# Another Chainring question.



## Kell (21 May 2019)

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 (21 May 2019)

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.


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## Kell (21 May 2019)

Good point. 

Never considered the chain guard.


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## 12boy (22 May 2019)

u_i said:


> 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.


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## u_i (22 May 2019)

12boy said:


> 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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## Schwinnsta (27 May 2019)

I wonder how big a jump on a double the derailleur can handle.


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## u_i (27 May 2019)

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?


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## Schwinnsta (28 May 2019)

Could I do a 44 / 22 FD and take up the slack in the folded position.


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## u_i (28 May 2019)

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.


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## ukoldschool (28 May 2019)

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:







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/


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## Kell (28 May 2019)

ukoldschool said:


> 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
> 
> ...



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?


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## ukoldschool (28 May 2019)

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


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## Schwinnsta (28 May 2019)

ukoldschool said:


> 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



It can be used by both 2-speed and 6-speed.


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## Kell (28 May 2019)

Schwinnsta said:


> 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.


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## mitchibob (28 May 2019)

ukoldschool said:


> 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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## u_i (29 May 2019)

ukoldschool said:


> 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



I never saw any evidence of this getting done successfully in practice. From my my own inspection an attempt to file an extra slot has no chance of accomplishing anything and will just irreversibly damage the shifter. 3-speed shifters can be had for cheap and there is an advantage in being able to go back to the previous configuration, if the new one fails to work out. There is an advantage in going with an indexed shifter in that the pusher should be set so that it is not rubbing the tensioner wheel in either of gear positions and thus refrains from damaging that wheel in the long term. This is trickier for 3 speeds than 2.


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## kais01 (10 Jun 2019)

i reckon the shifter can take some filing. 

but balancing the derailer for the middle sprocket will be hard because there is no direct connection between the cable and derailer; it is suspended in both directions.

reason for this i have guessed is that you can use the shifter without damaging the mechanism also at standstill. nevertheless makes it hard to find a middle position.


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## u_i (10 Jun 2019)

kais01 said:


> reason for this i have guessed is that you can use the shifter without damaging the mechanism also at standstill. nevertheless makes it hard to find a middle position.



Whether or not you can shift when not moving depends on the gear side. Incidentally even with sprockets, though you shift while standing, the shift is completed only when you start moving. In any case, I use the same SA shifter for the hub and sprockets, not the same as original Brompton's, but functionally equivalent.


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## Schwinnsta (10 Jun 2019)

I was able to make the the SA 3 speed indexed shifter work. The index points are off for the rear derailleur. SR friction shifter works great. 3-speed is nice upgrade. I used Bikegang kit.


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## u_i (10 Jun 2019)

Schwinnsta said:


> I was able to make the the SA 3 speed indexed shifter work. The index points are off for the rear derailleur. SR friction shifter works great. 3-speed is nice upgrade. I used Bikegang kit.



Index points for 3 speeds can be set incorrectly, but should not be off as a matter of principle. For 3 speeds you set the middle position by cable length and high and low by limit screws. The tolerances for mthe iddle are very narrow for Brompton with 3 speeds. Even though the friction shifter may seem to work fine in short term, you should examine the top pulley of the tensioner, after a more extended use an look for thinning and ridge developments near the pulley's circumference. The Bikegang kit is indeed fine. They could have added a shim/washer to prevent locking of the tensioner against the outer sprocket.


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## Schwinnsta (11 Jun 2019)

I have the limit screws set up well. So are you saying the tension is incorrect?


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## u_i (11 Jun 2019)

Schwinnsta said:


> I have the limit screws set up well. So are you saying the tension is incorrect?



SunRace thumb shifters lack cable adjustment and there is no fine adjustment on the Brompton pusher side other than by securing the screw on the cable that works very coarsely. The solution are add-on barrel adjusters such as by Ritchey or Jagwire. One can also place inline adjusters on cables but these are less convenient on Brompton, due to the complicated cable layout, than adjusters placed on shifters.


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## Schwinnsta (11 Jun 2019)

I have already added an inline adjuster. So are saying that it is a matter of getting the tension just right or does it have to with spacers? It seems like the amount of cable pull (distance) of the indexed three speed is off.


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## u_i (11 Jun 2019)

Yes. You can set the shifter in middle position, flip the bike upside down and tweak the adjuster so that the chain is on middle sprocket and the tensioner wheel stays clear of the pusher's fingers. Then you can put the shifter into either of the extreme positions and adjust the corresponding limit screw so that again the chain is on the respective sprocket and the wheel stays clear of the pusher's fingers. You can do that without turning the bike upside down, but it is hard to see then whether the wheel rubs against the pusher or not. The tolerances are tight.


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## Schwinnsta (11 Jun 2019)

u_i said:


> Yes. You can set the shifter in middle position, flip the bike upside down and tweak the adjuster so that the chain is on middle sprocket and the tensioner wheel stays clear of the pusher's fingers. Then you can put the shifter into either of the extreme positions and adjust the corresponding limit screw so that again the chain is on the respective sprocket and the wheel stays clear of the pusher's fingers. You can do that without turning the bike upside down, but it is hard to see then whether the wheel rubs against the pusher or not. The tolerances are tight.




Thanks. I will try it. Does you have tension in the cable when it is on the 12T cog?


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## u_i (11 Jun 2019)

Actually, no tension on the smallest cog and a lot of excess slack. I worked to contain the excess length within the run of the cable. However, with SunRace shifters the simplest might be to let the excess stick out of the shifter.


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## Schwinnsta (11 Jun 2019)

The 3 speed indexed shifter I have is a Sturmey Archer, right? The friction shifter is a SunRace. They look the same.


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## u_i (11 Jun 2019)

The company name is now SunRace Sturmey Archer. My impression is that they name the shifters Sturmey Archer when they market them for hubs and SunRace otherwise. The tricky part of the shifters for hubs is that increments in the cable pull may be uneven between gears. This should not matter for 3 speeds because of the way you tune the shifting, but can matter for more. I use 3-speed Sturmey Archers both for the hub and for the sprockets.


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