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27-Speed Brompton

Old 01-23-19, 11:12 AM
  #26  
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Originally Posted by fietsbob View Post
My thought . because of the molded single piece, flanges & toothed pulley design, the chain oil dirt combined solids, packed in, have no place to go..
Wondering if a few holes thru the flanges .. a part of some of the CNC after market pulleys . gives some of that inevitable accumulation a way to sluff off and out..
3 speed , its no issue , backing disc gets a bit grimy , but it does not rotate in unison with the lower pulley
The side holes are there but indeed the flanges and plastic, rather than metal, likely contribute to the grime accumulation. When I looked at the aftermarket of pulleys and tensioners for Brompton, it seemed that you needed to pay a lot of money for a dubious gain. However, I may have another look.
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Old 01-24-19, 04:40 PM
  #27  
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back of the envelope design ...

A scheme to add the flanges to a good commercially available sealed bearing pulley , like Tacx , sandwiched between them popped in my mind ,,
the flanges need not be part of the pulley to work as far as I can grasp the mechanics involved..

brass or oil bronze tubing can join the 3 pieces and slide along the pin in the chain tensioner.. as required.. & separate to do the occasional cleaning..

pulley can even turn faster than the flanges.. fixed to the bushing sleeve the bearing rolls around ..





.....

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Old 01-26-19, 03:09 PM
  #28  
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Originally Posted by pastorbobnlnh View Post
Ahhhhh! A clean transmission is always appreciated by changing gears! Glad this solved many of your shifting issues.

I wonder if the "skating" could be solved by a new chain?
The "skating" when riding with the largest ring turned out to be the residual problem with poor shifting to the middle cog from the smallest cog that I hoped to have solved with cleaning of the pulleys. (The latter helped but evidently not fully.) The problem that developed could be best illustrated with the diagram describing shifts: 12t -(pathologically hard)-> 14t -(pathologically easy)->16t and 12t <-(normal)- 14t <-(normal)- 16t. If tension in the shift cable was too low, the derailleur was failing to move the chain from 12t to 14t. This seemed tied to an insufficient stiffness in the plastic derailleur yielding hiccups in the derailleur operation. If I increased tension in the cable, the derailleur immediately started to overshift, jumping from 12t to 16t for the middle shifter position and then falling back to 14t, and so on, yielding the "skating".

I could not find a middle-ground cable tension that would solve the problem and I went with a nuclear option. Given that I had cassette pieces for all kinds of speeds, I reduced the gap between 12t and 14t, by using 10-sp 12t cog with built in spacer, and I increased the gap between 14t and 16t, by using a 9sp spacer there w/o filing. In my estimate one gap was reduced by just 0.15mm and the other increased by that amount. This nuclear option took care of the pathologies (or basically went along with them) and all shifts fine now for all gears in all combinations. In the back of my mind I worry though that, if 0.15mm matters, then with temperature changes or something, and the derailleur arm softening or stiffening, the problem might come back. If you do not try, though, you will never know .

The bike is now all ready for a trip in 2 weeks from now, where my survival crucially depends on this bike - my lodging location will be inaccessible by public transport for much of the week. The bike better perform there.
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Old 01-26-19, 03:43 PM
  #29  
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@2 I, where are you traveling to? Sounds like an interesting adventure. For the three rear sprockets and the Brompton RD, is the shifter friction or indexed? I've been assuming friction.
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Old 01-26-19, 04:14 PM
  #30  
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Originally Posted by pastorbobnlnh View Post
@2 I, where are you traveling to? Sounds like an interesting adventure. For the three rear sprockets and the Brompton RD, is the shifter friction or indexed? I've been assuming friction.
It is just Germany, but I will be thrown into fields, with public transport there only to carry people to work and back and the nearest shop 20min away by bike, not even on the way of the public transport. There might be snow there, so I ponder taking along a studded tire for the Brompton, but I will check the forecast right before my travel. The shifter is an indexed SunRace M90. I have also a friction version of this shifter, that largely uses the same components. Friction can be easier when you are free to concentrate on the shifting, but I want to be ready when the surrounding is rough and I have to concentrate on making it through.
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Old 01-26-19, 05:54 PM
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That sounds like a great trip. I hope you have pleasant weather for the duration of your trip.

I'm using friction barend shifting on the 9 speed cassette of my Dahon. IMO, sometimes index is over rated. But I'm a vintage guy at heart and most of my bikes are 30-50+ years old.
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Old 01-26-19, 06:20 PM
  #32  
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I spent one winter at the particular location in Germany and the snow was quite challenging there on occasions, sticking to a bike when riding over agricultural roads and making it look as if it belonged to a snowman . The brakes were obviously completely taken out of operation.

My leaning is towards indexed, but I am not dogmatic about that. I did offbeat things though for the cause in the past such as RHS on the left, Shiftmate and microstops with redundant stops filled with epoxy.
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Old 08-18-19, 01:50 PM
  #33  
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Improved 3-Cog Shifting

From all my Brompton modifications, the shifting over 3-cogs, that replaced 2, has been the most frustrating, with gears sticking and not matching index shifter position. (For replacement details see here.) I looked at the issue again and arrived at a perfect match between the shifter position and gear. The fixes in the order of perceived importance were as follows:

1. Going to pre-2017 cable anchorage from new-2017.
2. Installing stiffer spring for pusher return.
3. Tweaking tensioner pulley wheels.

For all of the above you can get some aftermarket parts that you can use directly or as a start. You need a bolt that grabs the shift cable in 1, replacing the Brompton bolt, but everything else is optional.

Regarding 1, I found setting cables with new-2017 anchorage extremely frustrating. In addition the complexity of the new anchorage seems to play the primary role in gear sticking. Ti Parts produces a replacement anchorage for pre-2017 that adds a cable adjuster. However that anchorage bolts stiff to the frame, while the shifting likes flexibility. At first the stiffness makes low gear stick, but after a while the system seems to adjust itself for shifting to progress smoothly.

For 2 you can get a stiffer Bikegang spring, but you need to reduce its diameter at one end to make it fit the original Brompton anchorage - it fits Ti Parts anchorage fine, though, without modification.

Given that the pusher needs to travel over a longer transverse distance with 3 than 2 cogs, it is of an advantage to get longer axles for tensioner pulleys. Since the axle needs to also hide inside the pulley, you also need taller caps for the pulley wheels. Bikegang provides longer axles and taller plugs (by H&H), but the combination is too long for the pulley closer to the wheel axle, with the Bikegang plug hitting the spokes. The combination works fine for the more outer pulley, farther from the spokes. Even before noticing these axles at Bikegang I made my own axles in-between in length between Brompton an H&H and combined them with Brompton plugs made taller by heating (focused 250F) and these fit fine in the space that the pulley closer to the wheel axle gets. Finally you can get replacement pulley wheels out of alu that fit fine the original Brompton tensioner, with the advantage that the cog rotates independent of the rest of the pulley, eliminating most of the friction of the pulley against the pusher. You actually need only one such pulley for the inner position.

Below ae the photos illustrating the replacement options, with original Brompton components to the left, aftermarket to the right and my own, if I came up with something, in the middle.



Working set


Brmpton (L) Bikegang (R)


Pulley axles: Brompton, Mine, H&H (L to R)


Pulley Wheel Plugs: Brompton, Mine, H&H (L to R)


Anchorage: Brompton (L), Ti Parts (R)


Pulley: Brompton (L), Unnamed CNC (R)
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Old 08-18-19, 08:48 PM
  #34  
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Thanks for posting this. I tried unsuccessfully too get mine indexed. I reason that spacings between the cogs (10 speed) have to match an indexed three speed front derailleur. I have tried with the three speed Sturmey Archer that Bikegang sells with his kit and it was no go. The rest of the kit is fine with exception that on mine there was a very slight interference with the frame but I was able to fix this by adding a thin washer-spacer to the axle on the inside of the drop out. I have no problems with the SunRace friction shifter. It's nice but I would prefer crisp indexed shifting.
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Old 08-18-19, 09:31 PM
  #35  
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I use Sturmey-Archer hub twist shifters both for BWR and cogs. I.e. from the cog perspective it is a random 3-speed shifter. The spacers that I put between the cogs are also on the random side - I tried to push them aside and put spacers that the hub could still tolerate. However, if you eliminate stickiness in the connection between the pusher and shifter, any 3-speed shifter should work in my opinion, since the stop screws decide on where the pusher ends up in the extreme positions. As to the extra washer, I put a cutout one on the outside of the dropout, but it does not really matter as long as the tensioner is pushed out by 1mm or so. Bikegang offerings can be quite inexpensive compared to other suppliers, but these can be on the unfinished side - i.e. you get more means to accomplish your goal, but you still have to improvise how to get there, just a shorter distance .
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Old 08-19-19, 09:01 PM
  #36  
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Originally Posted by 2_i View Post
However, if you eliminate stickiness in the connection between the pusher and shifter, any 3-speed shifter should work in my opinion
I don't understand what you mean. If I go with the stiffer spring, would this make a difference? I bought a very cheap indexed front derailler shifter off the eBay. It would shift from first to third in one shift. The SA shifter was better but erratic.
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Old 08-19-19, 10:17 PM
  #37  
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A stiffer spring does not allow the cable to go slack on the smallest cog and generally maintains a higher tension in the cable counteracting any perturbations that the cable might encounter on its way.

As to the shifter, if that aspect is adjustable, it must be set so that it stays put in its stop, not being dislodged by the tension in the cable. In compact thumb shifters, such as suitable for a folder, including SA/SunRace, the tension that the shifter can withstand, without jumping, is regulated by tightening a screw/nut on the shifter axle. My impression is that people often miss that, but are often lucky with the degree of tightening, so it just turns out OK anyway. However I would look into that if there were problems.

I controlled the Brompton pusher with 3-speed twist shifters by SA and Sram and with thumb shifters by Sram and SunRace. With each of these shifters the quality of the shifting was similar and with each I could achieve a satisfactory, but fragile shifting. It was good after you set it but after a day or so the gears started sticking and you had to retune and I was getting fed up. These last changes yield an enduring satisfactory shifting that does not need retuning. I doubt that the latter depends on the shifter.
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Old 08-20-19, 10:42 AM
  #38  
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I didn't check the gear range, but out of curiosity, isn't the three-chairing + three-sprocket cassette + BWR gear hub a bit overkill?
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Old 08-20-19, 12:24 PM
  #39  
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Originally Posted by Winfried View Post
I didn't check the gear range, but out of curiosity, isn't the three-chairing + three-sprocket cassette + BWR gear hub a bit overkill?
The answer to that is no. The gears are spaced wide just 6 speeds. The additional cog yields an evenly spaced 9 gears. I added a gear to the 2 speed wheel,12-14-17, but my terrain is very flat.
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Old 08-20-19, 12:29 PM
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I was refering to 2_i's…
  • three chairing
  • three cog cassette
  • BWR
setup.
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Old 08-20-19, 12:55 PM
  #41  
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Originally Posted by Winfried View Post
I was refering to 2_i's
  • three chairing
  • three cog cassette
  • BWR
setup.
Ug, I agree. On the other hand, if you are touring in the mountains a few very low gears is nice. Still, I suggested he add a mountain drive Shlumpf bb and then he could 54 gears.
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Old 08-20-19, 01:26 PM
  #42  
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Originally Posted by Winfried View Post
I didn't check the gear range, but out of curiosity, isn't the three-chairing + three-sprocket cassette + BWR gear hub a bit overkill?
Depends on one's situation. When riding around home during fair times of the year, I would use only two top rings. In winter I would use only two lower rings. During the last 2 years I worked for one month per year in Rwanda. I would ride on my next lowest gear just to get out from my work site to the street. Rwanda is on the continental rift in the footsteps of Kilimanjaro, with no bridges or tunnels to level out height differences. Even to get around the capital you need to climb steep hills over and over, with distances counted in the number of hills you need to climb. With all my gears maybe I did not need to ever walk up in the city due to gradients but if went outside I would still need to walk up occasionally.
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Old 08-20-19, 01:40 PM
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To supplement from another thread, this is a random street behind my bank in Rwanda, on the way to a coffee place.

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Old 08-20-19, 02:00 PM
  #44  
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Ugh, that's a serious hill. Now I see why you'd want such gearing.
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Old 08-20-19, 02:01 PM
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How steep ? 20% ?
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Old 08-20-19, 02:12 PM
  #46  
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I would walk that too. Impressive hill.
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Old 08-20-19, 04:16 PM
  #47  
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Actually, from the photo the grade is about 30%. I actually was able to start the bike up from this parking, without zigzagging and my smallest ring was then 24T. Since then I went down to 20T. For steep enough hills lower and lower gears provide no real gain for steady riding as you start to roll back anyway during these portions of the turn of pedals when you have no leverage. You can get though a momentary boost for starting or temporary increase in slope.

My challenges are nothing though compared to those for people cultivating fields in Rwanda. Here is a typical hill there used for agriculture.


Rwandan Landscape
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Old 08-20-19, 05:16 PM
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Originally Posted by 2_i View Post
To supplement from another thread, this is a random street behind my bank in Rwanda, on the way to a coffee place.
Dear God man!!! I give you total respect!!!
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Old 08-20-19, 08:19 PM
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Originally Posted by tds101 View Post
Dear God man!!! I give you total respect!!!
Not at lot to my credit - just adaptation to the surroundings and on occasion adaptation for the Brompton . Most people in Rwanda ride single speed and just walk up when it gets steep. I could sit at home and watch the streets with envy, or get out and join . First year I was there I rented an MTB. Most of my life I lived in postglacial regions, so the hills were a shock to the body. For the second year I worked on the Brompton thinking to give it a shot. There were some trials in-between demonstrating that two rings would not be enough. The Brompton ended up working better than the local MTB, no matter that there were quite a few ruffles to be smoothed out still at the time.
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Old 08-30-19, 03:08 PM
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Turns out the inner bolts on the triple chainset I installed to get a 46/30T rub against the chainstay when folding the bike :-/

I currently use a Shimano BB-UN55 118x68mm bottom bracket, which is also available in 122.5mm.

Before I order it, is there a simple way to move the crankset away from the frame by 1 or 2mm?

Thank you.

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