KTM USD forks for r80gs

Discussion in 'Old's Cool' started by cgoodwin, Jul 17, 2009.

  1. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Does anyone know which KTM USD forks can be made to fit a 1983 R80GS???
    #1
  2. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Any idea where I can find triples like these, I have fouynd several sets of KTM USD forks but do not really know which ones to get and judging from the caliper mounting differences, I would rather know for sure than spend money on forks I can not use. Distance between forks, caliper mounting, fork diameter....
    #2
  3. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    #3
  4. Airhead Wrangler

    Airhead Wrangler Adios Mexico

    Joined:
    Mar 4, 2008
    Oddometer:
    6,659
    Location:
    Back in Seattle, FINALLY
    I wouldn't buy KTM forks and plan on using the beemer wheel and brakes. You're better off replacing the WHOLE front end. WP USD forks are going to jack up your front end quite a bit. Have you looked at lengthening your swingarm and also hopefully reinforcing your frame for using longer forks?
    #4
  5. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    #5
  6. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Yes, the frame reinforcements are basic and well outlined in the last post I referenced, I have a complkete fab shop and plan on making patterns for the front frame/steering head plates then welding them in as well as the swing arm pivot point reinforcement.

    Any idea which fork set is most easily adapted???

    I am going to cut a spare mono I have and add 100mm, then have the shaft lengthened similar to what was done here.

    http://www.advrider.com/forums/showthread.php?t=467221

    and here

    http://www.stephenbottcher.net/BMW/R100ST_2.htm#extension
    #6
  7. Airhead Wrangler

    Airhead Wrangler Adios Mexico

    Joined:
    Mar 4, 2008
    Oddometer:
    6,659
    Location:
    Back in Seattle, FINALLY
    Both touratech and HPN sell kits to fit the WP 4860 forks which are used on the KTM 640 950 990 Adventures as well as many others.
    #7
  8. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Here is a photo of a similar extension from a company in Europe

    [​IMG]
    #8
  9. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    I can find nothing for the early r80gs in the touratech catalog... Got a link?
    #9
  10. Airhead Wrangler

    Airhead Wrangler Adios Mexico

    Joined:
    Mar 4, 2008
    Oddometer:
    6,659
    Location:
    Back in Seattle, FINALLY
    You also might consider reinforcing the shock mounts, both on the frame and the swingarm.
    #10
  11. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    #11
  12. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    It appears that the BMW R1200C had a monolever that was 90mm or 3.54" longer, similar to the HPN which was 100mm or 3.94 longer, I wonder if I can just find one and swap it out???

    From http://www.raditude.com/bmwboxer.htm


    Extra-long Monolever instead of the Paralever. Apart from the lower angle of the Telelever fork, the rear-wheel swinging arm extended in length by 90 mm or 3.54" also contributes to the much greater wheelbase of the BMW R1200C. Since a long swinging arm is just as efficient in balancing the reaction of the shaft drive as a short, but more complex double-joint single swinging arm, the BMW Paralever, BMW’s suspension and running gear experts have chosen a longer version of the original single swinging arm, the BMW Monolever, for the R1200C for reasons of function and design. Here, too, smooth and superior suspension is ensured by a central spring strut with a single-sleeve gas-pressure damper mounted on the swinging arm. Yet a further feature is that pre-tension of the coil spring may be adjusted mechanically according to load conditions, spring travel being exactly 100 mm or 3.94".


    Looking at images, it appears to be a paralever bike some years, and mono others...????
    #12
  13. Airhead Wrangler

    Airhead Wrangler Adios Mexico

    Joined:
    Mar 4, 2008
    Oddometer:
    6,659
    Location:
    Back in Seattle, FINALLY
    One big thing those FJ forum guys missed: The other reason that driveshaft splines need to be able to slide (apart from swingarm travel) is that whenever a UJ rotates with a bend in it (ie the two segments are rotating non-coaxially) the shaft lengthens and retracts at the joint with every half rotation. This inherent behavior of universal joints intensifies with sharper angles. If the splines don't slide smoothly, you're putting a rapidly pulsating load on your UJ's bearings.:eek1


    Although I will encourage the destruction of as many R1200Cs as you want, I'd stick to the known good solution for this. Reinventing the wheel like that brings a BUNCH of unknowns into the equation such as swingarm pivot bearing spacing, final drive attachment, driveshaft fit, shock mounting points, etc.
    #13
  14. Solo Lobo

    Solo Lobo airhead or nothing

    Joined:
    Mar 16, 2004
    Oddometer:
    9,241
    Location:
    Shoreline, WA
    Three answers here...

    1. Pick the best forks - one with both on-the-fly tuneable comp and rebound and use the complete front end off of a KTM.. pay somone to shorten and tune the forks... loose steering lock using the stock KTM 18mm or 20mm triples..

    2. Buy the triples from Boxer toko that go with 1999 and 2000 KTM conventional WP "Extreme" 50mm forks and be able to use the stock wheel, headlight bucket, etc (I think)

    3. Contact member HPMGuy to have him make another set of R-Dubb's custom triples that can be machined to run the Extreme's or the modern KTM USD's...
    #14
  15. Solo Lobo

    Solo Lobo airhead or nothing

    Joined:
    Mar 16, 2004
    Oddometer:
    9,241
    Location:
    Shoreline, WA
  16. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Stock from the BMW?
    #16
  17. Solo Lobo

    Solo Lobo airhead or nothing

    Joined:
    Mar 16, 2004
    Oddometer:
    9,241
    Location:
    Shoreline, WA
    No, it's an aftermarket BMW guy in the netherlands...

    http://bmwboxersupplies.com/

    click on the "stainless steel modifications" link to see the triples
    #17
  18. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Wow, he is proud of those! I contacted HPMguy to see what he is offering. Ebay is full of KTM forks for cheap. It looks like making an aluminum 100mm space is simple enough and lengthening the driveline should be straight forward.
    #18
  19. Solo Lobo

    Solo Lobo airhead or nothing

    Joined:
    Mar 16, 2004
    Oddometer:
    9,241
    Location:
    Shoreline, WA
    Remember to take off the 19% VAT so $638 plus shipping ... when HPNGuy made fie or eight sets of these for R-Dubb, I think they were around $500-ish...

    roadsacallin used a set and put the WP 50mm's onto his G/S and is making his way around the world right now.
    #19
  20. cgoodwin

    cgoodwin Adventurer

    Joined:
    Sep 17, 2006
    Oddometer:
    96
    Any idea what bikes the 50mm units come off or if there is a thread about roadsacallin
    #20