Headlight beam aim

Discussion in 'UK Motorcycles' started by Ben, Nov 12, 2008.

  1. Ben

    Ben Guest

    It's apparent from my first ride in the dark on the GSXR tonight that
    the headlamp aim is a bit on the high side.

    http://www.motuk.co.uk/mcmanual_160.htm suggests from the pictures
    that the beam shouldn't be more than 850mm high using an aiming
    screen. Which I obviously don't have, so I'll just stick a line on
    the wall 850mm high.

    Which raises the question; how far away does the bike need to be from
    the wall?
    Ben, Nov 12, 2008
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  2. Ben

    Pete Fisher Guest

    Main or dipped beam?
    Oddly, I have just had the lights on the MX5 re-aligned at an MoT place
    round the corner. Long story, but in changing the bulbs I disturbed the
    alignment. The owners manual sold me a dummy by not mentioning different
    arrangements for models like mine with load levelling adjustment.

    I got them roughly right using my garage door. For a car, about 10
    metres with the centre of the pools of light on *main* beam at the same
    height as the headlights.

    Mine ended up a bit too low by this method apparently.

    When I changed the headlight on the Voxan for a UK dip unit (off an MZ
    Skorpion) I set the height off the bike by having the two units side by
    side on a bench and powered by a battery. Just tweaked the new one until
    it hit a wall at the same height as the original on dip, so distance
    irrelevant. When it had its MoT and MSVA they said it was spot on.
    | Pete Fisher at Home: |
    | Voxan Roadster Gilera Nordwest * 2 Yamaha WR250Z |
    | Gilera GFR * 2 Moto Morini 2C/375 Morini 350 "Forgotten Error" |
    Pete Fisher, Nov 12, 2008
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  3. Pointless anyway, as you'll generally find the MoT-approved headlamp
    beam height is just a bit too low for real use. It's handy to know where
    to set it for the test, though.
    Grimly Curmudgeon, Nov 12, 2008
  4. Ben

    Pip Luscher Guest

    Far enough for the intended beam pattern to resolve itself is good
    enough; usually a couple of dozen feet is plenty. If the dip's
    more-or-less level with rider seated then it shouldn't make any
    difference how far.

    I actually rode the R1 in the dark for the second time today and I
    reckon it's a bit marginal, though I have learned that Police cars,
    with their highly-reflective tailgates, aren't good for judging
    headlight aim. Or for making progress.
    Pip Luscher, Nov 12, 2008
  5. Ben

    bod43 Guest

    To the OP:-

    The 850mm bit refers to the two different possible
    headlamp heights. Up to and including 850mm and
    over 850mm.

    In each case they must aim down a bit as follows:-

    The best plan is probably to get the testing station
    to adjust it to their satisfaction.

    If you want to do it yourself then here are the numbers.

    One thing that is NOT mentioned is whether the vehicle is
    to be loaded or not. In the case of a bike this could make
    a BIG difference. Check with your test centre.
    I would think that these numbers would be with rider
    but that is a total guess.

    The flat cutoff (on the right hand side) must be depressed
    as follows:-:-

    If the headlamp centres are 850mm or less from the ground
    between 0.5 and 2 degrees down.

    If the headlamp centres are more than 850mm from the ground
    between 1.25 and 2.75 degrees down.

    The "break point" where the elevated portion to the
    left starts must be between straight ahead and
    2 degrees to the left.

    Need some trig.
    Using google. Put the left hand expression into
    google and we get the output given here.

    To check we are on right track -
    sin((90 / 90) * (pi / 2)) = 1
    sin((45 / 90) * (pi / 2)) = 0.707106781
    Looks good to me.

    # <=850mm height case #

    0.5 degrees
    sin((0.5 / 90) * (pi / 2)) = 0.0087265355 - i.e 9mm per metre

    2 degrees
    sin((2 / 90) * (pi / 2)) = 0.0348994967 - i.e 35mm per metre

    So for <= 850mm height every meter INCREASE in distance
    from the target must cause the beam to drop by between 9mm and 35mm.

    For 10 metres change of distance it would be 90mm to 350 mm.

    Midpoint is 1.25 degrees.
    sin((1.25 / 90) * (pi / 2)) = 0.021814885 - i.e 22mm per metre

    # > 850mm height case #
    1.25 degrees
    sin((1.25 / 90) * (pi / 2)) = 0.021814885 - i.e 22mm per metre

    2.75 degrees
    sin((2.75 / 90) * (pi / 2)) = 0.0479781285 - i.e 48mm per metre

    So for > 850mm height - every meter INCREASE in distance
    from the target must cause the beam to drop by between 22mm and 48mm.

    Midpoint is 2 degrees
    sin((2 / 90) * (pi / 2)) = 0.0348994967 - i.e 35mm per metre

    In decades gone past - the usual plan was for garages
    to set it PLENTY low. As far as they were concerned
    the lower the safer. (Safer in terms of possible
    complaints). Most garages set the lights FAR too low.
    bod43, Nov 13, 2008
  6. Ben

    Cab Guest

    On Wed, 12 Nov 2008 17:04:54 -0800 (PST), bod43 wibbled:

    It's really weird, but I was going to say exactly that.
    Cab, Nov 13, 2008
  7. (Deliberately left unsnipped)

    Holy shitfire. I'm impressed (plus I have the nagging worry that you
    might be conning us all).

    PS: I just clout the top of my headlight wiv a fist.
    The Older Gentleman, Nov 13, 2008
  8. Ben

    Ben Guest

    That sounds reasonable.
    Ben, Nov 13, 2008
  9. Ben

    Pip Luscher Guest

    Indeed, though it's more critical with bikes with long-travel bouncy
    suspension than sprotsbikes.

    My old XT600Z, at out-of-town cruise speed, would also pitch-up
    slightly too, probably due to rider drag. I had to set the dip ever so
    slightly lower as a result.
    Pip Luscher, Nov 13, 2008
  10. Ben

    Pip Guest

    Our favourite tester *always* sits on the bike to check the beam
    setting - as he's fairly recently qualified, I'd assume this is the
    approved method. Makes sense to me, as it can't really be assessed on
    the sidestand and the centre stand is out of the question - therefore,
    the tester (or assistant) would have to hold the bike upright, and
    might as well be sat on it. Sitting on it is the only way to obtain a
    representative result, in any case.
    Nidge never bothers, as he rides everywhere on main beam, of course.
    Pip, Nov 13, 2008
  11. Ben

    wessie Guest

    is he dead, imprisoned, morphed or found somewhere else to spout bollocks?
    wessie, Nov 13, 2008
  12. Ben

    Pip Luscher Guest

    Heh. I experienced his headlight first-hand at a bike show somewhere
    between Stevenage & Bedford.
    Pip Luscher, Nov 13, 2008
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