Raleigh three-speed gearing question
 

I have an old Raleigh Sports from 1966--it used to be my dad's bike--that I'd like to keep as an occasional rider. It's in decent shape. From what I've read, the old Raleighs usually came with 46/18 gearing, but for some reason this one has a 48 chainring to go with the 18-tooth cog. That's ridiculously high, it seems to me. I'm planning to switch the cog to something bigger, but can't decide between a 22 or a 24 tooth. The 22 would give a middle gear of about 52 or so, the larger cog would be maybe a 57. Any thoughts? I live in the steep hills of Vermont. Also, if I went with the 22-tooth cog, is it possible that I might be able to get by without a longer chain? Looking at it, it seems possible, but never having tried it I don't know. I'm pretty sure that going to a 24-tooth cog would require a new chain.
JV

I say go for the 24-tooth cog; it'll give you a low gear of about 41 inches, which should help on the hills, and a high gear of 73. You might find yourself riding in high gear on the flats a great deal, but you'll improve your spinning technique! I'd also suggest you splurge for a new chain.

Neal

From what I have heard with an S-A hub you don't want to go lower than a 41" low gear because it can destroy the hub.

I have never heard that... and we have done everything in our power to destroy one of them. The only sure method I have found is run them with out oil while abusing them.

Also jonwvara go to Bikesmith Design the last I knew he was working on a 28t cog/conversion for SA hubs:D FWIW that is MnHPVA Guy here on the boards and he probably knows more about the limits and capabilities of the SA hub than anybody I know.

Aaron:)

I can't quite see why a low, low gear would "destroy" the hub. I'd think it would be the opposite as too high a gear would apply lots of force, as opposed to all the spinning you'd do in a low gear. But then physics was never my strong point.

Neal

You are thinking backwards.

High gear = high force at the pedals but low force at the hub.

Low gear = low force at the pedals and high force at the hub.

But I agree I would go with as low a gear as you can get. I used a 1:1 granny gear with a AW hub for 20 years (pictures here), though I did have to occasionally replace a few gears with broken teeth. I mostly got away with it because I have a smooth pedaling style. Also I think the gears that broke were probably newer ones. I believe they made them stronger back in the 40's and 50's (and maybe 60's, I'm not sure when they changed the manufacturing process).

The torque load on the hub is determined by;
The force on the pedals x the length of the cranks x the teeth on the cog / teeth on the chainring.

So all things being equal, more teeth on the rear = more load on the hub. However things are never equal. With the exception of cargo bikes for heavy loads, anyone looking for oversized cogs is doing so because they don't apply as much force to the pedals as someone who gets by fine with an 18t.

I don't make 28t cogs, but I do make 25s by welding a 25t Sturmey 8 speed cog (which fits an oversized 63mm driver) to an 18t cog. http://bikesmithdesign.com/SA/25t.jpg Price is $20 and how you keep them from rusting in the area of the welds is up to you.

Let me know if you do find 24s. Last I heard Harris was out of them. I have been told by SRAM-USA that they are no longer made. However the US guys aren't all that internal hub savvy, so they may still be available in Europe. Perhaps Sheldon can clarify whether 24s are or will be available.

Mark Stonich
mark@bikesmithdesign.com

BTW the best way to get low gears is with a small rear wheel. http://bikesmithdesign.com/MyBikes/20/20-2.jpg

cyqlist,
While it has nothing to do with the current thread, I'm interested in the rack. Did you make it yourself?

We sell a lot of the 24 tooth sprockets http://harriscyclery.com/saparts

For each tooth you add, the axle will need to move forward by 1/8", so going from 18 to 22 would be 1/2", 18 to 24 would be 5/8".

48/24 would not be nearly a low enough gear to cause damage to the hub, especially one of the old ones like you have. (Later English-made models were not as good steel as the older ones.)

I've gone very low with AW hubs, probably the lowest is 28 front 36 rear on my 54-speed tandem. I generally avoided using anything but the lowest hub gear when riding in the lower chain gears, so there is less strain on the driver prongs.

I am also quite careful about securing the axle against rotation, using two nuts on the left side for extra oomph. Threads well greased.

Sheldon "Sturdley-Armchair" Brown

I have a bike with a 3-speed SA hub with a triple crank and FD. This gives me 9 speeds. I used an old RD with a broken cable clamp to take up chain slack. I just used the limit screws to lock it in front of the cog. My chain rings are 48-38-28. The only modification required was thinning the cog so it would accept 3/32 chain instead of 1/8 chain as the 1/8 chain is too wide for the front and rear derailleurs. I have a metal lathe so I chucked the cog up and machined one side and used a file to correct the profile of the teeth on the cog after machining it. You can find cogs ready made for 3/32 chain. Check your cog and see if 3/32 chain will run on it. I did a bike like this for a friend and the cog on his hub fit narrow chain nicely without modification. In his case it was a simple assemble and ride setup.
You can't use a SA hub with coaster brake! Using the coaster brake will destroy the rear derailleur.

That's a cool modification and likely gives you a nice range of gears. And that's much cheaper than a 9-speed internally geared hub!

Neal

IIRC the Shimano? or is it SRAM? sprockets will run either chain size. I know the S-A won't. Neat idea!

Aaron:)

no need to thin 1/8" cogs for use with a derailleur. Modern SRAM 1/8" chain has nearly flush rivets and thin plates. It is narrower than derailleur chain was 20-30 years ago.

I know Harris has sold them in the past. But when a friend tried to buy one a few months ago he was told they were out. Have they gotten more in stock?

I read someplace that there was Cyanide used somewhere in the process to create these harder yet tougher steels.

It's not just the SA internals that were better back then. This morning I overhauled the BB and front hub of a well worn 1960 Rudge. Both were out of adjustment, grease all dried up and dirty. Neither the cones, BB spindle or cups showed any pitting at all, just a nicely polished ball track. A welcome surprise compared to parts from only a few years later. Especially front cones, which I rarely find to be good.

that really impresses me.. especially since rohloff warns about gearing too with their hubs in tandem applications

btw, i've asked in the past but can't recall a specific method, but is there a good way to visually determine the earlier well-hardened s-a internals ?