Alfine 11-speed hub gear ratios

[martynr]

Hi guys

Back in January I hadn't ridden a bike in 10 years and had little interest in them. 6 months on and I'm less than 2 months away from setting off with 5 other people on a cycling expedition from London to Cape Town in aid of charity. The learning curve has been a little steep!!

We've got ourselves Dawes Nomad 26" bikes with Alfine 11-speed hub gears and we've found them to be configured more for going down hills than up them! As someone who is very new to the technical side of cycling I've been checking online to see what options I have for changing the ratios down and if anyone could offer advice or confirm that I'm doing the right thing that would be fantastic!!

The bike has a Shimano Alfine 45T chain ring and 18T rear sprocket. I understand that if I change to the Shimano Alfine 39T chain ring and 20T rear sprocket then it will effectively give us one new gear below the current first gear (and one in-between the old 1st & 2nd gears). It doesn't seem to be a big difference and it will cost us around £80 each (for 6 bikes). Is it worth it?

Does anyone else have any experience with these Alfine hub gears?

Thanks!!

Martyn
www.cycleafrica.org

 

[alfeng]

FWIW. It never amazes me how some bike shops are willing to gouge a customer ...

That isn't to say that you are experiencing such a bike shop ...

BUT, if 'I' were advising you, then I would suggest that you consider [COLOR= #0000ff]SIX[/COLOR] 23t cogs ([COLOR= #808080]they should be [/COLOR][COLOR= #ff0000]<£10, each [/COLOR]... [COLOR= #808080]they are currently $9US on Amazon (http://www.amazon.com/Shimano-Nexus-Alfine-tooth-silver/dp/B0040ME7TY) ... of course, THAT Amazon price doesn't include a VAT-or-import-tariff BUT I would think that the retail price in the UK should certainly be under £10 after including the VAT[/COLOR]) + a new chain ([COLOR= #808080]you will be cannibalizing ONE of the six existing chains for the extra links you will need to lengthen existing chains ... YES, you can join Shimano chains with-or-without the special pins AND should learn how to do it using a standard chain tool[/COLOR]) which will cost another[COLOR= #ff0000] £20[/COLOR] ... by my reckoning, a total of [COLOR= #ff0000]£80 [/COLOR][COLOR= #000000]should cover the cost of changing the gearing FOR ALL SIX BIKES if someone in your group does the work ...[/COLOR]

[COLOR= #000000]IMO, at least ONE of the riders should learn how to break-and-join a chain ... and, s/he can do the necessary work.[/COLOR]

[COLOR= #000000]BTW. Since I suppose that I am a wuss, if the current 45t chainring is alloy then I think that I would be overly cautious & I would be inclined to replace the existing 45t chainrings with STEEL chainrings ... [/COLOR]

• [COLOR= #000000]steel chainrings are cheap(er) and will be worry free ...[/COLOR][COLOR= #000000] [/COLOR]
• [COLOR= #000000]certainly, 42t [/COLOR][COLOR= #008000]130BCD/5-arm[/COLOR][COLOR= #000000] & [/COLOR][COLOR= #000000]42t [/COLOR][COLOR= #008000]104BCD/4-arm[/COLOR][COLOR= #000000] steel chainrrings are commonly available and really shouldn't cost more than a 2-or-3 GBP each[/COLOR]

... If the current, 45t chainrings ARE alloy, then I would actually consider carrying one spare for each bike + 1 additional spare for the group ([COLOR= #808080]yes, that's an added expense[/COLOR]) -- THAT may seem like too much of a belts-and-suspenders approach, but I am sure there will be some places where you will be far away from a bike shop & a damaged chainring would be unnecessarily catastrophic.

[COLOR= #ff0000]FYI. [/COLOR][COLOR= #000000]The ALFINE cog is presumably held on the hub using a C-ring ... that was-and-presumably-continues-to-be the common method for securing the cog on most internally geared hubs. [/COLOR]

[COLOR= #000000]The cog is NOT particularly difficult to remove ... but, NOT particularly easy, either ([/COLOR][COLOR= #808080]at least, the first time![/COLOR][COLOR= #000000]) ...[/COLOR]

• [COLOR= #000000]you can "pop" them off using a pocket knife ... the first time, shroud the assembly with a plastic bag just in case the C-ring flies off-and-away-from the hub! [/COLOR]
• [COLOR= #000000]putting the C-ring back on is easier ... vaguely akin to putting a tight tyre on a rim ... because the C-ring is split, you can nest one end of the C-ring in the groove, first, and then work the ring into place.[/COLOR]

[COLOR= #ff0000] [/COLOR]

 

[martynr]

Thanks for the fantastic, detailed reply alfeng!!

I've read that Shimano recommend a minimum 1.9:1 ratio between the rear sprocket and chainring - is that a rule that would prove damaging to break? A 23:42 ratio would give us a couple more gears below our existing 1st gear but this is just outside this recommended ratio.

The chainring is aluminium. I read last night on the blog of a touring cyclist that the sand and grit had worn down his rear sprocket into something akin to a ninja star but I'd not heard of risks with the chainring. Thanks for the heads up! I'll look into changing it as we're keen to deal with any avoidable pitfalls while we still can.

Time for a rookie question: I'd have to add chain links with a larger rear sprocket but if I also reduce the teeth on the chainring would I still need to add links or remove them (assuming we're using a 23:42 setup)? I've broken then reconnected a chain whilst changing a front derailleur on an old bike but I've no experience of installing a new chain and figuring out the required length.

The bikes were given to us by Dawes at a significant discount as a charitable offering so you won't hear any complaining about them!! The hubs are so new that they weren't aware of the problem and have seemingly already changed the model spec for newer orders. Unfortunate timing for us but I'll look at it as another chance to learn more about the bikes we'll be spending all of our time on very soon!!

 

[martynr]

One of the other guys in our team wondered whether a steel chainring would increase chain wear. Would that be a side effect of the change?

 

[alfeng]

Originally Posted by martynr .


I've read that Shimano recommend a minimum 1.9:1 ratio between the rear sprocket and chainring - is that a rule that would prove damaging to break? A 23:42 ratio would give us a couple more gears below our existing 1st gear but this is just outside this recommended ratio.

I do not know why Shimano recommends 1.9:1 as the lowest ratio ...

• BUT, I will speculate that it may simply be because the subsequent lowest gear would be considered barely faster than walking the bike by a fatigued rider ... hence, unusable ([COLOR= #808080]i.e., less than 3MPH?[/COLOR]) in a real-world-situation as far as their engineers are concerned unless the bike is going to be used for pulling out tree stumps ...
• (1.9 x 0.53) x 312mm [[COLOR= #808080]radius for a 26x1.5 tyre[/COLOR]] x 3.1416 == 980mm == 38.4 inches (?) per pedal stroke [[COLOR= #ff0000]my presumptions AND arithmetic could be wrong![/COLOR]]
  

Originally Posted by martynr .


The chainring is aluminium. I read last night on the blog of a touring cyclist that the sand and grit had worn down his rear sprocket into something akin to a ninja star but I'd not heard of risks with the chainring. Thanks for the heads up! I'll look into changing it as we're keen to deal with any avoidable pitfalls while we still can.

An aggravating factor in how quickly cogs & chainrings wear out is the number of teeth ... a 16t cog paired with a 32t chainring will wear out faster than a 21t cog paired with a 42t chairing -- many hands/[COLOR= #808080](teeth)[/COLOR] make the load light(er) ...

By my reckoning, a steel chainring should last 3x longer than an alloy chainring.



Quote: Originally Posted by martynr .



Time for a rookie question: I'd have to add chain links with a larger rear sprocket but if I also reduce the teeth on the chainring would I still need to add links or remove them (assuming we're using a 23:42 setup)? I've broken then reconnected a chain whilst changing a front derailleur on an old bike but I've no experience of installing a new chain and figuring out the required length.



To oversimplify the arithmetic ...

• a 45t chainring + an 18t cog == 63t
• a 42t chainring + a 23t cog == 65t
• a 42t chainring + a 21t cog == 63t ... [COLOR= #808080]perhaps, a better (!?!) choice since it probably means you won't have to add links to the chain + the ratio is a comparatively robust 2:1[/COLOR]

In practice, because the diameter & circumference changes by an indirect (?)/( ... [COLOR= #808080]meaning, I don't know what it is ... it probably requires knowing the angle & consequent sine-or-cosine[/COLOR]) ratio because the slope which the chain traces between the cog & chainwheel affects THAT distance ([COLOR= #808080]and, consequently the length of the chain[/COLOR]) varies with different size cogs & chainrings even if the composite number of the two is the same ...

The slack is usually taken up by use of either a horizontal dropout whereby the axle is moved slightly fore-or-aft OR a chain tensioner OR a few other methods ...


As far as the actual length of chain, I just determine the length of the chain with the wheel in situ ...

• I just put the wheel in the frame & wrap the chain around the cog & chainring and then join the chain accordingly ...

Presuming a reasonably good chainline ([COLOR= #808080]say, less than 3mm deviation in the plane of the cog & the plane of the chainring[/COLOR]), having a chain that is too long ([COLOR= #808080]and sagging[/COLOR]) is better than having a chain which is too short whereby the axle is at the opening of the dropout instead of half-or-all-the-way back ...

• a bad chainline results in unnecessary friction as the chain scrubs the sides of the teeth ...
• worse, if the chainline is really bad ([COLOR= #808080]more than the width of the chain[/COLOR]), then the chain may want to crawl over the teeth PARTICULARLY if Road "stuff" which has shaped-or-shorter teeth is used ... hopefully, chainline is not an issue with how the Shimano's components are integrated with one another ([COLOR= #808080]I don't know if the Shimano Alfine crankset has a different chainline than a regular Shimano "Double" crankset would have ... I'm presuming an Alfine crankset is installed on the bike for the sake of simplicity[/COLOR]).

Quote: Originally Posted by martynr .


One of the other guys in our team wondered whether a steel chainring would increase chain wear. Would that be a side effect of the change?





If there is grit present in the drivetrain components, then there MUST be some level of wear that is greater for the chain when using steel chainrings than when using alloy chainrings since an alloy chainring will be sacrificial and absorb the brunt of the wear ...

• basically, I think that [COLOR= #ff0000]grit & lack of sufficient lubrication are the greater enemies to the chain[/COLOR] than the material the chainring is made of
• I just use 3-in-1/([COLOR= #808080]general household-type[/COLOR]) oil to lubricate my chains