Different width rims on front

It's time for new tires and I was wondering why my IM has 4 1/2" rims on fronts and 5 1/2" on rears? Did original '57 Speedsters have a setup like this? Does it improve handling or aerodynamics? Should my new tire sizes also be different? Right now my tires are the same, 165SR15 on chrome 5 lugs.
Thanks for any info.
Brian

Brian, some owners run the same size front and back, while others run a wider tire in the back, because that's where most of the weight is situated. The one good thing about running the same size tires front and back is that you can rotate them, for a longer tread life. You could run a 165 in the front and a 185/65 in the back, if it will fit (without rubbing on the fender). This depends on your wheel offset. The difficulty would be getting the same brand of tire in those two sizes. There is a world of difference (in handling) between a 165 and a 185/65 tire. I would recommend running 185s all the way around, but your front rim is too narrow for a 185.
Ron