Brompton double

Kassida

Regular
Hi does anyone know how to fit a double chain ring on a Brompton (that would be a 44/28) I’m old so would like a choice of lower gears, only for severe hills, no changer, my bike has the new JIS bb so is not compatible with the old Stronglight one piece chain set, thanks PW
 

Cycleops

Legendary Member
Location
Accra, Ghana
Calling @chriscross1966 and @Fab Foodie.
They might even be able to recommend suitable footwear to kick the chain across ^_^.
 

12boy

Veteran
Location
Casper WY USA
The only way to get 28/44 is to use a 110 BCD crank, since you won't find a 130 BCD 28 chain ring. Another way to go is to keep the 130 BCD and change the sprockets on the hub to achieve the gearing you want. You could go with the chainring you have and put it on the outside, adding a 38 tooth on the inside. By consulting the Sheldon Brown gear inch calculator you can enter different combos. The Sheldon gear inch calculator is the only one I've found that provides the 349/ x1 3/8 wheel and tire combination used by Bromptons. Having said all that, mine has a 110 BCD with 38/58 and a 2 speed hub with 12/ 16 sprockets that gives me 78 /58 with the 58 and 51 /38 with the 38. If I were to use a 28/44 I would use the inner 2 options but probably need a longer bottom bracket to allow for a fold. I have considered having three chain rings but it doesn't look like it will fold properly. Unless you use a 3 speed hub, the problem for me is getting high enough gears with those little wheels.
 

steveindenmark

Legendary Member
Change your chainring to a 39T. I have a 6 speed and the - 3 is fine for normal riding. The - 1 would get over the alps... hopfully... I will let you know

I think this is the cheapest and easiest solution. It cheap enough to give it a go.
 

steveindenmark

Legendary Member
A simple and cheap way to do this is to just change your chainring for a 39T. Im old as well and it worked for me.
I have a 6 gear and the - 3 is good for normal riding and the - 1 will go up mountains.

Its cheap enough to try.

Screenshot_20190706_075603_com.strava.jpg
 

Kell

Über Member
The Schlumpf Mountain Drive is also an (expensive) option to get two ratios on the front.

View: https://www.youtube.com/watch?v=uwycL3WQiVY



As are other way of achieving a wider spread.

The Shimano Alfine rear hub which will give 8 gears and then the Rohloff hub which has 14.

I went for a smaller 44T chainring on the front last time I replaced just to try it out and see if it would help on the hill on my commute.

It does, but it compromises the rest of the ride as it just shifts all of your ratios down. Now, I top out at about 22mph for a comfortable ride. Which I don't hit that often, but do hit at least once a ride.

I think it was a useful experiment for me, but I'm planning on going back to the 50T when I replace again.
 
Last edited:

chriscross1966

Über Member
Location
Swindon
The best engineered method is to use a Kinetics or Vostok rear triangle. That way you get disc brakes and proper alignment... spreading a Brompton triangle is a bit fraught, ive done it to use Campagnolo Record hubs at 126mm, and the dish on that wheel is pretty horrifying..
 

chriscross1966

Über Member
Location
Swindon
Probably the best value hub upgrade if you are changing the triangle is the Alfine 11-speed... bigger range than the 8 far cheaper than the 14-speeds... the two 8-speed hubs on the market have a bit wider range than the Brompton 6 but not a vast amount.
 

u_i

Well-Known Member
Location
Michigan
Reading about 'best' and 'value' makes me worried given that I might be sitting on the other side and trusting the advice. I have a triple crankset mounted, giving me the span from 1.0 to 8.4 gear m development, 15 effective gears, for relatively little money, no change in the triangle and hardly discernible change in the folded bike width.
 

Fab Foodie

hanging-on in quiet desperation ...
Hi does anyone know how to fit a double chain ring on a Brompton (that would be a 44/28) I’m old so would like a choice of lower gears, only for severe hills, no changer, my bike has the new JIS bb so is not compatible with the old Stronglight one piece chain set, thanks PW
Hi, I just unbolted the standard chainset and bolted-on a Stronglight Double of choice. No fuss, no drama. Can’t remember exactly but I think 50/36 or 34.
However, the Brommie derailleur only has a certain tooth capacity and mine is on the limit (in the small sprocket the chain falls off when folded). Other than that it works a treat!
 
Similar threads
Top Bottom