Brompton 3 speed gearing question

[DBrown67]

Thanks for all the advice guys... very helpful!

I would like to reiterate that the bike I tested was factory standard 3-speed. The B75 is already -12% so I'd have to do nothing if it suits me. Only other Brompton option is to fit the 14 tooth rear sprocket to get the -18%.

It's nice to see the 3rd party option from SJS for the 39 tooth ring. Didn't know about that. But as you say you're getting into the realms of having another chain and I certainly won't be riding around any mountains. Though I do live in Yorkshire and there's a few hills knocking about once I get outside Leeds.

Been doing my due dilligence and it's good to see there's a thriving 3rd party market for Brompton parts and accessories. I have looked at other folders like Dahon but their range is so big and they seem to discontinue models on a whim. With Brompton the frame is the same throughout. Just everything around it is choice.

 

[jay clock]

I have a S3L and found the standard 3 speed tough. Dropped the front ring from 50 to 44 I think and problem solved. On the flat I am between 2 and 3 and spinning out at about 30kmh.

 

[12boy]

The nice thing about Bromptons is how easy they are to modify. Easy to swap sprockets and to add a chainring, sprocket swapping being the cheapest. Because the wheels are small, a Brompton sprocket doesn't last as long as the same size sprocket on a larger wheel. You will be replacing them fairly frequently, at least as often as you replace a chain or two. A 1 tooth difference on a sprocket changes gear ratios far more than on a few on a chain ring. Right now, for example, I am running 58 and 38 chainrings and 12 and 17 tooth sprockets on a two speed, saving some pounds from an SA 3 speed. Since Shimano sprockets work fine and I have a cluster or two lying around I may try 18 and 19 tooth sprockets to incease my range. Going up a steep hill for any distance calls for gear inches in the lower 30s if not lower, especially if there is a headwind as well. As a grinder, not a spinner, I prefer higher gear inches than you folks appear to, but that is just my preference.

 

[DBrown67]

Thanks for all the help guys... I take delivery of my B75 in 2 days from Halfords (got 10% British Cycling discount). I've already got mudguards ordered and plan to ride the standard bike a short while and see how i go before making any other decisions.

But just as a thought...would this crankset fit a 3-speed Brompton? It seems to have the correct square taper fitting.
http://vi.raptor.ebaydesc.com/ws/eB...tegory=109118&pm=1&ds=0&t=1564939840000&ver=0

Reason I ask is because I have a Giant Escape 2016 model fitted with this crankset that I am currently not using. The granny ring is removed on mine so is just a 48/36 at the moment. Would be great to try out for a quick 6 speed if it fits. Might be some overlap though and probably wasting my time. :P

 

[12boy]

Looks like a 110 BCD crank and I have one on my Brompton with 58 and 38 tooth chainrings. The only issue with the 58/38 is the chain comes off when folding with the 38. Shimano crankarms are JIS and should fit on the BB. You might check how much closer to the ground your pedal will be with a 175 crank arm though.