mornview

I know most 3 speed IGH's are usually set-up with a low gear, direct drive, and a high gear. I normally ride single-speed with 66 gear inches. That's about the common gear-inch set-up for most three speeds in direct drive.

Now I don't really have a use for more than 66 gear inches. I mean, I guess it would be nice, but not nearly as useful as having two lower gears would be. For being the midwest, there are some pretty nasty climbs out where I'm currently at.

Would it be safe to run a larger cog on the hub to effectively make high gear 66 gear inches? I just seem to remember reading something saying that the internals of these three speeds don't take kindly to having low gear geared so ... low. I've overhauled a few AW's and don't see why this should be true.

Also, what about non-AW 3 speed hubs? Are other 3 speed hubs tolerable to being geared so low? I ask this mainly because I'd really like to run with a 3 speed coaster brake hub, but I know Sturmey's early attempts at 3 speed coaster brake hubs don't have the best reputation ...

Thanks in advance!

bulldog1935

here's sheldon's gear calculator with your IGH already built into the algorithm.
Sheldon Brown's Bicycle Gear Calculator

I turned my daughter's Nexus 8 from city gears to touring gears by adding 2 teeth to the drive cog and subtracting 2 teeth from the chainring - kept the exact same chain length. Something to consider.

fietsbob

It Depends .. generally the middle gear is a result of the Gear ratio of the chainring & Hub cog.

the overdrive 3rd is 100% + the reduction gear a % minus [ AW3 its 1.33 & 0.75 (4/3 & 3/4) ]

S-A S3X direct Drive is 3rd, 2nd is .75, 1st is .63.


New Owned by Sun Race of Taiwan S-A Hubs are quite nice .. I have the 3 speed they supply to Brompton Mfg.

My 2nd Brompton, 1st one had a British made hub the trigger shifter pulled into 1st gear with some effort

The new Shifter and hub combination shifts quite easily.





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mornview

Exactly. By setting the bike up so that high gear is 66 gear inches (effectively giving me two gears below 66 gear inches), I'm looking to achieve high gear (100%, at 66 gear inches), middle gear (67%, at 44 gear inches), and low gear (42%, at 28 gear inches) by switching to something like a 44/26 setup for chainring/cog.

I understand the math behind it; my question is if these hubs tolerate something as low as 28 gear inches? Obviously that's a good deal lower than what they were geared for stock.

mornview

Good to hear. Going for something like an 8 speed would obviously solve a lot of my concerns here, but I really want to stick with a three speed if possible.

fietsbob

S-A Hub cogs are now made from 13t_22t in 1/8" and 3/32"

Sachs was a tiny % wider .. .73; 1; 1.36 X (data source the sheldon chart)

IMO the gears never dis engages, the pawls are what changes their functions.

by 28 you mean 1:1 in a 28" wheel?





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bulldog1935

No, I think you should try the +2/-2 thing with your existing 3 speed - at least plug it in and see what you get.

Here's the gear-chart on my daughter's Nexus. It gave her four useful climbing gears. It's a 400' climb to get to our house, including some 14% grade.



guess the other choice would be add 4 teeth to the rear cog and keep the chainring, but you'd need to add a chain link.

or, keep the cog, subtract 4 teeth from the chainring and remove a chain link

mornview

No, I mean I would get 28 gear inches in low gear riding with a 44t chainring and a 26t rear cog (available from bikesmithdesigns).

bulldog1935

28" is low enough to spin-climb a 14% grade

mornview

Adjusting the amount of teeth on the chain is just something I've accepted I'll have to deal with. Not a big deal in the grand scheme of things.

I'm pretty set on this gearing, though. 66 gear inches has always been what's felt right as my main gear, so I don't want to lose that as one of my gears. On the other hand, a buddy of mine that rides with a derailleur set-up needs to get into a gear combination that works out to be almost 28 gear inches on the dot just to get up some of the hills around here. So I really feel like I'd be set if I could pull off this conversion ... just looking for some input before I potentially destroy a hub doing so .

bulldog1935

you're doing great - here's how I do it on two other bikes:

cyclotouriste triple I've climbed 18% grades on this



wide compact double

fietsbob

I run my folding Brompton with a 2 speed Mountain drive crank & a 3 speed hub

15:54 low range acts like a 21.6t chainring ( Crank runs thru a reduction gear)


my low in low range (1)is 17.4 High in high range (6) is 77.1

low in high range (4) is 43.4 high in low range (3) is 30.8





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3alarmer 

...to the OP. I've run AW hubs on a lot of stuff, with various cogs on the hub freewheel up to about 24. The hub itself has presented no problems in doing this, and this is the first I've heard of any recommendation about avoiding low gears. I've never seen a cog for these larger than about 24 teeth, but it's a standard cog with the three indents like you see on a lot of coaster brake and other geared hubs, so if youi say you've found something, I believe you.

You could, of course, go with a more compact crank chainwheel, but I don't know what youi're working with.


Lastly, if you can find one, SRAM makes a very nice five speed IGH, and I think it comes in a coaster brake model. I just did a project bike designed around one of these on a track frame. But SRAM has terrible marketing and service in the United States for their internally geared product hubs.

Darth_Firebolt

just as a note, you can use any individual sprocket from a cassette as a sprocket on an IGH if you have some machining ability (dremel and patience).

noglider 

In theory, gearing your AW hub low is dangerous, but not many people have had problems. Besides, you know how to overhaul it, so if you wreck your pawls, you can replace them.

But you may not be happy with it. You're riding single speed now. One low gear might be nice, but the lowest one will probably be useless. Then again, I've never been happy with all three gears on a 3-speed. At best, I'll use two of the gears. They're just too far apart for me.

I had one of those newfangled 3-speed fixed gear hubs. Gearing is a little narrower than in an AW. It was a fun toy, but I got bored with it and converted the bike to a regular old fixed gear. I haven't regretted it. The bike is nice and light.

fietsbob

The S3X is the lower 3/5 of their 5 speed hubs.. they dont use the 2 overdriven gears..

You could use a Patterson metro crank Patterson Bike - Rocket Fast Shifting | Cannot Throw a Chain for the higher gears ,
if you were willing to spend the Dosh.

bulldog1935

My daughter's Nexus was her first real bike, and the idea was to get her to learn to anticipate shifting on our hills - it worked.

kingston 

I run 34T/20T (35/46/62GI according to sheldon's calculator) on my Sturmey Archer X-RD3 and haven't had a problem so far, but I also don't have a lot of miles on the hub either. I'm not that worried about it.

3alarmer 

...just in passing, I've been experimenting with a SRAM two speed Automatix hub on a track bike I didn't want to drill for brakes (it has a coaster brake). So far, I like it. I think my knees are too old for a single speed fixed gear bike any more.