Square to round swingarm

[doc9339]

There was a post on this but I cant find it on search.

What must be changed out to go from a square SA to a round SA on a frame that came with a square one?

I have a round one Id like to place on my 1975 SA frame

[RooDog]

All you will need are axle adjusters, 13" shocks, and the correct axle to go with your wheel hub....

[RUBONE]

All you will need are axle adjusters, 13" shocks, and the correct axle to go with your wheel hub....

Actually a bit more as no round swingarm ever came with other than drum brakes, so depending on the wheel/brake combination you want to run there could be fabrication involved.

[kitabel]

If you have to fabricate something, the torque stay which provides anti-rotation for the backing plate (drum) or caliper (disc) should not anchor to the swing-arm, but run forward in tension and attach to the chassis itself and rotate on the attachment point sufficient to allow free movement throughout the wheel's range of suspension travel .
This prevents brake torque from changing the rear suspension load.
I've written more comments on my site here: http://victorylibrary.com/brit/chassis-2.htm#torque

[RooDog]

?

[nifty]

Kitabel,
What you say is technically correct, and with proper execution improves swing arm function to the point where it prevents/reduces rear wheel hop under extreme front & rear braking (when a lot of weight comes off rear tyre). Which is a major reason race bike builders invented it and use it

But IMO, on a 65up BT, in the real world, very few riders would ever ride so aggressively as to ever need a rear brake caliper, or drum backing plate floating on axle & anchored by in-tension, rose jointed parallelogram link to frame. Many more riders would simply not want the unused complication, one-off fabrication and increased maintenance. To get a real benefit, everything would also have to be way lighter than H-D parts.

With caveats, sticking with the lighter 73 up swing-arm and stock brake anchor might be slightly more beneficial through the twisties,

A BT is what it is, why go to a lot of trouble to turn it into a dog's breakfast?

But whatever mods float your boat.
If you are going Pan-Shovel Bagger road racing and the rules allow, could give you an edge, until everyone else does it.

Nifty

[nifty]

Just want to add: "with no real improvement" after dogs breakfast.
Nifty

[kitabel]

Thanks, I'll try not to help in future.
Please: show us something you wrote.
BTW: stock on most British bikes for the last 70 years...

[nifty]

Kitabel,
PM sent
Nifty