wheatonFJR
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I sure like the look of the backrest...The backpad was designed to give lumbar support, which it does. If you draw a line straight down from the thickest part of the pad, yes it would be about 3 1/2". However this is not where the passengers butt would be. They would be sitting back a couple of inches behind that, because of the contour of a persons back while in the sitting position. Also the pad has some give in it , about 3/4"-1". My wife and I rode 1600 miles in 4 days and it was very comfortable for both of us. With out a backrest the passenger is usally jammed right up against the driver holding on. This backrest eliminates that. Now your passenger can relax, look around, and not worry about the next time you may hammer the throttle unexpectedly.
just an idea...maybe you can come to one of the regional or national meets and show it off. That way you can show in person what you are trying to explain here. Maybe contact the organizers of the meet to get info. and get on the list of vendors.