Thinking about making my own leading link forks

Discussion in 'Hacks' started by val. h., Dec 27, 2011.

  1. val. h.

    val. h. On the wrong planet

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    Is there anyone here who can help me with geometery questions? I'm thinking about making leading link fork for my outfit, but I'm not sure how much or little trail I should build in to them.

    From looking at various different types of sidecar forks it's unclear as to the correct amount the axel needs to be moved forward. Some seem to have as much as six inches and others seem to have no more than an inch. Why might this be?

    I want the steering to be light enough for my other half to to be able to ride the outfit easily, as well as being sutible for mild off road use. The outfit is an R80 with a Velorex chair.

    Your advice is much appriceated.


    Val.
    #1
  2. toastmuncher

    toastmuncher I be new round here! Ello

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    Might I ask where you be?
    There is a sticky at the top of the hack page which may help with your dimensions.
    #2
  3. val. h.

    val. h. On the wrong planet

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    Thanks I'll have another look. see if I can make any sence of it.

    I'm about fifty miles up the M4 from you, in Wiltshire.



    Val.
    #3
  4. val. h.

    val. h. On the wrong planet

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    Well I've read about half of the thread and although it's very interesting and usefull for someone building an outfit from scratch. It doesn't actually answer my questions.

    I know that leading link forks are made/set-up in different ways to suit different driving conditions. But what I don't know is what amount of trail is cood for what I want to do with the outfit and what is likely to be wrong. I don't have a lot of cash I can throw at the project inorder to find out by trial and error, so any advice would be valuable.

    I'd like to achieve a set up similar to that of the 750 Urals built after 2003, as my outfit is of a very similar type (BMW R80) and I'd like to be able to use it in a similar way to that of the Urals. IE gental touring and light off road.

    Does anyone know how much trail the Urals have?


    Val.
    #4
  5. nieppi

    nieppi Been here awhile

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  6. nieppi

    nieppi Been here awhile

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    And here is pick just for leading link
    [​IMG]

    Sent from my HTC Vision using Tapatalk
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  7. val. h.

    val. h. On the wrong planet

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    Thanks for that nieppi, looking good. How did you work out where to put the front axel? Did you just measure it to negetive trail or did you leave some trail in? If so how much and why?

    Have you used any bushes or bearings in the pivot point?


    Val.
    #7
  8. Salsa

    Salsa Been here awhile

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    I built a set in 1970 and put extra adjustment attachments for the trail and for shock position. I would make one the same as the stock position and one the same as a Ural or other hack and one in between if you can.

    Don
    #8
  9. cleatusj

    cleatusj Dirt floor engineer

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    On my '76 Guzzi I moved the axle forward 1and 5/8 inch. This reduction has worked well for me.
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  10. val. h.

    val. h. On the wrong planet

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    Thanks Cleatusj,

    How did you come to that measuement? was it a percentage of the total length as sugested in the 'Sidecar Design Formula' thread or another method?


    Val.
    #10
  11. largemouthbass

    largemouthbass Adventurer

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    I am also wanting to build a set of leading link forks and wondering what is typically used for bearings at the
    pivot point? Needle bearings are what I am considering so far as that is what is usually used in the rear swingarm.

    This will be for my 95 KLR 650 with a DMC Enduro hack using 08 triple trees and one and five-eights x three sixteenths chrome-moly as the fork legs.

    Any useful information would be very appreciated. :ear And yes I already used the search function.
    #11
  12. cleatusj

    cleatusj Dirt floor engineer

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    Val, I read that section and every build tread in this forum and some where along the way that figure stood out, so I used it.

    LMB, I used bushings from a 350 Honda and cut down two swingarm bolts from the same model.

    Here's a link to my build. http://www.advrider.com/forums/showthread.php?t=648570
    #12
  13. jaydmc

    jaydmc Long timer

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    Our links are double wall tubing using .120 wall DOM tubing. We pivot the links on ball bearings, for most links there are two on each fork leg. For the 08 KLR 1.5 inch tubing is slightly to small so we make shims, 07 and back tree's 1.5 inch tubing fits well. For the BMW links depending on year the upper tree can be a bit tricky to attach to, We thread the upper part of the tube and make a shim/washer/spacer that we bolt through the tree's using a 1/2 inch bolt. If the BMW uses ATE brakes we convert them to Brembo like the newer BMW's the problem here is if the bike has wire spoke wheels the rotors must be spaced out. If it has snow flake type or lester's then no spacing is needed. There are a couple of photo's of our links in the hack venders section, one under custom link and other posted in the build for the BMW F800GS. The F800GS has floating calipars which is nice as you can set the front end to either climb, dive or stay level depending on how the tie back links are built.
    Jay G
    DMC sidecars
    www.dmcsidecars.com
    866-638-1793
    jay@dmcsidecars.com
    #13
  14. jaydmc

    jaydmc Long timer

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    How much trail you want depends on how you are going to use it, Very little trail and it can be a bit of a handfull at speed, to much trail and it steers heavy. On my wifes R100S that she had for a while I set the trail at 1.2 inches. This was very nice with the short bars the bike has. On my own R100/7 that I had for a while, I set it at 2 inches which worked well for me. Stock depending on the R80 is about 4.2 inchs
    Jay G
    DMC sidecars
    #14
  15. NortwestRider

    NortwestRider TRIPOD ADVENTURER !!

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    I'm getting ready to build my own LL's and I'm going to use a swingarm of a old twin shock bike.This kills 2 birds with one stone.I get bushings/bearings for the pivot point and I get adjustabilty for trail ( chain adjuster) .Gordon Scott did this and I thought it was a good solution!!!.
    #15
  16. largemouthbass

    largemouthbass Adventurer

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    val. h. I have the same needs in design as you... light enough steering for the little women...some light touring 50 - 60 mph... and capable of handling the Black Dog Rally. Have you settled on a trail dimension what about shocks?

    If I had to start building today I would extend the axle 2" reducing the trail to 2.2". And I am looking at shocks from early models of ATV's from around 1999 to 2004, these years seem to be smaller in overall diameter than newer ones. Wish I could actually be of some help to you but since I've started this "easy project" I feel I've got a lot more to learn than I thought. Some of my original ideas need a lot of tweaking. But I won't let ignorance get in my way :D
    Thanks to all of you who have contributed your experiences and ideas.
    #16
  17. val. h.

    val. h. On the wrong planet

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    I have a cunning plan:

    I will be keeping the front forks in place but adding a rocker arm that will run under the fork legs and place the spindle forward in the same manor as the LLs would. The rocker arm will extend behind the wheel and be linked to the bottom yoke (or there abouts) with two link arms.

    This will do 3 essential things for me. 1, It will allow me to rais the hight of the front end. 2, It will give the bike greater suspension travel. 3, It will save me the search and extra cost of the replacement front shocks. I'm also looking into raising the rear and the sidecar suspension to keep things level and making best use of the increased ground clearence.

    I've been thinking about this for some time and even thought that it was only me who had thought of it. I couldn't believe that no one else had tried it before. Just like Triumph tested the oval pistong thirty years before Honda got it to work. Then I found the attached photo (no not the amazing two drive BMW). Have a close look at the V-Max on the right. I've since been passed a few more examples in discussions off site, which has convinced me that this is worth a closer look.

    Val.

    Attached Files:

    #17
  18. NortwestRider

    NortwestRider TRIPOD ADVENTURER !!

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    Food for thought !!!!!!:freaky

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  19. val. h.

    val. h. On the wrong planet

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    Hmm, I'm a bit sceptical of using the brake and fender bosses to support the front wheel. Stresses and extra ware in the wrong places etc. Especialy as I intend taking the rig off road 'all be it very gental off road'. I've no intension of turning it into any sort of rally rig. I'm just going to give it a bit more ground clearence and a tiny bit extra front suspension travel.

    The advantage of extra suspension travel and the fact that the forces from the front wheel will go where they where desined when using the original forks is I think an imoprtant consideration when doing something like this. Keeping it passive IMO keeps it reliable. My budget is small, I'm also interested in things that are not the norm. If I build full on LLs I will be forced to use cheap or very old, well used secondhand shocks. I recon the the forks as fitted will be better (cheaper to rebuild even) than anything else out there that I can buy within budjet.

    Heres a better pic of what I intend to do. You can see that the lower rocker arm is supported directly on the original spindle point and that at the back of the arm the tie rods support the arm so that it moves up and down along the normal fork travel. Changing the shape of the rocker arm and the length of the tie rods will create an increase in spindle travel compared to the fork travel.


    Val.

    Attached Files:

    #19
  20. leejosepho

    leejosepho Sure, I can do that!

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    At least in theory, some stronger springs could be necessary here, but I think you have a good plan. I also like the idea of hacking unconventionally on a tight budget and will now be taking a new look at my own forks with your plan in mind after the sun comes up!
    #20