A shy person said:I am trying to upgrade my 1970's screw type freewheel to a 7 speed.
The bike was originally a 120mm 5 speed. It was stretched to a 126mm
6 speed and a Suntour Ultra 6 installed. The same chain was used.Now I'd like to go to a 7 speed. But, I am confused about the spacing
on 7 speeds. Are they the same width as the 6 speed cluster that I
have or are some 126mm and some 130mm ?If it's a 7 speed in 126 mm, do
I need a new narrow) chain to fit the freewheel and will that
work on my vintage (1970's) Stronglight crankset ? If I need a
narrow chain, what do I look for when buying it?I'd rather not stretch the frame again and deal with all the related
issues... including alignment, a longer axle, etc so I'm hoping that
there is some way to do this in the same space I have.
This is a bit confusing, because the whole idea of an _Ultra 6_ is that
it's skinny so it fits on the same wheel, same 120 spacing as a standard
width 5-speed. If the freewheel you bought is really an _Ultra_, there
was no need to have spread the frame.
Your memory may be playing you false here...you should measure the
actual frame spacing. See also my article on this:
http://sheldonbrown.com/frame-spacing
7-speed or full-width ("regular"😉 6-speeds fit 126 mm spacing.
7-speed sprocket-to-sprocket spacing is basically the same as Ultra 6,
so they use the same chains. Any modern chain will work with any
7-speed freewheel. I generally go with the SRAM PC-58.
You should always replace the chain when you install a new freewheel.
Sheldon "Numbers" Brown
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