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Varying gaps on Sun Tour freewheels

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Varying gaps on Sun Tour freewheels

Old 07-31-14, 07:47 PM
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avhed
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Varying gaps on Sun Tour freewheels

Freewheels like the New Winner and AP.
Does anyone know the advantage of this? Makes sense to me that the gap is smaller on the second to first gear because you have the derailleur stop for that shift, but why doesn't the second smallest cog to the first also have this?
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Old 08-03-14, 01:11 PM
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Might have something to do with the old Suntour indexed shifters. Sheldon says something about this on his website. The clicks weren't evenly spaced because....I forget.
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Old 08-03-14, 03:08 PM
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If you observe a derailer shifting across all but the smallest "corn-cob" or "straight-block" freewheels, you'll immediately notice that there is a bigger gap between the top pulley and the cog when the smaller cogs are used.

So, with a bigger gap there, the chain doesn't get angled as sharply for a given amount of shifting motion, and hence one has to have a greater shifting movement to effect a shift.

But, with a larger shift movement, there is the tendency for the chain to over-shift and then shift two cogs over, not what the rider wanted.

So, with wider spacing between cogs at the smaller end of the freewheel, the shifting is more-forgiving of less-than-precise lever movements, and over-shifts are more-easily avoided.

Shimano, for their part, when introducing their first (indexed, btw) 7-speed freewheels and cassettes, made the 2nd-to last spacer on the smaller end of the freewheel a wider 3.3mm, instead of the other spacer's 3.1mm.
And as you noted at the larger end of the freewheel, here as well the last (driveside) spacer also didn't so much need to be wider because the last shift is precisely positioned by the limit screw instead of by the rider's hand.

One result of Suntour's narrower 7s spacing (as compared to Shimano's, at least between the larger cogs) is that Suntour's 7s indexing is much-improved by using 9s chain, since so little clearance exists and the result can be over-shift to a larger-than-intended cog.
Shimano's more-sophisticated "UG Narrow" chain and "Uniglide" cog teeth allowed some extra clearance and didn't need so much overshift freeplay built into the indexing shifter, so overall shifting performance was more-robust imo (not that Shimano's indexing drivetrains don't also benefit from a newer, next-narrower width of chain).
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