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  1. #1
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    Tall riders--longer crank arms?

    My inseam is 38", as measured from heel to perenium--is this right? I wear 34" inseam jeans, so I'm kind of surprised to measure 38" unless I shouldn't be measuring to that high up...

    According to this website, which I have no idea if it's accurate, says I should have 185mm crank arms.

    Optimum Bicycle Crank Length Calculator

    I have a Trek Superfly and a Fuji Gran Fondo, which both appear to have 180mm crank arms. I don't imagine that 5mm is a huge difference but I thought I would ask.

  2. #2
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    Huh, based on the formula in the link, i should be riding 160.5 crank arms. I guess the 175's on my bike are overkill...
    Remember when we were kids and our Mom's said we could not play in the mud? I'm making up for it now!!

  3. #3
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    I have 38" inseam too and was riding 200mm cranks for a while (I used the formula multiplying inseam (in mm) by .215. For this formula, inseam should be measured from the floor up to the pubic bone while barefoot, you can do this by pulling a book or broom stick up to your pubic bone and making a mark on the wall, then measuring from the floor up to the mark. Easier to do more accurately with some help. I've talked about longer cranks here including who sells them.
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  4. #4
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    I don't doubt your measurement. I wear the same size pants and have similar inseam. Unless you replaced the stock cranks on your bikes, I'm almost certain neither have 180s (both list FSA cranks, which to my knowledge don't make anything longer than 175).

    I do question the optimum crank length formula. Optimum in terms of what? In terms of maximum number of pedal strikes? The current trend toward lower bbs is bad news for longer cranks. I'm not sure I'd be able to pedal my favorite trail bike at all with 185mm cranks. None of the major brands (shimano, sram, race face...) make anything longer than 180.

    For the most part, someone with your leg length, I'd just go 175 and not worry.

  5. #5
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    I'd like to try some 200mm cranks, but I can't afford the cranks and the custom frame it would require to do so. I do have 180mm cranks on my bikes and find them more comfortable than 170 or 175mm cranks.

    Joules - it stands to reason that some people can use cranks shorter or longer than the mainstream market provides - which is the same for all kit us clydes/tall riders talk about on here. It makes sense to me that, with my much longer legs than yours, I could make better use of something that has been scaled up for my dimensions.
    Your preceived problem with longer cranks is more to do with frames not accommodating them rather than the effectiveness of the crank itself.

  6. #6
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    Trouble becomes BB drop/pedal clearance. I run 180's on an Ogre XXL, it's about the limit of what I would want for pedal clearance. I think the calculators say I should run 205s. Zinn frames continue to be a curiosity for me.

  7. #7
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    There are specific angles a cyclist's joints will move through that will allow for optimum efficiency or power. Though these angles will change from one person to the next, they do not change simply because a person is of a different height. Hence, the bike geometry must change to allow for similar joint angles regardless of leg length. This means proportionally sized cranks. A useful analogy I have come across is that of a person jumping; just because a person is taller, doesn't mean they should bend there knees to a lesser degree when they jump. Using 21.6% of inseam is a decent starting point for selecting a proportionally sized crank.

    Of course there are other factors that must be taken into account such as flexibility, type of cycling, the bike's gearing, your preferred cadence, and any injuries or joint abnormalities.

    TooTallUK, the cheapest long cranks I have come across are from universal cycles for 128 bucks. There are some types of stock mountain bikes with super high bottom brackets, perhaps you could get one of those rather than custom...

    I have put 200mm on my 62cm Surly Cross Check and only clipped a couple times, but then I was super careful and only road on fairly smooth trails and on the road. Always lift the inside crank when banking!

    Besides stock bikes having too low of bottom brackets for long cranks, the other problem is that the seat tube angle has been made too slack (to match up with unproportionally small cranks). With longer cranks on, you end up lowering your seat and moving it forward, thus shortening the cockpit and so needing a longer stem etc.

    I also have the KHS Flite 747 designed by Lennard Zinn with a high bottom bracket and 200mm cranks and steeper seat tube angle (just posted about it here). Sadly I have only got to ride it once because of a hip injury, but it was a sweet ride!
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  8. #8
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    Quote Originally Posted by TooTallUK View Post
    Joules - it stands to reason that some people can use cranks shorter or longer than the mainstream market provides - which is the same for all kit us clydes/tall riders talk about on here. It makes sense to me that, with my much longer legs than yours, I could make better use of something that has been scaled up for my dimensions.
    Your preceived problem with longer cranks is more to do with frames not accommodating them rather than the effectiveness of the crank itself.

    I'm not doubting that in terms of putting power to the ground, sure crank length could scale somewhat with leg length, and no I'm not so far outside the mainstream that I feel I really need something non-standard. I'm also not aware of any rigorously controlled studies that have established the 'inseam x whatever constant' to really be optimal in terms of generating power (and optimal in terms of generating power is not the same as optimal in terms of riding; a thing isn't just "optimal"; variables are optimized sometimes at the expense of something else). The best study I've seen, and of course I can't dig it up now, found no predictable correlation at all: some longer-legged riders did better on shorter cranks, some shorter riders did better with longer...

    pedal strikes are not simply a perceived problem. If you ride in rough terrain you need a frame designed around longer cranks if you wish to use them, and unfortunately bb height doesn't scale with frame size on any production bike I'm aware of. I'm also not aware of any custom builders doing 'modern' (i.e., multi-link) suspension. That's another debate to be sure, I for one am sold, but then again, 175mm cranks aren't an unacceptable compromise for me.

    And I'm not aware of any what I would consider good quality cranks made longer than 180. I can't imagine feeling longer cranks were enough of an advantage to go back to square taper, and the zinn gxp cranks are $800 without rings (and are pretty basic, comparable quality to deore only 10 times the price) .


    All I'm saying is yeah, there may be some advantage to going to longer cranks, but there are some major disadvantages as well; that's life: compromise. Is generating 10 or 20 more watts going to make you enjoy riding that much more? If so, do you already have a coach (because that would improve your power output more than a longer crank, I can practically guarantee)? Not trying to steer anyone to a specific answer, just pointing out that when people talk about "optimal" crank length, they are talking about one specific benefit which might not really mean that much to everyone.

  9. #9
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    I'm 6'9" and cant stand riding on anything less than 180mm cranks.

    There have been a lot of studies showing that longer cranks dont necessarily produce more power but it's hard to objectively assess comfort and I'm much more comfortable in out and of the saddle with 180mm cranks.

    Good to know about those IRO cranks being available in longer lengths. Seems like it would be better if they were available in a stronger interface like the Profile 48 spline interface rather than square taper. . .

  10. #10
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    My purley not scientific feel is that I, being 6'4 with longish legs that anything less than a 175 doesn't feel right. The cranks on my road bike came with 170mm, and I could especially notice the difference while mashing out of the saddle. It just felt like the circles I was spinning were too small and it was unformfortable, almost to the point of making me feel akward and unstable while standing mashing.

  11. #11
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    One thing to consider about striking the ground with 200mm + cranks, if you modify a 26er with 650b's or 29's it will get you to the proper ground clearance for the pedals.

    I run a 26er with 29er wheels and 40cm tires and want to get back to the proper ground clearance for many reasons and 200mm cranks should work for me.

    Zinn I guess has this all figured out, are his bikes reasonably priced for what you get?

  12. #12
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    it seems like as the crank arm is extended fully out front headed towards the front wheel you would want the center of the pedal shaft to line up with the top of your femur bone? in order to get the maximum power thrust down because of the straighter down push by your leg. 175 are to short for me in that regard.

  13. #13
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    Quote Originally Posted by Realslowww View Post
    Zinn I guess has this all figured out, are his bikes reasonably priced for what you get?
    Tough call that I've pondered quite a bit. By contrast for $1350 I think, you can get a fully custom geo Gunnar frame made to your specs and I've seen similar prices for other alternatives. I think Zinn starts at $2500 for just the frame. Some say there is a 'lore' to Zinn that isn't concrete, but if you read his writings he takes into consideration multiple pieces of the geometry where I don't know if a standard shop doing a fitting for a custom would result in the same geometry numbers.

  14. #14
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    Quote Originally Posted by Realslowww View Post
    it seems like as the crank arm is extended fully out front headed towards the front wheel you would want the center of the pedal shaft to line up with the top of your femur bone? in order to get the maximum power thrust down because of the straighter down push by your leg. 175 are to short for me in that regard.
    Dont confuse saddle setback with crank length. Conventional fitting has the saddle setback marked so that your knee will be directly above the pedal spindle. Longer cranks means less setback. Typically setback is easier to adjust than crank length but both work together for proper fitment.

  15. #15
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    I dunno how I was exactly 5mm off measuring but I found that both of my bikes actually have 175's, not 180's. Didn't know it said on the arm itself.

  16. #16
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    Quote Originally Posted by Joules View Post
    I don't doubt your measurement. I wear the same size pants and have similar inseam. Unless you replaced the stock cranks on your bikes, I'm almost certain neither have 180s (both list FSA cranks, which to my knowledge don't make anything longer than 175).

    I do question the optimum crank length formula. Optimum in terms of what? In terms of maximum number of pedal strikes? The current trend toward lower bbs is bad news for longer cranks. I'm not sure I'd be able to pedal my favorite trail bike at all with 185mm cranks. None of the major brands (shimano, sram, race face...) make anything longer than 180.

    For the most part, someone with your leg length, I'd just go 175 and not worry.
    You're right! See my post above.

  17. #17
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    Well shouldn't it be like where your femur attaches to your hip is where the crack arm begins and is the same length more or less as your femur to the end of the crank arm?

    I know with 175's my calf bones are always in the bent back position for the full circle of motion.

  18. #18
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    'Way back when'; my first mtb was an '88 cannondale, those had 13" high bbs, I almost put long cranks on it (36" inseam here), it would have also lowered my center of gravity on that high bike. Bullseye was the best source for longer cranks at that time, but the cost was too much. I have 180s on my old bike, but I seem to do fine with 175s. I would put 180s or 185s on my race bike, if I change to 2x10 I think I would do that, but my current xtrs work fine for now.

  19. #19
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    6'8" / 38" inseam and ride 175 on all my bikes, except my SS came standard 180. 175 to 180, I can't tell the difference. I ride a lot of roots and some rocks and my two main bikes are FS, so have no desire to go longer....no advantage, only more pedal strikes IMO.

  20. #20
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    I guess this is a debate, the only way to find out is try them for yourself.

  21. #21
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    Quote Originally Posted by Alias530 View Post
    My inseam is 38", as measured from heel to perenium--is this right? I wear 34" inseam jeans, so I'm kind of surprised to measure 38" unless I shouldn't be measuring to that high up...

    According to this website, which I have no idea if it's accurate, says I should have 185mm crank arms.

    Optimum Bicycle Crank Length Calculator

    I have a Trek Superfly and a Fuji Gran Fondo, which both appear to have 180mm crank arms. I don't imagine that 5mm is a huge difference but I thought I would ask.
    Hopefully you measured your cycling inseam correctly.

    I run 180mm cranks on all of my mountain bikes (I use Shimano, Middleburn, and Race Face). I prefer them over the 175mm length.

    Shimano comes in 180mm length crankarms.
    Surly Mr. Whirly crankarms come in 180mm and 185mm.
    Zinn comes in 190mm up to 215mm.

    There are a few others as well (SRAM/Truvativ, White, e.13, RaceFace, etc...) that have at least 180mm arms available.

    You can also run your leg inseam length in Zinn's calculator to get a range of optimal crankarm lengths for mountain biking. Zinn suggests using 20-21% of inseam for mountain biking as opposed to 21-21.6% for road bikes.

    Using his formula, my range for a mountain bike crank should be 180mm to 189mm. I use the 180mm's on all of my mountain bikes.

    From Zinn's FAQ...

    Should you use the same length for a road bike and a mountain bike or cyclocross bike?

    It depends.

    1. Unlike most road riding, which is more steady state with consistent cadence for long periods, thus making full use of the long crank, mountain biking in technical terrain and cyclocross racing involve frequent drastic changes in cadence. Spinning the cranks back up to speed is better accomplished with a shorter crank, while powering up long climbs is best accomplished with a longer one. So I try to strike a balance between those requirements and look for crank length more like 20-21 percent of inseam length for the mountain bike or ‘cross bike (as opposed to 21-21.6 percent of inseam for a road bike).


    I run pretty tall/high volume tires which certainly counters any issue I have with pedal strikes using the 180mm's over a shorter crankarm.

    I also reverse engineered my crank arm shorterners that I bought for the kids when they were stokers on our tandem years ago. I can use the "shorteners" flipped around to test out my cranks to see what they would feel like in lengths all the way up to 205mm. Unbelievable torque with the longer lengths, but I ride just fine using 180mm on my mountain bikes.

    A higher bottom bracket would be ideal for going really long in the cranks (say 190mm and beyond) and that would require going custom or getting one of the Zinn bikes. In terms of a road bike, I looked really hard at the KHS Flite 747 that Zinn helped develop for KHS, but the stock 200mm cranks were a bit longer (5+mm) than the longest recommended crank for my leg length. So I went with a 64cm Specialized Roubaix that came stock with 175mm cranks. Go figure that such short cranks come on such a HUGE bike.

    But the industry targets the "averages". Once you get to 6'4" and beyond, you are no longer average.


    Tall Chart

  22. #22
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    Quote Originally Posted by kingsqueak View Post
    T... By contrast for $1350 I think, you can get a fully custom geo Gunnar frame made to your specs and I've seen similar prices for other alternatives. I think Zinn starts at $2500 for just the frame.
    Did this - was easy since I'm in Wisconsin. Richard Schwinn and the local dealer and I worked out the geometry over a few weeks. I'm running 210mm cranks.

    Zinn had a lead time that was not attractive.

    Happy to answer any questions.

    Ended up doing a Gunnar Sport, basically close to a 64cm. It's great for long rides, very comfortable.

    Am I faster with the long cranks? I DO like it on the big hills. But spinning on the flats, less so.

    LAXPatrick

  23. #23
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    I am fixing to order some 200mm, I run 46 11 gearing on a 175mm. In theory for some it should work good but I do not know till I try. Any input on this would be great from people who have run them.

  24. #24
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    Bump>>>>>>>>>>>

  25. #25
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    Quote Originally Posted by Realslowww View Post
    Bump>>>>>>>>>>>
    You run 46 x 11 - as in SS?

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