yet another index question
 

Hey all,
I've searched, but can't seem to come up with a useful answer to this question:

What, exactly, dictates the rear-derailleur's movement along a cassett or freewheel - spacing-wise?

I have a 6-speed freewheel with 5mm spacing (actually measured at 4.9, but I'll call it 5). I've got a Shimano STX rear derailleur (I'm pretty sure it's 7-speed, but could be 8 "RD-MC30").
http://www.fa-technik.adfc.de/Herste...RD-MC30-GS.jpg

I'd like to get a pair of 6-speed indexed clamp-on-stem shifters; I've seen some sunrace 6-speed shifters that claim to work with Shimano stuff.
http://biketoolsetc.com/Product_Images/SU-137--6.jpg

My real question is which component actually translates to the 5mm spacing that I need? For example, if various-speed derailleurs all move the same distance laterally when the cable is pulled X inches, then the spacing is dictated by the shifters alone. That's what I've been led to believe, which means it doesn't matter which derailleur I use, as long as it's shimano and meets the max-teeth and chain capacity requirements.

So for the short answer, is my setup going to work? For the long answer, spill your guts!

Thanks guys/gals.

Starting with 7-speed (and not-including Dura Ace 7 or 8-speed) all Shimano rear derailleurs shared the same geometry so the shifter was the sole determinant of how far it moved with each click. What I'm not sure is if this commonality dated back to 6-speed. I believe it did but maybe someone else has experience that can confirm or refute it.

Also, one more quick question, since I've got your attention (hehe). I seem to have lost the master link to the 6/7-speed chain I just bought from nashbar:
http://www.nashbar.com/profile.cfm?c...eid=&pagename=

I was going to order this one to replace it, just wanted to make sure it's compatible. I'm sure it'll work fine, but I wanted to check to make sure.
http://biketoolsetc.com/index.cgi?id...m_id=KM-710SCS

Thanks again.

Correct me if I'm wrong, but 7-speed cog spacing was also 5mm. So, from your response, I should be ok if I get 7-speed shifters, and just limit the rear derailleur to 6-speed, right? I haven't seen any 7-speed indexed stem shifters anywhere, but I've seen resonably-priced downtube versions.

Yes, I think 6 and 7-speed cogs were spaced the same, or close enough to work. 7-speed downtube shifters should work well. Stem shifters were usually very cheaply made since they only came on very low line bikes and few survived.

Yep, the master link from Bike Tools Etc will fit your Nashbar chain. Nashbar chains are made by KMC so its the same chain.

HillRider, thanks for all the help - you've been awesome. One more question, I promise. Is there some unwritten rule about not putting mtb shifters on a road bike? I could go for the sunrace downtube shifters, but these intrigue me:
http://www.biketoolsetc.com/Product_.../SU-218--7.jpg

Eah, I'm sure that OCP will get the best of me, and I'll decide against it.

Last time I looked you could get a 7 speed freewheel pretty cheap on Ebay and most frames have sufficient width. I also think those mtb shifters will work well with the 7 speed freewheel and the derailleurs you have. Have fun setting it all up.

The handle bar diameters are different so MTB shifters won't fit on road bike bars which are too large. You could, I suppose, file or Dremel the shifter clamps to make them fit but it might weaken the clamps too much.