Bicycle Mechanics - Sheldon's Sturmey Archer 3 spd conversion
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05-28-08, 07:48 AM
I've been reading Sheldon Brown's article about a SA AW 3 spd hub with a 6 or 7 speed cluster added onto it, I can follow it OK, but I just want to know how he secured the cluster to the hub.
Also, he mentioned that he used the longest SA axles available..where can I find one of those?
I know it would be easier to get a Sachs 3x7 or even a Sram dual drive 3x9, but I've got most of the parts needed for what would be an interesting project.
05-28-08, 08:31 AM
The longer axle is the 6 1/4 one listed on the Harris website: http://sheldonbrown.com/harris/sturmey-archer-parts.html
I got one of off ebay.
..how he secured the cluster to the hub.
Apparently there are two different drivers available for the S-A hubs, one splined that's more common and one threaded that's quite rare. If your hub have the splined one there are no easy solutions, if your hub has the threaded driver then it will take a standard freewheel.
05-28-08, 03:30 PM
Thanks for the replies,
I have the more common splined one so this may be a problem, however, I have a friend who has done this conversion a few years ago so I will check to see how he did it.
It would be better do the Sram Dualdrive,as the 3 speed hub is better and it is an off-the-shelf solution.
The best option for Sturmey would be to get a custom driver machined that accepts standard Shimano cassettes, along with the threading for the lockring.
Another option involves using a triple crank, adding a FD and shifter, and an old RD as a chain tensioner. Using a triple crank turns your 3 speed into a 9 speed. The only problems you can run into is the cog on the 3 speed hub must be compatible with 3/32 chain and it can't be a coaster brake hub. You don't need a cable and shifter for the RD, you just use the limit adjusting screws to align the RD with the cog. As you switch crank chain rings the RD will take up slack. If I remember correctly Sheldon Brown had an article about how to do it.
Another option involves using a triple crank, adding a FD and shifter, and an old RD as a chain tensioner. Using a triple crank turns your 3 speed into a 9 speed. But that doesn't do as much as you might think. Either you can pick 3 fairly close chainrings that'll let you split the old 3 into smaller increments w/o widening the range much. Or you can use bigger differences between the chainrings for a wider range and get duplicate gears.
06-01-08, 02:26 AM
Sixty Fiver from the folding bike forum has mounted a 16t and a 18t Shimano dished rear cogs back to back, to his hub, then added an old style claw hanger and RD making it a 6 speed. He says it works smooth as butter.
If I added a FD to a double or triple crankset.........
But that doesn't do as much as you might think. Either you can pick 3 fairly close chainrings that'll let you split the old 3 into smaller increments w/o widening the range much. Or you can use bigger differences between the chainrings for a wider range and get duplicate gears.
I've done it and got a huge range from it, especially when using a 42-32-22 ATB crank set. Most SA hubs came with a 16 tooth cog and fitted with a 44 tooth chain ring. Considering top gear was too high for 80% of riders dropping 2 teeth on the chain ring is an improvement on the top end. Gearing is much wider with SA hubs and it's common to find them in thrift stores and flea markets on old bicycles. Granted; a couple of gears will be very close such as mid gear on the 32 chain ring and low gear on 42 chain ring but you have the same problem with typical full front and rear dérailleur systems as well with the same ratios found between chain rings and cobs. The real advantage is when your hill climbing with the 22 chain ring in low or middle gear providing gear inch ratios lower than is possible on any standard front and rear dérailleur system.
I've done it and got a huge range from it....
Assuming a 26" wheel and feeding your numbers through Sheldon Brown's gear calculator I get:
Which is a little less than you'd get from middle & big + 9-spd cassette for a hybrid running a triple front. A decent range, distributed over say 7 gears with significant differences. You'd need a fairly narrow frame of reference to call it huge though.
...The real advantage is when your hill climbing with the 22 chain ring in low or middle gear providing gear inch ratios lower than is possible on any standard front and rear dérailleur system.
You better check your math. A front triple 22-32-42 together with a 11-34 cassette would give you:
3.9 5.7 7.4
3.3 4.8 6.3
2.9 4.1 5.4
2.5 3.7 4.8
2.1 3.1 4.1
1.9 2.7 3.5
1.6 2.4 3.1
1.4 2.1 2.7
1.3 1.8 2.4
which would be quite a lot lower than your 2.0, and all that's using all standard components.
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