4 speed Superlight Brompton

Kell

Über Member
That's not too tough. 3*3 has become a regular customization over the last years. Here's my setup:

View attachment 619112

https://ritzelrechner.de/?GR=BBWR&KB=44&RZ=14,12,16&UF=1330&TF=75&SL=2.6&UN=KMH&DV=development

Shifting is pretty linear (three times derailleur, then one time hub) and nicely spaced in this variant. Not more confusing than the actual BWR.
Is it possible to use that gear calculator to measure RPM? Or can the figures it spits out be interpreted to see if my guestimate of 15-18RPM (ish) between gears is correct?
 
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Kell

Über Member
Is it possible to use that gear calculator to measure RPM? Or can the figures it spits out be interpreted to see if my guestimate of 15RPM (ish) between gears is correct?
OK - so It doesn't seem to directly give you that answer, but by pulling the cadence slider about, you can see that to get 15.1 mph in 4th would be 79 RPM and in 5th it would be 62RPM - so 17RPM or roughly where I thought.
 

berlinonaut

Über Member
Location
Berlin Germany
The point remains, the P line isn't revolutionary light (indeed the 2005 SL2 was 630g lighter than the SL3) as some of the improvements over the 16 years you mentioned weigh a bit more, all its done has reversed some of that bloating to get back to ~10kg.
Fully agree with that as I wrote earlier:

So overall from my personal perspective the new 4-speed setup is not very attractive: It is not as reduced as the 2-speed and while the higher high gear is nice it is less flexible, nothing not already achievable today plus it still does not solve the issue of getting stuck on hills relatively early. I also find the claim of Brompton "1,5 kg lighter than the comparable steel Brompton" misleading as they do use the 3-speed hub as a comparison. The 2-speed would be a more adequate alternative in my eyes. But then the weight difference would be just 700g, same as it used to be with the old titanium/superlight model... Harder to market.
They are probably doing a bit of overmarketing here.
 

u_i

Well-Known Member
Location
Michigan
However, the sales guy did say they're bringing out a 9-speed soon.
This is really exciting.

That's not too tough. 3*3 has become a regular customization over the last years. Here's my setup:

Shifting is pretty linear (three times derailleur, then one time hub) and nicely spaced in this variant. Not more confusing than the actual BWR.
In my experience, the pusher system has not been well suited for the shifting to an intermediate cog. I would list at least 3 indicators for that. 1. The tolerance in the cable pull has been far more narrow for proper shifting than in the standard rear derailleur systems. 2. The shifting to the intermediate cog would generally not work unless the smallest and intermediate cogs were matched (came from the consecutive positions in the donor cassette). Standard derailleurs usually tolerate mismatched cogs. 3. Sticky snow would disable the 3-cog shifting on Brompton far sooner than for similarly low placed standard derailleurs on other bikes. Yes, I ride with 3 cogs on Brompton myself, and it works OK, but on the technical side I view it as a 'get by' solution'.

With all that I look forward to seeing what Brompton came up with for the purpose. The standard derailleurs fit poorly in the space there and their tensioners are marginal in picking up slack compared to the Brompton tensioner. I hope that latter capability is not compromised.
 

Dogtrousers

Kilometre nibbler
Shifting is pretty linear (three times derailleur, then one time hub) and nicely spaced in this variant. Not more confusing than the actual BWR.
So shift with your left (sprocket) until you hit the end of travel of the left shifter. Then shift the left shifter all the way the other way and shift with the right (hub). So starting in bottom gear it goes L, L, L&R, L, L, L&R, L, L.

My 6 speed goes L, L&R, L, L&R, L. I think I'd find the 9 speed pretty confusing. But I'm easily confused!
 

u_i

Well-Known Member
Location
Michigan
So shift with your left (sprocket) until you hit the end of travel of the left shifter. Then shift the left shifter all the way the other way and shift with the right (hub). So starting in bottom gear it goes L, L, L&R, L, L, L&R, L, L.

My 6 speed goes L, L&R, L, L&R, L. I think I'd find the 9 speed pretty confusing. But I'm easily confused!
I moved my hub shifting to the left and sprocket to the right, to make it consistent with other bikes: big jumps on the left and small on the right. I try to make other things consistent too, like bell and light, to reduce reaction times.
 

Dogtrousers

Kilometre nibbler
I moved my hub shifting to the left and sprocket to the right, to make it consistent with other bikes: big jumps on the left and small on the right. I try to make other things consistent too, like bell and light, to reduce reaction times.
This has crossed my mind, too. But I've got used to it now.
 

Kell

Über Member
I moved my hub shifting to the left and sprocket to the right, to make it consistent with other bikes: big jumps on the left and small on the right. I try to make other things consistent too, like bell and light, to reduce reaction times.
Did you need to switch shifters somehow too?
 

u_i

Well-Known Member
Location
Michigan
Did you need to switch shifters somehow too?
I put twist shifters on. I got used to them on other bikes and, for me, they allow for faster, near perpetual, shifting.
 

Kell

Über Member
TBH - 9 speeds to me is only achievable in a few ways.

1x3x3. Probably the cheapest solution as it would utilise their existing 3-speed BWR hub and then three sprockets.

1x9. Where you have a cassette, a short cage derailleur and a modified rear wheel or new rear triangle to make additional room.

3x3. Where they add two more chainrings AND an additional sprocket and use a single speed rear wheel. This actually makes more sense than the 1x9 to me. Or at least feels more achievable.

I don't see the second one working, I'm not sure there's enough space even if you take out a lot of the dish on the rear wheel. So IF* what the guy said is true, the most obvious solution would be the addition of an extra sprocket.

*Obviously, it's just a rumour. Google 9-speed Brompton and so far, nothing comes up - except the aftermarket solutions. But by the same token, I don't think my friend would lie to me about it, so he's just taken what he was told at face value... time will tell.
 
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TheDoctor

Europe Endless
Moderator
Location
Stevenage
The simplest 9 speed by far would be the BWR hub with, say, 12 14 16 or 13 15 17 sprockets. 9 gears and a slightly wider range.
 

rogerzilla

Legendary Member
Giving the BWR a wider range would mean impracticable gear sizes internally. You'd need a very big sun and, given that the OD of the shell is limited, the planets would be too small - the ratio of a single epicyclic is given by the teeth of (sun+gear ring)/gear ring. The BWR already pushes it about as far as it can go.

You can use cascading gear trains but they are pretty inefficient. You lose at least 3% in an epicyclic with perfect tooth shape and lubrication, but over 6% in a two-stage hub.
 
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