- Bob - 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.
This really confuses me. The selling point on SunTour's Ultra 6
freewheel was that it (mostly) fit in the *same* space as a 5-speed
freewheel. It did, however, require a *narrower* chain than was normal
at the time.
You *may* have a "regular"-spaced SunTour 6-speed freewheel. SunTour
marketed both 5- and 6- speed "regular"-spaced freewheels as well as 6-
and 7-speed "ultra"-spaced freewheels. The really nice part was that
several of their freewheel bodies would fit all four configurations.
Another possibility is that your frame was spread to 126, an ultra-6
freewheel went on, your chain was already "narrow", the axle spacers
were rearranged and the wheel built "dishless." I got a Centurion
Pro-Tour in the 70's that came this way, (but with a regular-5). It was
an oddball design, but made a strong rear wheel for touring.
*** HOW TO TELL WHAT YOU'VE GOT***
*** SunTour "regular" spacing is about 5.8mm center-to-center for
freewheel cogs. "Ultra" is about 4.8mm ***
If you can read the embossed text on the freewheel face and report here,
we can probably guess.
Note I put "regular" in quotes since what was regular in the 70's is now
abnormally widely spaced.
Quoted message said: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?
If you have 126mm spacing and a "regular" spaced 6-speed as I suspect,
switch to a 7-speed narrow and a narrow chain. If your shifting is not
indexed, no other changes needed....
....except... SunTour is long out of the freewheel business (the current
SunTour is no relation, as I understand it). You can get nice SunTour
7-speed freewheels on Ebay. Nashbar (and your LBS, probably) have other
brand 7-speed freewheels, not sure what the width is, but would probably
work (almost certainly with 126 spacing).
....except... Make sure the spacers on your rear axle stick out past the
new freewheel. If you have to move the spacers much, you may want to
have your rear wheel redished. If your current freewheel is, as I
suspect, a regular-6, you may need no spacer changes at all, or only
slight changes and no redishing.
Quoted message said: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.
Definitely no need to re-spread. Some variation of the above should get
you running 7-speed with the existing frame.
Mark Janeba
(adjust address in obvious way to reply)