Originally Posted by
Jixr
I'm wanting to have it so I can use my 16 when its flat, but if I want to do more distance riding I can use my larger one without burning out my legs so badly on the hills
What you are describing is a multi-speed freewheel bicycle.
That are surprisingly common and might even be in general use.
If you were riding a proper fixed gear I would suggest a Sturmey Archer 3 speed S3X internal fixed gear hub, but for your application the 3spd AW with freewheel has been available since 1936 and has proven eminently successful. An AW equipped 46X16 will yield your current 76 Gear Inches with a useful 57GI reduction and a leg busting 101GI for descending.
-Bandera