Crank arm length

Discussion in 'General Discussion' started by mike, Feb 20, 2020.


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  1. mike

    mike iMTB Hooligan

    Location:
    Western US
    Name:
    Mike O
    Current Bike:
    HT, FS
    175mm forever guy here.

    Are pedal strikes more or less common on a SS? 180mm, crazy thinking?

    Not sure what the "BB height" would be for my config (probably not super low with 29/2.4-6), but the BB drop is 33mm. Also, spec'ing a fork initially at the middle of travel recommended for the frame, so could raise the BB slightly with a different fork length.

    175 feels short for my long-for-my-height legs. The weez has super short legs and rides 175 no issue. In fact when she switched from 170, she became a better uphill pedaler. If pedal striking is not an issue, putting more mechanically-advantaged power into the SS drive seems like a way I could have more fun with such a bike.

    TIA for input! :geek:
     
  2. fos'l

    fos'l Well-Known Member

    Name:
    Bob
    Current Bike:
    2005 Santa Cruz Superlight
    Possibly not much help, but I rode a 2000 GT Zaskar SS (magic ratio) for about 15 years with a rigid "390 mm" (AIR) fork and 175 cranks; don't remember a pedal strike, so you should be good with 180 (IMO).
     
  3. Faust29

    Faust29 Moderator

    Location:
    irgendwo
    Name:
    B. Bunny
    Current Bike:
    I gots some bikes.
    175s forever... This sounds strange, but I don't worry about pedal strikes on the single speed anywhere near as much as on the Hightower. I think the BB is actually lower on the hardtail, but I'm more in tune with each pedal stroke. I always know where the pedals are... Zen Trail in Utah is lippy edgy rocks from bottom to top. So much easier and smoother to climb on the single speed... The caveat is that there are a couple short steep sections where the engine runs out of steam. :oops:

    Not exactly conventional wisdom...
     
  4. Cyclotourist

    Cyclotourist iMTB Hooligan

    Location:
    Redlands
    Name:
    David
    Current Bike:
    Don't fence me in!
    I think wider platform pedals lead to more strikes than the crank length.
     
  5. rossage

    rossage iMTB Hooligan

    Location:
    East Sacramento
    Name:
    Ross Lawson
    Current Bike:
    Highball
    Crank and pedal strikes are usually the result of a lapse in judgement, not crank length.
    When I'm in the zone on a techy section, eyes up, arms loose but ready, and I'm paying attention to where my feet are. Often, I am able to set my pedal on top of a rock or ledge and use it to step up and over the obstacle.
    Sometimes I just crash...
     
  6. evdog

    evdog iMTB Rockstah

    Location:
    San diego
    Name:
    Evan S
    Compressing the suspension on many bikes lowers the BB making pedal strikes more likely. A hardtail SS doesn't have that problem. I was getting crazy bad pedal strikes on the Mojo3 til I increased the rear shock pressure. And I was already running it above recommended pressure. That solved some of the problem. Being in a higher gear also helps - when you're climbing faster it seems like you have more control and can keep your pedals away from rocks easier. Spinning a low gear at high RPM you have the pedals spinning more times with less movement so you're more likely to strike any rock within reach. 5mm crank length can make a bit of difference, but less so than the factors above I would think.
     
  7. Faust29

    Faust29 Moderator

    Location:
    irgendwo
    Name:
    B. Bunny
    Current Bike:
    I gots some bikes.
    Evdog and Ross have put hardtail nirvana into words...
     
  8. herzalot

    herzalot iMTB Hooligan

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    2020 Revel Rail,Yeti SB 130 LR
    No one rides 180s, you rebel!

    all of the long travel 29ers I’ve been demoing are spec’d with 170 cranks to compensate for low bottom brackets and lots of sag. I use 175s.

    Like the others said, you don’t have rear sag to worry about - at least not on your bike. So what you start with is what you get!
     
  9. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    @mike, on a hardtail frame, an extra 5mm is not going to make any difference in strikes.
     
  10. DangerDirtyD

    DangerDirtyD iMTB Hooligan

    Location:
    CA
    Name:
    Chicken Nugget
    Current Bike:
    2018 Guerrilla Gravity SMASH
    Hell yea it is.
     
  11. Sidewalk

    Sidewalk iMTB Rockstah

    Location:
    The road is where I call home
    Name:
    Josh
    Current Bike:
    N+1
    There is a lot of data out there to support that short crank lengths tend to actually be better overall. No loss in power produced, but the power tends to be produced at a lower HR. Less pedal strikes. Less weight. Less stressful to the knees.

    That said, I have found I (myself) am more comfortable on 172.5-175 cranks. My Enduro came with 165's, never felt quite right. But didn't think about it until I destroyed that crank and bought a replacement, and my LBS mistakenly got the wrong length of 175. It instantly felt better (to me) and I have stuck with it. My first gravel bike was also 165, never felt right. The replacement bike came with 170, feels better (but could be frame geometry).

    Moral of the story, go with the shortest cranks you comfortably can. Going longer doesn't actually improve performance nearly as much as you think. Though, on an SS, it will be more obvious.
     
  12. mike

    mike iMTB Hooligan

    Location:
    Western US
    Name:
    Mike O
    Current Bike:
    HT, FS
    You guys have all been very helpful, so thanks.

    One concept I will not entertain is that crank length does not affect power output. Not even a discussion here; pure fantasy. I know it does, so I’m trying to figure out if easier pedaling is worth adding to a SS.
     
    Mikie, fos'l, Faust29 and 4 others like this.
  13. evdog

    evdog iMTB Rockstah

    Location:
    San diego
    Name:
    Evan S
    I does - it's physics. But other factors like wheel diameter + tire size/weight, chainring size and cassette also contribute. So it may be one of those things where you can put on longer or shorter cranks but end up with the same ratio by adjusting your chainring size.
     
    Mikie, bvader, fos'l and 4 others like this.
  14. mike

    mike iMTB Hooligan

    Location:
    Western US
    Name:
    Mike O
    Current Bike:
    HT, FS
    A boost-chainline DM-ring 180mm-arm crankset that will be useful for both SS and a cassette is apparently not so easy to find. White Brothers M30 or bust. Shimano has the arm length but with a spider.
     
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  15. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    Oh stop it! :laugh:

    You have to practically make an effort to have a pedal/crank arm strike on hard tail frame if you want one. It's one of the magical things about rolling on a frame that is rigid.
     
    Mikie, Danmtchl and mike like this.
  16. mike

    mike iMTB Hooligan

    Location:
    Western US
    Name:
    Mike O
    Current Bike:
    HT, FS
    When I first got my Pedalhead hardtail I was pedal striking like mad. I think it's pretty dependent on the individual frame (and setup). Which is why I included the BB drop for reference, but companies seem to be just starting to list BB drop instead of "height."

    The best long-run solution is probably Evan's. Size down the chainring and call it a day.

    I'm not much of a powerhouse, so just looking at options. Surprised to see so few 180mm arm options.
     
    Mikie, fos'l, DangerDirtyD and 3 others like this.
  17. da big hills

    da big hills iMTB Rockstah

    Location:
    pearl harbor
    Name:
    cagey
    Current Bike:
    enduro 29
    25.4 mm / inch so 5 mm is only .2 inches.
    happy trails on the big 29
     
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  18. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    Modern geo, with it's "long and low" design has increased pedal and crank arm strikes for most of us. So, for some added clearance on my FEX, I recently switched from 175 arms to 170 arms and I think I like it. I happen to be a short legged guy, 29" (maybe 30") inseam. Every single mountain bike I have ever owned had 175mm crank arms on it. "175" is synonymous with "mountain" in the cycling world. But I beg to differ, now.

    My first ride on my new cranks was uplifting to say the least. Sure, the CF numbness (compared to alloy) was instantly detectible and similar to that feeling you get from CF handlebars. But what I really noticed was a faster cadence due to shorter throws. That made me able to push a harder gear than I was pushing before because I was spinning out in the gearing that I used with 175 crank arms. These shorter arms make my mountain bike pedal like a road bike. I never realized that leverage effects gearing. We shall see how that pans out on long, sustained climbs.
     
  19. herzalot

    herzalot iMTB Hooligan

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    2020 Revel Rail,Yeti SB 130 LR
    My last four bikes came spec'd with 170 cranks. Being somewhat long legged, and needing every mechanical advantage I can find, I converted every one of them to 175. I have had no problem with pedal strikes, despite the low BB of the Megatower and even lower BB of the Rail (337mm). Then again, I don't spend much time pedaling through chunk. I am guessing I would notice if I did.
     
  20. Runs with Scissors

    Runs with Scissors iMTB Hooligan

    Location:
    West Anaheim
    Name:
    Mark Whitaker
    Current Bike:
    Giant XTC with pedals
    180mm cranks are available too....

    The idea that a 5mm (for the sane, that's .197" - the difference between 170 and 175) change will have any meaningful effect on power delivered to the rear wheel is ludicrous. It might make things more comfortable for the longer-legged amongst our species (but 1/5" - really?), but other than that????
     
  21. Derkderkall

    Derkderkall iMTB Rockstah

    Location:
    Monrovia
    Name:
    Derek Allison
    Current Bike:
    2020 Specialized Fuse 29
    A lot can be done with that small number...

    Think a 2.2 wide tire, vs a 2.4.
     
    Mikie, Danmtchl, mtnbikej and 2 others like this.
  22. DangerDirtyD

    DangerDirtyD iMTB Hooligan

    Location:
    CA
    Name:
    Chicken Nugget
    Current Bike:
    2018 Guerrilla Gravity SMASH
    Paging @Varaxis
     
  23. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    Some people are more "in tune with" the bike. :whistling:
     
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  24. scottay

    scottay Well-Known Member

    Location:
    Gods Country
    Name:
    Scottay
    .
    .
    .
    Same with fork offset!
    .
    .
     
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  25. OTHRider

    OTHRider Well-Known Member

    Name:
    Duke
    Current Bike:
    '18 Salsa Cutthroat
    As an older member of the species, I'm falling prey to knee issues. It got to the point that I had to quit a few rides when my knee wouldn't "loosen up" to allow a complete pedal stroke with 175s. 170s were like magic for about 5 years. When I transitioned to the gravel scene in '15, I moved down to 165s and it was magic+, or voodoo. Either way, it allowed me to get back into pedaling without pain and climb without reservation.
     
    Faust29, Cyclotourist, UPSed and 3 others like this.
  26. TherealJohnG

    TherealJohnG Member

    Location:
    Yucaipa, CA
    Name:
    John Groenhof
    Current Bike:
    Stanton Sherpa
    I had some 180's, a month ago I swapped for 175's. My knees felt better immediately, so much better that I ordered 170's for my upcoming build.
    I'm not doing time trials over here, I just want to be comfy.
     
    Faust29, Mikie, Stkx66 and 5 others like this.
  27. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    Offset is another thing that I instantly noticed. In fact it transformed my FEX (going from 51 to 44) into a quicker responding, better handling bike. .
     
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  28. herzalot

    herzalot iMTB Hooligan

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    2020 Revel Rail,Yeti SB 130 LR
    Shorter offset leads to more stability, not quicker steering. Just saying. Shorter offset increases trail. Increased trail increases stability. I think.

    From this article:
    Increasing trail improves straight-line stability. The front wheel feels harder to turn but also harder to knock off line.
    Decreasing trail improves agility. The front wheel feels easier to turn and it can make a bike feel more nimble.


    But I am glad you like the change! There's a reason most of the manufacturers went to shorter offset for slacker, longer bikes.

    I got off a test ride on a Yeti SB 150. Everything was the same as my Megatower - tires, transmission, geometry. I said, "I think this has 170mm cranks." It did.

    Fork offset? I've never done a back to back comparison on the same bike. I think the engineers know why they are spec'ing shorter offset on the longer, slacker bikes - and it's not for profit motive. Logically, seems like the longer slacker bikes might benefit from quicker steering (more offset) but perhaps that would make the bike feel like it's pushing the front tire in turns - too floppy.
     
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  29. SnakeCharmer

    SnakeCharmer iMTB Hooligan

    Location:
    Front Range, San Gabes
    Name:
    Mike, aka "Ssnake"
    Current Bike:
    YT Izzo
    Simply put, shorter offset shortens the wheelbase. Better handling, quicker steeering, shorter turning circles. Easier tight switchback turns. More lively.
     
    Mikie likes this.
  30. herzalot

    herzalot iMTB Hooligan

    Location:
    Laguna Beach
    Name:
    Chris
    Current Bike:
    2020 Revel Rail,Yeti SB 130 LR
    :facepalm:

    True about wheelbase. And most likely better handling - but not for the reasons you might think. Euclid don't lie. BUT - it makes your bike handle better - and that's what counts.
     
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As a former Amazon Associate I continue to get screwed trying to stay qualified as an Amazon Affiliate. So I quit!


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