teazer said:Unfortunately that box section/engine mount is not as rigid as it might appear. Some years ago I gave myself a nasty fright following another guy on a CB77 racer. the back end was flapping about in the breeze.
Unless teh holes are reamed and super tight fitting mounting bolts used, the frame walks around the motor mounts with a stock bend swingarm and will act like a spring with a more rigid swingarm and grippier tire. That center section is too narrow to resist the twisting forces effectively. The wider the support, teh more resistance to twist, so adding tubes outside the swingarm pivots is a good idea.
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