Instead of buying a second, larger windshield that you would swap out occasionally with your stock shield, to give you more wind protection for highway speeds (necessitating changing shields back and forth - bolting, unbolting, re-bolting, etc.), maybe you can investigate adding an X-creen 'clamp-on' addition to your stock screen. These come in different sizes and are adjustable; they don't take up a lot of room, and really don't change the overall profile all that much. They will help deflect more highway speed air. I use one on my F3L, and there are a number of others on SL who do the same. You could unclamp it more easily than unbolting a whole windshield, if you really wanted it off and don't get what you need by adjusting, lowering or flattening it. Cost runs around $125; somewhat cheaper than buying a second shield. Pics show what I have on F3L, but I'm sure there may be something else that might suit you better.
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