Ordering An MTB Frame: How to specify non-standard measurements?

Discussion in 'Cycling Equipment' started by x, Mar 28, 2003.

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  1. x

    x Guest

    I've just come out of my first custom frame and it turned into a debacle - mostly, I think,
    because of me and my big mouth sounding like I knew something when trying to specify a frame that
    would fit me.

    So, now I've got a $1,400 utility bike (too twitchy to really ride, seat about three inches behind
    KOPS, fork shoulders hit down tube if wheel turned too far).....and I'm ready to try to try to do it
    right. "No pain, no gain"...right?

    I'd throw myself on the mercy of Habenero and expect a good outcome except that one of my
    requirements is S&S couplings and Hab doesn't do them.

    So, it's steel again for this one and I'm thinking Sycip's "Diesel" (
    http://www.sycip.com/Pages/diesel.html ) but sized for my somewhat-strange bod.

    I've got an FS that, IMHO, is a perfect fit for me except that my weight is so far back that the
    front wheel is really, really light. A mixed blessing. Really easy on the front wheel and shocks,
    but it tends to come unglued too easily when climbing. Just once in my life, I'd like to try riding
    a bike that actually, officially, fits.

    I've dropped a plumb line next to the center of the BB spindle and measured the distance back to the
    center of the saddle clip and I'm told that this measurement is called "setback". To get my butt on
    the saddle at KOPS, I've had to increase the setback by exactly two inches (via a HellBent set back
    seatpost and moving the saddle all the way back in the clip).

    I'd like the custom bike to put the saddle where I want it without resorting to a set back seatpost
    and give me a little room to play with by allowing the saddle clip to hold the saddle in the center
    of the rails instead of all the way forward.

    The only other oddball dimension that I want is a 180mm head tube. (i.e. about 7"). I want this just
    to reduce the number of spacing rings used to set the bars where I want them.

    I know they're going to ask me to measure myself twenty different ways, and I know that at least
    some builders have a strong notion of what a proper fit and riding posture is....but I've got
    about 5k miles of FS riding and the last 3k have been in my preferred position and frankly I'm not
    about to change it for anybody. To me, the only issue is how to wind up with a frame that supports
    this position.

    SO: What's the right way to communicate this to a frame builder? "Setback" by itself seems
    meaningless - it would depend on the amount of seatpost extension.

    -----------------------
    PeteCresswell
     
    Tags:


  2. Matt O'Toole

    Matt O'Toole Guest

    "(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...

    > I've just come out of my first custom frame and it turned
    into a debacle -
    > mostly, I think, because of me and my big mouth sounding
    like I knew something
    > when trying to specify a frame that would fit me.
    >
    > So, now I've got a $1,400 utility bike (too twitchy to
    really ride, seat about
    > three inches behind KOPS, fork shoulders hit down tube if
    wheel turned too
    > far).....and I'm ready to try to try to do it right. "No
    pain, no
    > gain"...right?
    >
    > I'd throw myself on the mercy of Habenero and expect a
    good outcome except that
    > one of my requirements is S&S couplings and Hab doesn't do
    them.
    >
    > So, it's steel again for this one and I'm thinking Sycip's
    "Diesel" (
    > http://www.sycip.com/Pages/diesel.html ) but sized for my
    somewhat-strange bod.
    >
    >
    > I've got an FS that, IMHO, is a perfect fit for me except
    that my weight is so
    > far back that the front wheel is really, really light. A
    mixed blessing.
    > Really easy on the front wheel and shocks, but it tends to
    come unglued too
    > easily when climbing. Just once in my life, I'd like to
    try riding a bike that
    > actually, officially, fits.

    Some of the "light front" effect is due to compression of the rear suspension on a steep slope. If
    your FS bike was rigid you'd find less of this effect. Why not try it and see? Lock the shock any
    way you can (pump it up hard, replace the spring with a pice of pipe, etc.). Go for a ride, and see
    what happens. If this bike fits you well, it's probably the best template to start with -- so make
    it emulate a hardtail, see how it feels, and make adjustments from there.

    Matt O.
     
  3. Klydesdale

    Klydesdale Guest

    "Matt O'Toole" <[email protected]> wrote in message
    news:[email protected]...
    >
    > "(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...
    >
    > > I've just come out of my first custom frame and it turned
    > into a debacle -
    > > mostly, I think, because of me and my big mouth sounding
    > like I knew something
    > > when trying to specify a frame that would fit me.
    > >
    > > So, now I've got a $1,400 utility bike (too twitchy to
    > really ride, seat about
    > > three inches behind KOPS, fork shoulders hit down tube if
    > wheel turned too
    > > far).....and I'm ready to try to try to do it right. "No
    > pain, no
    > > gain"...right?
    > >
    > > I'd throw myself on the mercy of Habenero and expect a
    > good outcome except that
    > > one of my requirements is S&S couplings and Hab doesn't do
    > them.
    > >
    > > So, it's steel again for this one and I'm thinking Sycip's
    > "Diesel" (
    > > http://www.sycip.com/Pages/diesel.html ) but sized for my
    > somewhat-strange bod.
    > >
    > >
    > > I've got an FS that, IMHO, is a perfect fit for me except
    > that my weight is so
    > > far back that the front wheel is really, really light. A
    > mixed blessing.
    > > Really easy on the front wheel and shocks, but it tends to
    > come unglued too
    > > easily when climbing. Just once in my life, I'd like to
    > try riding a bike that
    > > actually, officially, fits.
    >
    > Some of the "light front" effect is due to compression of the rear suspension on a steep slope. If
    > your FS bike was rigid you'd find less of this effect. Why not try it and see? Lock the shock any
    > way you can (pump it up hard, replace the spring with a pice of pipe, etc.). Go for a ride, and
    > see what happens. If this bike fits you well, it's probably the best template to start with -- so
    > make it emulate a hardtail, see how it feels, and make adjustments from there.

    Hmm... I'm Pete's height but a bit heavier. My two bikes - a hardtail and a FS are almost identical
    to each other in how I'm positioned on them. I actually find it easier to keep the front end down on
    the FS when the rear suspension compresses. This is because not only does my center of mass drop
    down some but also because the rear wheel moves back a bit.

    I think the root of his problem is that he's simply got his center of mass too far back with that
    Hellbent seat post and the saddle all the way back in the seatpost clamps. The spacer/stem/handlebar
    combo that he's running doesn't help things either.
     
  4. x

    x Guest

    RE/
    > The spacer/stem/handlebar combo that he's running doesn't help things either.

    Really steep climbs *definately* go better with the bars dropped about three inches. Problem is that
    after lowering them and riding 20 miles or so my neck and shoulders are so messed up I give up and
    raise them again. Also, I ride five miles or so along a highway and various residential streets to
    get to where I do most of my riding and visibility is a real issue there - bars too low and I've got
    sort of tunnel vision.
    -----------------------
    PeteCresswell
     
  5. Mark Hickey

    Mark Hickey Guest

    "(Pete Cresswell)" <[email protected]> wrote:

    >I know they're going to ask me to measure myself twenty different ways, and I know that at least
    >some builders have a strong notion of what a proper fit and riding posture is....but I've got about
    >5k miles of FS riding and the last 3k have been in my preferred position and frankly I'm not about
    >to change it for anybody. To me, the only issue is how to wind up with a frame that supports this
    >position.
    >
    >SO: What's the right way to communicate this to a frame builder? "Setback" by itself seems
    >meaningless - it would depend on the amount of seatpost extension.

    Here's how I handle similar situations.

    IF you can get a good position on your current bike, a good designer should be able to take the
    "hard points" (bars, saddle and bottom bracket), and design a bike supporting them around the type
    of riding you plan to do.

    If you can't get the current bike set up reasonably close, you can still use it for a reference and
    interpolate the rider's impressions as to what they think will fix the fit issue (with some expert
    guidance as necessary, of course).

    It can be dangerous letting anyone decide what "fit" means - that's one reason why so many people
    end up with fit kit sessions suggesting they buy a bike that would position them similar to
    similarly-sized europros.

    Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
     
  6. x

    x Guest

    RE/
    >It can be dangerous letting anyone decide what "fit" means - that's one reason why so many people
    >end up with fit kit sessions suggesting they buy a bike that would position them similar to
    >similarly-sized europros.

    I don't have any expertise to back it up, but my overwhelming impressing when reading most "proper
    fit" threads and books about "proper fit" has been something in that vein.
    -----------------------
    PeteCresswell
     
  7. Klydesdale

    Klydesdale Guest

    "(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...
    > RE/
    > > The spacer/stem/handlebar combo that he's running doesn't help things either.
    >
    > Really steep climbs *definately* go better with the bars dropped about
    three
    > inches. Problem is that after lowering them and riding 20 miles or so my
    neck
    > and shoulders are so messed up I give up and raise them again. Also, I
    ride
    > five miles or so along a highway and various residential streets to get to
    where
    > I do most of my riding and visibility is a real issue there - bars too low
    and
    > I've got sort of tunnel vision.

    I think you're just at odds with geometry and physics here. Moving your body center of gravity
    rearward with respect to the rear wheel is not a great thing to do climbing wise if you carry some
    of your mass up higher than the average rider. I disliked climbing on the Fisher Genesis bikes I've
    ridden for this reason. They claim that shortening the rear chainstay makes climbing more efficient
    but how can you be more efficient if you're always working to keep your front wheel on the ground?

    I've been tinkering with a CAD sketch of a custom frame for my next bike. Using it and dimensions
    taken from the bikes I'm presently riding, I'm examining things like slackening the seat tube angle
    an impacts the position of my COG. I, like you, seem to be more comfortable further rearwards but to
    achieve a more optimal weight distribution between front and rear wheels, I see no suitable
    alternative to lengthening the rear chainstays.

    What kind of dimensions did you specify for your first custom frame (eff. top-tube, angles, etc)?
     
  8. Per LöWdin

    Per LöWdin Guest

    > The only other oddball dimension that I want is a 180mm head tube. (i.e.
    about
    > 7"). I want this just to reduce the number of spacing rings used to set
    the
    > bars where I want them.

    - hmm, not necessarily a good idea, as the spacing rings facilitates adjustment of the headset.

    > SO: What's the right way to communicate this to a frame builder?

    If you are custom building, i.e., they make the frame to your specifications, that should not be a
    problem, they should take the time and know what they are doing how a change in one variable affects
    other variables etc., and discuss the pro and cons with you.

    I never had a frame built for me, but Chris at Speedgoat helped me fit a Switchblade on line and get
    the right components before they built it for
    me. Worked excellently, got some good advice, and when the bike came out of the box it had
    perfect fit.

    If I had a frame custom built I would have Seven make it for me. Unfortunately, they are not
    represented in Sweden.

    Per http://user.tninet.se/~ipg289h/English.html
     
  9. x

    x Guest

    RE/
    >I, like you, seem to be more comfortable further rearwards but to achieve a more optimal weight
    >distribution between front and rear wheels, I see no suitable alternative to lengthening the rear
    >chainstays.

    With me, it's like my butt just sort of finds it's way to a certain fore-aft position - whether
    there's usable saddle area there or not. I can force the issue and conciously sit on a saddle that's
    two inches forward of where it should be for me, but as soon as my mind wanders and I start pedaling
    hard enough to get some of the weight off the saddle, my butt just sort of slides back to where it
    wants to be.

    For me, this corresponds almost exactly with KOPS.

    To me, one of the biggest issues in today's bikes is the limited fore-aft saddle adjustment. Except
    for something like WTB's Speed V or a downhill-specific saddle, the range of adjustment on most
    saddles is only about an inch. Geeze!... just a singlespeed with eccentric BB eats that up.

    >What kind of dimensions did you specify for your first custom frame (eff. top-tube, angles, etc)?

    I didn't, except for one extraordinarly stupid request: I specified a distance from the tip of a
    particular make/model saddle to the center of the steering tube - thinking that that would give me
    the cockpit length I wanted and that's all I had to worry about.

    I'm kind of huge, have a big mouth, have a way with words, and am used to talking technical stuff -
    so the framebuilder, rather than argue with some lunatic that was three times his bodyweight,
    assumed I knew what I was talking about...

    $1,400 later, I see the folly of my ways. Never did do very well in those spatial relationship
    aptitude tests they gave in school... 98th percentile in the verbal stuff...20-something-th in the
    spatial realtionships...

    Part of me says that the way to a decent frame is to specify *nothing* - let the guy who knows about
    this stuff make all decisions.

    The probem I have with that is that the framebuilder is probably a vastly stronger, more skillful,
    and more hardcore rider than I am - or at least is used to dealing with same - and that he'd put me
    in a position that favored aerodynamics and efficiency over things like visability and a certain
    rider-specific posture.

    So, what I'm coming around to is specifying only three things, maybe four:

    1) Setback at a certain saddle height. i.e. the distance from the center of the saddle clip to a
    plumb bob line through the center of the BB spindle when the clip is a certain number of inches
    from the center of the BB spindle. On my stock Isis, it was 9.5" - although I neglected to
    measure the distance from saddle clip to BB spindle when I took that measurement...

    With my saddle all the way back and a HellBent setback post, that measurement is currently 11.25"
    with the center of the clip 31" from the center of the BB spindle. I guess if I could remember my
    trig, I could crosscheck those measurements by computing the seat tube angle and comparing it to
    Ellsworth's spec.

    I think I'd go for 11.5" just to regain a little adjustment range in the saddle position.

    2) Steering tube 6". It's 5" on my Isis but I've got a 1" spacer stack and some fairly-humungous
    risers. Seems like 6" would get rid of the spacer stack and varying the rise of the bars and the
    stem would give me all the downward adjustment I'd ever want in the unlikely event that I see the
    light and lower my bars any further.

    I'm assuming anything that reduces the height of the spacer stack and the height of the stem without
    unduly limiting downward adjustablity has to be an improvement in terms of lessened chance of
    stem/steering column failure.

    3) Standover height less than a certain figure. Dunno what that figure would be, but the longer
    steering tube could create a problem if the top tube weren't sloped somewhat more-seriously
    than most.

    4) (MAYBE) Getting my center of gravity somewhere close to where a normal-sized person's is on a
    normal bike. But this last one is still suspect for me. Seems to me like when I'm in my preferred
    riding position and I start to hammer enough to get my butt just sort of touching the saddle but
    not bearing on it; my fore-aft position does not change at all - I just sort of rise up an inch
    or so. Hence my COG is already at the BB spindle.

    The floaty front wheel doesn't get me until I hit those inclines where it's a matter of juggling
    fore-aft position so as to maintain enough rear wheel weight for traction yet enough front-wheel
    weight to keep it on the ground. There are some inclines where, even on pavement (*really* steep
    pavement...) once I get the front wheel touching enough to steer with, my rear wheel starts to break
    loose. Spinning in a low enough gear mitigates this somewheat - but I still think I run out of
    traction a lot sooner than somebody who is lighter.

    OTOH, in those circumstances, I'm barely touching the saddle (if I really sat on it, I'd be taking
    the tip of the horn up my butt...) it seems to me like saddle location is moot because all my weight
    is on the pedals and bars....so I'm back to square one on #3.

    -----------------------
    PeteCresswell
     
  10. x

    x Guest

    RE/
    >.so I'm back to square one on #3.

    Oops! SHB "#4..."
    -----------------------
    PeteCresswell
     
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