Alfine 8 minimum gearing...

[ratherbeintobago]

Quick technical one:

I’d read somewhere that there was a minimum input gearing for Alfine 8 (and presumably 11) hubs - 32/18 rings a bell but might be wrong.

Is this true, and if so, what is it?

Thanks!

[simonineaston]

Screenshot from dealer's manual, here.

recommended sprockets for 8 / 11 Alfine

[Brucey]

p7 here

https://si.shimano.com/pdfs/dm/DM-SG0004-05-ENG.pdf

shows a chart with shimano's recommendations; input ratios of 1.8-2.0 for the 11s hub, 2.0 to 2.25 for the 8s hub. Plenty of people exceed these values, and in the early days of Alfine 11s shimano USA issued a statement in response to a query saying that these were just recommendations rather than absolute limits.

Actual loads on the hub will vary with rider, wheel size and crank length, as well as input ratio.

cheers

[ratherbeintobago]

Exceed or go lower?

[Brucey]

exceed in torque, so lower numerical input ratio

cheers

[ratherbeintobago]

Thanks!

[RickH]

I've been running a 39/24 on an Alfine 8. That's on a tandem with 20" (ETRTO 406) wheels with 2 adult riders in hilly terrain (primarily NE Wales for the hills when I'm using the big sprocket).

I've not had any problems but someone will probably be along shortly taking sharp intakes of breath & telling me just how out of spec my usage is!

[simonineaston]

I've been running a 39/24 on an Alfine 8. That's on a tandem with 20" (ETRTO 406) wheels with 2 adult riders in hilly terrain (primarily NE Wales for the hills when I'm using the big sprocket).

I've not had any problems but someone will probably be along shortly taking sharp intakes of breath & telling me just how out of spec my usage is!

No tutting here, chap! Only goes to show how "advisory" those values are!

[LuckyLuke]

Hi, my commuter / tourer uses the 'red band' Nexus 8, which has the same or near same innards as the Alfine 8 apparently.
I have recently, since 1 month ago, changed to a 23T Sturmey Archer 1/8 sprocket on the back, and a 50/34 compact double on the front for a greater range. When touring or laden I'm in the inner ring up front, running 34:23. I'm pretty light (67kg), not a powerful rider and spin rather than mash the pedals, so hopefully it will be ok... all was well last week on a loaded tour (C2C & Reivers Way), incl. some climbs out of the saddle. Will report back if it goes pear shaped.
Best Wishes,
Luke

[Cyril Haearn]

What happens if one uses an inappropriate sprocket/chainwheel ratio, what damage may be done?

[hemo]

On my e - bike I geared 1:6 ratio.

[simonineaston]

What happens if one uses an inappropriate sprocket/chainwheel ratio, what damage may be done?

I imagine that the chart's primary purpose is legal and as much to do with warranty claims as practical advice. So much depends on other variables, beyond the control of the manufacturer - rider's weight / power, daily usage, water ingress over years / lubrication / age of the component, etc. etc....

[simonineaston]

It's tempting to imagine that I'm immune to such constraints, as I am, like an earlier poster, a lightweight user, prone to twiddling and unlikely to apply anything like unhealthy forces to the hub... however my understanding of mechnicals and physics in general is shall we say, naive, and I've probably firmly grasped the wrong end of the stick, with respect to the application of torque and the limitations of the Al-fee-nay hub.

[Brucey]

via the interweb I have seen a few broken axles. Mostly these were 8 speed hubs which had seen extensive offroad use with a lower than specified input ratio. There have also been question marks over the NTWs; in vertical dropouts the axle can be flapping back and forth under torque loading, perhaps only restrained by one NTW instead of two.

In A11 hubs one problem is that the side thrust from the helical gear can cause wear and/or a failure to occur. This thrust is seen in gears 1-6 so again heavy MTB use tends to expose this weakness.

So it is possible to break these hubs, but realistically in road use, you would have to be going some to do it.

cheers

[simonineaston]

Horray! Thanks, Brucey