Spend enough time around the Three Speed Internet (admittedly, not that big of world), and you’ll see some variation of this question come up:
I heard that you should never go over the 2:1 Ratio on a Sturmey-Archer hub, but I want to get lower gears. If I went over this ratio, will I wreck the hub’s internals?
This ratio mentioned pertains to gearing, which is figured out by front chainring and rear cog. Because too much torque can destroy the workings of a Sturmey-Archer hub, AW or otherwise, the rule of thumb is don’t go over the 2:1 ratio, meaning if you have a 46 tooth chainring, go no bigger than a 23 tooth cog.
But there is big interest in “going over”, namely, getting a bigger rear cog. This will lower the gearing, and lower gearing means easier hill climbing. With the 2:1 ratio the lowest gear is going to be in the high 30 gear-inches. And that’s not particularly low. For instance the lowest gear on my old Surly Long Haul Trucker touring bike was probably 17 gear-inches, and even with that low of a gear I still would want lower if the hill was steep and/or long enough. So the temptation to go lower is definitely there.
So when someone considers going lower, they’ll always ask the Three Speed Internet first for validation or condemnation. They’ll eventually get two responses: “I’ve had a 26 tooth cog and 44 tooth chainring on my LTD for five years and no problems, mate.” And then: “I tried a 26 tooth cog and 44 tooth chainring on my LTD and within three months the inside of the AW hub was dust.” The original poster will end up getting the big cog if they feel compelled enough by the first story, or scared off of the idea if the latter strikes stronger.
So why two different results? I am not a bicycle mechanic, so take this all with a grain of salt. But I feel it comes down to three factors:
- How much the rider weighs
- The style of riding
- How good the hub is in the first place
It’s entirely possible that you can flaunt the 2:1 ratio and get away with it if you weigh 140 pounds, don’t mash the pedals, and your hub was an earlier example before Sturmey cheaped out. But if you’re closer to 300 pounds and load up your bike frequently, mash those pedals, and have one of the late period British Sturmey hubs from the era when they let the tooling wear down to nothing, well, you probably won’t get away with going over.
I’m generalizing here. It’s not a black/white thing, it’s more of a spectrum. And just because you got away with the 26 tooth cog and 44 tooth chainring for five years doesn’t mean it’ll last for six. I’m sure pure luck is also a factor.
Me? I make sure I stay within the 2:1 ratio. But maybe you want to take your chances. Go for it. The worst that can happen is the hub and/or axle gets destroyed. The beauty of AW hubs is you can simply dump out the old broken one and plop a good one in. So factor in how much risk can you take. Is the hub a garden-variety AW, or a more esoteric and rare one that can’t be easily replaced? Do you just ride around town or do you go on long rides in the country, away from bike shops, transit, or cabs/rideshare?
I wish the 2:1 ratio was as hard and fast as Sturmey-Archer insisted it was. But it isn’t. Life is inherently risky, and that’s what can make it exciting.
Society Of Three Speeds 
Where is this 3-speed internet you speak of? I have not, as yet, been ab
Did you mean to write more? All I got is what we see here. Was this somehow filtered through a Shimano 333 hub? 😉
“I wish the 2:1 ratio was as hard and fast as Sturmey-Archer insisted it was.” I’ve had several folks tell me SA specifies 2::1 for their 3-speed hubs. I’ve asked for links or verification from a Sturmey document. No one has been able to provide one. So, official or mythology?
It was definitely official at one point, but where that original document(s) are now, I don’t know. I’m sure if I really dig through some old books I’ll find something. It probably wasn’t mentioned much at the time, as three speeds were typically geared high (18 tooth cogs) and people didn’t change them out.
The Bike Shed mentions the 2:1 ratio and Sturmey’s recommendations here:
https://bikeshedva.blogspot.com/2014/12/a-few-sturmey-archer-ratio-notes.html
Good summary. The 2:1 limitation was given in one of the Sturmey Archer repair guides many years ago (I should dig through my stuff and find which one it was because this comes up so often). But most of the repair guides, including later ones, don’t have this limitation included (it isn’t mentioned). I don’t know whether that means it was a guideline that was given for awhile and later withdrawn, or whether they just decided to omit it because the stock cog was 18 teeth. I think people obsess over it too much sometimes.
The question of whether going past the 2:1 limitation is safe, as you say, really does not get a bright line “yes” or “no” answer. The allegation is that exceeding 2:1 exerts too much input force to the hub. However the sprocket-cog ratio is not the only factor for input. You have to also consider the weight of the rider, the exertion of the rider, and the crank length (leverage). If you’re a careful rider and not thrashing on the gears, I would think exceeding 2:1 would be OK. A powerful, heavy rider who tends to mash will damage the hub sooner, in a variety of ways.
You also have to consider that guidelines like this (regardless of whether given and withdrawn or not) tend to be conservative. A company will usually give these guidelines based on the most conservative engineering advice. It will be something that limits warranty claims, so safe for 99% of riders.
Before getting hung up on the 2:1 advice, the bigger factors for the life of the hub will be proper lubrication, proper adjustments, and reasonable behavior while riding. If the hub is ridden a lot or in bad weather, it should be broken down periodically to check and replacement of the higher-wear parts.
I think 2:1 is a good ratio for hilly terrain, though I will add you’re taking a lot of the top-end away in high gear. My preferred ratios are 46 front 22 rear or 48 front 22 rear. They help a lot with climbing and leave just enough top-end to pick up steam going downhill. Low and normal gears are climbers in those ratios. I found 2:1 took away too much top end for my liking on the downhill. I’m not really a “fast” rider either.
Just remember to have fun and not overthink this stuff.
Thanks for the comment, Mike! You are right that if you concentrate too much on getting a low-low, your top end will suffer. Ideally Sturmey would have created a hub with a lower low altogether, instead of the 75%-100%-133% gearing of the AW, the low would be like 60-66%. But we have to work with what we got.
I’ve had this question on my mind as well for quite awhile. I recently ran across an excellent YouTube video titled “Pedaling Dreams: The Raleigh Story”. Right around the 28 minute mark, the video delves into a discussion of the increasing interest in bicycle touring in the late 50’s and early 60’s (at least in Europe). It mentions a cyclist by the name of David Sore who used a modified Raleigh Sports to cycle around the world.
He wrote a book about his experience a number of years later which I found to be a pretty good read titled “A Journey Around the World; A Cycling Memoir”. In one of the appendixes, he describes his bike and the gear modification. It specifically identifies the use of a Sturmey Archer AW 3 speed wide ratio hub. However, he not only changed the standard cog from 18 teeth to 21 teeth, he also added a second cog of 28 teeth, which is quite beyond a 2:1 ratio given a 48 tooth front chainring. BUT…..and here is where it gets very interesting….he also added a 32 tooth front chainring alongside the stock 48 tooth ring giving him a range of 79 to 22 gear inches!!!
Remember, he rode this bicycle around the planet….quite an endorsement of the durability of the AW hub! He mentions that this was done before the advent of mountain biking which then made available extra low gearing for grunting up steep off-road climbs. Touring bikes into the early 80s like the vaunted Trek 720 came with a stock low gear of 27 inches, high by today’s standards.
For those adventurous souls out there in three speed land….I’d say have at it and let us know how it works out for you.
Thank you for all that!
Since my first experience with the 2 1/2 mile Maiden Rock Hill on the Lake Pepin tour, I’ve been working each successive year on engineering my way over the top. I’ve run a SA FW four speed, a Taiwanese SA 5 speed and this year, the plan is to go back to the Raleigh Sports with an AW. The twist here is I will have a derailleur with a 16 and 24 tooth cog fitted to the back. I’ve got a Williams Raleigh chainset with a 40 tooth on the front and expect the best of all worlds.
I am the proverbial heavy rider, and I’m flaunting the 2:1 rule right in it’s face. There are more AW hubs in the world, and I’ll take my chances. I do have to question the rule. I paid attention in 7th grade physics and figure it is the same amount of “work” expressed in foot pounds, to move my mass (with an “m”) over the hill, and if I apply that force by standing up or sitting down, at the top, the same stress has been applied to the pawls. I realize it may be the “bursts” with low gears, but between maintaing an AW hub or my heart, I’m going to preserve the more valuable one. I don’t think I can replace my heart for 30 bucks.
Well, maybe not now, but give us a few years with advances in biotechnology, they may be able to replace your heart for $19,99!