Originally Posted by monogodo
I know it's not STI, but I'm currently shifting a 7 speed fw with 8 speed Record Ergo shifters with no issues. And as sydney said, the spacing difference is close enough.
8s Campy spacing is the same as everyone's 7s spacing (5.0mm). Here are two good, well tested options for perfect shifting (provided we're talking about a road bike):
1. Use an older pre-2001 Campy rear derailleur and 8s Campy Ergo levers (or any other speed Ergo lever converted to 8s). You'll have one extra click, but that's locked out by the limit screws of the RD when you get it set up, so it'll act just like a 7s shifter.
2. Use a Shimano index rear derailleur (but not pre-1997 Dura-Ace) and 7s Shimano STI levers. Sora are the only ones still available, but you might find something else used.
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In memory of Jim Price (aka. sydney) ...