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Thread: Rear suspension linkage calculator

  1. #16
    Join Date
    5th May 2022 - 21:56
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    2010 Triumph Street Triple 675
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    Berlin, Germany
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    Quote Originally Posted by erik View Post
    Ok, I've updated the spreadsheet. I've also added a .dwg and .dxf (best to use the dwg and have the triumph675linkage.png in the same directory so it can show in the drawing file) that I used to get the appropriate measurements for the spreadsheet. Your drawing was missing a dimension for point D relative to the swingarm centerline. I've copied the distance from your drawing. Also, it might be good to measure the heights of the axle and swing arm pivot or some other point to check that the angle of everything relative to the ground is correct. I've also added a slider that lets you move the linkage display as you move it, but it only works in the .odf version in LibreOffice or probably also OpenOffice (I don't think it'll work in Excel). The calculations for the triumph linkage are done kind of backwards to the others. As such, you have to enter the vertical distance from the swing arm pivot to the axle rather than it all being controlled by the shock length.

    https://1drv.ms/u/s!AkrSBqY_mHqzkUv6...XB4zU?e=176UFW

    I hope it's helpful.
    Hi Eric,
    with the vertical distance between wheel axle and swingarm pivot (96mm) the swingarm angle should be 9.3°. The horizontal distance is 585mm measured and calculated. I controlled everything as good as possible on a smooth and horizontal concrete ground and found out the following:
    vertical distances to the ground:

    A:411 mm
    G:569 mm
    H:156 mm
    C:315 mm

    Horizontal distance from the swingarm pivot (A):
    G:~60 mm
    A: 585 mm
    H:~14 mm

    The shock length is 284mm (static sag 6mm), the free length of the shock is 290 mm.

    Why does the calculator state a vertical distance of 153 mm between axle and swingarm pivot? This would need very long legs...

    Have a nice day!

  2. #17
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    5th May 2022 - 21:56
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    2010 Triumph Street Triple 675
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    Berlin, Germany
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    Quote Originally Posted by F5 Dave View Post
    So. . . Have you serviced the linkage and checked Swingarm moves freely? Wouldn't be the first time.
    Hi Dave,
    everything clean and smooth moving freely.
    Without play in the bearings. Don't get me wrong, everything fine so far. I have no mechanical issue, but I want to improve the function. Working with different angles in the link plate and lenghts of the dogbone do change the leverage ratio. But trial an error is a very expensive and long lasting thing here. With eric's calculator the behaviour could be predictable.
    Best regards

  3. #18
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    25th March 2004 - 17:22
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    Worth asking. Local guy here has done revalve work a few times before hes asked customer to bring bike in. Customer much happier with moving linkage.
    I've been told. Dreaming`s free.
    Think I'll go, back to sleep.
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  4. #19
    Join Date
    29th October 2003 - 21:14
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    1999 Suzuki SV650S
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    Auckland, New Zealand
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    Quote Originally Posted by Dirk777 View Post
    Why does the calculator state a vertical distance of 153 mm between axle and swingarm pivot? This would need very long legs...
    Because I treated the edge of your drawing as level. That's why I asked you to measure from the ground to the axle and swing arm pivot, to check if it was.

    So I've rotated the drawing (I'm using Nanocad free version) and made another pdf. The measurements are slightly different to what your new measurements are measuring from the ground, I don't know which are more accurate.
    I also changed the free shock length to 290 but assuming those height measurements were under free sag conditions, it says the shock should be 282.5 at static sag. Anyway it's not too far off. I also changed the spring rate to 8.5kg/mm. I have no idea what the preload, or top out spring should be. I've just left them the same as my old zx6r shock (I can't remember how accurate they were for that either...).

    I've updated the spreadsheet and the zip file at the same link: https://1drv.ms/u/s!AkrSBqY_mHqzkUv6...XB4zU?e=176UFW

    With the corrected measurements, you can see the angle between FH and DF is bigger which makes the suspension even more progressive. It stands out in the effective spring rate graph.
    I think the easiest way to reduce the progressiveness would be to change the triangle linkage plates. I tried changing the dimensions DF to 100mm, FK to 79mm and DFK to 45 and it's greatly reduced the progressiveness (probably too much?). I adjusted them so that the shock was close to 282.5mm in the first line of the results, but I think it'd be better to do it based on laden sag. Anyway, those numbers are just an example that the progressiveness can be changed, not a suggestion of what dimensions to use. It seems other people have had the same thoughts, there's this thread here (I haven't read it): https://www.triumph675.net/threads/r...ed-them.26006/

  5. #20
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    5th May 2022 - 21:56
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    2010 Triumph Street Triple 675
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    Hi Eric,
    thanks a lot again! I know the thread you referred to very good, and built the link plates according to these designs. But you won't find the geometrical theorie which lead to the differnt approaches.
    There are problems concerning the rideheight and RSU length in many cases and I wanted to improve the design but avoid trial and error.

    The linkplates you put into the calculator are "Flux II" plates, that should be an improvent to former "Flux I". But these "Flux II" give a more progressive feeling even than the OEM Triumph plates.
    Therefore I want to find out the progression of the different designs and compare it with the feeling on the road/track. I'll be back with the results! I'll take your comments into account.

    Best regards
    Dirk

  6. #21
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    5th May 2022 - 21:56
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    Oh,
    I made a mistake...... 284 mm shock length is free-sag (bike weight only) , 290 mm free length . Sag with driver not measured.

  7. #22
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    29th October 2003 - 21:14
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    1999 Suzuki SV650S
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    I look forward to seeing your results. Are you familiar enough with spreadsheets to copy the triumph worksheet and change the graphs so you can compare several different linkages?

  8. #23
    Join Date
    5th May 2022 - 21:56
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    2010 Triumph Street Triple 675
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    Berlin, Germany
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    Hi Eric!
    Yes I think so. I alter the dimensions of the different triangles and dogbones in the input section and look for the resulting GK and lever Ratio. Then I check which combination fits my shock length and take the most linear combination.... That's the plan.

    Best regards!

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