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Old 09-01-17, 01:22 PM   #1
Hisamatsu
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Brompton chain length

Going to replace my 44t with a 38t on my 6spd brompton. What chain length is recommended?

https://brompton.zendesk.com/hc/en-u...gth-do-I-need- from this I'm guessing 96 links?


Curious what chain comes std by brompton? Went out to the LBS to get masterlinks but then noticed at the shop my chains were sram 7spd with masterlink already there lol.
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Old 09-01-17, 01:36 PM   #2
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44-38 =6 so 3 links , 6 rollers... the math is quite straight forward.

Zendesk not good enough? 6 speed uses a derailleur chain, since it derails between the 2 cogs.. (5,6,7,8, all use same chain , these days)

3 speed an 1/8" cog on the hub, an 1/8" chain..



I just figure out the length when I put a new chain on, my B, by functional parameters , not link counting..




...

Last edited by fietsbob; 09-01-17 at 01:44 PM.
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Old 09-01-17, 02:55 PM   #3
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Originally Posted by fietsbob View Post
44-38 =6 so 3 links , 6 rollers... the math is quite straight forward.

Zendesk not good enough? 6 speed uses a derailleur chain, since it derails between the 2 cogs.. (5,6,7,8, all use same chain , these days)

3 speed an 1/8" cog on the hub, an 1/8" chain..
54-44 = 10 so 5 links, but the zendesk page show only 4 link difference.
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Old 09-01-17, 04:49 PM   #4
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Quote:
Originally Posted by fietsbob View Post
44-38 =6 so 3 links , 6 rollers... the math is quite straight forward.

Zendesk not good enough? 6 speed uses a derailleur chain, since it derails between the 2 cogs.. (5,6,7,8, all use same chain , these days)

3 speed an 1/8" cog on the hub, an 1/8" chain..



I just figure out the length when I put a new chain on, my B, by functional parameters , not link counting..




...
Because the chain wraps around HALF the chainwheel you only remove HALF the difference. Remove 3 rollers. That's not possible so remove the next even number smaller. If there is ample length remove the next larger even number.

Last edited by jur; 09-01-17 at 04:55 PM.
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Old 09-02-17, 09:12 AM   #5
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Whatever, my overthinking comrades, chain tensioner, for the fold, has a long swing, so it's not as fussy
as building a tensioned chain IGH bike with no chain spring tensioner.

OP could just leave it as is,, try that and report back.








.....
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Old 09-03-17, 11:24 AM   #6
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Optimal length in inch = ((Chainstay*2) + (Chainring/4) + (Cassette/4) + 1)
1" length = 2 links
Optimal links = ((Chainstay*2) + (Chainring/4) + (Cassette/4) + 1)*2
Brompton chainstay = 16"
Cassette largest sprocket = 16T


54T = (16*2 + 54/4 + 16/4 +1)*2 = 101L but round up to 102L as link pair needs to be even #.
50T = (16*2 + 50/4 + 16/4 +1)*2 = 99L but round up to 100L
44T = (16*2 + 44/4 + 16/4 +1)*2 = 96L

which almost matches https://brompton.zendesk.com/hc/en-u...cles/203295641. 44T they recommend 98L, but formula says 96L. However, this also says 44T uses 96L

so...

38T = (16*2 + 38/4 + 16/4 +1)*2 = 93L but round up to 94L

Currently have 98L on my 44T. So should I do 94L or 96L going to 38T?

edit: I'll try 96L first, but 98L definitely seems too loose on a 38T.

edi2: Road around with 96L, works fine, and able to fold up without chain rubbing. Also, the guys on brompton yahoo groups also use 96L for 38T.

Last edited by Hisamatsu; 09-03-17 at 06:12 PM.
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Old 09-03-17, 11:36 AM   #7
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take a tiny risk, any?
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