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Thread: Rear suspension linkage calculator

  1. #1
    Join Date
    29th October 2003 - 21:14
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    1999 Suzuki SV650S
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    Rear suspension linkage calculator

    Here's a spreadsheet I've put together to help understand changes to the rear suspension. It's for bikes with a 4 bar type linkage like my bandit 400 and sv650.
    I thought I'd tidy it up and post it on here in case anyone else found it interesting.

    I made it using OpenOffice, but I've saved it as an Excel spreadsheet also only it seems in the Excel version some of the formatting was odd - the linkage graph labels had changed and one of the lines went missing. There's also a pdf with the calcs to help understand it.

    I got most of the measurements for my bandit and sv by taking a photos (zooming in and standing far away hopefully helped to reduce the distortion) and then importing them into a CAD program and taking measurements.

    Here's the link:
    http://cid-b37a983fa606d24a.skydrive...se.aspx/Public

  2. #2
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    13th September 2012 - 06:41
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    yamaha tzr250
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    I wouldn't normally dig up a thread this old, but it looks like the author is still around and this calculator is very very useful!

    So Erik, can you explain the calcs a little further? My first question(s) is a simple one...

    What does the three capital letter convention mean? Is FAD the angle between the two links FA and AD?

    and also what does the capital 'X' stand for?

    I would like to adapt this sheet to handle a linkage with only 2 links, so i can analyse the TZR250 2ma linkage that i race (similar to the pic attached). i need to understand it before i can change it.

    Thank you
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  3. #3
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    29th October 2003 - 21:14
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    Yes, FAD is the angle from line AF to line AD. For angles beginning with X, the angle is from a horizontal line running through the first point. Counterclockwise angles are positive, clockwise are negative (eg angle DAC between the swing arm dog bone attachment, swing arm pivot and rear axle is negative for the bandit but would be positive for your TZR).

    I think you shouldn't have to modify any of the calcs for the TZR. From your photo it looks like the same bolt mounts the dog bones and shock to the lower linkage, so if you set lengths FH and HK the same and the angle FHK to 0, that should be correct.
    You'll probably want to un-protect the sheet and change the x-axis minimum to -100 or so, so that point H is still on the chart.

    I'm glad someone has found it interesting/useful.

  4. #4
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    13th September 2012 - 06:41
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    Thanks for your explanation Erik, that makes much more sense. Your spread sheet is exactly what I was after.

    A bit of background.
    I race a 1986 Yamaha TZR250 1KT in a series called the Yamaha Past Masters here in the UK. There are two types of linkages on these bikes (1KT & 2MA/2XT). They also suffer from ground clearance issues in standard form, so they are 'jacked up' in different ways depending on the linkage.

    These little bikes handle great, but I reckon the rear could be improved. When pushing on, it can wallow a bit, and this has left me thinking if there is anything that can be done to alter the linkage to improve this. I've always been intrigued to find out if there is a difference between the two linkage types (I have the early style), or if the linkage is super progressive to allow for a pillion.

    Here's the bike in action
    https://www.youtube.com/watch?v=aO0keMiR9L0

    Cheers
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  5. #5
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    10th December 2009 - 22:42
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    ...cool bit of racing...

  6. #6
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    13th September 2012 - 06:41
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    I drew up a quick and dirty model of the linkage at lunch today. The image attached shows the plot the your calculator, overlaid on the original image that I used to get dimensions. I'll measure up the linkage properly after I better understand the result.

    I guess I'm aiming for some results to compare this data
    http://www.promecha.com.au/leverage_linkages.htm

    The first is the lever ratio, which I assumed is [force at shock/force at wheel]? Although a ratio of 4 seems high, and the leverage looks like it tails off...
    But that could make sense, as the the spring is stiffer than the SV (10.5kg/mm).

    It's early days, ill keep researching
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  7. #7
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    29th October 2003 - 21:14
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    Nice start, it looked like a perfect day for a race.

    The leverage ratio is [force at shock/force at wheel] or (change in suspension travel)/(change in length of shock), but neither of the graphs in my chart show that. I've added a new spreadsheet with a graph to show it: https://1drv.ms/f/s!AkrSBqY_mHqzkUv6BU2f2tnXB4zU

    Most of my measurements for the bandit and sv were from photos, so I'm not sure how accurate they are. I posted this on svrider.com and someone replied saying the shock mount was 35mm out, which is a bit hard to believe but may be true. But don't read too much into it if you compare your results to those from the bandit and sv.

  8. #8
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    5th May 2022 - 21:56
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    Modification of equations?

    Hi Eric,
    found your very nice worksheet through a websearch. Registered here although I come from the opposite side of the globe, hope this is no problem.
    I try to optimize the rear suspension of my 2010 Triumph 675 and have several different link parts on hand. I want to save time mounting the different link plate and dogbone combinations and measure the travel(s) in hundreds of positions, so I tried to finde an appropriate excel sheet in the web.
    Unfortunately math is not really my friend!

    Due to differences in the construction of the rear linkage between Triumph and Suzuki I could not use your sheet. Because the lack of knowledge in math and geometry i am not able to modify the equations in your sheet to fit my demands. I kindly ask if you'd do this for me. Attached you find information about "my" suspension linkage, that hopefully will be sufficient.

    I' be very glad for your help!

    Thanks in advance.

    Greetings to NZ
    Dirk

    Click image for larger version. 

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  9. #9
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    29th October 2003 - 21:14
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    Hi Dirk,
    I'll have a go at modifying it tomorrow morning.

  10. #10
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    29th October 2003 - 21:14
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    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.

  11. #11
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    25th March 2004 - 17:22
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    Hi Dirk. Have you got the 675R? If so the real issue is the 12kg spring fitted and the rebound damping to match. If you are less than say 120kg then a 10kg spring and a revalve will make the bike really quite good.
    Don't you look at my accountant.
    He's the only one I've got.

  12. #12
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    5th May 2022 - 21:56
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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.
    Hello Eric,
    thank you so much! This is very helpful. Sorry for the late answer, but I'm short on time right now. It's mother's day....
    I'll check and measure everything and contact you soon.

    Best regards
    Dirk

  13. #13
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    5th May 2022 - 21:56
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    Measurements

    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,

    The wheel Axle is 315mm from the ground, The swingarm pivot 411mm. The distance from the axis through the wheel axle and swingarm pivot to D (where the linkplates are connected to the swingarm) is ~55mm. My equipment for this kind of measurment is not the best.

    Thanks again!

  14. #14
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    5th May 2022 - 21:56
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    Triumph 675

    Quote Originally Posted by F5 Dave View Post
    Hi Dirk. Have you got the 675R? If so the real issue is the 12kg spring fitted and the rebound damping to match. If you are less than say 120kg then a 10kg spring and a revalve will make the bike really quite good.
    Hi Dave,

    it was standard originally, but I got hands on a Ohlins TTX from a later Daytona 675 which was equipped with a 10kg spring. Now I drive a 8.5 kg spring which works better. I'm 75 kg with gear.....on the light side.
    But the rear is still unsensitive and I try to get better feedback and grip.

    Best regards

  15. #15
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    25th March 2004 - 17:22
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    So. . . Have you serviced the linkage and checked Swingarm moves freely? Wouldn't be the first time.
    Don't you look at my accountant.
    He's the only one I've got.

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