Roll-Monroe-Co

From the unknown mists of time in my hub drawer, I have a Sturmey-Archer X-RF8, the first production batch of these "low-normal" eight-speed hubs.

I'm thinking of setting up a 559-wheeled MTB with this hub.

I've read the John Allen's Sheldon Brown article about this hub, which only says that you have to consider smaller chainrings for this hub to get a range of gearing that goes up and down.

What I'm wondering is whether the tiny chainring necessary to get a useful gear range with a 26" wheel will put unsustainable torque on the internals (or, as Mark Stonich once memorably said, "make guacamole"). Any thoughts? Probably not, or Sheldon Brown article would have mentioned this. But I thought I would check.

There is also the consideration of the hub's reliability. What is the typical failure mode? If they fail, can they be repaired, or are they toast? Would building a wheel with this generation of the hub be a dumb investment?

Also out of curiosity, I could mentally reclassify the X-FR8 as a sunk cost and buy a new, complete wheel if the cost was similar to building one from the hub I have. Anybody know where one can get a pre-built, 559 7- or 8-speed IG wheel?

Thanks.

fietsbob

Low is the 1:1 cog drives hub directly.. that x wheel diameter is your low .. 26"

If the chainring has the same tooth count [made somewhat difficult .. hub goes for odd numbers, 25, 23, 19.

chainrings, at least the little ones, typically, are even numbers.. 24, 26, 28.



Advantage comes with building up the hub in a smaller wheel ,

you might build up a minivelo with 406 or 451 rims.. or a folding bike..


as to last Q , dont you have a bike shop around you?

Roll-Monroe-Co

Uh, thanks, I think. As I said, I'm aware of how it's geared and what would be necessary to make it work in principle, which is the reason I posted.

My question was whether gearing it so low would turn the internals to goulash.

Yes, lots of bike shops. I'm assuming you didn't mean to be as condescending as you sound. I had in mind sources on the internet or not local to me that built them (or had them built) that would be cheaper than asking my LBS to do it. That's why I used the word "pre-built." Around here I could have them custom-build me anything, but it would not be very cheap, compared to retail prices I have seen on already-built IGH wheels in the past.

fietsbob

the torque of reduction gears tends to be harder on little internal gears,
because the force you are resisting is Gravity + the added leverage of the gear ratio.

so companies like Rohloff state the minimum chainring size for a given cog.

on the upper end no limits are stated , because the force to over come, is acceleration &
air resistance of you moving through the air. on more level or even downslope ground.


another example : Schlumpf makes a mountain drive and a high speed drive , the gear is the same 2.5:1

reduction gear it needs a strap around the chain-stay, and a reaction strut lever ..* or a stop knob

overdrive , you just chamfer the BB shell and put a compressible
gripping conic washer between the 2..
friction and the compression-ring digging in is sufficient.

* I have a MD on my Brompton .. there is a shelf behind the BB shell
to set the Torque levers stop knob on top of it.

Roll-Monroe-Co

Yes, that's why I'm asking if anyone knows the specified or practical limit of this particular hub.

fietsbob

S-A USA Rep's office is is in California , North Bay Area , drop him an EMail .

NB: there are no reduction gears in the SA X-RF8, to re-state.
1:1.2 has been used by others .

28:25

cycle_maven

Well, Sturmey-Archer sells a 38-toothed crank to go with the 8-speed hub. The low gear would be 38:25 and the high would be the equivalent of 38:8 or so (which would be about the same as a 52:12). That's a little high for my tastes.

They did have some longevity problems on that hub when laced to larger wheels. I feel pretty safe with my 20" folder, but it seems a little fragile for putting 1.5 times the torque on it...

Bottom line: Try it with a 34-36 chainring, but use cheap spokes since you might be rebuilding the wheel with a Shimano Alfine.

ntdt

Sturmey-Archer has crankset FCS80 with 30t. I currently have a bike with 32t crank, 25t sprocket on 622 wheel.

surreal

Some notes:
-the earliest SA 8speeds were plagued with reliability problems; later ones have been better, but if yours is, indeed, an early example... beware.
-The torque-making-guac-of-an-IGH problem occurs in the underdrive gears; since you'll have the most torque in the robust 1:1 ratio low gear, and less torque as you move up thru the planets, you'll not likely have problems directly related to the gearing. I have seen, on the interwebs, folks with incredibly low-ratio SA 8 speed drivetrains; they didn't report any more problems than the folks with a more "normal" ratio.
-fietsbob has trouble posting here without chastising ppl for not supporting their LOS. Sometimes, when we're very lucky, he'll forgo the LBS support post and instead randomly suggest a Magura HS33 hydraulic rim brake. I have no idea why, but I will say that F-bob seems to mean well, mostly.

As I see it, you already have the SA 8 speed; it's not quite free, but it's money you already spent, and you'll likely wonder how it would've worked out if only you had built it. so, yeah, I'd go for it, if I were you. Just remember the limited cogs available for the hub, and select the ring that will give you your intended gearing, without concern to the torque-monster. If the small 'ring kills the hub, than it simply wasn't meant to be....

fietsbob

Even Joking , I'm well intentioned. ..

Dan Burkhart 

I have a wide range SA 8 speed in a 700c wheel, geared 30/25 for about 31 gi in low gear. I did experience a hub failure a while back when it started freewheeling in 4th gear.
I'm pretty sure it was caused by a sticking shift cable. It chipped a pawl and ring gear tooth, and as near as I can figure, the debris must have caused the freewheeling condition.
Sturmey Archer sent me a replacement internal assembly, but a thorough cleaning of the broken internaland lubing with ATF, and it's still buzzing along just fine.
My theory is, that you can pretty much gear it as low as you want to go, as long as you only use first gear for hard pedaling, as it's direct lockup across all 3 stages, and no torque is borne by the gear train.
I
m short of time right now, or I'd link to some videos I did of this hub. Maybe later.

tcs

Numerous posters on various forums have claimed the 'all up' Sturmey 8-speed hub was intended for small wheel bikes. When pressed, not a single one has been able to document any official statement or claim by the company stating that was actually the case. As previously mentioned, Sturmey sells a companion 30T chainset, and for the 2009 Interbike show they displayed bikes fitted with the XRF8(W) and 700C wheelsets.

I've ridden an XRK8(W) with a 30x25T primary on ISO35x590 wheels for 3+ years. It's schweeeeet. But where the XRF8(W) is a man, the older XRF8 is a boy. Seriously, the two designs share only concept and cogs. The original XRF8 design turned out to be the least valuable piece of intellectual property SunRace bought from Nottingham. Most posters on several forums report a lifetime of 500-1200 miles for XRF8 hubs, although the occasional user gets long, trouble free service. Production of the XRF8s ended in 2008, the warranties have long since expired and I can't advise on the availability of spare components.

tcs

Soma offers them.

tcs

SunRace built Sturmey-Archer hubs have a four character alpha-numeric code stamped in the hub shell. The first letter is the year of manufacture: A = 2001, B = 2002, etc.

Dan Burkhart 

There is no question that the all overdrive design lends it'self to small wheel bikes, and for a time, I bought into the line that this was a limitation, but my experience has convinced me otherwise.
They can quite safely and successfully be used in full size wheels.

Dan Burkhart 

Your build should be workable. The 28/25 combo will give you a gear inch range of about 29 to 96 which is quite serviceable and still well within the safe zone for torque input.
My XRF8 did experience a failure. I lost 4th gear. I contacted Sunrace USA and they sent me a new set of internals.
With the new internals in hand, and with nothing to lose but a bit of time, I cleaned and lubed the old broken internal assembly and put it back in. It worked fine. I can only assume it was the broken pieces preventing engagement.
I have not used the bike for a year or more. Too many bikes, not enough room, so it's stashed away in a dis assembled state.

fietsbob

Noting, They have a 4 speed now, still direct low, other gears go up in 25% increases.

fietsbob

Nope, not me.. I have , discontinued now, Sram i-9.. in a small wheel bike they're 4 reduction gears 4 overdrive gears..

AnkleWork

1. Make some assumptions or measurements of your maximum input force (weight + pull on bars + safety factor) at zero speed.
2. Calculate chain tension and torque at the hub for each combination of chainring and sprocket as recommended by SA (wheel diameter does not factor in).
3. Observe the maximum values from step 2 as design limits to select your desired chainring/sprocket combination.

It's just arithmetic, not scary.

Dan Burkhart 

To be honest, I think the Shimano Alfine is a better option for an 8 speed hub. The main reason I built up the 8 speed SA in the first place was to have a demo bike for prospective customers to try out.
I have dealer accounts with two North American Sturmey Archer distributors, and neither of them have stocked 8 speed hubs for quite some time.
Not to discourage you from your build, I'm sure it will serve you well. I'll just caution you from my experience to be sure to keep the shifting adjusted properly, and ensure the shift cable is free running. I think it was a sticky cable that lead to my failure.

Dan Burkhart 

I just ran your numbers through this gear calculator, and came up with this. Note the high torque warning in red.



It shows the gear inch range to be about 23.5 t0 75. Probably about what you want,
By massaging the numbers a bit, replacing the 25 tooth cog with a 23 and moving the chainring tooth count from 22 to 23, the high torque warning is gone, and the gear inch range is about 26 to 85. Still pretty rideable, except I don't know if there is such a thing as a 23 tooth chain ring.

The graph illustrates the greater ratio gaps at the top and bottom of the range compared to the 6 closely grouped ratios in between.

I think you will find the 33 tooth cg too big.

Dan Burkhart 

Well, that combo will be just inside the high torque warning, so assuming there is a margin for safety, and you won't be applying huge amounts of torque anyway, I'm sure you will be OK.
I have always felt that the low gear in this hub is capable of handling higher torque input because each stage drives the next in direct lockup. No torque is transmitted through the gear train.

Dan Burkhart 

Great stuff! Thanks for the update. My SA 8 speed bike has been passed on to my grandson and it's working great for him.

GamblerGORD53

Great bike brianhamp. Sure looks like my 1973 CCM, except the crank, chain guard and mine had an Alu stem. What is the name on your headbadge??

I bought mine 3 years ago all original with a SA 3. I wanted a drum brake on the back, so I went all in and got Dyad 584 rims and 38mm Marathon Plus tires. I'm disappointed it is 10% slower than the SA RD5w with 700c. After wearing out the antique front tire, 1930 miles LOL, I put the nice old hub with the new rim and spokes. The braking got WORSE, WTH. So the rims got lighter and the tires got heavier. LOL My SA 5w shifting went goofy with the indicator always sticking going back in.

Anyway, I have ridden My CCM to S. Cooking Lake, Millet and Gibbons. I had it 46/18T first, now 46/19T. Shift speed went from 14 to 10 mph. My tour super heavyweight is going great with a Rohloff. All last summer I was on tour to Oregon and back, 3,900 miles.

Dan Burkhart 

One thing I can say about the 8 speed Sturmey Archer is that from my experience and perception, it is the most free running, efficient multi speed gearhub I have or have had in my fleet. I seems to lose very little efficiency to internal drag.