Sturmey Archer SRF3 Gearing

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AaronR
Posts: 272
Joined: 18 Jul 2014, 8:12pm

Sturmey Archer SRF3 Gearing

Postby AaronR » 18 Oct 2016, 7:16pm

Evening all (Hi Brucey!)

After a few weeks and now up to about 300 miles having a review of the gearing on my Kona Paddy Wagon 3, especially after adding luggage

Standard gearing (thank you http://www.sheldonbrown.com/gear-calc.html ) makes gear inches (42t front, 16t rear, 170mm cranks and 700*28 tyres) approximately 56.2", 70.2", 102.2" if I manually input the rear sprocket sizes as 20t, 16t and 11t for gears 1 (-25%), 2 (100%) and 3 (+33%)

Changing the rear sprocket to 18t would make that (approximately) 51.1", 62.4" and 93.7", next jump would be 20t to give 45", 56.2" and 86.5" as 19t makes very little difference for comparison

On paper the 18t would be best for my regular use of the bike, and would make gear 2/direct drive the most used, but I understand that Sturmey don't make the 18t in flat, only dished as seen here https://www.sjscycles.co.uk/sprockets/s ... cp-hsl838/

If anyone knows different and can point me in the direction of a flat 18t sprocket for the SRF3 https://www.sjscycles.co.uk/hubs-intern ... n-36-hole/ that would be perfect! Kona have been generous enough to fit a steel front ring, so replacing that is expensive in comparison to £3 for a rear sprocket just to change gearing, standard chain is 3/32, so other question is how much would the +/- 2mm change in chainline affect things? The dish will move it out towards rear stays, chain now has a bit of play in it, and if it makes things tight could change chain to 1/8 for a bit of lateral play?

Apologies for prattling on... I know that for £3 I should just buy one and see how it goes, but if there are flat sprockets out there I'd rather go for one of those!

gerrymcm
Posts: 446
Joined: 30 Oct 2012, 2:52pm

Re: Sturmey Archer SRF3 Gearing

Postby gerrymcm » 18 Oct 2016, 7:50pm

I think this will fit but please wait for confirmation from more knowledgable folk here.

https://www.sjscycles.co.uk/sprockets/1 ... -hubs-332/

I have Paddywagon and like it a lot but knees are playing up so can't SS any longer, I'm interested in how you get on.
good luck

Brucey
Posts: 35590
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer SRF3 Gearing

Postby Brucey » 18 Oct 2016, 8:41pm

yup, a SRAM or Shimano IGH sprocket will also fit. BTW these (in 3/32" form) will in theory also allow the chainline to be fine-tuned, because the sprocket is ~1/8" thick where it mounts and the mounting is offset by ~0.6mm. A word of warning though; if the three drive lugs are facing rightwards (rather than leftwards) the sprocket may wear and then slip on the driver, because it won't be engaging with the slots in the driver properly.

If you want to use a dished sprocket, you may be able to respace the hub and redish the wheel slightly. Another option is to use spacers on the BB to move the chainline a bit.

BTW a 23T sprocket (I think that SRAM make such) would give you a ~66" high gear (and a nice low bottom gear too);

http://www.gear-calculator.com/?GR=SAAW&KB=42&RZ=23&UF=2150&TF=90&SL=3.5&UN=MPH

hth

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

AaronR
Posts: 272
Joined: 18 Jul 2014, 8:12pm

Re: Sturmey Archer SRF3 Gearing

Postby AaronR » 18 Oct 2016, 9:36pm

Thanks

Will give one of the Shimano/SRAM sprockets ago, and probably the Shimano as it's cheaper

The Paddy Wagon 3 is great, very compact frame, have had to resort to SKS race blade 2/3 length guards and P clips for rear rack

Might regret fitting Marathon + tyres as they aren't very confidence inspiring at pace

Should be able to fit an IGH hub to a Paddy Wagon easily enough?

Brucey
Posts: 35590
Joined: 4 Jan 2012, 6:25pm

Re: Sturmey Archer SRF3 Gearing

Postby Brucey » 18 Oct 2016, 9:46pm

AaronR wrote:

Should be able to fit an IGH hub to a Paddy Wagon easily enough?


back end is 120mm, so an SA 3s hub can be made to fit OK. I can't see any big problems arising...?

cheers
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