Ride, Wrench, Swap, Race
Join Date: Jan 2010
Location: Northern California
Posts: 9,194
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
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The "dogleg" of the Arabesque and certain of the later Simplex derailers doesn't use the slanted parallelogram, and so wouldn't violate any patents.
The difference with the slant parallelogram was that the parallelogram pivots were off-axis from being perpendicular to the axle, so that the shifting motion moved the cage further away from the axle as the larger sprockets were engaged.
Shimano spent years developing SIS, knowing full well when the patent expired. Thus, when the first SIS gruppos appeared around the same time that Suntour's patent expired, Shimano was able to have slanted derailers ready for sale to give SIS the best performance (and market acceptance) possible.