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New SA AW gearing idea for Rudge, needs some sprockets!

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New SA AW gearing idea for Rudge, needs some sprockets!

Old 01-11-23, 07:57 PM
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Road Fan
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New SA AW gearing idea for Rudge, needs some sprockets!

My Rudge Return to Road project slowly rolls forward, at the moment a little more steadily than just a few moments ago. I have classic alloy rims laced up on the original Raleigh Industries front hub and on a 1953 allow AW hub. The OEM sprocket is a 17 tooth, dished with three tabs/notches, and it needs a ⅛" chain. Tires will be 27 x 1 Pasela Tserv, which fit the Wolber 58 rims like the old days! The rims will save about 120 grams each, and I guess the alloy IGH shell will weigh about 100 grams less, but it's just a guess. I'll also be going with an alloy stem for another 50 grams reduction. Probably will stay with the original GB Maes bars, if the bar clamp diameter matches that of the stem. Oh, forgot, I got a Kalloy plain seat pin for saddle mounting relative to the original steel one, but I'll need to double check the fit relative to the old steel one, with the actual saddle on board, whatever that is gonna be.

The chainset is also a weight savings: gone with the 48 tooth steel 165 mm crankarms/chainset, since I caused some damage in removal. Instead i'll use a TA 5-Vis in pista chainring configuration with a TA ⅛" 49 tooth chainring. I'm just guessing the mass savings of the alloy chainset is not more than 100 grams, for a total haircut of 100 + 100 + about 340, + another 50 for the stem. Total estimated mass reduction is 540 grams, or 1.3 lb.

So as it is I'm headed for a pure single gear of 49/17 = 2.88. Considering the slightly non-original components, the original is 48/17 = 2.824. The crank arms are longer by 1.03, for a new drive ratio of 2.88 * 1.03 = 2.969 versus 2.824 in the original specifications. The drive wheel diameter will be 27.32", so the natural gear inch value will be 2.969 *27.32", for 81.1 gear inches in the N gear position of the AW. Adding in the 4/3 and step up and step down values of the gearing H, N, L will be 108", 81.1", and 60.9." Sounds a little hard on my old knees! I have an FM hub which opens up the spread somewhat, but I haven't sorted out the needs for that conversion - a project for next winter!

This seems pretty high, if I go for a 42/21 sprocket combo, the new gearing spread will be 75, 56.3, 42.3. Sounds good for just starting out again!

So, I need a 41 tooth pista chainring and a pair of 21 tooth dished Sturmey rear sprockets.

Does this seem feasible?

Now for the WTB part: Anybody have spares of these parts, with non-hooked teeth?
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Old 01-12-23, 06:02 AM
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Shimano Nexus 21T should fit, are dished, will work with 1/8" chain, cheap enough to try.
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Old 01-13-23, 02:25 PM
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Does anyone know if current-production S-A 3-spline cogs listed as "for 5-speed hub" fit the old drivers like on classic AW? They must, right? It'd be crazy to come out with a new, incompatible 3-spline format unless it was way different, and these look pretty similar.
Example here: https://www.modernbike.com/sturmey-a...8---24t-chrome
That's for 24t, not what Road Fan was asking for, but maybe consider it, keeping the 49t chainring? A bit more weight, but longer service life.
The same site also lists a 20t, but I don't see a 21t.

Ooh how about this, NOS real Sturmey 22t cogs on ebay only $9 and free shipping. I might buy one of those myself. They say "More than 10 available"

Mark Stonich of Bikesmith Design used to sell AW-compatible 3-spline cogs, several brands, but his site says they're all sold out.

BTW be sure to read Mr. Stonich's article on S-A hubs, especially the section on lubricating them. He speaks from long experience and a lot of experimentation. He even named his cat Raleigh.
He calls the article a work-in-progress and there's no link to it on his homepage, but I still find it about the best thing out there. You need an app that can open MS Word .doc files.

I converted my FW to a 5-speed, essentially an S5. With the new higher high gear I was able to gear down in back, with a 26t sprocket. Yes it looks weird but it runs smooth and should last forsever. Here's my '71 Super Course "downshifted" from original 10-speed to 5-speed:



Note, such a large rear cog puts more twist on the internal parts than is recommended for hard pedaling. You can permanently twist the axle inside the hub if you stand up and stomp, unless you're a pretty light rider. So, being aware that I'm pushing the envelope, I pedal somewhat gently in the low gear. I get off and walk before standing on the pedals, since I'm a clydesdale.

Mark B
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Old 01-14-23, 09:47 PM
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Having moved from the mountains to a flat coastal island, I'm finding IGH more and more interesting. I just finished a build with the AM Sturmey Archer alloy hub. I also have my SA FW back in action. Thanks for this additional info.
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Old 01-15-23, 07:47 AM
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Originally Posted by bulgie View Post
Does anyone know if current-production S-A 3-spline cogs listed as "for 5-speed hub" fit the old drivers like on classic AW? They must, right? It'd be crazy to come out with a new, incompatible 3-spline format unless it was way different, and these look pretty similar.
Noooooo. That cog is for Sturmey's newish rotary shift 'C50' five-speed and has a larger I.D.
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