Bicycle Mechanics - will this work!

Will 7 speed rsx sti shifters work on a bike that has currently got a 6 speed friction shifting system? I thought about trying this but I was wondering if the spacing difference is too much for the sti shifters to work smoothly. My old hubset has a freewheel instead of a cassette so I cannot use the 7speed cassette I have on hand.

Since you already own the parts, why don't you just try it and see what happens? I'm pretty sure it'll work, but it's not a combination that I've tried personally. You'll obviously have to dial in your derailleur limit screw a bit.

You should be able to work that out . I have used suntour index shifters with shimano components and shimano sti shifters with a six speed suntour freewheel, all of which are not suppose to be compatable. The best way to adjust is to start from the 3rd or 4th cog and then you should be able to get it to fall into the detents either way with some fine tuning. Just remember to set the derailluer limit so you dont go over the top.

Can't you switch to a 7 speed freewheel?

I don't think it will work. 6-speed cog spacing is larger than 7-speed spacing. Use a 7-speed freewheel or switch to a freehub and use the 7-speed cassette.