Brompton virgin questions!!

[robgul]

Being a Brompton virgin ... with a neglected machine to refurbish I have a few questions please.

The machine I have is, I think, a T type c 2003/4 - had a 3-speed hub and 2-speed deraiilleur - AFAIK the chainset is original. The previous owner in his wisdom removed the derailleur but didn't twig that with "modern vertical dropouts" it would need a chain tensioner!

Technical info on the net for Bromptons is pretty sparse, so:

1 If I get a chain tensioner for a 3 speed (i.e. one cog at the back and dispense with the 3 extra gears) will it work, making it a 3 instead of 6 speed.
2 What sort of gear ratios will I get - depending on which cog I use? (ideally expressed in gear inches 'cos I understand them) - my use is likely to be on pretty much flat roads
3 There are 2 cogs on the hub at the moment - it looks like I can remove one - is there a shim of some sort to get the chain-line correct?
4 How many links do I need in the chain, and I assume a magic link will be OK
5 The cables (inner and outer) are pretty poor - I assume other than the gear inner trigger cable for the hub that the outers are standard issue brake or gear?
6 I'd like to separate the rear triangle to either get it powder coated or paint it - the two Allen bolts are rock solid - I assume if I got them out it's all pretty straightforward to put back? [I may leave this for now - or put the frame on its side and keep dosing with PlusGas to see if one of the bolts moves]

For the most part the rest of it seems OK, just very dirty - the RH pedal was rubbish and I've ordered a new one, together with the clip on the headtube that holds it folded (the spring was missing) - and when I want something else from Spa to justify the postage I'll buy one of their "non-fold" clips for £4 instead of the £26 Brompton wants for the retro fit (larger seat clamp bolt) trigger clip gadget.

All answers and tips gratefully received!

Thanks

Rob

 

[mjr]

I don't own a Brompton but I have used and seen various ones over the years as well as other hub-geareds so I can help with three of them...
1. I don't see why not.
2. 16" x chainring teeth / cog teeth as middle/normal gear, then -25% and +33%
4. Measure it and a magic link will be fine - remember that it's probably using 3/32" chain, unlike some hub-geared bikes.

 

[robgul]

4. Measure it and a magic link will be fine - remember that it's probably using 3/32" chain, unlike some hub-geared bikes.

.... there is no chain on the bike otherwise I would have counted the links ....

Rob

 

[mjr]

.... there is no chain on the bike otherwise I would have counted the links ....

That would assume the previous owner got it right. Measure it and use http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

 

[Poacher]

Hi @robgul , I'd already responded to a couple of your questions from your identical post on yacf, but I'll repeat them here:
I'm not aware that there's a different tensioner for 3 speed and 6 speed. Even if there is, I'd be inclined to keep it as a 6 speed.
My owner's manual for a 2009 6 speed recommends Sram PC1 (1/8") chain for 3-speed, PC10 (3/32") for 1-, 2- & 6-speeds, and is very specific on chain lengths. If you have a 54t chainring and one rear sprocket(12t or 13t), 100 links; a 50t chainring and one rear sprocket (12t or 13t), 98 links; a 44t chainring and one rear sprocket (12t, 13t or 14t), 96 links. If you have 2 rear sprockets (inner 12t or 13t, outer 15t or 16t), then for a 54t chainring use 102 links, for a 50t chainring use 100 links, and for a 44t chainring use 98 links.

Hope this helps - I'd have liked to lay it out in tabular form as in the manual, but it ought to be just about comprehensible.

Edited: my 6-speed had standard gearing (can't remember offhand what size chainring and sprockets that entails, but I'd guess at 50t with 13t and 16t?) which equated to a gear range of 33" to 99". Note that that's with a Brompton Wide Range (BWR) hub - your 2003/4 model may have a different ratio SRAM or Sturmey Archer - I think the BWR was introduced in early 2009.

Edited again! There are two different tensioners, but I'd still be inclined to use the derailleur version. With regard to gear ratios, Bromptontalk reckons the narrow range 6-speed gives a range of 205% - 214% (depending on sprocket choice?) and BWR 302% - 307%.
In terms of inches, ISTR that tyre size also makes a slight difference, e.g. with marathons fitted, the gearing will be slightly lower than with narrow racing slicks!

 

[robgul]

Hi @robgul , I'd already responded to a couple of your questions from your identical post on yacf, but I'll repeat them here:
I'm not aware that there's a different tensioner for 3 speed and 6 speed. Even if there is, I'd be inclined to keep it as a 6 speed.
My owner's manual for a 2009 6 speed recommends Sram PC1 (1/8") chain for 3-speed, PC10 (3/32") for 1-, 2- & 6-speeds, and is very specific on chain lengths. If you have a 54t chainring and one rear sprocket(12t or 13t), 100 links; a 50t chainring and one rear sprocket (12t or 13t), 98 links; a 44t chainring and one rear sprocket (12t, 13t or 14t), 96 links. If you have 2 rear sprockets (inner 12t or 13t, outer 15t or 16t), then for a 54t chainring use 102 links, for a 50t chainring use 100 links, and for a 44t chainring use 98 links.

Hope this helps - I'd have liked to lay it out in tabular form as in the manual, but it ought to be just about comprehensible.

Edited: my 6-speed had standard gearing (can't remember offhand what size chainring and sprockets that entails, but I'd guess at 50t with 13t and 16t?) which equated to a gear range of 33" to 99". Note that that's with a Brompton Wide Range (BWR) hub - your 2003/4 model may have a different ratio SRAM or Sturmey Archer - I think the BWR was introduced in early 2009.

Edited again! There are two different tensioners, but I'd still be inclined to use the derailleur version. With regard to gear ratios, Bromptontalk reckons the narrow range 6-speed gives a range of 205% - 214% (depending on sprocket choice?) and BWR 302% - 307%.
In terms of inches, ISTR that tyre size also makes a slight difference, e.g. with marathons fitted, the gearing will be slightly lower than with narrow racing slicks!

Thanks - really useful stuff. I've just sent a list of bits to a shop to ask for a price, based on my machine being T 6 speed from 2003. I knew Bromptons were complex .. but not this confusing!

Rob

 

[Brommyboy]

6-speed and 3-speed tensioners are different! The former has sliding jockey wheels to allow for the two sprockets. If only one sprocket is fitted then there is need for another spacer to keep the single sprocket in line. A 3/32" chain is required for the 6-speed but 1/8" for the 3-speed. For a 50T chainring the length should be 100 links, or 98 for a 44T one. The hub gear is a Sram but probably marked as a Sachs (the former maker).

 

[mjr]

A 3/32" chain is required for the 6-speed but 1/8" for the 3-speed.

Yes, but as it was a 6-speed, even if converted to 3-speed, it may still need 3/32" chain unless the chainring is 1/8" compatible and a 1/8"-compatible sprocket is fitted. If it's SRAM rather than SA, I'm less sure of things.

 

[robgul]

Thanks - it's an SA hub and takes a 3/32 chain - I'm going to get the bits and it'll be a 6 speed again.

Rob