BMW G650XChallenge FRONT SUSPENSION

Discussion in 'Thumpers' started by lkongo, Oct 21, 2007.

  1. mikeysduck

    mikeysduck Slow Ride to Nowhere

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    Alpi , That's one of the eBay contact's I'm waiting to hear back from. Go figure. Either they don't know how to measure it, or business is so good they don't need us.

    It appears the TT ABS kit is no longer available. I would like a close look at some WP axle clamps. I would guess it could be drilled and tapped for a couple short 4mm bolts. This should allow a plate to be mounted to carry the ABS sensor. Maybe even use the fork guard lower mounting location. I need to see one in person.
  2. alpi

    alpi Adventurer

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    I have some doubts about that, given the # of sold vs. available is been like that ever since, more than 2 weeks ago... something is a bit fishy about that deal, unless there's something that keeps him from being able to answer (broken arms/neck... who knows). Oh, and he did promise to do measure them in his initial answer to my first contact: "Hi, not a problem, I will measure the diameters this afternoon and get back to you with some numbers - powersportsparts7777"

    Yeah, the site lists it as special order, which might mean they may still build one on order (I'll call on Monday to check directly), but the image seems to be quite revealing (found it on faq.f650.com), while I doubt the comments about the magnet and Reed sensor has anything to do with what we need:
    [​IMG]
  3. WayneC

    WayneC Long timer

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    From memory the magnet and reed sensor are for the TT road book/computer
  4. Colebatch

    Colebatch "Moto Porn"ographer

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    Depends what you are doing with it ...

    If you are doing enduro work on it then what Lukas suggested are about right.

    If you are doing adventure travel with it, or general purpose riding, then you want lighter. (KTM 950-990 Adventure use 0.48 and thats a much heavier bike - AND with less travel on their forks)

    I would recommend about 0.44 if linear springs. I used progressive springs from Hyperpro that started at about 0.42 and go up to about 0.56 later in the stroke
  5. alpi

    alpi Adventurer

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    Walter, you mentioned your front forks "4860s were from a 640 Adventure". I was wondering, how complicated was the adaptation in the frame head... I contemplating a front assembly (fork, triple, wheel, calliper) and I found out the triple neck length is 185mm with a 52mm inside diameter of neck tube. Does that sound similar to what you have ?
  6. Colebatch

    Colebatch "Moto Porn"ographer

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    The only issue was machining a new stem.

    You need the stem slightly longer for the XC than a standard KTM one (cant remember exact details ... maybe 5-10 mm) and it needed to be 28mm inside bearing diameter. The XC uses 28x52x16 bearings (which are quite common and easy to get at any bearing supplier) ... and a KTM stem is 29mm at the bearing points.

    You can get away with just machining down the KTM stem to 28mm but it really should have about an extra 5mm or so of length. Ideally get a machinist to make you a new stem.
  7. WayneC

    WayneC Long timer

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    The X steering head is the same length (185 mm) as the 650GS and the bearings on both are STD BMW

    The comments earlier in the thread that the 4357's slide into the X yokes suggest that the X yokes would be a bolt on to the GS for any GS owner looking to fit 4357's. Dependent on the stock X forks they may also be able to be used.
    I always wondered about the steering head and yokes on the X

    This would potentially make GS owners a market for those here who have swapped out to other forks. The sticking points would be yoke width and yoke offset, I have not seen any info on those or the axle diameter for the X

    Anyone have yokes lying around and willing to take some measurements, I have an accurate yoke offset calc on line
    http://www.f650gs.crossroadz.com.au/CalcYoke.html
  8. Colebatch

    Colebatch "Moto Porn"ographer

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    well the yoke (fork tube) spacing on the XC is 210 mm, and on KTMs its 190mm ... dunno what it is on G650 GSs.

    Either way its not a show stopper. Quite a few folks have put KTM yokes and front wheel (at 190mm ) onto the XC. I remember mesuring with Adv forks and EXC triple clamps, the offset was about 2mm less than the XC stock ... meaning the bike was (slightly) even more stable than stock.
  9. WayneC

    WayneC Long timer

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    Thanks for adding to the info

    The GS forks are 185mm c-c spacing and accurate offset is 21 mm, there are other less accurate offset figures floating round

    The c-c width of the XC forks at 210mm would seem to be a bit wide to fit the GS unfortunately, I dug around and also noticed the offset ignition lock mount, that could also add to the difficulties. It was worth checking the figures though
  10. alpi

    alpi Adventurer

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    After much deliberation, feedback from Jim @ Cycle Improvements and taking advantage of a visit south, I had my last change of mind in favour of WP 4860. This time is pretty final, as I just got them in for rebuild. They look a bit worn out, but I hope cleaning the sticker residue and changing the orange covers (with proper black ones) will fix some of that :bmwrider

    [​IMG]

    They were described as being "06 KTM 525 Exc forks, .48 springs installed and valved with race tech internals". Until the rebuild is done, I can only hope those mighty race internals (whatever that means) are in good shape.

    I also got the axle and calliper with bracket (as backup, as I knew the BMW calliper would have fitted). Next I need the complete triple clamp (got the lower one which is obviously not matching the upper stock one)... and an Excel A60 21" wheel :rolleyes

    Question is: can someone confirm the stock triple clamp offset (25 mm ?) vs acceptable KTM equivalent for 4860? Lukas was saying in #122: "KTM triple clamps have 20mm offset vs. the stock 25mm", but is that 5 mm variation in offset not without some instability consequences ?
  11. WayneC

    WayneC Long timer

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    Offest is a pain to accurately measure, I created an online system of accurately measuring it as I kept hearing different figures for both the GS and WP forks, An ancient greek's triangle calcs makes it all easy, you can use it here http://www.f650gs.crossroadz.com.au/CalcYoke.html
  12. alpi

    alpi Adventurer

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    Thanks Wayne!
    I was hoping, though, someone would have the official factory offset spec, as it seems the precision in measuring "Distance to Post" (51) and "Post Hole Diameter" (32) is very important in that algorithm (a slight 1mm variation can throw the offset value by some 30%)... I may not have the right tools to measure precisely :dunno


  13. WayneC

    WayneC Long timer

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    Yes, need a good vernier, WP stamp the offset on their yokes (18 & 20mm mostly) but other mfr's dont and the numbers quoted for the STD BMW yokes varied too widely between those measuring it, as did the the YZ figures quoted. The system I put online was the most accurate I could come up with and using a vernier I was able to get consistent figures cross checking the WP yokes I had access to and knew the offset for.
  14. gsstampeder

    gsstampeder Long timer

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    Need some advise from the wise...had my x-c in for fork seals and some other work and the tech called to tell me my left damper unit was pooched. The part from Max's is $350, plus shipping to me. Is there another solution? I'm not opposed to upgrading the forks with others, but I'm not sure of availability to locate replacement upgrades. Any suggestions?
  15. aprilian

    aprilian Can I change this?

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    ping inmate mbfj40, he had a complete set of forks for less than that one part.
  16. Colebatch

    Colebatch "Moto Porn"ographer

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    You have to measure the total offset ... not just the triple clamp offset. The offset in the axle clamps (perpendicular distance between the centreline of the fork to the centre of the axle hole) has to be added to the offset in the triple clamps.

    I remember when I changed 3 years ago from the BMW triples and BMW axle clamps to the KTM 20mm triples and standard KTM axle clamps, I barely noticed a difference ... the steering remained inherently stable. If anything, its even a touch more stable.

    From memory the KTM axle clamps have more offset (I think about 3 mm) than the stock XC ones (that largely countered the fact that the BMW triple clamp offset was 5 mm more) ... and so the total offset was different by only 2mm (less offset via the KTM setup).

    Less offset = more trail = more stability, so the 2mm less offset (total offset) in the KTM setup delivered more stability to the front wheel.
  17. gsstampeder

    gsstampeder Long timer

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    Thanks, I checked the thread and I believe his forks came off an X=Country. I have an X-Challenge and I think the travel is less on an x-country....????
  18. Colebatch

    Colebatch "Moto Porn"ographer

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    X-Challenge has 270mm fork travel
    2007-2008 X-Country has 240mm
    2009 X-Country has 220mm
  19. Bli55

    Bli55 -

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    I thought (and read, and measured) it was 280 for xchallenge...
  20. mbfj40

    mbfj40 Been here awhile

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    That mbfj40 guy has both a set of XCountry forks with 232mm (9.4") travel and a set of XMoto forks with 270mm (10.6"). Numbers from BMW sales brochure. It also implies that XMoto and Xchallenge travel is the same.
    BMW Microfiche calls out the same part numbers for the XChallenge and the XMoto for the damping units:
    31427708795- Damper unit, left
    31427708796- Damper unit, right

    mike :-)