Scratching an itch + getting some eyes on a drawing.- Mtbr.com
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  1. #1
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    Scratching an itch + getting some eyes on a drawing.

    Hey Folks,

    Last time I swung my leg over a MTB was around 2001. Citron 517s, 9-speed XTR, a SID XC, a 120mm stem, and Easton flat bars I cut 2 inches off of.

    I haven't really thought too much about MTBs until this summer and now I've got an itch! So why not build myself a hardtail? (I can + have built frames before but they've all been TIG road bikes).

    I'm hoping that getting some collective eyes on a drawing before I dip my toe into things. One of the issues I'm having a hard time wrapping my head around is how to transfer my road fit to a modern MTB fit.

    Thanks!
    -T-

    Oh, if this in an inappropriate ask, lemme know.

    The bike:
    27.5 hard tail. steel. Revelation RC 27.5" 120mm travel (brand new, given to me by a friend).

    Me:
    5'8" 31" inseam. 155lbs.

    Riding Location:
    Santa Monica + San Gabriel Mountains from fire roads to single track.

    Road Contact Points:
    saddle height (Spec Toupe 143mm): 702m
    setback: 47mm
    saddle-bar-drop: ~70mm
    saddletip - handlebar center: 515-520mm
    Attached Thumbnails Attached Thumbnails Scratching an itch + getting some eyes on a drawing.-tommtb.jpg  


  2. #2
    pvd
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    If you are 5'8", that bike is impossibly short and will suck. Suck really really bad.

    Here's a bike that I made for my wife:

    PVD Glamorous Glennis | Peter Verdone Designs





    If you take the time to learn how mountain bikes are made in the modern era, you will have some fun.

    Forward Geometry | Peter Verdone Designs

    Also, 27.5 sucks for hardtails, go 29". Trade that fork for the right wheel size. Also, get to a 140/150mm travel fork at least.

  3. #3
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    Quote Originally Posted by pvd View Post
    If you are 5'8", that bike is impossibly short and will suck. Suck really really bad.
    Hey Peter, thanks for the quick feedback. I''m unsure how to deal with ETT/drop when moving from a road frame to a MTB.

    I've been trying out some bikes at the LBS and seem to be more comfortable on in the medium range which are in the low 60s ETT (reach between 415-435mm). Can you explain a bit more what you mean by "impossibly short? -- maybe quantify it somehow?

    If I'm seeing things correctly you've designed a bike for someone that's 5'6" but has reach of 499.

  4. #4
    pvd
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    We don't use top tubes to fit bikes.

  5. #5
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    OK, we can talk about reach? Or saddle tip to h-bar?

  6. #6
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    Your design is just fine for all-around XC riding. If you want to shred the gnar and ride flow trails constantly, a longer front end can be nice, but it's not mandatory. And that longer front end can be a pain in the neck other places.

    Quick look says to me that you're good to go. Build it and ride it. 27.5 wheels will be plenty of fun, though I'd tend to agree that 29" make more sense for XC.

    -Walt

  7. #7
    pvd
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    We use the saddle, hand grips, and pedals to fit the rider to a frame.

    Fyi, my wife's bike is very conservative and not very extreme. It's a good reference for most folks.

    My bike that will be released in a few weeks is on the bleeding edge of design and not for the faint of heart.

  8. #8
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    Quote Originally Posted by Walt View Post
    Your design is just fine for all-around XC riding. If you want to shred the gnar and ride flow trails constantly, a longer front end can be nice, but it's not mandatory. And that longer front end can be a pain in the neck other places.

    Quick look says to me that you're good to go. Build it and ride it. 27.5 wheels will be plenty of fun, though I'd tend to agree that 29" make more sense for XC.

    -Walt
    Hey thanks for the input Walt! When you're speaking of a longer front end are you referring to the HTA (and thereby the front-center), reach or a combo?

  9. #9
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    Quote Originally Posted by machine View Post
    Hey thanks for the input Walt! When you're speaking of a longer front end are you referring to the HTA (and thereby the front-center), reach or a combo?
    All of the above, really. The modern trend is to go as long as possible on the reach and head tube angles in the 66-67 range for normal trail bikes. Lots of people your size are riding around on hardtails that have 3-4 degree slacker head tube angles and an extra 20-40mm of reach, so obviously much longer front centers to.

    Those bikes are IMO mediocre for old-school XC riding. They shine on steep and rough downs, so long as you can get to those downs via something low-angle and non technical, because they climb like crap (lots of them now have super steep seat angles to try to keep the front wheel weighted going uphill).

    I mean, you can go lots of ways here. You have a pretty traditional XC/race geometry there. It'll ride just fine. Build it.

    -Walt

  10. #10
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    Quote Originally Posted by Walt View Post
    All of the above, really. The modern trend is to go as long as possible on the reach and head tube angles in the 66-67 range for normal trail bikes. Lots of people your size are riding around on hardtails that have 3-4 degree slacker head tube angles and an extra 20-40mm of reach, so obviously much longer front centers to.

    Those bikes are IMO mediocre for old-school XC riding. They shine on steep and rough downs, so long as you can get to those downs via something low-angle and non technical, because they climb like crap (lots of them now have super steep seat angles to try to keep the front wheel weighted going uphill).

    I mean, you can go lots of ways here. You have a pretty traditional XC/race geometry there. It'll ride just fine. Build it.

    -Walt
    Got it. Thanks for the input and guidance. Gonna be a fun project and, after this week's close call on the road, a good distraction.

  11. #11
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    Quote Originally Posted by pvd View Post
    My bike that will be released in a few weeks is on the bleeding edge of design and not for the faint of heart.
    I'm not such a fan of blood and a-fib definitely runs in the family but maybe your write up and some numbers can help me make sense of the hyperbole.

    I'm still not sure what you mean by "impossibly short" means and what "possibly long" would be when it comes to a bike for me.

    You're obviously seeing something that I'm not and obviously have the experience to see it off the bat. I'm guessing I'm just not experienced to suss out what it is and could use some elucidation.

  12. #12
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    I always get a chuckle out of these threads. A lot of MTB frame builders got started because they wanted to ride something no sensible businessperson would produce. They have goofy ideas. You've been out of the sport for an eternity and bikes that look like your design have become a niche market, but you don't have the context and whose to say you're wrong?

    Your design looks a lot like my (rigid, but i've run a 110mm fork and it's better rigid) commuter. I ride it several times a week along with my modern hardtail and my 'bleeding edge in 2016' FS. It's very very fun to ride on smooth, flat, and/or tight trails and to cruise around town. Its handling is a bit frantic on technical XC and it's completely overwhelmed and not fun on advanced trails where my hardtail is a blast. Both bikes climb at the same rate, but since the hardtail is 4" longer it's very different subjectively.


    Here's my trail hardtail for something to look at. It's a pretty unremarkable design by modern standards, and aside from being kinda dull on fire roads and flat XC it's fun and versatile. When it's overwhelmed i want to be on FS anyway. I'm 6'3.
    Scratching an itch + getting some eyes on a drawing.-overkill.jpg

    I might reference a good road fit when setting up a MTB, but i wouldn't start copying numbers over. Ultimately the details of a MTB's set up are dictated by handling.

    I agree with walt, i think you should build it. It looks fun. My only concern would be that the steep HTA, long-ish fork, and stubby stem is going to make for some very quick steering. I might be tempted to do something to slow it down... but that speaks to my personal preferences.




    Honestly, i'd probably go buy a modern hardtail and ride it for a season to see where MTB design has gone. (also cuz then you know someone has gone through and designed/specced a pretty great bike and you're not inadvertently hampering your re-introduction) Everything is a trade-off, but we're making some pretty awesome trade-offs nowadays that you just can't appreciate in a test ride. A nice Scott Scale 29er might make you swoon.


    Have fun!
    Last edited by scottzg; 08-24-2018 at 10:54 PM.
    "Things that are complex are not useful, Things that are useful are simple."
    Mikhail Kalashnikov

  13. #13
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    Damn close to what I consider perfect, I would ride the crap out of it!

    Quote Originally Posted by machine View Post
    Hey Folks,

    Last time I swung my leg over a MTB was around 2001. Citron 517s, 9-speed XTR, a SID XC, a 120mm stem, and Easton flat bars I cut 2 inches off of.

    I haven't really thought too much about MTBs until this summer and now I've got an itch! So why not build myself a hardtail? (I can + have built frames before but they've all been TIG road bikes).

    I'm hoping that getting some collective eyes on a drawing before I dip my toe into things. One of the issues I'm having a hard time wrapping my head around is how to transfer my road fit to a modern MTB fit.

    Thanks!
    -T-

  14. #14
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    Quote Originally Posted by scottzg View Post
    My only concern would be that the steep HTA, long-ish fork, and stubby stem is going to make for some very quick steering. I might be tempted to do something to slow it down... but that speaks to my personal preferences.
    Since the fork is already in hand I seem to be limited to 3 options to slow down steering

    1. Shorten reach, add longer stem(my preference on a road bike).
    2. Slacker HTA
    3. Combo of 1+2.

    Can you all speak to these options?

    I'm pretty sure I'm just going to have to build a few iterations to understand things and that my preferences will change as skills develop.

  15. #15
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    I mostly agree with Walt that while your design is a few years dated for current trends, it will still ride fine, especially for someone who's used to road bikes and hasn't been on a mountain bike in years.

    If you want to modify, I'd make the HA a degree or 2 slacker, and maybe make the reach (I won't judge you if you want to use ETT) a bit longer. I'd challenge you to go with a stem that might be a bit shorter than what you think you may want coming from a road background and use bars that are wider. I know about bars, when I started riding, 580 was super wide (vs the more common 560). I went a little wider at a time and it always felt good until I got up to 800 and never got comfortable with it. I cut them back to 780 and that's my personal sweet spot. But I digress... Point being (which I've really failed to make) wider bars and shorter stems are symbiotic IMO.

    Doing 27.5 wheels just because you were given a 27.5 fork and not because you want to use that wheel size is not the best reason. OTOH, there's nothing wrong with 27.5 wheels and if having the fork inspires you to build then its great. And I can't say that I haven't built frames around parts that I just happened to have on hand. Like Walt (and you have) said, this doesn't have to be your last mountain bike.

    One last point: think about a dropper post. People who haven't used them tend to not get them (I also remember when riding down stupid steep stuff with a high post and bars 6" below the seat was a point of pride--I now don't understand how I managed to ride like that), but people who use them tend to not be able to imagine riding without them. So make the seat tube short enough to accommodate one. It looks like you're using Bikecad. Dropper are an option for the drawing so you can check clearance.

    Get to it and keep us updated!

  16. #16
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    Just do a slacker HTA. Stem length has negligible effect on steering.

    -Walt

  17. #17
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    Quote Originally Posted by machine View Post
    Since the fork is already in hand I seem to be limited to 3 options to slow down steering

    1. Shorten reach, add longer stem(my preference on a road bike).
    2. Slacker HTA
    3. Combo of 1+2.

    Can you all speak to these options?

    I'm pretty sure I'm just going to have to build a few iterations to understand things and that my preferences will change as skills develop.
    1. I don't really see any circumstance where i would do that. If it's flat and smooth enough to do that, the current steering would be great. I'm with you on a long stem for a road bike, but 40-70mm is my happy place on a mtb. Stem length doesn't seem to impart as much stability to a mtb as it does a road bike, i guess cuz you carry more of your weight on your feet...? Roadie cornering only works on some corners off road, and for those you can just 'choke up' on the front of the bike. (i would opt for shorter chainstays, or adjustable chainstays-- smart for a 1st build, imo)

    2. If it were me i would just slack it out 2* and not change anything else. It would lengthen the front-center, but i personally would see that as a benefit.

    3. That would be the way to do it if you wanted to slow down the steering and preserve the wheelbase.




    I'll mention again that there's been a major shift to longer front-centers for MTB. Steeper seat tubes, slacker head tubes, longer reach... all tools to make a longer bike that works well, and some of the design language has been changed to look at the problem that way. The different responses to your questions are biased by how the hot the responder likes their porridge.

    i'm 7" taller than you; my primary interest in frame building is how to make bikes that work great for big, tall, strong riders.


    I look forward to seeing what you create!

    Quote Originally Posted by Feldybikes View Post
    I know about bars, when I started riding, 580 was super wide (vs the more common 560). I went a little wider at a time and it always felt good until I got up to 800 and never got comfortable with it. I cut them back to 780 and that's my personal sweet spot.
    It's weird how it's like that. I got some 820s cuz 800s are great! ...nope, never felt right. Cut them down.
    Last edited by scottzg; 08-28-2018 at 12:28 AM.
    "Things that are complex are not useful, Things that are useful are simple."
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  18. #18
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    You can also change air-shaft in the fork to get more(or less) travel. It's really cheap and easy.

    2018 Ibis Ripmo
    2016 Transition TransAM 275

  19. #19
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    Quote Originally Posted by Gilgo View Post
    You can also change air-shaft in the fork to get more(or less) travel. It's really cheap and easy.
    I don't see much benefit in this. A revelation is an OK fork, not worth throwing money at prematurely. With hardtails fork travel is a fairly subtle thing if the rest of the design is effective.


    ...and the fork is such a huge factor in how well a hardtail performs. Building around a 120mm revelation implies a bunch about the intended use of the bike. Not that OP knows that going in, but the fork and his intentions match.
    "Things that are complex are not useful, Things that are useful are simple."
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  20. #20
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    Since you're asking for opinions, I might as well throw mine into the ring.

    All I would do is bring the HT angle to 68 and the reach to something like 435. Use a 10mm shorter stem than specced in that drawing, and go for it. That would give a pretty conservative (by modern standards) mountain bike. Honestly I wouldn't go back to head angles that steep if someone paid me. I became a significantly better rider with today's modern geometry. But you do have to be open to it when you ride it, it'll feel odd at first. Embrace it and have fun and believe me, you'll realize how awesome it can be.

    And definitely post build pics, we love that around here!
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  21. #21
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    At a 700mm saddle height (that's pretty short legs even for 5'8") I would not be looking to make the reach or wheelbase a bunch longer, personally. But it's true that for most riders, a wicked long bike is a good/safe thing.

    Just drop to 68 or 69 and leave everything else alone. It'll be great.

    -Walt

  22. #22
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    Quote Originally Posted by Walt View Post
    At a 700mm saddle height (that's pretty short legs even for 5'8") I would not be looking to make the reach or wheelbase a bunch longer, personally. But it's true that for most riders, a wicked long bike is a good/safe thing.

    Just drop to 68 or 69 and leave everything else alone. It'll be great.

    -Walt
    Done and done. Will post when it's finished.

    -T-

  23. #23
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    Don't forget the dropper! Sleeves for a 31.6 dropepr are easy to make. Put some sort of access for the cable in the ST - keep it simple especially if you plan a couple of iterations.. This "modern geometry" business works much better if you are using the dropper all the time - not just drops and gnarly downhills. Getting low in the corners is just as important. This "modern geometry" makes a great bike, but it is more work I feel. Good to see you over here - you'll find much more mtb focus than VS.
    Departing from East Hampton, CT

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