Another Chainring question.

Kell

Über Member
I'm still undecided about the 44T chainring.

Loving the fact it makes the hill near home easier, but for the sake of one 6 minute climb, it's compromising other aspects of the ride.

As Brompton only do a 44T, 50T and 54T, is there any reason why I couldn't switch to any other 130BCD 3/32 chainring? Probably looking for something in the middle of 44T and 50T.
 
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u_i

Well-Known Member
Location
Michigan
I live in a relatively flat postglacial area and have a triple 50/32/20 combination, on 110BCD crank. In practice, with some load in the T-bag, sometimes going up a bridge and dealing with still some waving of the terrain there, I find that I ride most of the time with 32. If I were to go back to one ring, it might be that less than 44 would be optimal for me and certainly I would not look to go above 50. I.e. different choices might be optimal for different people and certainly look for other options than those offered by Brompton. However, if you care about the chainguard, pay attention to the issue whether one is available for your ring choice or whether you need to go to one of those that mount as an extra ring.
 

12boy

Veteran
Location
Casper WY USA
I live in a relatively flat postglacial area and have a triple 50/32/20 combination, on 110BCD crank. In practice, with some load in the T-bag, sometimes going up a bridge and dealing with still some waving of the terrain there, I find that I ride most of the time with 32. If I were to go back to one ring, it might be that less than 44 would be optimal for me and certainly I would not look to go above 50. I.e. different choices might be optimal for different people and certainly look for other options than those offered by Brompton. However, if you care about the chainguard, pay attention to the issue whether one is available for your ring choice or whether you need to go to one of those that mount as an extra ring.
Any problems with the chain tensioner with that setup? I also have a 110BCD but with 58/38, greasy finger shifting. I could add a 28 as a granny gear, and in combo with a 2 speed rear wheel should be able to deal with most situations, although I would like to go a little higher than 77 gear inches on the top end.
 

u_i

Well-Known Member
Location
Michigan
Any problems with the chain tensioner with that setup?
Surprisingly the tensioner gathers in practice all that extra slack. The big capacity of the tensioner is there to cope with the chain slack due to folding. However, I also converted 2 cogs in the rear on BWR into 3 and the chain width is such that a loose chain can squeeze into the space between cogs and get stuck there. When I fold with the front on 20T ring and the chain is pretty loose upon folding this occasionally happens. I learned to grab the tensioner then and move it slightly to get the chain unstuck. Usually no grease is involved then and all is fine. An option might be not to fold with the front derailleur/mech in the small ring position, but I prefer not to bother with that and just unstick the chain if the problem occasionally surfaces.

By the way, I also tried a regular long-cage derailleur in the rear. While it shifted fine and absorbed slack on unfolded bike, it failed miserably on a folded bike, leaving chain loose and letting it tangle. The tensioner in a regular derailleur has far less capacity in gathering the slack than the Brompton tensioner.
 
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u_i

Well-Known Member
Location
Michigan
How far do you want to go? What is the drivetrain situation that you want to build upon? Are you concerned about the capablility of the front to shift or rear tensioner gathering slack?
 

u_i

Well-Known Member
Location
Michigan
In my experience the Brompton tensioner would have no problem taking off the slack. However, I would worry about the front derailleur shifting over such a gap, specifically the chain managing to grab pins in the upward direction and not falling off in the downward direction. I am sure these can be taken care off with a chain stopper in the down direction and enhancing the bottom of the back derailleur cage in the up direction, but I am not sure whether you can get the arrangement to work fine without such provisions. There may be also an issue of the capacity of a double derailleur, but then you could go with a triple operating as double. The latter might be also a remedy for the upshift.
 

ukoldschool

Well-Known Member
Ill say it again.... 3 rear cog conversion...... Retain your front 44 for an ultra low hill climber, but have the ability to have top gears more or less the same as a standard BWR (a bit lower), or if you can live with a very slightly higher 1st gear go back to the 50t front:

3spd.JPG


Bikegang sell a kit, you will also need a 10 speed chain and depending on which type shifter you have you may need either a new shifter for the left hand, or to modify your current one to give a new position in the middle (I have the newer style shifters which is the reason I havnt done this yet...)
https://bikegang.ecwid.com/#!/Bromp...ter-Kit-MiniMODs-x-Sturmey-Archer/p/115439619

Or you can put one together yourself (@berlinonaut wrote up a list of things to buy, all the cogs are available individually from 10 speed casettes in this thread:
https://www.cyclechat.net/threads/anybody-installed-a-modified-3rd-gear-to-a-bwr-hub.243473/
 
OP
Kell

Kell

Über Member
Ill say it again.... 3 rear cog conversion...... Retain your front 44 for an ultra low hill climber, but have the ability to have top gears more or less the same as a standard BWR (a bit lower), or if you can live with a very slightly higher 1st gear go back to the 50t front:

View attachment 468396

Bikegang sell a kit, you will also need a 10 speed chain and depending on which type shifter you have you may need either a new shifter for the left hand, or to modify your current one to give a new position in the middle (I have the newer style shifters which is the reason I havnt done this yet...)
https://bikegang.ecwid.com/#!/Bromp...ter-Kit-MiniMODs-x-Sturmey-Archer/p/115439619

Or you can put one together yourself (@berlinonaut wrote up a list of things to buy, all the cogs are available individually from 10 speed casettes in this thread:
https://www.cyclechat.net/threads/anybody-installed-a-modified-3rd-gear-to-a-bwr-hub.243473/
The bike gang kit looks interesting, but I wonder why they don't utilise the existing Brompton three speed hub shifter? Is the Sturmey Archer one a friction shifter and not indexed?

And without my bike to hand, could it be flipped and used on the left hand side of the bars for a six speed?
 

ukoldschool

Well-Known Member
I think its more aimed at the 2 speed non hub gear people than those of us already blessed with 6 gears, its apparantly quite easy to file an extra slot into the old style 2 speed left shifter to create an index for the 3rd gear
 
OP
Kell

Kell

Über Member
It can be used by both 2-speed and 6-speed.
I think the response was in relation to my question about why not use the existing 3-speed shifter made by Brompton.

While the 3-cog conversion can be used by anyone, the kit is obviously aimed at those without hub gears as it comes with a RH shifter.
 

mitchibob

Well-Known Member
Location
London, UK
I think its more aimed at the 2 speed non hub gear people than those of us already blessed with 6 gears, its apparantly quite easy to file an extra slot into the old style 2 speed left shifter to create an index for the 3rd gear
You say that about 6 speed owners, but there's an argument for making the ratios between those gears a little closer than they are currently, e.g. 13/15/17, instead of 13/16. Gives you a little more variation on the direct drive middle hub gear too. I've certainly been toying with the idea.
 
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