Gearing Question

[wrongway]

I was on my way to duplicating a Raleigh Lenton Convertible that is currently on Ebay. Nice bike there, but just too short for me. I have the Cyclo Benelux Shifter and it works, but while I was sorting things out the other day I realized I liked just having the 3 speed hub instead. The Benelux has a 23 tooth sprocket for it's biggest gear. Do they make a 23tooth Sturmey Archer gear? I've seen 24. I hate to change things as it feels perfect to me. Good hill climbing and speed. The chain ring is 44 which I'd like to keep. Any thoughts?

 

[TR6SC]

I was on my way to duplicating a Raleigh Lenton Convertible that is currently on Ebay. Nice bike there, but just too short for me. I have the Cyclo Benelux Shifter and it works, but while I was sorting things out the other day I realized I liked just having the 3 speed hub instead. The Benelux has a 23 tooth sprocket for it's biggest gear. Do they make a 23tooth Sturmey Archer gear? I've seen 24. I hate to change things as it feels perfect to me. Good hill climbing and speed. The chain ring is 44 which I'd like to keep. Any thoughts?

Hey wrongway, I'm with you on the SA 3-speed. The cogs come in different numbers of teeth depending on whether you go with flat, dished, or deep dished. I haven't seen a 23, but there's lots of stuff I've not seen. Perhaps @SirMike1983 can chime in. I've got a 48/24 set-up. Perfect. SA suggests you do not exceed the 2:1 ratio on the AW hub. That would limit you to the 22 tooth rear with your 44 chainring. Surely the wings won't fall off with an extra passenger on the plane, but that's what SA says is the tops.

 

[wrongway]

I did see a 23t on ebay just a bit ago. It was 1/8" chain. I think that's appropriate....isn't it? I have a 48/22 set-up on my '63 Raleigh Sports, but wanted to go with fast and somewhat of a climber. What would 46/24 feel like?

 

[bulldog1935]

http://www.sturmey-archer.com/en/products/rear-hub-sprockets

22t and 24t seem to be readily available. Changing between 23t and 24t is about 3 gear-inches difference in high gear, and less in lower gears, which you'd hardly notice.
If the bike has 26" wheels, I'd use the 22t.

http://www.sheldonbrown.com/gear-calc.html

fwiw, I changed my daughter's Nexus 8 from 44T/20t to 42/22t, and it essentially changed it from a city bike to a touring bike.
High gear dropped from 97 inches to 88 inches, and two lowest gears on the 8sp became load-climbing gears for steep hills.

And honestly, I sure would keep a factory Convertible original - even if you don't use the RD

 

[TR6SC]

Here's the math....Front teeth divided by rear teeth times the wheel size equals gear inches. 48/22X26=57 so 46/24X26=50. Count all the teeth on your 10-speed, do the math to find out what each combo gives you in gear inches. Remember to use the correct wheel size. This will allow you to use your road bike to get the feel.
Whatever ratio you end up with for sprocket sizes will give you Second Gear or N on the Sturmey AW. Factor in the percentage changes to find the gear inches for Hi and Lo.
First or Lo gear is 75% of N or 2nd, and Third or Hi gear is 133% of N or 2nd.

 

[wrongway]

http://www.sturmey-archer.com/en/products/rear-hub-sprockets

22t and 24t seem to be readily available. Changing between 23t and 24t is about 3 gear-inches difference in high gear, and less in lower gears, which you'd hardly notice.
If the bike has 26" wheels, I'd use the 22t.

http://www.sheldonbrown.com/gear-calc.html

fwiw, I changed my daughter's Nexus 8 from 44T/20t to 42/22t, and it essentially changed it from a city bike to a touring bike.
High gear dropped from 97 inches to 88 inches, and two lowest gears on the 8sp became load-climbing gears for steep hills.

And honestly, I sure would keep a factory Convertible original - even if you don't use the RD

Oh, I didn't explain that quite right. I got in a hurry. I don't personally have a Convertible. I just have a '69 Raleigh Sports that I've been playing with and have added the Cyclo to. No, I wouldn't change an original Convertible. I wish I could get that one on ebay, but it's just too short.

 

[SirMike1983]

Going 2:1 (front to back) will give you a climber gear in low on the AW. It will be a dedicated climber, because you'll spin out on a flat, even pushing into a steady wind. Exceeding 2:1 will produce an even more dedicated climber. Sturmey's advice back in the day was not to exceed 2:1 because it would supposedly cause accelerated wear on the hubs. I've never destroyed a hub that way, but then 2:1 is the biggest ratio I have on any bike right now.

I would not be afraid to exceed 2:1 if only one cog is "too big". Sturmey assumes a single rear cog running all the time.

Once you've decided on low gear, then go to a gear calculator like you'd find at Sheldon Brown's site, and space your rear cog sizes to avoid redundant gears. You should be able to keep your 44 tooth front. If it were my bike, I'd have a 22 rear large to go with the 44 front (2:1 in your low Cyclo gear) and then space using a calculator to avoid repeating gear ratios. I can see needing an even bigger rear if you live in a really hilly area though.

Just be aware that Cyclos usually have a set number of gears (the cage often will tell you how many cogs it takes).

You may end up needing the longer 6 1/4 axle to make space.