30.1 Headset Cups. JIS or ISO??
Hello. It is my understanding that JIS headset cups are 30.0 mm in diameter and ISO cups are 30.2 mm in diameter, no? My question is this:
I have an old Ross Super Grand Tour (insert unremembered Roman numeral here) that I am purchasing a Surly Steamroller fork for, and in the process am going to convert to a threadless 1" stem/ headset. I know the new fork has a 26.4 crown race diameter, so a standard 1" headset crown race should fit no problem.
The original fork used a 21.1 diameter stem, so that set me to wondering if it was a JIS headset. I measured the old cups, and they came out at 30.1 at the widest spot. I measured the headtube, and it is 30.2 in some spots, and 30.1 in others. Will ISO 30.2 cups fit in this frame? It seems to me that one tenth of a millimeter would not be that much of a difference, a difference that could probably be sanded off if it's tight. I have very little experience with headset installation, so I thought I might ask before ordering my new headset. Thanks to all who reply.