I am betting it has something to do with structural integrity of the plexiglass. I am a mechanincal engineer on the side, and I know a little about things like arm of force, moment of inertia, elastic modulus, etc. However, I usually deal with metals, not polymers. I assume the folks at Memphis Shades have done testing to determine the necessary curve and shape of the windshield to make it strong enough to not break when the bike is going 70mph in one direction and hits a wind blast from a freight truck going 70mph the other direction. However, given that you are cutting yours down from its original height, you should be able to lessen the curve some and not worry to much about over-stressing the material. There also may be some corelation between shape and amount of wind buffeting, but that is totally out of my area. Just always remember engineering rule #4: It is usually easier to take a little more off, than it is to put some back on.
'07 VN900 Classic
Horsepower is an illusion.
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