Sturmey Archer AW3 info

[Bromptonlad]

I have began racing the local time trial league with my S1E for a bit of fun, so that is single speed with S flat bars. Unfortunately, a 54 x 12 only gives me a 73 inch gear, which is a bit short for our local course... I still managed to average almost 21 mph, but I was spinning like a mad man and I feel I need a bigger gear if I want to go faster, which I do.
A bigger 58T ring will only give me 79 inches, which is better but still a bit short and of course I will need a longer chain.
I was offered an old Sturmey Archer AW3 hub, which I could build into a wheel, which gives a 1.33 up in its third gear, so that would open up ratios in the 80 and 90 inches, depending on the sprocket. However, I don't want to have to fit the shifter, as I am quite happy keeping the bike as single speed.
My question is: if I remove the cotter pin and chain, will the hub naturally jam in the biggest gear? And if so, is there anything else I need to be aware of, like chain tensioner issues or else?

[LittleWheelsandBig]

The AW hub will naturally default to top gear.

There is some possibility of the hub jumping in top gear under heavy load, more so if very worn. I raced the 2019 Brompton World Champs, mostly in 5th and 6th gears and had no problems with the BWR hub jumping but the AW hub is more susceptible.
https://yarchive.net/bike/sturmey_archer_hubs.html

[Bromptonlad]

I guess the good thing about testing is that I won't be standing on the pedals when the gear jumps... 

[Pickled Onion]

In terms of mechanical efficiency, top gear on an internally-geared hub is the worst one to be in. But I guess if you're testing on a Brompton you're not that bothered about efficiency.

http://ihpva.org/HParchive/PDF/hp52-2001.pdf

[LittleWheelsandBig]

Efficiency generally improves with increased power, so TTing is a good use.

[Bromptonlad]

there is no real alternative. Even with a 58 t ring, which is a bit of an awkward fit, I only get 79-80 inches with direct drive, I can maybe do 22-22.5 mph, so the hub gear is the only way to unlock higher speeds.
I suppose I could try an 11t sprocket from Aliexpress, I have seen them in titanium… they look scarily thin

[LittleWheelsandBig]

I have cracked a Sturmey 12t cog but not a Shimano-splined 12t.

[Bromptonlad]

I have cracked a Sturmey 12t cog but not a Shimano-splined 12t.

the problem with the 11t is that once you remove the ridges that end of cassette sprockets have, as a splined sprocket has very little material left. Take a look

https://www.aliexpress.com/item/1005002329848302.html?src=google&src=google&albch=shopping&acnt=494-037-6276&slnk=&plac=&mtctp=&albbt=Google_7_shopping&gclsrc=aw.ds&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&src=google&albch=shopping&acnt=494-037-6276&slnk=&plac=&mtctp=&albbt=Google_7_shopping&gclsrc=aw.ds&albagn=888888&ds_e_adid=&ds_e_matchtype=&ds_e_device=c&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=en1005002329848302&ds_e_product_merchant_id=109237970&ds_e_product_country=GB&ds_e_product_language=en&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=17866112291&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gclid=Cj0KCQjwu8uyBhC6ARIsAKwBGpTmtSHGBLzdw2oS9rpw5BV2BNmRouxPl6y-9txqNTtEJPVPRMCg3E4aApqNEALw_wcB&aff_fcid=7dc7a56aa97d4d79aa8d5dfaf3001087-1716755634598-06413-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=7dc7a56aa97d4d79aa8d5dfaf3001087-1716755634598-06413-UneMJZVf&terminal_id=4ef24ec12a9544c5810a3ad130fd554c&afSmartRedirect=y

[LittleWheelsandBig]

Too true.

[Bromptonlad]

If it stops raining, I'll be racing tonight with the 58 x 12, around 79 inches with my tyres... see how that goes.

[Bromptonlad]

28:25, 39 seconds faster than last week… 79 inch is a better gear, but I was still spinning on some downhill bits… on balance an 83 would probably be just about right, maybe tall on the draggy bits, but there aren’t many on our Tuesday night course.
Now tinkering with the AW3 I have been given. The axle is too short on the drive side. I can only secure the hub in place with the nut that holds the tensioner, not the other. Dropouts are vertical and I am not doing jumps, so I think it should be OK… thoughts?

[Bromptonlad]

An update.
Got the AW3 hub from a friend for free, I got hold of a 13/32 nut that was missing and replaced the 1/8 sprocket with a 15T 3/32 one that fits my chain. Bought rim and spokes from SJS Cycles, original Brompton parts and I built the wheel. Easiest wheel I have ever built, it literally took less than an hour.
Just rode it into work this morning, stuck in an 83 inch gear... a bit of a grind, but it seems to work fine. I Haven't tried to ride it in anger yet, but I am looking forward to 
Shame you can't post photos on this forum

[Tim Hall]

An update.
Got the AW3 hub from a friend for free, I got hold of a 13/32 nut that was missing and replaced the 1/8 sprocket with a 15T 3/32 one that fits my chain. Bought rim and spokes from SJS Cycles, original Brompton parts and I built the wheel. Easiest wheel I have ever built, it literally took less than an hour.
Just rode it into work this morning, stuck in an 83 inch gear... a bit of a grind, but it seems to work fine. I Haven't tried to ride it in anger yet, but I am looking forward to 
Shame you can't post photos on this forum

Sounds like a good bit of fettling.  Re posting of photos, you can, just not directly. There's several threads on how to do it in Office Reception

[rogerzilla]

I used to TT on a 90" gear because the start was downhill.  86" would have been better for the flat bits, but spun out for the first half mile.

[Bromptonlad]

I used to TT on a 90" gear because the start was downhill.  86" would have been better for the flat bits, but spun out for the first half mile.

I have a few options now. I have ordered a Brompton 13T sprocket, which is 3/32.
So that will give me 84 inches with a 50T ring (accounting for the 1.33 upgear) or 90 inches with a 54T ring. I can archive the 58 T ring, which was an awkward fit.
Our Tuesday course has a downhill start, but then a few drags, not sure I can hold 90 inches all the way, but it will be worth trying, at some point.

[Bromptonlad]

I seem to have stalled at around 33-34km/h depending on the course/wind. Aim for the season is to get to 35…
AW3 is doing fine, no issues once I bought a pair of those washers that prevent the axle from spinning… no advantage as yet by using 83 inches as opposed to 79

[Bromptonlad]

Back to the old hub… 50x17= 48 inches… I did a hill climb race, 126 vertical meters, average grade 10%… managed to do 6:39, which is a minute slower than I did last year with a more suitable 7kg race bike…
Quite impressed with the Brompton