How do I measure head angle?

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  • This topic has 36 replies, 18 voices, and was last updated 5 days ago by  Bez.
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  • How do I measure head angle?
  • Premier Icon yoshimi
    Member

    I’m guessing with my iphone level thing, but

    It’s a tapered steerer tube so can’t place it directly on that – can I go off the angle of my fork or are the lowers/crown etc raked out from the steerer?

    Go on the fork stanchion, make sure you don’t have volume button that kicks on a few degrees, and also take measurement off floor too.

    geex
    Member

    Don’t whatever you do turn the bike both ways and take the average of the two angles off the stanchion. Just keep looking for the perfect piece of ground that gives you whatever H/A is in fashion. Remember to ask on here first.

    “Don’t whatever you do turn the bike both ways and take the average of the two angles off the stanchion.”

    Useful advice carefully concealed in the wit…

    Remember to always round down because less is more (rad). Don’t be surprised if the angle you measure is a degree more or less than you were expecting, especially with an alloy frame and/or different tyres front and rear.

    greyspoke
    Member

    Also possible with a tape-measure and some trogonometry, but only really as an exercise in geekiness.  Unless you are working from a bare frame when it might make sense.

    trogonometry

    Or some simple Konamatics…

    greyspoke
    Member

    How would konomatics help you measure something stotic?

    Premier Icon Bez
    Subscriber

    less is more (rad)

    And therefore less is more (deg) as well.

    “And therefore less is more (deg) as well.”

    I wish I’d done that deliberately…

    Premier Icon Bez
    Subscriber

    especially with an alloy frame

    Maybe my caffeine level has dipped critically low, but you’re going to have to explain that one to me.

    Premier Icon Bez
    Subscriber

    I wish I’d done that deliberately…

    Well, as we know from The Reverend Spooner’s Guide to Trigonometry, that’s the benefit of sined height.

    chevychase
    Member

    Go down something really steep.  If you go over the bars your measurement is “too steep”.

    Seriously. If the bike feels good… 😉

    hols2
    Member

    you’re going to have to explain that one to me.

    Steel frames breath with the trails innit.

    “Maybe my caffeine level has dipped critically low, but you’re going to have to explain that one to me.”

    I should have said “welded frame”. The manufacturing tolerances on a carbon frame are tighter than on an alloy or steel frame because it’s made in a large mould, not tubes welded together.

    hols2
    Member

    I should have said “welded frame”. The manufacturing tolerances on a carbon frame are tighter than on an alloy or steel frame because it’s made in a large mould, not tubes welded together.

    Based on what? Are there any published studies of that or is it just more marketing bollocks from a frame manufacturer claiming that their bike is somehow special?

    Premier Icon Bez
    Subscriber

    I should have said “welded frame”. The manufacturing tolerances on a carbon frame are tighter than on an alloy or steel frame because it’s made in a large mould, not tubes welded together.

    Even if that were true (and I’d agree that it has a whiff of bollocks about it) it’s completely irrelevant if the aim is to find out the head angle of a specific bike.

    Van Halen
    Member

    the chief is a proper nerd. Things like welding tolerances matter to him….

    I photograph mine side on with the camera in line with the centre of the frame.

    Then on a PC I project a line along the tyres/ground contact patch, another through the centre line of the stanchions and measure the angle between them.

    hols2
    Member

    the chief is a proper nerd. Things like welding tolerances matter to him….

    Which doesn’t answer the question. The aerospace, automotive, and other industries have been welding stuff together for many decades. Some uses require high precision, others not. The issue is really how expensive it will be to achieve a particular precision, not whether it is possible. So the question is, what evidence is that claim based on, not who typed the (so far unsubstantiated) claim into a web forum?

    Premier Icon 40mpg
    Subscriber

    I’d just Google the frame dimensions for the bike 🙄

    Premier Icon Daffy
    Subscriber

    Download an inclinometer app for your phone, place your phone against the headtube.

    Premier Icon Bez
    Subscriber

    I’d just Google the frame dimensions for the bike

    That assumes (a) that you have an off-the-peg full bike and (b) that the manufacturer has published the head angle.

    Stevet1
    Member

    Measure wheelbase. Stack up bricks/books/small mammals under rear wheel until a plumb line shows your headtube is vertical. Measure how much stuff you had to add under rear wheel. Do some trig to work out the Head angle.

    Keith @ Banshee quoted me 1/2 degree angle tolerances on their alloy frames when I asked. I can hit tolerances like that when CNC milling plywood, and a CNC milled carbon frame mould will be far tighter.

    “The aerospace, automotive, and other industries have been welding stuff together for many decades. Some uses require high precision, others not. The issue is really how expensive it will be to achieve a particular precision, not whether it is possible.”

    High end MTB frames (at factory, not retail, prices) are cheap for what they are. They can’t be made to aerospace levels of precision for that money.

    Premier Icon matt_outandabout
    Subscriber

    Turn bike upside down at bottom of stairs.

    Measure back wheel to floor distance as well as vertical and horizontal separation of hubs.

    Set up a rope from upper bannister to front wheel. Now hoist up front wheel until rope and forks are inline.

    Now measure the distance between back wheel and floor, hub separation.

    Then Google trigonometry….

    (Method B involves a friend, long distance manuals, laser levels and nudity, highly inappropriate for a family site such as this)

    You don’t measure it.

    You go and ride your bike and have fun and don’t think about it.

    FFS what is it with MTBers these days.

    Charlie, you’re assuming some of the folks on here actually ride MTBs….

    philjunior
    Member

    I should have said “welded frame”. The manufacturing tolerances on a carbon frame are tighter than on an alloy or steel frame because it’s made in a large mould, not tubes welded together.

    The tubes are held in a jig whilst being welded, and usually the final machining is done post heat treatment, so it shouldn’t really be an issue (although it is a possibility on more traditional external headset frames where often there’s no machining done post welding/heat treatment).

    On the other hand, it’s well known that plastics in general and composite laminates in particular are very prone to distortion depending on the layup – good design software to minimise this is available these days, but then bike frames are pretty complex shapes and I wouldn’t be surprised if quite a few molds still get binned or layups have to be fiddled with to correct distortions. I guess that as long as the layup is accurate the distortion will be repeatable though, so you can just claim to deliberately have a weird head angle.

    hols2
    Member

    They can’t be made to aerospace levels of precision for that money.

    As usual, you’re completely ignoring the point. The point is that it’s not inevitable that a welded frame will be low precision, it’s a matter of how much a manufacturer is willing to spend. The exact same calculations on cost will be made with carbon frames, which won’t be made to aerospace level tolerances. As philjunior points out, if the headtube and bottom brackets are machined post welding and heat-treating, it makes no difference if there’s a bit of distortion during the welding process. So, the “welded frames are less precise” just sounds like more marketing bollocks. As I asked above, is that based on any published studies of the real manufacturing tolerances or just something some marketing clown pulled out of their arse in order to differentiate their supposed wonderbike from all the others?

    Premier Icon Poopscoop
    Subscriber

    I swear to God.

    Sometimes a thread on here has the ability to create a singularity.

    You can almost see beyond the event horizon on this one.

    And it’s both beautiful and weird. I feel privileged.

    geex
    Member

    Who’s beyond the horizon though?

    The folk who think they ride bikes? or the ones who think they design them?

    I do agree though there’s a hell of a lot of science fiction going on in here

    jonnyboi
    Member

    So, two different bikes I owned measured significantly steeper HA than the published geometry.  Unique to me of would they all be that way then?

    Premier Icon Poopscoop
    Subscriber

    Won’t the HA change when the weight of the rider compresses the suspension anyway?

    jonnyboi
    Member

    Yes, and also on a full suss you can make it slacker by running with less rear preload and compression damping

    geex
    Member

    So, two different bikes I owned measured significantly steeper HA than the published geometry.

    But was your iphone the latest model?

    😉

    Premier Icon matt_outandabout
    Subscriber

    Won’t the HA change when the weight of the rider compresses the suspension anyway?

    Lets et snot confuse the guy as to how much different tyres can change it too..

    Premier Icon Bez
    Subscriber

    So, two different bikes I owned measured significantly steeper HA than the published geometry.  Unique to me of would they all be that way then?

    Are they both catalogue-spec full builds? Are they full suspension bikes where the published measurements may account for sag while seated? Does your measurement process have an inherent error that you haven’t noticed?

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