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I may be wrong but expect the rear sprocket is for the hand brake/only brakes?
Picture is 1915 @ the Mack factory w/ car one of six 1909 Blitzen Benzes built, same as Oldfield's 1910 Daytona winning racer.
Powered by massive 1310 CID 4-Cyl. engines, these were the Supercars of their day capable of 140+ Mph which was almost double even aircraft speeds at the time.
More info here...
http://theoldmotor.com/?p=131775
~ Pete
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