Brompton Adapted for Hills

[Fab Foodie]

View attachment 362971
Mine has 52 and 38 teeth. It is a Spa touring double chainset that cost something ludicrous like £20 without rings. I had to experiment with the bottom bracket to get the right length and wish I had thought to write that down somewhere.

Mine seems to work fine on the standard BB.

OK so 10 and 14T difference seems to be OK for the rear tensioner but 16T (50/34) is possibly a step too far for foldability on the inner ring.

 

[The Jogger]

Can you remove a crank arm and a bottom bracket? If so easy. If not easy for a bike shop.

Bike shop me thinks, Adrian................thanks

 

[chriscross1966]

If you have the current crank it's a 130BCD, so you could just fit a 39T chainring. Slightly more exotic would be fitting a different crank, I do it for aesthetics purposes, but it wouldn't be expensive to get a double chainring in the front and have say 50/34 compact loaded onto it, assuming a 3-speed then maybe go up a tooth or two on the rear sprocket. It's not hard to get a Sturmey 8-speed into the standard rear triangle, once again go down to the smallest chainring you can on the front.... in a more exotic world you can fit a Vostok rear triangle and either a Rohloff 14-speed or Shimano Alfine 11-speed hub, If you had 39-18 chanring and sprocket on an Alfine you'd be able to climb pretty much vertical faces, that bottom gear would be around 20", and you'd still have a top gear that would allow you to play SB's down the hills...

 

[The Jogger]

My LBS said they would fit if I sourced it as apparently because they're not a Brompton agent they can't. Would this do the trick

https://www.sjscycles.co.uk/chainsets/alloy-compact-double-square-taper-chainset-5034t-170mm/

Mind I did ask them to fit a marathon + and I've just picked it up with just a marathon on it, never mind, they are a nice bunch in there.

 

[12boy]

The 50/34 will be fine. You haven't said how old the bike is. Before they went to the 130 bcd crank with removable chain rings they were ISO. However, I used a JIS 119 mm bottom bracket with a 54 and 38 and it worked fine except for throwing the chain when folded on the 38. I had to stop to change the chain from one ring to the other but it only takes a few seconds. Others have said they can do the down shift with their shoe but not the other way around. I have used ISO crank arms with a JIS spindle but I am not sure you can use JIS cranks on an ISO spindle. A better BB than the original is not a bad idea anyway. The only tools needed to switch chain rings is a 5mm allen key and perhaps a wrench made to hold the nut side still. https://www.parktool.com/product/chainring-nut-wrench-cnw-2 is an example.

 

[The Jogger]

Thanks 12boy, I got the bike about three years ago. I'm not confident enough or technical enough to carry out the work so I'll get the lbs to do it. Just good to know that compact is the right one. I know @Fab Foodie has a similar one.

 

[chriscross1966]

..... A better BB than the original is not a bad idea anyway. ....

It isn't hard to find a better BB than the old Brompton one :-).... I like the Campagnolo Ultratorque, but recognise there is a significant technical challenge in getting one into a Brompton, the Shimano UN55 is available in many lengths, although one method that might work very well is to investigate the use of 73mm (Mountain Bike) Hollowtech2 cranks with a 4mm spacer under the drive side and a 1mm spacer under the NDS... that would give clearance for the inner ring, and you could look at adding a front derailleur mounted on a 40mm derailleur hanger https://www.ebay.co.uk/itm/322544758574

 

[Kell]

You're probably the right person to ask @chriscross1966 - has anyone successfully added a front derailleur and shifter to a Brompton?

 

[chriscross1966]

You're probably the right person to ask @chriscross1966 - has anyone successfully added a front derailleur and shifter to a Brompton?

There's a fair number on the far-Eastern Brompton fan pages on Facebook, Steve Parry built a few too. I'm in the process of trying to get one together ATM, mostly late 80's or early 90's Campagnolo parts, including the bottom bracket. I plan on using that 40mm clamp to work out positioning for the front mech then have a mount brazed on when the frame goes off for repaint. For the rear mech I have the hanger that came with the Vostok triangle on another bike so will use that with the modified stock triangle I'm fitting. She's called Francesca because of all the Italian parts.

 

[Fab Foodie]

You're probably the right person to ask @chriscross1966 - has anyone successfully added a front derailleur and shifter to a Brompton?

Yes, it’s been done and it’s not to complicated. Ask on the London Brompton Club forum.