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Thread: Anti-dive Springs

  1. #1
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    Question Anti-dive Springs

    My 78 RS has a spring instead of the rubber bumper thing inside the bottom of the forks. i think this is what is called an anti dive spring. Anyone know where these can be had?

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    do you know the history of the bike?

    iirc,

    there should still be rubber/plastic bumpers. but often they have disentegrated and "disappeared"

    stan at rocky poiint cycles sells a good value fork rebuild kit

    the anti-dive kit was aftermarket from luftmeister? or someone -- not sure if something similar its still available.

    some try progressive springs, but often find them too harsh, others prefer stock BMW heavy duty.

    hope that helps

  3. #3
    shire2000
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    There used to be springs that were sold as "Anti-Dive" springs. I think that you are right that Luftmeister marketed some, along with some others. I had some in an RS and they were OK, but nothing great.

    In my opinion, which may not be worth much to some, the best fork setup for airheads for the way I ride is Progressive springs and 7.5 weight oil. I add 10cc more oil than what is stock. It seems to work well for me. I have used it in all my airheads, R100RT, R100RS , R80/7, R75/5, R100/7. The only one I have not put progressives in is my R45. I imagine I could as the forks are the same as an R65, but the bike just does not go fast enough nor get used enough to warrant it.

    The caveat to the above setup is for the way I ride, which may not be at all like the way you ride. You have to find wat works best for you.

  4. #4
    Focused kbasa's Avatar
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    I use a 1" section of PVC pipe as a preload for the springs. It still allows ample travel and isn't harsh, but dissipates much of the brake dive airheads are famous for.

    You can tune the PVC to a length that works for you pretty easily. Start with about an inch and a half, then tune it until you get the amount of dive and ride quality you like.
    Dave Swider
    Marin County, CA

    Some bikes. Some with motors, some without.

  5. #5
    airhead butcher
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    a set of progressive fork springs and some 10wt will transform your frontend.

  6. #6
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    I think I will try the Progressive in the RT.

    I liked the idea of the spring instead of bumper in the bottom, since then you don't get all that pulverized crud clogging damper holes etc

  7. #7
    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by ducatipaso View Post
    a set of progressive fork springs and some 10wt will transform your frontend.
    +1 on the heavier fork oil, but going to a straight rate spring appropriate for your weight and riding style gets rid of that bouncy suspension stuff. I really loathe progressive rate springs.
    Salty Fog Rally 2007, 2009, 2011, 2012, AND LOOKING FORWARD TO 2014!

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  8. #8
    Dances With Sheep GREGFEELER's Avatar
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    The older Airhead forks have a lot of dive in them. After '87 or '88 BMW used the K-bike forks which don't dive nearly as much.

    IMHO, the way to set up these forks is in three parts:
    1) Get some new BMW HD springs, or Progressive springs.

    2) Set the preload with a spacer to archive a static sag of about 25% to 35% of total travel. Suspension has to be able to absorb bumps (unused travel) and also drop to follow dips in the road (sag). Be sure you also set the sag on the rear shock to match.

    3) Start with the stock 7.5wt fork oil of the correct amount, and then experiment. Add more oil to reduce dive on *hard* or *quick* stops (in 10cc increments up to a max of 50ccs). Use a heavier oil to firm up the fork dampening over the range of normal travel (normal bumps in the road).

    This last part will take some time, but it's amazing just how good your forks will work many times after some trial and error with oil weight and amount.
    Greg Feeler
    BMW MOA Director & Ambassador
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  9. #9
    airhead butcher
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    Quote Originally Posted by tommcgee View Post
    +1 on the heavier fork oil, but going to a straight rate spring appropriate for your weight and riding style gets rid of that bouncy suspension stuff. I really loathe progressive rate springs.
    im fortunate that i have the lightest R bike evar, and I weigh in at only 165 so progressive is nice for my setup

  10. #10
    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by GregFeeler View Post
    The older Airhead forks have a lot of dive in them. After '87 or '88 BMW used the K-bike forks which don't dive nearly as much.

    IMHO, the way to set up these forks is in three parts:
    1) Get some new BMW HD springs, or Progressive springs.

    2) Set the preload with a spacer to archive a static sag of about 25% to 35% of total travel. Suspension has to be able to absorb bumps (unused travel) and also drop to follow dips in the road (sag). Be sure you also set the sag on the rear shock to match.

    3) Start with the stock 7.5wt fork oil of the correct amount, and then experiment. Add more oil to reduce dive on *hard* or *quick* stops (in 10cc increments up to a max of 50ccs). Use a heavier oil to firm up the fork dampening over the range of normal travel (normal bumps in the road).

    This last part will take some time, but it's amazing just how good your forks will work many times after some trial and error with oil weight and amount.
    I agree with all of this and the K75 I picked up in May went through most of the process, however, what you're doing in this process is compensating for the progressive rate spring coil. Progressive rate springs are still terribly bouncy and the front end dives too much before getting to the part of the spring stiffness curve that is appropriate. Progressive rate is old technology.

    I went to 1.0Kg/mm straight rate springs on my Vstrom and that's the way I want the K75 to feel -- a good solid front end without any of that goosey handling or brake dive. I'm sending one of my old OEM BMW springs to Sonic Springs in Oklahoma so he can match it up size-wise with a straight rate replacement.
    Salty Fog Rally 2007, 2009, 2011, 2012, AND LOOKING FORWARD TO 2014!

    -Tom (KA1TOX)

  11. #11
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by tommcgee View Post
    I agree with all of this and the K75 I picked up in May went through most of the process, however, what you're doing in this process is compensating for the progressive rate spring coil. Progressive rate springs are still terribly bouncy and the front end dives too much before getting to the part of the spring stiffness curve that is appropriate. Progressive rate is old technology.

    I went to 1.0Kg/mm straight rate springs on my Vstrom and that's the way I want the K75 to feel -- a good solid front end without any of that goosey handling or brake dive. I'm sending one of my old OEM BMW springs to Sonic Springs in Oklahoma so he can match it up size-wise with a straight rate replacement.
    Let me know what he comes up with for you in a straight rate spring. I have two K75's and wouldn't mind trying this approach.
    Greg Feeler
    BMW MOA Director & Ambassador
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  12. #12
    Registered User PHMARVIN's Avatar
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    Hi,
    I bought a new '76 R90/6 in April, 1977. After riding it for a while, I thought the forks were too soft, so I bought an "anti-dive kit" from San Jose BMW. It included the springs (about 6" long) and a quantity of fork oil. I never used the fork oil, but I immediately installed the springs and was happy with the results. I sold the bike in 1984 (never should have sold it, but that's another subject) and I suppose, if the bike is still on the road, it still has the "anti-dive springs" in the fork lowers.
    Ride Safe,
    Phil Marvin - El Paso, TX
    '94 K75A/3
    '95 K75RTP

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