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Motorcycle "girder" Fork

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#1 Guest_Joe McGlynn_*

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Posted 06 January 2006 - 08:05 AM

I've been playing with this design for a while, it is a variation on a proven functional design. I've modified the spring mechanism slightly to work more like the springs on a Harley springer fork.

I've been reading through this forum and I'm interested to hear your feedback on the aesthetics and how well the overall design holds together.

One of the design constraints is that I have to be able to fabricate this as a one-off. So I have to stay away from anything that would dictate overly-expensive manufacturing processes.

The feeling I want the design to have is mechanical, vintage and and a little elegant.

The first render is of the entire fork; I need to do some refinement on the bottom (like adding a wheel and poking some holes in the brake discs and cleaning up the caliper mounts)

Here is a close up of the actual suspension mechanism.

The links pivot on bronze bushings, the springs are connected to the lower front cross brace and the top triple tree.

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#2 Renzsu



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Posted 06 January 2006 - 12:03 PM

I'm not sure how much of a real issue this would be, but using various alloys together might cause the areas of contact to corrode depending on the kinds of alloys used, perhaps something to look into (again, could be a neglectable issue).

About the looks, it does look like it could go on a chopper or custom harley, it has that feel to it. Have you done some strength/stress analysis of this model?

#3 Guest_A-Line_*

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Posted 06 January 2006 - 05:59 PM

The links look like they could use a little more "beef". Take a look at the girder system on a Britten to see a well engineered system. You can just see the suspension links in the pic on this page: Britten Front Suspension

Are you at all worried about the geometry of the fork? Again, check out the Britten to see a good one. Also check out http://www.tonyfoale.com/ to learn about suspension geometry etc. The positioning and length of the links is crucial to determining the axle path.

#4 Guest_Joe McGlynn_*

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Posted 07 January 2006 - 08:39 AM

Thanks for the feedback.

I'm pretty confident of the geometery; I've worked out the "trail" and the links stay parallel through the range og motion so there is the minimum of change in the trail.

I haven't done any stress analysis yet, I need to learn more about that aspect.

One of the parts I'm not happy with is the top tree; I want it to be mechanical and simple to make, but not look like some trash welded together.

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#5 Guest_booj_*

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Posted 07 January 2006 - 11:17 AM

Hi Joe,

This could be a useful website, all about the requirements of suspension stuff; http://www.yojimg.ne...ment/susfaq.php

Being an old mountain biker, I don't know if you knew but this design was susccessfully used by a US company called Girvin. Can't find their website, used to be www.girvin.com

Found this picture on ebay of a similar design?!

Cheers, Ben.

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#6 Guest_Kai_*

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Posted 13 January 2006 - 12:55 PM

Hello Joe,

I too am a mountain biker and immediately thought of the Noleen Crosslink when I came across your thread. I hope the following link will aid you on your project: http://www.k2bikes.c...link_om_eng.pdf.



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Posted 20 July 2006 - 06:16 AM

Look up the older gt mountainbikes they sported that same design. As recent as the 2002 / 2003 marin full suspension bike styled hte same front end with a fox air shock instead of a elastomer for bump absorption.

#8 Guest_sixto62_*

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Posted 27 July 2006 - 06:09 AM

Looks good. But i think the two links on the main fork might need more strenght/reinforcement. The riggors of biking might bend the fork where it is connected to the lower links. Keep it up.

#9 Guest_storminsince73_*

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Posted 29 July 2006 - 06:30 PM

I would really like to know where this project stands. I am trying to either design, or adapt a girder fork onto my 99 shadow 1100. I like the girder design much better than a springer design.


#10 Guest_A-Line_*

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Posted 31 July 2006 - 03:03 PM

To look at mountain bike girder forks doesn't really make much sense because motorcycles have been using girders for decades before mountain bikes, and none of the mountain bike designs were all that successful in the long run (much like their motorcycle counterparts).

The debate rages on as to what front suspension design is truly the best, but for performance vs. cost vs. weight vs. complexity vs. maufacturability, the telescopic fork is the only way to go at this time, for both motorcycles and mountain bikes. Yes, there are alternative front ends in production now (aka FFEs, or Funny Front Ends, as some motorcycle designers like to call them), but if you look at the top levels of racing and the majority of production bikes, teles are far in the majority. Same with MTBs.

However, it is also very true that a well designed girder front end is a thing of beauty and can perform at least as good as a conventional tele (or maybe better: see Britten, in my earlier post). I am assuming this is why you would want to go this route - beauty instead of lower cost and less complexity.

Beef up those links! :)

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