6sp to 7sp and dishing
 

If I go from a 6sp freewheel to a 7sp freewheel do I need to redish the wheel?

Maybe, maybe not.
I've done 6 to 7 conversions that only required unscrewing one freewheel and screwing on another, some that also required a couple of 1mm spacers, and others that needed a full axle re-space and re-dish. Only way to find out is to dive in.
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You probably won't need to. 7 speed freewheels usually have the cog spacing compressed a bit compared to standard 5-speed pitch, to allow them to fit on frames set up for 126 mm OLD rear spacing. 6-speeds with standard spacing fit the same hubs. So the 7 should fit the same space as a 6.

The major exception is if your 6-speed is a SunTour narrow-spaced or Ultra 6 design. These were designed to add a speed to a 5-speed rear end, within a 120 mm OLD format. If you want to put a 7 on one of these, you should get a longer axle, suitable drive-side spacers, adjust the wheel dish, and possibly cold-set the frame. I'd say that the "standard" 126 mm dish isn't guaranteed to work unless you cold set the frame and hence have the dropouts symmetrical.

There are some oddballs out there. My Woodrup, to accept a Shimano Megarange7, needed the hub opened up to 128, with a small dish adjustment. Can't really justify it, it's just the only thing that worked. Other 126 bikes I have accepted the Megarange without issue.

Only if you need to change the spacing on the axle.

txvintage,

Check out this thread on the same topic and see if this helps:
http://www.bikeforums.net/showthread.php?t=571407

Now that we're at it, I've got a 5 sp MTB with 126mm spacing. If I go to 7 sp will it require a redish?

Thanks for the replies. I'll be using a 105 hub (126) that is currently a 6 speed set up that had indexed DT shifters and a double. The new and improves set up will be 7 speed with 7 speed STI and running a triple for my broken down knees.

Just waitin' on the frame to get back...........

I'm not sure how MTB hubs were set up, I'm a road guy. I'd expect there isn't extra room, so if so the 7 will require more cogset or freewheel width than the 5 did. In that case, yes, you'll need the new axle, redish, and possibly cold-set the frame.

:thumb::thumb::thumb:

See above comment.