Commando vs featherbed frame

Frank,

You posted this last year. The current Cycle World magazine has an article about a featherlastic hybrid with a '72 750 Commando combat engine in an Atlas frame. The supposition is the featherbed with isolastic engine mounting is superior in handling and vibration compared to either of the originals. Why is that?

Thanks,

David

Posted: Tue Jul 11, 2006 6:29 pm Post subject:

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Although the Commando frame is light, it's not because it's weak. For a structural design that pre-dated finite element analysis, it's quite a remarkable piece of work. I personally tested both bending strength in the vertical plane (between front and rear suspensions) and torsional strength between the headstock and the swing-arm axis (trying to twist the front wheel out of alignment with the back wheel).

The tests were done on bare frames (no engine/transmission or Isolastics installed) and compared to the same tests on an Atlas Featherbed frame. From memory, the torsional strength was about 8 times better and the bending strength about 5 times better.

The only real weakness on the Commando is that the two downtubes can get splayed apart by braking forces. With the original Italian (Campagnolo?) TLS front brake that was never a problem!

I need to get Mick Duckworth's book to find out more about what happened to the Commando after I left N-V. I guess that's the next use of a gift certificate to Amazon.com.
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David:

I'll have to find the Cycle World issue and read the article. My gut feel is that the handling, specifically high-speed cornering, will not be as good on the Featherbed frame.

I wasn't able to sense it on the road, but I remember Peter Inchley pointing out a torsional deflection when we took an Atlas round the test track with me on the back.

The isolastic concept would have worked just fine in the Featherbed frame, but there would have been as much re-design effort as designing the Commando from scratch.