Shimano alfine IGH - single vs double pulley?

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amacyc
Posts: 6
Joined: 23 Mar 2019, 12:29pm

Shimano alfine IGH - single vs double pulley?

Postby amacyc » 21 Jul 2020, 9:37pm

Hey all, hope you're all doing well in these Covid times. I have a quick question: I've seen that some bikes with Shimano Alfine IGH come with a Single pulley chain tensioner and others come with a Double pulley chain tensioner. What is the difference, if any, between a single and a double pulley? Which is better? Thanks for any answers. :wink:

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 21 Jul 2020, 11:44pm

the single pulley one is meant for frames with vertical dropouts when you are running a single chainring. The twin pulley version is meant more for when you are running more than one chainring; it is spring loaded and will accommodate a fair amount of chain slack, much as a derailleur might do.

cheers
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amacyc
Posts: 6
Joined: 23 Mar 2019, 12:29pm

Re: Shimano alfine IGH - single vs double pulley?

Postby amacyc » 22 Jul 2020, 12:50am

Thanks a lot for the answer Brucey. If the twin pulley is meant for running more than one chainring, why does shimano offer it for IGH? Is it simply for taking up additional chain slack compared to the single pulley? According to shimano both the single (https://bike.shimano.com/en-EU/product/ ... -S510.html) and twin (https://bike.shimano.com/en-EU/product/ ... -S500.html) pulley are for vertical dropouts.

I'm just confused why manufacturers sometimes use twin pulley for IGH bikes - seems to me single pulley would be sufficient?

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 22 Jul 2020, 7:30am

I'm repeating myself here but shimano intend you to use Alfine hubs with more than one chainring if you want a wider gear range/closer ratios, and for that a twin-pulley tensioner is mandatory. Note also that the single pulley tensioner is not spring-loaded; you need to adjust the chain tension manually with that one, but there is less parasitic drag.

As a general rule it is a much better idea to read the service instructions not just the sales blah;

https://si.shimano.com/pdfs/si/SI-50D0A-001-ENG.pdf
https://si.shimano.com/pdfs/si/SI-50F0A-002-ENG.pdf

edit; the single-pulley tensioner attaches to the axle and replaces one of the NTWs. This means it normally only works at all well with vertical dropouts, and even then only if you want the gear cable routed along the chainstay. The twin-pulley tensioner mounts to a conventional gear hanger, so can be fitted to any dropout design for which you can have appropriate NTWs. Since a (old type) bolt-on gear hanger would interfere with the RH NTW, it is best used on frames which have a gear hanger built in.

cheers
Last edited by Brucey on 22 Jul 2020, 8:08am, edited 1 time in total.
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Greystoke
Posts: 323
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: Shimano alfine IGH - single vs double pulley?

Postby Greystoke » 22 Jul 2020, 7:39am

Is it possible to add an additional cog on the Nexus/alfine 8/11 hubs like you can on sturmey archer?

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 22 Jul 2020, 8:01am

Greystoke wrote:Is it possible to add an additional cog on the Nexus/alfine 8/11 hubs like you can on sturmey archer?


Well SA have done their best to deprive you of that option in their more recent designs, hence BWR hubs have to use a special driver to allow two sprockets whereas older (pre-NIG) hubs could accept two sprockets without any difficulty, provided they were not too small.

Asides from obvious exceptions such as those meant to accept whole cassettes, currently no new IGH other than the BWR type is designed to accept more than one sprocket easily; the spline length on the driver simply isn't long enough.

In Nexus 7/8 and Alfine 8/11 hubs the driver splines are short and additionally the cassette joint and the hub's dust cover sandwich the sprocket such that if you wanted more than one sprocket, they would

a) have to be attached (probably welded) to a single carrier (sprocket centre)
b) be larger than a certain size and
c) carefully chosen for dish/spacing to avoid a clash on either side.

I think it should be possible, but I've never done it.

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

Greystoke
Posts: 323
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: Shimano alfine IGH - single vs double pulley?

Postby Greystoke » 22 Jul 2020, 8:33am

Sounds like a challenge :D
Just thinking of replacing the old 5 speed rear wheel and worn chainrings and weighing up options

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 22 Jul 2020, 8:59am

Greystoke wrote:Sounds like a challenge :D
Just thinking of replacing the old 5 speed rear wheel and worn chainrings and weighing up options


Your choices may be limited by the width of the frame between the dropouts, especially if it is 120mm; relatively few IGHs will fit 120mm, and the smallest a Nexus 8 (for example) can go is a little over this, even when modified. It is easy enough to spread a frame but that somehow seems like the wrong thing to do in many cases.

5s/~120mm OLN derailleur options are mainly limited by current freewheel choice. However it is usually possible to contrive a workable 'half-step plus granny' or 'one and a half step plus granny' arrangement using fairly readily available parts.

One option I am working on at present is seeing if I can revive that 'MIA, assumed dead' format being the compact 6s freewheel. BITD this was a popular choice but these days no-one makes the correct freewheels. Such freewheels would be attractive because being 5.0mm pitch they would work with 7s indexing equipment, and would fit to ~122mm OLN frames.

As it happens I think it may not be difficult to respace a (standard-spaced) SunRace 6s freewheel, (which is available in either 14-24 or 14-28 formats) to 'compact' specification; I plan to try this before too much longer.

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

Greystoke
Posts: 323
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: Shimano alfine IGH - single vs double pulley?

Postby Greystoke » 22 Jul 2020, 10:01am

Interesting. It would appear my bike already worked with 'variable spaced' sprockets ok :shock:
I have some 6 speed sprockets and aim to try one on at some point. Shimano do a mega range version although I need a new gear shifter.
I have an old aw3 in the garage, maybe that's the correct old measurement for my existing frame.
The drivetrain is quite worn so ideal for an upgrade but as it's a commuter/heavy duty tourer I want a rugged set up.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 22 Jul 2020, 10:24am

the issue may be that standard 6s fits to 126mm OLN hubs and 7s slightly wider than that. And that is at the maximum advisable wheel dish. If you want a heavy duty arrangement, favouring lower wheel dish is a very good idea. So starting with the hub OLN which will fit in your frameset, this defines what is likely to fit/work or not.

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

Greystoke
Posts: 323
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: Shimano alfine IGH - single vs double pulley?

Postby Greystoke » 29 Jul 2020, 7:45am

I've measured the rear wheel old and it's c125mm. The wheel isn't dished to one side either, looks the same. The 5 speed could probably be replaced with a 6 speed, I may try this.
I also note that the rotary sturmey archer 5 speed could fit that axle spacing.

Brucey
Posts: 39933
Joined: 4 Jan 2012, 6:25pm

Re: Shimano alfine IGH - single vs double pulley?

Postby Brucey » 29 Jul 2020, 8:49am

Greystoke wrote:I've measured the rear wheel old and it's c125mm. The wheel isn't dished to one side either, looks the same. The 5 speed could probably be replaced....


if the wheel is correctly built, the flange spacing won't quite be uniform vs the wheel centreline and the spoke tensions won't be the same each side of the wheel.

a) If the wheel is correctly built reversing it in the frame leaves the rim in the same place between the brakes.

b) If you sight through the valve hole to the spokes on the other side of the rims (on a correctly built wheel as per a) above) you can make a mark on the hub barrel that represents the wheel centre. If you measure from this to each flange you get the flange spacings.

Commonly on a rear hub with standard dishing for the wheel the RH flange is spaced ~18 to 20mm from the hub centreline. If a 126mm OLN hub is built with the least dish for 5s then the RH flange is still spaced ~21-24mm. This is usually low-dish, not no-dish, because the hub flanges are usually spaced about 54mm apart. Such a wheel is however appreciably stronger than a standard-dished wheel.

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

Greystoke
Posts: 323
Joined: 8 May 2018, 7:41am
Location: Lincolnshire

Re: Shimano alfine IGH - single vs double pulley?

Postby Greystoke » 29 Jul 2020, 9:44am

I'll check it out later thanks