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F800GS - RXV Shiver'ed Fork Conversion

Discussion in 'Parallel Universe' started by Gangplank, Jul 25, 2010.

  1. Gangplank

    Gangplank Advenchaintourer

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    This.

    Take one donor fork leg & the bottom damper unit to machine shop along w/ both BMW fork tubes. Ask them to make it so the bottom unit fits in the BMWs.
  2. rem47

    rem47 Adventurer

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    Oh if life was so simple! Parts now with machine shop. He is a biker and he makes parts for old Triumphs, but he asks a lot of questions in response to "make it like that".:huh

    So critical dimensions:

    1)inner bore diameter which he has to measure from donor fork - my calipers are not long enough (about 28.5mm)
    2)depth of inner bore - has to be measured from internal face because the casting dimensions are so different between the BMW and RXV lugs. this seems not so critical (could be 8.5-9.0mm)

    I was thrown by the photos on page 1 of this thread which seemed to show the BMW damper tube much narrower than the RXV. They are very close the RXV tube is about 1/10 mm wider in diameter so should fit snugly.

    Thanks to the encouragement from you guys on this forum it gave me the courage to take apart my first set of forks without too much grief.
  3. Mconnell

    Mconnell Adventurer

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  4. rem47

    rem47 Adventurer

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    Interesting thread, thanks.

    I have got my forks machined now and ready to assemble. :clap

    From this thread and yours it seems like any spring rate of .55 up to .75 could be used if you have revalving, oil weights, air gap adjusted which should give similar results for "plush" off-road use.

    I am 110kg (250lbs) so I am thinking it would be best at the upper end of this range but there is not much off-the-shelf (UK) in this spring rate range other than the 0.55 ohlins and 0.6 bitubo.

    There is a supplier here k-tech who makes a .65 and .70 (OTS) for the Triumph 800XC, but it is only 445m long and has 269mm of stroke, and 1mm smaller diameter.

    Any reason why I should not use one of these? obviously need different preload spacer and the damper rod spacer to reduce the fork stroke to 230mm.
  5. motolab

    motolab Long timer

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    You can calculate the target rate from the current rate and the current span between unladen and laden sag.

    Regards,

    Derek
  6. rem47

    rem47 Adventurer

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    Thanks Derek - you mean along the lines of Sarathmenon:

    I think I must have incorrectly measured my sag as I got 67mm and 84mm to his 26mm and 76mm.

    If i use his free sag of 26mm and my rider sag of 84m then I get a spring rate of .80

    I dont know why he chose 10% and 25% of travel for his ideal. I was going to work on 10% and 30% which would give a spring rate of .60

    My local suspension guy is questioning why I would want anything stiffer than .55 saying that motocross bikes on big jumps are only using .55 max and though much lighter bikes he thinks for a plush off road ride with no intent to makes jumps would be better. (he does only stock the ohlins .55 which makes me a little suspicious but he is happy to fit a different spring if I choose)

    Back to my original question - I would still be interested to know if the shorter spring from theTriumph (regardless of rate) would be a problem.
  7. motolab

    motolab Long timer

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    I think a spring that is less than a mm smaller would be OK, but I don't know if I would install much smaller than that. Race Tech offers springs for the F800GS in .75, .85 and .95 kg/mm.

    Regards,

    Derek
  8. sarathmenon

    sarathmenon Armchair Adventurer

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    Also, my stock spring rate when measured was .485 or so. A significant difference from the .44 and .42s reported earlier. My bike was a 2012 model, built in 2011, probably the 2009s had softer springs. Why BMW would change it, I don't know. Maybe they got fed up of the people complaining about the soft springs. When I did the swap, I really didn't have much complains other than the nose dive. But after getting the new forks, I am much happier with the result, I didn't believe that this bike could be so good.

    Also, you may want to read up on Mconnell's thread where he explained the science behind his choice of springs. Basically, get the springs that put you in the ball park of sag that you want, and have it valved to your riding style. When in doubt, just go with what your suspension guy is telling you,.

    Although, 67 and 84mm for the sags does not seem to add up, where did you measure from? It's probably a moot point if your forks are already off.
  9. rem47

    rem47 Adventurer

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    Checked out Mconnells thread already

    You are right there is no point in me trying to tell a suspension expert how to do his job.

    Yeah the horse left the stable so no more measurements of sag. I measured stanchion from top of lug to dust seal front wheel off ground, then same with front wheel loaded, then distance from lug to zip tie after sitting carefully on bike. My bike is the same year as yours so I think your free sag and my rider sag make sense.

    Its easy to forget that I will actually have some adjustment anyway in the end.:thumb
  10. motolab

    motolab Long timer

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    To think rate through a bit further, Sarath weighs (or weighed) somewhere around 200 lbs. I measured the rate of the standard springs, which Sarath found unacceptable, at .48 kg/mm. Sarath had me install .55 kg/mm even though I recommended .60 to .65 kg/mm based on the difference between the unladen and the laden sag with the standard springs. .48 to .55 is not a very big jump. That said, let's just assume that the .55 kg/mm springs were correct for him, how can they be correct for one rider as well as one that weighs 50lbs. more?

    Regards,

    Derek
  11. sarathmenon

    sarathmenon Armchair Adventurer

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    Now that's with gear. I am not that fat :lol3
  12. rem47

    rem47 Adventurer

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    The way I see it is the only way spring rate is relevant is to ensure you achieve the correct difference in free and rider sag with a static bike. Where the sag happens can be determined by preload - within bounds. I am guessing that what happens when you actually ride the bike is governed by valving and fluid dynamics.

    There does not seem to be universal agreement regarding the % values for free and rider sag - Sarath went for 10 and 25% of travel, I have been steered by others to for for 10 and 30%. This vagueness can lead to big differences in theoretical spring rate than a difference in rider weight.

    It be a black arrt it be!
  13. rem47

    rem47 Adventurer

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    Yeah we are big-boned.

    Have you guys read the great suspension blog by Mark Lawrence http://motorcycleinfo.calsci.com/Suspension.html

    I love his quote:

    "In order to keep the motorcycle seat perfectly still no matter what, the motorcycle frame, engine, and rider should be infinitely heavy. Remember, next time you're out drinking beer, you're not drinking beer because you enjoy it, but to improve your suspension"
  14. rem47

    rem47 Adventurer

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    Well I have not done much polishing in the past 7 years and I found these tapered mop spindles are the perfect size 12.5mm ID and 19.0mm OD. Even come with a grub screw ready fitted. Just cut to length and drill through.

    I have decided to go with the 0.65 or 0.70 springs for the Triumph 800XC. As they are shorter I will need the spacer.

    Attached Files:

  15. Anti

    Anti Νέος

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    I‘ve managed to make this upgrade....... I found the shiver cartridges from eBay (Italy) at 70 euros and the whole operation/ change cost me 200 euros (machining, oil, parts etc.)- all together 270 euros... I think fair enough! The outcome, up to now, impressive..... it has been stiff, passes through anomalies smoothly and stable!!!!! And the breaking has been improved also!!!! I have to try it now off-road..... but I'm sure it will be better by far.........

    My only objection is that it stands a little bit higher about 1.5-2cm..... but it does not concern me that much....

    Few photos..... uploadfromtaptalk1409765711500.jpg
  16. Anti

    Anti Νέος

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  17. Anti

    Anti Νέος

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    Last one to how higher stands.... uploadfromtaptalk1409766009948.jpg
  18. sarathmenon

    sarathmenon Armchair Adventurer

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    Be careful about front end wobbles when you raise it that high. That was my primary problem because I am running it with no preload. I had to jack up the front end compression to make it work on the interstates
  19. Reaver

    Reaver How Did I Get Here?

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    Too much preload for your weight maybe?

    When I did mine it sat higher because my forks bottomed out in a higher place and the extended length was longer so I lowered the tubes 1 inch (25mm) in the clamp to get the factory ride height. You have the 20mm handlebar risers so you can still adjust the settings.


    [​IMG]
  20. Anti

    Anti Νέος

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    Which tubes did you lower (sorry for the silly question...)?

    The risers are 30mm, custom made at a machinery!

    But now operates much much much better! Impressively good.....