Brompton higher gearing option

[Holeshot]

Hi guys.
Have been away from the forum for years but have viewed regularly - so first post for a long time.
Anyway.....

I have a 6L at the moment with the 8% higher gear option which I’m happy with.
I’m considering changing this and taking advantage of Evans’ discount on the raw lacquer 6LX (titanium) but trying to weigh up the pros and cons.
The thing I’m not clear on is how Brompton achieve the increased gearing: Is it done through a larger chainring, rear sprockets or is it in the hub?
I’d like to have the higher ratio but wondering how much it would take to change from the standard ratio that this bike will come with(the offer is only available on the standard bike build....not a bespoke build) and whether I may spend the money I save on modifying it to how I want it. If it’s a simple thing like changing just the chain ring then that’s OK.

Hope this makes sense.

Cheers.

 

[Pale Rider]

The standard, low and high gearing on factory Bromptons is achieved by different sized chain rings at the front.

As far as I'm aware the rear sprocket - or sprockets on a six speed - and hub gear is the same on all bikes.

 

[Cycleops]

@chriscross1966 is your man regarding modding the gears on Bromptons.
If you want a wider gear choice why don't you consider a Dahon or Tern?

 

[mickle]

Or learn to spin. Bromptons don't fare well when muscled along by tall gears.

 

[Holeshot]

Ah, thanks Pale Rider.
That’s great - and an easy fix. Not expensive either.

Cyclops - Good thinking and thanks for telling me about Mr Cross. I’d be interested to see what other gear options there are but really, I need a Brompton purely because of the fold size and the ease in which it is achieved. Just suits my needs for getting to work and stashing it under my desk etc.
I’m pretty happy with the spread of gears on the 6 speed with the higher ratio option but my only niggle is the overlap of ratios when changing into the higher 3 which involves a bit of a juggle between levers.
Have read about the 8 speed mod but not sure what to think. Interesting thought though.

Anyway, thanks again for the replies chaps

 

[Holeshot]

Or learn to spin. Bromptons don't fare well when muscled along by tall gears.

Haha! Too true....though ‘muscle’ may not be the term that applies to me!

 

[12boy]

Perhaps you already are familiar with gear inch calculators, but if not I like Sheldon Brown`s (RIP). Plug in the wheel size, chain ring and sprocket sizes and if there is an IGH, that too. You can easily see what would happen as you change sprocket and chain rings. Or, you could simply use what is one your .existing bike to duplicate the 8% increase.

 

[chriscross1966]

The +8% is achieved with a 54T chainring, you can go up to a 60T chainring before it becomes an issue with affecting the hook that locks the front fork during the fold. Next easiest options would be a toss-up between fitting a Schlumpf speed drive to the bottom bracket or an 8-speed Sturmey hubto the rear... about equal complexity... finally there is the whole-hog go bananas option and fit an aftermarket rear triangle from Kinetics or Vostok and put either a Shimano Alfine 11-speed or Rohloff 14-speed hub in it... The Sclumpf unit costs about the same as a cheapo Brompton 3-speed on eBay, the Sturmey setup is a bit cheaper, you could buy a recent Brompton for the cost of an 11-speed conversion once fitted and you could by a new top-end one for the cost of the 14-speed. The Sainted Sheldon's Gear Calculator shall be your One True Word...

 

[chriscross1966]

A +8% 6-speed is 34 to around 103 gear inches through the range. A Sturmey 8-speed set up 44T chainring to 20T sprocket is 35 to 114 inches with slightly closer ratios through the range.

The Schlumpf is a x1.65 increased gear on the bottom bracket, so you'd probably go to a smaller chainring, a 40T chainring would give you the equivalent of a 66T when the increased is engaged, whilst giving you some serious granny gears when not...

The Alfine 11 set up 60 to 16 gives 31 to 129 gear inches and a trendy big chainring.

To get really big ratios out of the Rohloff you'll need to get a BikinGreen 70T chainring and mod it to get the fork hook to fit.. 70T to 13T gets you 24 inches to 129 and a very trick Brompton... as in be prepared for other Brompton owners to want to talk to you about it.

 

[chriscross1966]

@chriscross1966 is your man regarding modding the gears on Bromptons.
If you want a wider gear choice why don't you consider a Dahon or Tern?

Thanks for the mention :-)... but wash your mouth out for suggesting a D***n or T**n :-)

 

[Kell]

Don't know if this is still true, but I think it is...

 

[Holeshot]

Wow, thanks for the replies everyone.

That's absolutely answered my questions!

chrisscross1966 - thanks for taking the time to explain the gear system options - I'm liking the 8 speed Sturmey idea best.
Presumably with this, it would do away with the derailleur set-up?
Forgive my ignorance on these things, but what would the preferred changing mechanism be for these on a Brompton? (Twist grip vs. lever etc).
Also, where might one find the 44T chainring?

Thanks again for everyone's time

 

[Kell]

chrisscross1966 - thanks for taking the time to explain the gear system options - I'm liking the 8 speed Sturmey idea best.
Presumably with this, it would do away with the derailleur set-up?

Thanks again for everyone's time

It does away with the chain pusher, but you still need to chain tensioner (the bit that looks like a derailleur with the jockey wheels) to allow the fold.

 

[CopperBrompton]

Also, remember you're not limited to Brompton's standard options. Others available include:
- Sturmey Archer 8-speed
- Alfine 11-speed
- Rohloff 14-speed

 

[Kell]

I cannot confirm or deny this, but the mechanic at my local Brompton shop (an ex-engineer) rates the Alfine way more than the Rohloff and cited various reasons including cost, serviceability (i.e. because it's a pressurised unit, you have to take it to someone who knows exactly what they're doing and has the right tools, and ease of use due to the spread of gears.

On the last point, I disagreed as he said it's a twist shift and no-one has a wrist that can twist that far. But then, realistically, when do you ever go from 1st to 14th in one hit anyway?