Low, slack, and... short? Or: I actually built myself a bike!- Mtbr.com
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  1. #1
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    Low, slack, and... short? Or: I actually built myself a bike!

    It's been 3 years, I figured I was due for something new. And I had a set of, erm, repurpose-able Paragon rockers available from some repair work.

    I like low (this has 165mm cranks). I like slack (68.5 HTA, with a 44mm offset fork for >100mm trail). I don't like long - because Park City has not much in the way of steep technar, and for when I do that, I use a different bike.

    Drawing shows the wheel pulled about halfway back. In theory you can slam to 400mm, but the 3" tire won't really spin super well in that mode.

    I'll set it up SS sooner or later, but I need one of those wacky QBP adapters for the XD driver first. So I threw my roached 11 speed drivetrain on. 8 or 9 of the 11 gears work great!

    Low, slack, and... short? Or: I actually built myself a bike!-screen-shot-2018-05-08-8.20.47-pm.pngLow, slack, and... short? Or: I actually built myself a bike!-screen-shot-2018-05-08-8.21.43-pm.pngLow, slack, and... short? Or: I actually built myself a bike!-screen-shot-2018-05-08-8.21.50-pm.pngLow, slack, and... short? Or: I actually built myself a bike!-screen-shot-2018-05-08-8.22.01-pm.png

    -Walt

  2. #2
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    Nicely done. Tidy solution for the cs yoke.
    "These things are very fancy commuter bikes or really bad dirt bikes, but they are not mountain bikes." - J. Mac

  3. #3
    pvd
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    #supershort

    I'd be terrified, especially at your height. Then again, Park City is pretty smooth.

  4. #4
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    That's awesome! I built a bike with a reach shorter than I'm used to, and it's an absolute blast on non-steep trialsy stuff. Like a BMX bike or something.

    Do you find diminishing returns with short chainstays as a taller guy? I notice the ST angle is about normal.

    Sweet build!

    *edited because I didn't look at the drawing, oops.*
    Myth Cycles handbuilt bike frames
    Durango, CO
    http://www.mythcycles.com

  5. #5
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    Why is it again that you like such short bikes?

  6. #6
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    Quote Originally Posted by shirk View Post
    Why is it again that you like such short bikes?
    Because they corner like mad!

    Look, I get that long bikes feel really safe on steeps and rough stuff. They are.

    But when it's not steep or rough (which is all the riding out my door, and most of the riding in my immediate area) you get *nothing* out of a long wheelbase. It takes more lean angle and effort from the rider to corner, the wheels don't track each other as well, and it's harder to quickly transfer weight between wheels when you need to.

    There's zero chance of going OTB on any of my local trails unless you just run straight into a tree or have a muscle spasm/temporary insanity in your brake finger that locks up the front wheel. I'm not worried about front-wheel casing jumps, and I'm not trying to hook stuff to get up it on a trials course.

    I guess here's the best answer - turn the question around and ask when/why does a bike get too long?

    TANSTAAFL applies here as anywhere else - you both gain and lose things when you change the wheelbase/front center/chainstay length. Shorter sucks for some things, but so does longer.

    As an aside, does anyone remember the old "your handlebar should obscure your front hub from view when riding seated" rule of bike fitting from the 90s? It was stupid, just like making things as long as possible/running the shortest possible stem no matter what is stupid now.

    -Walt

  7. #7
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    Quote Originally Posted by Walt View Post

    As an aside, does anyone remember the old "your handlebar should obscure your front hub from view when riding seated" rule of bike fitting from the 90s?
    It makes zero sense, but then I'm always amazed at how on almost all my bikes I can't see my front hub. Even the poorly fitting ones!

  8. #8
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    it's almost as short as my road bike!
    "Things that are complex are not useful, Things that are useful are simple."
    Mikhail Kalashnikov

  9. #9
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    funniest thing about this is 68.5 is "slack". I don't think I'd buy another road bike that steep, and I certainly will never buy another mtb over 66. I guess maybe if I were on flat, smooth trails I might reconsider.

    Still, it's been at least a decade since I would have called a ha over 68 'slack'

  10. #10
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    Quote Originally Posted by Joules View Post
    funniest thing about this is 68.5 is "slack". I don't think I'd buy another road bike that steep, and I certainly will never buy another mtb over 66. I guess maybe if I were on flat, smooth trails I might reconsider.

    Still, it's been at least a decade since I would have called a ha over 68 'slack'
    Keep in mind that this uses a 44mm offset fork (and I'd use less if I could get it). It also has ~30.5" diameter wheels. So the trail number is (IMO) pretty high at 104mm. That's with the rider onboard. Unsprung it's about a degree slacker.

    For comparison, a 27.5" wheel trail bike would need about a 65.5-66 head angle (sagged, depending a bit on fork offset) to achieve the same trail number. Hence my description of it as "slack", which is more approachable than "high trail" for most people. I think most people would consider a 66 degree HTA hardtail to be at least relatively slack.

    Though I guess around here I could have just said it's got a lot of steering trail and a low BB and short wheelbase and left it at that.

    -Walt

  11. #11
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    Nice work in getting that Chainstay so short. I also ride in conditions similar to what you ride Walt in terms of being not so challenging. I also have built bikes with very short Chainstays. My dedicated gravel bike is at 385mm, and I also experience the ride characteristics that you describe, though I have 82mm trail on my front geo but am running a longer Front Center. Walt and I have similar leg lengths but I am longer in the back so I have a longer bike. The most notable difference that I notice on the gravel trails that I ride between my bike and 'contemporary' design is that at very high speeds going around bends, the shorter stays will, on fine pea gravel, let go grip wise, a bit more suddenly and you have to be quick to catch and gather up the slide or you end up on the ground. I have only done this once, as I don't like coming off, but learned a new technique so I can now do neat long drifts. Like all riding of bikes, you adjust quickly as it becomes normal pretty soon. It actually feels weird going back to convention after riding a sharp handler, they feel dead and un-responsive by comparison until the re-adjustment takes place. We all have our preferences.

    Eric
    If I don't make an attempt, how will I know if it will work?

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    that looks like it would rail corners! sweet.

    buuuut TANSTAAFL? i cant work the meaning out- help! :-)~

    aaaaand 165mm cranks? is that usual for you? or a trial? thoughts? i read hat article in Mountain Flyer - did you maybe build the frame in question, Walt? its interesting. I know Jeff Jones was a proponent of 165mm cranks for a while, maybe still is and his frames tend to the lower end of the bb height as well....i also like lower end of the spectrum bb but have not ever used shorter cranks along with it. i used to ride fixed off road once in a while and that has a way of teaching you about avoiding rocks with cranks, so feel i can just deal with it....but it is interesting.

  13. #13
    pvd
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    I haven't looked at trail in over a decade designing off road. It just isn't that great of a factor.

    Also, short offset forks are a waste of time.

    High Trail MTB | Peter Verdone Designs
    Last edited by pvd; 05-12-2018 at 08:57 PM. Reason: Link

  14. #14
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    Quote Originally Posted by dRjOn View Post
    that looks like it would rail corners! sweet.

    buuuut TANSTAAFL? i cant work the meaning out- help! :-)~

    aaaaand 165mm cranks? is that usual for you? or a trial? thoughts? i read hat article in Mountain Flyer - did you maybe build the frame in question, Walt? its interesting. I know Jeff Jones was a proponent of 165mm cranks for a while, maybe still is and his frames tend to the lower end of the bb height as well....i also like lower end of the spectrum bb but have not ever used shorter cranks along with it. i used to ride fixed off road once in a while and that has a way of teaching you about avoiding rocks with cranks, so feel i can just deal with it....but it is interesting.
    TANSTAAFL is "There ain't no such thing as a free lunch", a phrase coined by my great uncle in the 1960s. My point was that every time you try to optimize geometry for one thing, you sacrifice others.

    Yes, I built the frame that Mike used to do his testing for that article in Mountain Flyer. We based the whole idea on some existing studies that basically indicate that *crank length doesn't affect power output meaningfully* - at least within the range of about 140-175, for most riders. McCalla actually produced the most power (albeit by a tiny amount) with 152mm cranks in that test.

    Since there are HUGE advantages to using short cranks and having a lower BB, I figured I'd try it, but 165s were the shortest cranks I could easily come by that would work on this bike.

    They felt slightly weird for about 5 minutes. After that I didn't notice them anymore. Did some hard efforts on sections of trail I ride all the time and... no noticeable difference in speed/time (though I'm not using a power meter, so it's hardly top notch science I'm doing).

    The biggest disadvantage is that when standing/descending, your saddle is 10mm higher relative to the BB, which means with a rigid post the saddle is uncomfortably in the way to some extent. It's not a big deal on the trails I'm riding but I might put a dropper post on at some point to deal with that.

    -Walt

  15. #15
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    Quote Originally Posted by Eric Malcolm View Post
    Nice work in getting that Chainstay so short. I also ride in conditions similar to what you ride Walt in terms of being not so challenging.
    Eric
    Trails here are certainly challenging - to ride fast. If you just want to toodle along, they're easy. If you want to go fast, they're quite difficult - lots and lots of turns stacked on each other, enough rough stuff that you need to be able to unweight/jump little sections to set up for the next corner, etc. Short wheelbases rule on our terrain.

    This bike actually has *longer* chainstays (by 10mm or so) than my previous hardtail. But that bike was not built for 3" tires. So I'm quite used to short stays and never had any trouble losing rear wheel traction.

    Then again I don't ride gravel or road bikes much, and if I did I'd build myself one with the longest stays I could manage, since there's practically no cornering/bike handling involved with that type of riding in comparison. Curious, what was your goal with the short stays on the gravel bike?

    -Walt

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    thanks Walt - thats interesting.... :-)~

  17. #17
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    Hi Walt,

    Short answer is that I can. But, to counter the why question, I run steep seat tube angles along with ISM saddles that put me about 50mm further forward than normal. So the reach is out a bit more than usual. I weight my front wheel as a consequence somewhat heavily, but the grip off 35mm tyres is solid. The stabillity is re-assuringly secure but lively. Over here in New Zealand, many of the gravel stretches that I can access in the way of cycle trails are flowing in nature and can be riden at speed in a road riding sense, so the parameters are different. I have viewed pictures of open prairie types roads that are endlessly straight, but this is not the case here, so my preference is to make for an exciting but safe ride. The short Chainstay kind of helps in this aspect due to a more forward ride position, but I remain well balanced between the axles.

    Hope that makes sense. But we are talking about each individual environment and I have tuned my preference to suit mine. I think that if I make another bike of this type, I will go for something around the 440mm CS length and make a couple of forks allowing me to work between 75 - 90mm of trail. At age 60, I am slowing down a bit now and looking at different ride qualities.

    Eric
    If I don't make an attempt, how will I know if it will work?

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