Tuesday, 21 March 2017

New Shifters, and Nine Over Eight Gearing?

Winter dreaming about gearing.
Having recently got my hands on a pair of "old school" "thumb" friction shifters, I will have a bit of flexibility with gearing.

Three factors that influenced me buying the friction shifters are:
1) I have an almost unused rear wheel that came with Hoppy (that was quickly swapped out for the eight speed I was using on Mermaid) that has a seven speed freewheel. With friction shifters, to swap wheels I'd just have to alter the stop screws on the derailleur. Indexing is irrelevant on an unindexed system :-)
2) Having removed myself from the hegemony of having to have the same "speed" shifters as rear gears, I can run a variety of set-ups, including unorthodox ones. Irregular spacing between cogs? as long as the chain can handle it, so can the friction shifters!
3) If I fancy another go at an aero setup, then friction "thumbies" mounted on the aero bars will be MUCH cheaper than the "proper" aero "bar end" thumbies.

So lets have a look at gear spacing.
From Sheldon Brown's cribsheet:
Typical 7 speed "modern" "freewheel" spacing = 1.8 (ish) mm spockets with 3.2 (ish) mm spacing, for a total height of 32 to 33 mm
I could swap out the freewheel for a modern 6 speed (2mm sprockets with 3.5mm spacingm for a total height of 29.5mm
An 8 speed Shimano/Sram freehub takes a cassette with 1.8mm sprockets and a 3mm spacing, giving a total height of 35.4mm
A 9 speed Shimano/Sram cassette has 1.8 (ish)mm sprockets and 2.54 (ish) spacing, giving a total height of 36.5mm
I won't worry about the "10-speed only" hubs, because I won't be buying one!
An 11 speed Shimano hub is reported to be 1.85 mm longer than a 9 speed hub, so that gives a height of 36.5+1.85 =38.35mm

What if I wanted to mount nine 8-speed sprockets? How long would that be?
35.4mm (for an 8 speed) plus a 3mm spacer, plus a 1.8mm sprocket gives 40.2mm - 1.85mm longer than an 11 speed hub.

Would it fit?
Depends on the engagement of the lock ring, I suppose.
Certainly the SRAM 8-speed gears in the smaller sizes have the flange moulded in with the sprocket - all in steel. I have a 11-tooth and a 12-tooth rear cog like this. Their "true" width is 4.8mm, because they don't use a spacer. Indeed, the SRAM PG850 cassette I own only has 5 spacers for the eight gears, not 7 ... the 5 are between the 14,16,18,21,26, and 32t cogs, while the 11t and 12t have a "spacer flange" into the cog.
Similarly Miche 8-speed gears have the 11-tooth cog as part of a pair (the 11t clips into the 12t next to it), so, again, there is effectively a very wide flange for the smallest cog.

The only question is, then, how much of the lockring is engaged?
Guess there is only one way to really find that out.

Buy it, and try it!

Watch this space ...

Update: 14th April 2019
I replaced my 8-speed 11-32 gears with a 10-speed 11-42 cassette. Same wheel, same derailleur, same friction shifters.
Write-up here:

Shimano HG500-10 11-42 cassette fits nicely on my wheel
in place of the SRAM 11-32 I have been using for some years.

Cheap Sunrace friction shifter. It can handle 8-speed, 10-speed, whatever, because it is unindexed.

Hoppy sporting a new 11-42 cassette, still with the same M591 Deore derailleur.

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