Upgrading the swing arm? (2010)

J. M. Leadbeater said:

Wonder how many owners have ever calculate the torsion constant and relative second moments of area to compare even steel swinging arms manufactured from round tube and rectangular section tube?
Just a thought.

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To take that a step further, I wonder how much benefit even a theoretically rigid swing arm would give when fitted to a standard isolastic cradle? In other words, is it worth stiffening the SA if you don't also do the cradle?

A question relating to upgrading: Will the factory reinforced swing arm from a 73 850 Commando fit onto a 71 750 Roadster without any modifications?

Yes, have one on my 72.

Thank you, much appreciated.

Paddy_SP said:

To take that a step further, I wonder how much benefit even a theoretically rigid swing arm would give when fitted to a standard isolastic cradle? In other words, is it worth stiffening the SA if you don't also do the cradle?

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I use a high quality top steady, front steady (Windy Eads), and others also employ a rear/lower steady to provide 3-point hard limits to cradle movement in ONLY the fore-aft / up-down plane. The lower/rear has not found a readily accessible, easily mounted solution as with the top and front.

Slightly off-topic, but related, are the very ingenious cradle-mounted exhaust hangar systems that do away with rubber mounts for the mufflers. Very trick. I hope to add the lower/rear rose joint and exhaust hangar bracket, to the Dreer monoshock prototype (one of these days)

RennieK said:

Norton saw fit to improve the commando swing arm in 73 and again in 75 so if yours is earlier you could upgrade.

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altho the 75 is setup for the factory disc brake/wheel combo