[EricH]

Yes, it would. The speed would be affected (if I'm not mistaken, it would be faster). For another, the OD is what governs fit in fittings, and a smaller ID results in a smaller OD (or a thicker wall for the same OD), which affects how it fits in the fittings. I've seen very nearly identical pieces of tubing not fit the same in a fitting, though... but it wasn't the style normally used in FRC.

And, perhaps more importantly, 2011's <R65> and <R66-D>, read in that order, will tell you that anything other than 0.160" ID tubing functionally equivalent to the KOP tubing (or in the KOP) is prohibited for the 2011 season. This is one of those rules that is change-resistant; I would not expect it to go away for 2012.