Brompton Chainring - How large can it go with a chain guard?

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Brompton Chainring - How large can it go with a chain guard?

Postby ChrisL on Tue Aug 29, 2017 7:43 am

Which is the largest chainring which can fit on a Brompton while keeping a chain guard?
Is it possible to edge higher than the standard 54T chainring?

I have seen some 60T chain rings on Bromptons which push the standard 2-speed ratios from the standard 56"/75" gear inches to 61"/82" - however this larger front chain ring seems to really push the size to limit of what will still fold normally, and does not seem leave room for a chain guard.

Since the new post-2013 JIS sprocket fits the 130mm BCD chainrings, changing the ring and chain seems relatively straight forward. The standard two speed is a great combination of gears, but I do find that I can spin out on the higher gear on kojak tyres, and only use the low gear for pulling away from the traffic lights - hence would quite like to tweak it higher (cycling on relatively flat terrain).. while retaining a chain guard as I don't want to catch my trousers!
ChrisL
 

Re: Brompton Chainring - How large can it go with a chain guard?

Postby Eddie Miles on Tue Sep 05, 2017 11:31 am

Not sure how easy it is to change the rear sprocket on your set-up but probably easier than changing the chaining. It might be worth running the ratios through an on-line gear ratio calculator to see the results of changing either/both.
Eddie Miles
 
Posts: 5
Joined: Sun Sep 03, 2017 7:51 am

Re: Brompton Chainring - How large can it go with a chain guard?

Postby ChrisL on Fri Sep 08, 2017 6:53 am

A 10 tooth rear sprocket (or 11 at a pinch) could work but sounds "non-standard" - does anyone have an idea where I can find a compatible one?
Thank you in advance!
ChrisL
 

Re: Brompton Chainring - How large can it go with a chain guard?

Postby Eddie Miles on Mon Sep 11, 2017 6:45 am

I only know Sturmey Archer and sprockets are quite easy to find. Usually http://www.sjscycles.co.uk can help. I would still advise running the ratios through a calculator so that you can understand what can be achieved. There's one on Sheldon. http://www.sheldonbrown.com/gear-calc.html
Eddie Miles
 
Posts: 5
Joined: Sun Sep 03, 2017 7:51 am


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