F800GS unstable at higher speeds

Discussion in 'Parallel Universe' started by Baiazid, Dec 17, 2012.

  1. Snowy

    Snowy Long timer

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    There have been a few postings that deal with this issue. ITSATDM found that lowering the front end cured it. As did I.

    After a complete front end change, to a front that is about 40mm taller, I found that having more, or less ride height in the front seems to stop the instability. The standard ride height in the front seems to be particularly susceptible to ride height changes in the rear.

    That's why putting your wife on the back fixed it. It's effectively made the steering angle much lazier than standard. Make the steering angle a bit quicker than standard by dropping the front end and you'll fix it too.


    For 2 up fully loaded travel I went to a Ohlins rear, revalved and resprung with a 23kg/mm spring - the heaviest they make.

    Solo I have no preload on it and I get about 60mm rider sag. With full preload and wife and gear I get 60mm. No instability.
    #41
  2. vtbob

    vtbob wanderer

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    Lots of advice here...some good but pretty far out

    If the bike was ok before you put the K60s on....it is HIGHLY probable that it is the tires or the mounting process.

    Let's face it semi knobby tires are NOT designed for high speed...as best they are just OK. If you have checked the balance, check to see if the wheel is true(side to side and around) when it rotates, is the tire true when it rotates. do you have proper tire pressure.
    PS also check your rear wheel and tire for true as well. tire inflation pressure.

    If these are all ok....then have fun exploring some more of the far out recommendations here
    #42
  3. machinebuilder

    machinebuilder Long timer

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    How did you decide where to put it?:ear

    This setting (setting rider sag) does affect the steering geometry.

    Think of the bike pivoting on the front wheel, if you raise or lower the rear of the bike (by adjusting your preload) you are changing the angle of the forks. If you get things at a bad spot it will be unstable.

    The owners manual has a procedure for setting your preload.:deal

    I found this out when I rode a KLR, they are severely undersprung for a 200lb person + camping gear. The headshake scared the crap out of me.:huh
    #43
  4. Snowy

    Snowy Long timer

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    Having used them, I'd say.....yeah...no.

    Likely the tyres have exacerbated a problem that was already there but not so noticeable.

    Tyre profile also plays a part here. In combination with rake and trail the wrong profile can make things go to shit very quickly.

    I just fitted a Pirelli Rallye front....it's shit on road. I mean, it works ok, but the profile is all wrong. Handles so much worse than it has with just about every other brand of tyre you can buy.

    Some of this is the tyre type, some the tyre profile, and some is a combination of the rake/trail and the weight bias.

    It understeers like a mutherfucker. On tar, on dirt. Very disconcerting. Once you get used to it, very predictable. But it's hard to get used to skating the front end through a gravel corner at 100kph with wifey on the back. But you can do it.
    #44
  5. Baiazid

    Baiazid Been here awhile

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    Yes, before these tires all was perfect.

    Cannot say it does bother me too much since I don't travel often with 120kmph. Usually I do 100kmph. But it is the idea that is something wrong ....
    #45
  6. Baiazid

    Baiazid Been here awhile

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    I will search for some tutorials and see what I can do about it

    This one is for ST, but can have a look:
    http://www.uthd.com/jeremy/f800st_config_metric.html
    #46
  7. itsatdm

    itsatdm Long timer

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    #47
  8. Baiazid

    Baiazid Been here awhile

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    #48
  9. itsatdm

    itsatdm Long timer

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    I really wish I had the anonymous internet to guide me in 1968 when I started riding. Instead I had to learn for myself. :gerg
    #49
  10. runnin4melife

    runnin4melife Been here awhile

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    It is a grand thing, knowledge at your fingertips, a plethora of porn for your viewing pleasure.... This is truly the golden age of man!
    #50
  11. machinebuilder

    machinebuilder Long timer

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    I just realised you're talking about 60MPH, That is not that fast. I don't balance mine and have never had headshake with the K60's on the F800GS. I have had it over 70mph with all my camping gear.

    If properly adjusting the preload, tire pressure (I run about 32PSI in the K60's on pavement) doesn't help, AND you are not confident of your abilitys, PLEASE get a good mechanic to look at this before something bad happens.
    #51
  12. itsatdm

    itsatdm Long timer

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    That is why the cashier at McDonalds can't make change.:roflProbably something simple like, the tire bead did not get seated properly.
    #52
  13. runnin4melife

    runnin4melife Been here awhile

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    Don't they spit out the change now? I had some girl recently that couldn't figure out what she owed me for $19.95, I gave her a twenty..... :rofl
    #53
  14. Reaver

    Reaver Outta Here

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    I'd have said "Keep the change, you'll need it for college." :D




    And now back to our reularly scheduled programming.
    #54
  15. Baiazid

    Baiazid Been here awhile

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    :rofl:rofl:rofl LOOL
    #55