Frame sizes

Discussion in 'Cycling Archive' started by Nick Maclaren, May 5, 2015.

  1. Nick Maclaren

    Sam Wilson Guest

    See the tables at
    <>, particularly
    the comment in the Merckx section under Road Bikes.

    Sam Wilson, May 7, 2015
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  2. That's bizarre! It's inconsistent. It says that most companies use
    the virtual length corresponding to a horizontal top tube, so they
    SHOULD all be comparable. Including to older upright designs and my

    ''You can get a rough idea of the size of frame you require if you
    measure your inside leg - crotch to floor - then subtract 9" or 10".

    Road and Touring Bikes
    Bike Size Rider Height
    58cm 6'0"-6'3"

    Commuter/Hybrid Bikes
    Bike Size Rider Height
    21"-22" 6'0"-6'3"

    I am a fairly standardly proportioned person of that height (187 cm),
    and have an inside leg of 36". The first rule gives 25", but the
    second gives 23", and the third is much lower!

    I suspect that manufacturers do NOT quite the sizes that correspond
    to a horizontal top tube, but some bizarre 'estimate', so they are
    not comparable.

    Nick Maclaren.
    Nick Maclaren, May 7, 2015
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  3. Since the advent of the compact road frame the numbers have ceased to
    mean much. My 1984-vintage Revell Romany frame is a 25.5" job; my Cotic
    Roadrat is WAAAAY smaller in terms of numbers but has a much longer seat
    post. Both bikes are set up to have the same relationship- between
    saddle and bars in the local equivalent of the on-the-drops position.

    Or did, until the Romany's bars and stem migrated to the upright trike.
    Dave Larrington, May 7, 2015
  4. Nick Maclaren

    Rob Morley Guest

    No, seat tube length is the normal measure of frame size. The "stack
    height" (I've never seen it called that before) refers to a "virtual"
    horizontal top tube - you'll more often see reference to the length of
    this tube than its height, as it determines the saddle to handlebar
    distance. This is actually more important than the seat tube length
    when it comes to achieving a good position - saddles and stems can be
    adjusted more easily in the vertical than the horizontal (you can vary
    the reach of the stem, but this can have a bad effect on handling).
    But top tube length must be read in conjunction with seat tube angle
    and length, as everything ultimately depends on the position of the
    bottom bracket.
    Rob Morley, May 7, 2015
  5. Ish. The position of the imaginary horizontal top tube is inconsistent
    through different frame types, so it's no surprise that the sizing is
    also inconsistent.
    Which puts the whole "frames are smaller now" idea where? We've got a
    lot of less tall frames through both MTB fashion and higher-stiffness
    materials for them and the seat stem, and inconsistent virtual top tubes
    between manufacturers (and varied headset top height), so I'd suggest
    there's no data one way or the other.

    I bet anyone who knows how to set up a saddle to suit their leg length
    still does it to much the same distance as they did in 1930, pedal to
    crotch distance won't have changed. Hand position and back angle may be
    more varied with the profusion of different bars and cycling purposes we
    have now.

    But "frame size" does appear to be a thing as badly defined as ladies
    dress sizes.

    Cheers - Jaimie
    Jaimie Vandenbergh, May 7, 2015
  6. Still where it was. I.e. it's supported by the data, but is NOT as
    extreme as that page implies. In addition to the 'correct' saddle
    height recommendations (which are c. 2" lower), my bicycle is only
    c. 1" larger than the standard large men's frame of 1960, and it
    stands out in a modern bicycle shed. And the population is c. 1"
    taller since then, and 2-3" since Cycling Manual recommended a 25"
    frame for riders with a 34" or longer leg.

    Nick Maclaren.
    Nick Maclaren, May 7, 2015
  7. Nick Maclaren

    Sam Wilson Guest

    I did wonder about adding a "Nick will explode when he sees this"

    Sam Wilson, May 7, 2015
  8. Yes :) God alone knows what it's on about, but I am damn sure that
    any naive cyclist or would be cyclist who comes across it will leave
    less well-informed than when he began.

    Nick Maclaren.
    Nick Maclaren, May 7, 2015
  9. Alan Braggins, May 12, 2015
  10. The rules I'd come across were
    i) Use 1.09 times inner leg length as a starting point
    ii) If your pelvis is rocking from side to side, your saddle is too
    high, otherwise see if you can raise it. says the
    1.09x rule dates from 1967; I'm not sure if that makes it modern in
    Nick's context or not. (The page mentions the "heel-method" gives too
    low a starting point, but doesn't give a date for it.)

    However, I've never heard anyone say "I'd be more comfortable if I could
    have my knees straighter, but the rules won't let me".
    I have heard "I insist on being able to put a foot on the ground without
    coming off the saddle, so I am not going to raise my saddle no matter what
    your rule says".

    (I have heard "I'd be more comfortable if I could have my knees straighter,
    but this borrowed bike is too small". In fact I've said it myself.)

    Adults on child size BMX bikes being an extreme example, a fad that
    seems to have passed.

    When I tried a Brompton with a standard seatpost I found it very
    uncomfortable, but the extended seatpost was okay. A Dahon was okay
    on its upper limit, but some other Dahons I found too small.
    My old Dawes Kingpin folder I made an seatpost extension out of a
    tube cut from another bike and a second seatpost. My current Birdy
    has quite a bit of spare seatpost.

    (None of them had/has anything like as much stem height adjustment as
    they do saddle height; some have none at all. Folding bikes with a
    single frame size are a bit of a special case though.)

    I was recently surprised to find that a standard brake cable would reach
    the rear brake on my tandem. It wouldn't if the handlebars were 4" above
    the saddle, instead of merely 4" higher than the ones fitted when I got it
    (the previous owner had the saddle lower too), but then it is a tandem.

    However, last week I did try my road bike for the first time in a while,
    after fitting a new groupset. I've injured my arm[1], and decided after a
    quick ride round the block that a shorter higher stem might be more
    comfortable. And the threaded fork to threadless stem adaptor had some
    spare height, and I had a spare stem. Changing the cables again will be
    slightly tedious, but not hard.

    But the handlebars are 26.0mm, and the spare stem is for 25.4mm bars.
    (It came off a flat bar (folding) bike when I raised the bars on that,
    though they still aren't higher than the saddle. Some of you may be seeing
    a pattern here. That frame was sold as a "large", but I'm not sure it is.)

    Who decides these things?!? "Oversize" bars and stems, I can understand.
    But two close enough to look as though they fit but not really sizes?

    [1] "Probably stretched a nerve" was the doctor's verdict. It seems to
    be recovering now though, so I might not bother changing the stem after
    Alan Braggins, May 12, 2015
  11. I had forgotten that rule! It's 'cusp' by my reckoning, and is
    essentially the same as the one I quoted. It would give 3" extra
    for ankling on a 34" leg, and the 1920 rule says buy a bicycle that
    allows for about 2" to 4".

    The pelvis rule is generally a good one - I do rock, but that is
    because the critical aspect is to protect my damaged knees. Without
    doing so, I would use about an extra 3.5" for my 36" leg.
    Nor have I, but I have had several people say that they had knee pain
    despite having the saddle at the 'correct' height, and I have enabled
    them to resolve it by persuading them to ignore the modern rule and use
    a more traditional height. FAR more have said that they are just
    among the people who can't cycle, can't cycle above 10 MPH or can't
    cycle more than 3 miles.
    Yes, unfortunately :-( Very relaxed frame angles help with that, but
    only ones of 60 degrees or lower.
    Yes :-(
    Such issues vary immensely, but be warned that they are likely to recur,
    more so and more seriously as you get older. So you might like to still
    consider doing that, but with no real urgency.

    Nick Maclaren.
    Nick Maclaren, May 13, 2015
  12. Nick Maclaren

    Peter Clinch Guest

    How much is ankling your friend here?

    If a major part of the problem is being high enough to get straightened
    knees, wouldn't a minimal-ankling style mean you could achieve that from
    a lower seat? suggests that ankling style
    is an individual thing but unconnected with efficiency/energy. Due to
    the individuality it would presumably take a bit of dedicated
    re-learning, but if that's done it may remove the need for 3" of

    Peter Clinch, May 13, 2015
  13. I found the bars which had originally been fitted to the bike, which fit
    a 25.4mm clamp, so I was able to try the higher stem. It was actually less
    comfortable. But that might be for other reasons (partly that how the arm
    feels varies anyway, and partly that those bars are narrower).

    (The stem I was using with the 26.0mm bars was itself a bit higher than the
    stem that was originally fitted to the bike, around 25 years ago.)
    Alan Braggins, May 13, 2015
  14. Yes. But you have forgotten that cranks rotate :) What it also
    means is that your knees are much more bent at the top, and putting
    any force on them when very bent is probably THE main cause of knee
    problems. The point here is that no natural aerobic locomotion mode
    bends the knee more by about 75 degrees, but non-ankling cycling
    usually does so by over 90 degrees. Oh, yes, you can extend the
    dead spot until the crank is horizontal, but that's not a sane way
    of cycling.

    Look at it this way: ankling by 4" has the effect of using 50mm
    shorter cranks, WITHOUT increasing the force needed on the pedal!
    And that's why I need to do it ....
    More or less. Bicycling Science says that there was at least one
    experiment that indicate a higher than usual saddle increased power
    output, but it clearly doubted that was a general rule. Personally,
    I agree with Sheldon, and that your conclusion is why so many people
    nowadays ride with 6"+ of seatpost extension on conventional diamond
    frames. Which, of course, forces the rider into a semi-crouch,
    because of the more restricted stems and use of straight bars.

    Nick Maclaren.
    Nick Maclaren, May 13, 2015
  15. I gather the real use of that was and is felonious activity. You spot a
    policeman on foot; you want a bicycle you can mount in no time, that
    accelerates very quickly, that has a very reliable drivetrain, that you
    can cross rough ground on - but you don't need to ride it for a great
    distance, or faster than the copper can run.
    David Damerell, May 13, 2015
  16. In uk.rec.cycling.moderated on Wed, 13 May 2015 15:09:35 +0100 (BST)
    When I bought my 'bent the bod who had let me try his - and who is
    only a couple of inches taller than I am - told me I really must get
    short cranks because of my height. Else I'd find my knee bending too

    I did and have been quite happy with them.

    When I got the Brom I didn't notice a knee issue but I did have a
    dreadful time getting comfortable on the Brom saddle and later at B17.
    If I had the saddle right back (even using an extender at one point)
    my backside didn't hurt but otherwise it did. The idea being to
    lean over enough that I wasn't resting on my seat bones.

    Then I got a nice wide comfortable B67 with springs and suddenly I was
    putting the saddle well forward.

    On the Brom I really notice it if the saddle is even a little bit too
    low. I was using the heel on pedal method but it wasn't as good as
    having the seat higher. I saw Nick on ankling and have been playing
    with it on the Brom, works well on that.

    On the 'bent I am at the very limit of the frame, I can't get the seat
    any closer to the cranks. I feel that is too far away by a smidgen,
    that and the difficulty of getting rims and tyres for the 24" front
    led me to pull the trigger on a Encore[1]

    I have tried ankling on the 'bent but I dunno it works as well with
    your hips locked in place. I do find that I put a lot of work into
    the upstroke on the 'bent now I think because my previous pedal/cleat
    combo used to unclip if I did that...


    [1] and then of course an old order for 2x 24" rims suddenly was
    filled AND I managed to hit a serious pothole at speed tearing my
    current one damn near in half. So I have to decide what I am going to
    do about moving from one to the other and dealing with the abandoned
    Zebee Johnstone, May 13, 2015
  17. Nick Maclaren

    Phil W Lee Guest

    (Nick Maclaren) considered Wed, 13 May 2015
    11:17:59 +0100 (BST) the perfect time to write:
    If there's suspicion of nerve damage, get your vitamin B12 levels
    checked, asap.
    B12 deficiency is very common, and not only affects nerves, but their
    ability to heal. Once done, the damage can be permanent.

    Been there, Done that, Got the Wheelchair :(
    Phil W Lee, May 13, 2015
  18. Grrk. Thank you for that. I am having minor problems, and I tick
    three of the risk factors and several of the symptoms! It's
    apparently particularly common in vegans (which I knew) and in the
    elderly who have been on proton pump inhibitors for many years.

    Nick Maclaren.
    Nick Maclaren, May 14, 2015
  19. In uk.rec.cycling.moderated on Thu, 14 May 2015 10:05:34 +0100 (BST)
    I take it Marmite is not vegan?

    Zebee Johnstone, May 14, 2015
  20. It's suitable for vegans, but apparently some people dislike Marmite.
    Alan Braggins, May 14, 2015
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