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Thread: Girvin fork

  1. #76
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    Quote Originally Posted by smdubovsky
    I don't know that small fore/aft movements would affect braking much. The knobs/sidewalls/spoke windup/fork deflection probably dwarf it for a long enough arm. For short travel linkages maybe it needs to be factored in.
    Yeah, I don't know either. But it's the only thing that I've been able to hang any kind of criticism on, from a physics standpoint. SOMETHING must exist that makes people say "anti-dive locks out the suspension", but I don't know if it's just Internet Expert Syndrome, lousy anti-dive designs, or something real that just hasn't occured to me yet. I can find justifications in either direction for or against anti-dive.

    Right now I think I understand the generalized, idealized model of what's going on. Now I'm trying to poke my understanding here and there with more specific, detailed facets of the model.

  2. #77
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    Quote Originally Posted by dr.welby
    SOMETHING must exist that makes people say "anti-dive locks out the suspension"
    Thats because 99.9% of the forks out there implement anti-dive w/ a 'platform' damper (or some other old way that didn't work). Platform very much DOES lock out the suspension over small bumps. Telelever seems to be the only one thats ever gained mass acceptance into the motorcycle world. They even abandoned duolever for it so at least one company thinks its the best combination for their purposes. Many of the other leading/trailing arm designs have such short levers it prob causes other problems too.

    There are probably lots of the 'internet expert' opinions out there too Same ones that say brake jack is everywhere, using your front brakes will make you endo (anyone catch the 'tip' in bicycling mag this month), etc.

    What we need is a shock w/ a linear motor in the spring leg. Could vary the force and prevent dive like some of the new car suspensions are doing (though I think rover/merc/etc are using hydraulics in the sway bars for most of the anti-lean stuff). That coupled w/ rheomagnetic fluid in the other leg for active damping and you'd be good to go. Well, downhill at least. No way you could pedal all that heavy stuff up hills

  3. #78
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    Hey, is 'Anti-Dive' analogous to the way in that VPP 'minimises' the effects of chain torque and rider oscillation on the suspension system? ie: the fork linkage is configured in such a way to 'minimise' the suspension compression as a result of the brakes causing a massive weight shift to the front wheel?

    I'm just a lowly Industrial Designer, so the engineering is largely lost on me.

    Nobody commented on the USE S.U.B. fork, either.
    No longer member of the bike industry nor society, so don't hassle me.

  4. #79
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    So Walt, anyone get you a Girvin yet?

  5. #80
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    here just so evryone knows what a girvin looks like
    Quote Originally Posted by a stoned guy with a beer in his hand eyeballing your sisters bike
    "i fit my bike to fit me;not for looks...nice did you buy that bike from jc whitney?" Stoner Island 1984

  6. #81
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    just because this thread exists i had to think about the concept. if you make a dual crown with linear bearings. (like the ones used for cnc machines) you could still have the fork behave the same as a telescoping fork. you could make the shock move with the linkage instead. you know if you must practice , at least make something that will work. :P
    Quote Originally Posted by a stoned guy with a beer in his hand eyeballing your sisters bike
    "i fit my bike to fit me;not for looks...nice did you buy that bike from jc whitney?" Stoner Island 1984

  7. #82
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    How about the battery-powered piezoelectric damper that that fork came with?

  8. #83
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  9. #84
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    I didn't read every post, so maybe someone else has already mentioned this but....the Girvin linkage fork had an axle path that moved up and sightly back. As a result, on bigger hits, I sometimes felt like the bike would endo easier. This was especially true on large stair type drops, and any time you jumped the bike and landed front wheel first by accident.

    The other thing that I remember with mine, was actually how loose the linkage assembly would become after hard riding. look at the photo above. The linkage is made up of several smaller pieces bolted together. That was the Vector model. I replaced my Vector with what I think was called the cross link model. It was pretty cool, and came with carbon fork blades, and a noleen coil shock. That fork was stiffer because I believe it used a one piece machined linkage assembly, instead of smaller pieces bolted together. However, it still felt endo prone to me because the fork compressed up AND back at the same time.

    Another linkage fork from the era was the AMP Research, but it was pretty much junk, and people broke those easily on anything rougher than fire road.

  10. #85
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    Not mtb, but still an interesting example of a Hassock design on a small scale.

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    John Brittens's front end worked very well to come out of nowhere and smash factory super bikes in Daytona. RIP JB. Very advanced fork tech for its time. When road bikes start taking on full suspension, this could be the way to go for short travel front end.
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  12. #87
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    Quote Originally Posted by NonConformist
    Not mtb, but still an interesting example of a Hassock design on a small scale.
    Is that by Dave Wrath-Sharman/Highpath?

  13. #88
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    Quote Originally Posted by Freddy Salgado
    John Brittens's front end worked very well...
    The front end was considered the worst part about the britten, I belive. Most people that I've heard from say that it was going to be ditched in favor of a traditional telescope.

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    The front end of the Britten, was likely it's worst part.
    Last edited by frascati; 09-25-2009 at 08:34 AM.

  15. #90
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    Quote Originally Posted by pvd
    The front end was considered the worst part about the britten, I belive. Most people that I've heard from say that it was going to be ditched in favor of a traditional telescope.
    Ya the front end could have been the worst part, but it still smoked the factory rigs at Daytona! Guys like Britten think so far outside the box that who knows what that bike and front end could have been capable of?

  16. #91
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    You may want to add the caviate that the Britten did well in BoTT. Superbike is a different story.

    Don't get me wrong, Britten was amazing, but he hasn't been the onlyguy working on new things. His bikes had flaws, they never got fully developed, and we see little relection of what he did on bikes today.

  17. #92
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    The Britten fork looks like it could have been too stiff laterally. Sport bikes need flex designed into the chassis and suspension, b/c they require some semblance of suspension when banked at 60*. For a mtn bike, that's not necessary nor desirable.
    Too many bikes, not enough time.

  18. #93
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    Little bump on the British design 'U.S.E. SUB" fork from a few years ago.



    It didn't really catch on but was a nice piece of innovation in the mtb world.

    Walt. Did you get anywhere with this project yet? Really interesting thread.

  19. #94
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    I've now got 2 of the darn things...

    First step, I think, will be to just build some new legs for one of them with a thru-axle and disc mount. We'll see how that rides. Depending on how atrocious it is, I may or may not do one from scratch.

    I'll probably talk about this "project" on the blog, when I get around to doing some actual work on it.

    -Walt
    Waltworks Custom Bicycles
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    www.waltworks.com
    waltworks.blogspot.com

  20. #95
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    I would suggest further modding the fork to incorporate some proper bearings on the linkage. Its bound to improve it.

  21. #96
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    here a auction with a girvin i found on ebayhttp://cgi.ebay.com/PRO-FLEX-856-WOR...Mountain_Bikes
    Quote Originally Posted by a stoned guy with a beer in his hand eyeballing your sisters bike
    "i fit my bike to fit me;not for looks...nice did you buy that bike from jc whitney?" Stoner Island 1984

  22. #97
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    Good job!

    Ribi designed one for Roger Decoster when he was at Suzuki then revisited it again as in the pic in the thread above when R D was at Honda. Excuse was too expensive to make, but it was never said R D didn't like it!

    Build away Walt you might be onto something... Just do it with 13 inches of travel to make DC happy!!!!!!!!!

    Sorry DC I had to say it cause I know you will...

  23. #98
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    look up the muddy fox interactive ... from 1996 / 1997 designed by ... dave smart (I think).
    G-EVO

  24. #99
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    Bimota's Tesi 2D and the Vyrus 984C3 2V and the 985C3 4V have hub steering.
    (hopefully the attached pic will show...)
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  25. #100
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    first post so please pardon any forum faux pas!

    A quick intro is perhaps in order? I live in NYC and have been lurking here on MTBR for quite a while, finally broke down to register so I could see the pics here in the framebuilding area. My interests are cycle and motorcycle and I do a bit of fabrication relating to both. Sometimes one more than the other. Have not had a chance to post anything yet and this seemed like a good topic...

    In most motorcycle design circles the telescoping fork is well known for having it's issues. (http://www.tonyfoale.com/Articles/Dive/DIVE.htm) The Hossack and several other FFE designs have tried to address these. One thing that seems to come up in many of these is that the "traditional" headtube placement has to be let go. I road race vintage motorcycles here in the north east and have had the opportunity to see some of the designs (both old and new) in the paddock and on the track. One local engineer has done quite an impressive job (now on version 2?):
    http://www.cosentinoengineering.com/...s/page0010.htm
    I've done some interweb browsing fueled by these musings and see that there has been some experimentation, one notable example using the same a-arm type hossack is the Kimori: http://cyclesdeoro.com/events/NAHBS/2009/kimori_12.jpg

    It is an interesting concept and there is a lot of info available. From all the anti-dive stuff done for both road and mx to the various linkage forks and FFE's their is a lifetime of tinkering to be done. Take a look at some of the early ELF endurance bikes with their bolt-on anti dive system(which could easily be adapted for mtb use) or the VanTech/ Yetman linkage forks of the 60's/70's which could be made to bolt right up. Now, whether they work well or not.... that's a whole 'nother can o worms.

    Here's a few links for anyone interested in MC design and how some things might translate to the bicycle:

    www.EuroSpares.com home to mucho photos and info
    www.tonyfoale.com legendary MC designer
    http://micapeak.com/mailman/listinfo/mc-chassis-design an e-mailing list on MC design and fabrication

    That's all I can come with off the top of my head. Would love to see some people exploring this area. Seems like for something as new as the MTB their should be more folks trying out wacky ideas.

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