performance potential to the Nth*

    Only at the far ends of the size spectrum will comfort come into play and I would venture to guess more on the short-person-with-to-long-a-crank end of the size spectrum than the other way around.

    I am tall and I have ridden a bike with 165's and they did not feel 'uncomfortable' just tiny.

    I have been riding 180's for many years and am considering going longer. When I first switched from 170's to 177.5's then to 180's I noticed a difference and felt I performed better with the longer cranks, but it was not the type of earth-shattering change that would have jumped me from a mid-pack CAT-3 to a National-class cyclist.
    Yes, using a too short crank would only result in decreased performance, as the knee angle is more open and the stress greatly reduced at the top of the stroke; as opposed to a crank too long where the knee angle is more closed and the stress is increased. Here you get decreased performance, followed by pain.

  21. #21
    barnfullagts
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    Alfred E Bike has the 165mm Sugino XD600 crank in a 74/110mm bolt pattern at the link below. Sheldon Brown at Harris Cyclery had them listed also. If you have a favorite LBS have them check with QBP.
    My past experience with them is that you may be able to order the arms seprately and use your existing rings and bolts. They may even have some Fuse (500) arms.
    http://aebike.com/site/page.cfm?PageID=30&SKU=CR1034
    Last edited by gm1230126; 11-25-05 at 10:44 PM.

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    Update: I spoke with the folks at daVinci (very nice to) and the child stoker set does not have two spiders. I didn't really expect them to, but the size was perfect so I was hoping. They do have the three hole crank arms with 150 mm in the center which is perfect. However they are a bit pricey for us at this time ($260.00). What I have found is a component line by the name of Thorn who produce tandem cranks from 140mm to 180mm in 5mm increments, and they are priced at $158.00 including shipping from St. John Street Cycles in the UK. The pricing is tricky, as they have A 17.5% VAT which I assume to be value added tax which is dropped when they are shipped out of country. This offsets the cost of shipping. Sorry, they list for $150.00 and figuring out what I would actually pay with the notax and shipping charges is really a calculated guess on my part.

    I have emailed St. John to get more information about the Thorn line of components. Anyone familiar with them? Anyway, you should look at their tandems online. They are really interesting and different from what I'm used to seeing in the USA!

  23. #23
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    New Update:
    I received the Race2 crankarm shorteners today, 2 left ones :.( However, I put one of them on and really did not like the look of it. They are flat and the cranks are concave, thus the cams that hold the shorteners did not fully ingage the cranks and looked really scary! Sending them back. Dang. I emailed Linda at Peter White again about the 150mm's, and opened another thread to discuss another component line new to me named Thorn. It's a British company and they have tandem cranksets and arms from 140mm and up. Never heard of them though, and my wife says ordering something I'm not familiar with, online from London is just nuts. Oh well.

  24. #24
    Double Secret Probation R900's Avatar
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    Quote Originally Posted by TandemGeek
    Moral of the Story: Sometimes knowledge just gets in the way of progress. If it works, it works.
    Very True - John
    Time to Ride...

  25. #25
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    Updated update:
    For anyone who finds that they need short cranks (smaller than 165) I have located a builder/fabricator who shortens and remachines cranks: BikeSmith Design and fabrication: bikesmithdesign.com. He has an interesting web site to advertise his work, a lot of which is for recumbents.

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