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Project Bimota CB400F

Watch the movie to see a 3 dimensional view of the solid model for Project Bimota.

The basic frame layout is close to being finalized, and I am spending a lot of time right now getting the rear swingarm and suspension sorted. I have been using Tony Foale's Suspension Kinematics software, http://www.tonyfoale.com  to analyze the rear suspension system. As a baseline I have the performance curves from a 2005 CBR600RR, and a VF500 Interceptor, and I have been modeling my new parts to mimic the suspension action of the CBR. But, there are many ways to physically build the parts and have them generate similar curves.

Snap shot of the parameters used to calculate the wheel forces vs wheel movement, VF500.

 

 

Snap shot of the parameters used to calculate the wheel forces vs wheel movement, CBR600RR

 

This is the suspension rising rate curve generated by Tony Foale's suspension kinematics software for a VF500 Interceptor. What we are most interested in is the wheel force rate vs wheel movement. The curve steepens at the end of the suspension stroke, presumably to provide a smooth ride for a single person, and still deal with the load of a passenger without bottoming.

  

This is the suspension rising rate curve for a CBR600RR. Note the more linear curve of the wheel force vs wheel movement.  I think this reflects the fact that the bike's sporting intent. The designers were less concerned with rider comfort, or accommodating a passenger than when designing the VF500.

 

I have analyzed the design of swing-arms from a CBR600RR, a CBR600F1, and a VF500 to get an idea of how stiff Honda is making their swing-arms. It is interesting to see the progression in stiffness from 1983 (VF500) to 1990 (CBR600F1) to 2005 (CBR600RR) . I applied the same 400 lbs per side torsional load on the arms.

April 16/2010 - I have added in a new gull wing swingarm that I designed fabricated out of 1.5" OD x .0625" wall and 1" OD x .0625" round tubing. Because this bike is more street/custom oriented vs. a race/track bike I will probably go with the gull wing design, even though I could have made it simpler and lighter, I like the look of it, and it is reasonably strong and light.

 

  • CBR600RR swingarm assembly, strong but heavy - 17 lbs

 

  • 400lb load on each side of arm, 0.003" deflection 

  • CBR600F1 Swing-arm, welded steel - 11 lbs
 
  • 400lb load on each side of arm, 0.060" deflection
 

  • VF500 Swing-arm, Cast Aluminum - 6.5 lbs
 
  • 400lb load on each side of arm, 0.137" deflection

 

  • Steel tube swingarm, 11 lbs.

 

  • 400lb load on each side of arm, .06" deflection

 

  • Stock CB400F swingarm

 

  • 400lb load on each side of arm, (3.75mm) .147" deflection

While researching CBR shock specs, I came accross a site that had a really nice write up on rebuilding a CBR600RR Showa shock. I received permission from the site owner to reproduce the write up on my site, because I didn't want to risk losing the information. Click CBR600RR Shock Rebuild to see the reproduced article, or http://www.peterverdonedesigns.com/600RRshock.htm to see the original article. Thanks to Peter Verdone for a great write-up.

I am planning on building the wheels myself using a combination of a rear rim from an NS400R on the front, combined with a one piece machined spoke set, and a machined hub. The plan is to use a single CBR954RR disk and caliper to keep the weight as low as possible. My target weight for the whole bike is about 350lbs, so a single disk should be more than adequate.

Watch the video for a detail view of the front wheel.

 

The rear wheel will use the rear rim from a VFR1000R with a one piece machined spoke set and a machined from billet hub.

I am slowly getting around to actually building parts for this bike. Detail Pics

 

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