angles schmangles

blister pus
blister pus Posts: 5,610
edited May 2010 in MTB workshop & tech
head tube angle

let's say for every degree increase (or decrease) what is the actual physical shift in mm of the stem approximately? off the top of your head, like.

because I'm sure someone's already worked it out....like they do, like.

Comments

  • nicklouse
    nicklouse Posts: 50,673
    not really possible to say.

    too many variables.

    how is the head angle being changed?
    stem info...
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • blister pus
    blister pus Posts: 5,610
    for instance.

    take any bike with a 70.5 degree head angle and set up accordingly and make the head angle 69. keep everything the same. what would the stem shift in mm, forward and back be? ....forget altering stem angle, just the physical forward and backward shift.
  • nicklouse
    nicklouse Posts: 50,673
    so just buy changing the front sus length?

    every inch of Axle to Crown change is about one degree of head angle change.

    but this is rotation about the rear wheel axle so a bit of math is needed to work out the for/aft

    but there is not really a rule of thumb as stem length and rise will change the figures quite a bit.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • blister pus
    blister pus Posts: 5,610
    all this is nick, is purely a mental exercise to give me a rough idea of what stem size shift I'll be looking at going from one very comfortable set up to another set up with virtually identical geo but a slacker head angle. I'm figuring going from 60 to a 70mm will cover any difference to get virtually the same cockpit feel as i have now.

    but obviously I'll know for sure when I get my hands on the frame and do a side by side comparison with what I have now
  • Anonymous
    Anonymous Posts: 79,666
    the distance from your arse to the handlebars will be the same?!? changing fork lengths/head angle only rotates the bike around the rear axle.
  • blister pus
    blister pus Posts: 5,610
    reach will be slightly different but it's something you could compensate moving the saddle on it's rails but I need a new stem anyway so I might as well make the adjustment there. like i said it won't be much....but enough to notice if i get it wrong. what I've got now is pretty much perfect so I'll be replicating it as near as possible
  • Anonymous
    Anonymous Posts: 79,666
    It would be such a small change that I reckon even wearing gloves or not, or the thickness of your grips would affect it more.
  • blister pus
    blister pus Posts: 5,610
    everything I've bought so far is a virtual carbon copy of what I've got already, bar sweep, length etc etc. the only thing changing that is making a difference is head angle and head tube length compared to what I've got - but it's not surprising as I'm going from a dedicated 100mm travel set up to a 100 - 130mm set up. the real top tube length is shorter on the new frame by a smidge < 1cm, that takes me up to a 70 mm stem. I don't particularly want to go any longer as i like a relatively short stem. if the mental calculations are right then it should be sorted.

    no doubt I'll be back posting in the buying section in a fortnight. :lol:
  • nicklouse
    nicklouse Posts: 50,673
    so you are talking about different frame geometrys them not the same frame with a longer fork.

    totally different this and you will have to crunch numbers two time to work out where they are in relation to some fixed point.

    you also need comparative figures IE the head angle for a given AC length.

    download Linkage and have a play to see what happens to some designs and fork changes.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Anonymous
    Anonymous Posts: 79,666
    Or just quit being so anal, and just ride! :lol:
  • blister pus
    blister pus Posts: 5,610
    Chance'd be a fine thing. I've only been waiting 8 months for the ******. Probably puts a little more colour on the situation for you. Still, finally in stock tomorrow am and pre-orders dispatched within 24hrs (that's me).

    Nick. Were you linking to something?
  • jairaj
    jairaj Posts: 3,009
    I think Nick was talking about Linkage the software? Free demo can be downloaded here: http://www.bikechecker.com/demo.phtml
  • nicklouse
    nicklouse Posts: 50,673
    jairaj
    yep as linked in the Tech sticky that no one looks in :wink:
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • blister pus
    blister pus Posts: 5,610
    hey i've been through that sucker countless times and never seen that before. :lol:
  • nicklouse
    nicklouse Posts: 50,673
    down load it and have a play it will show so much better than words just forget about the rear sus.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • blister pus
    blister pus Posts: 5,610
    on it now. looks handy dandy. ta both.

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