Lowering Brompton gearing

[nomdeplume]

Hi, I have recently bought a 6-speed Brompton with which I am delighted except the gearing is too high for me (at 70 yrs!). I would like to lower the gear to the same as my mountain bike on which the lowest gear is I believe 18''. Wheel diameter 26'' X chainwheel teeth, 22, divided by rear sprocket teeth 32
= 18''.
If I change the chainwheel to a smaller one, to lower the gearing,what number of teeth will I need?

 

[RecordAceFromNew]

If I change the chainwheel to a smaller one, to lower the gearing,what number of teeth will I need?

Assuming you have a 6 speed BWR with 50T chainring and 13 and 16T rear sprockets you need to reduce the front ring size to 27T to give you a low of 18" (try this). The consequence is that the highest gear will then only be 54", which is equivalent to a 44T front and 21T rear (if you have such a rear sprocket or similar) on your 26" wheel mtb.

Obviously only you can determine whether you are happy with that, but there are more involved ways to allow such a low low without reducing the high so much, one is by replacing the 16T with a 19T at the same time which will enable a larger front ring to achieve a low of 18".

Hope it helps.

 

[Pale Rider]

Standard Brompton gearing is quite high, particularly if you aim for a cadence of 60pm or more.

I reduced mine by getting the smaller chainring from Brompton - about £25.

Fairly straightforward, although a couple of links had to come out of the chain.

 

[Bromptonaut]

Standard Brompton gearing is quite high, particularly if you aim for a cadence of 60pm or more.

I reduced mine by getting the smaller chainring from Brompton - about £25.

Fairly straightforward, although a couple of links had to come out of the chain.

I'd describe the standard BWR 6 speed gearing as quite low. Works well for me as a spinner in London traffic and round home where we have a few hills.

Bearing in mind Brompton have had supply problems with sprockets leading to bikes being built non-standard OP might want to count his teeth carefully!!

 

[Pale Rider]

I'd describe the standard BWR 6 speed gearing as quite low. Works well for me as a spinner in London traffic and round home where we have a few hills.

Fair enough, from what I can gather from your other posts, you ride the bike a lot more than me.

I take my hat off to anyone who can spin up sixth on a Brommie - that must be going some.

 

[nomdeplume]

Thanks for the info, I will try a 27t chainwheel ,fully appreciating that other ratios will be reduced proportionately. At my age and in a hilly area, low gears are more use to me.

 

[Bromptonaut]

Fair enough, from what I can gather from your other posts, you ride the bike a lot more than me.

I take my hat off to anyone who can spin up sixth on a Brommie - that must be going some.

I doubt many people will spin 6th but it being as high as it is a product of the range of the BWR setup rather than being symptomatic of a defect. I'd only use it on a downgrade or lolloping along with the wind on my back . The lower and middle gears are ideal for spinning off in town with rapid acceleration and low enough to climb gradients painlessly.

I wouldn't advise messing with them at least until the out of the box setup has proven lacking for the OP's use.

 

[Brommyboy]

I have a 44T and 28T ring for my Brommy: the 28T is hardly ever used as the gearing is very low (22" to 47" on Sram hub - lower and higher on BWR). I would have thought that 32T is about the lowest useful size. When you change the ring, the chain will need shortening, too. (big sprocket+chain ring)/2 [if odd no then +1] +68 will give correct length.

 

[ufkacbln]

Are you very rich?

If so consider a Shlumpf mountain drive

 

[Rickshaw Phil]

If you're merely well off, you could consider a Patterson Drive.

Not quite as pricey as the Schlumpf.

 

[nomdeplume]

Patterson looks interesting, any idea of price and stockists in UK or Europe?

 

[Rickshaw Phil]

Patterson looks interesting, any idea of price and stockists in UK or Europe?

At the moment I don't know of any stockists in Europe, just the ebay link given above which shows a price of £159.22 plus shipping.

 

[Night Train]

I like the look of the Patterson, and would get one when I start building my trike.
I prefer the idea of the cable change rather then the heel tap button on the Schlumpf.