[Brompton] Disk brakes + Nexus hub?
 

Hello,

Out of curiosity, do you think Brompton could offer a 16" model with ~ the same weight and price (ie. ~12kg and ~€1,800) but with disk brakes and a Shimano Alfine 8 gear hub using the following features to save weight:

• Titanium fork + rear triangle
• Hybrid disk calipers
• Lighter saddle and rims

?

I know the Shimano gear hub isn't the most efficient in the absolute, but experience show it's perfectly fine for riding in the city, which is how it's used by the vast majority of its owners.

Cheers,

There are lightweight hydraulic disc brakes like the Magura MT8 SL or Trail SL that weight less than hybrid disc calipers but their aren't cheap.

Titanium fork and rear triangle save weight but aren't cheap.

Same for the saddle and rims.

Lightweight bike parts are never cheap.

So, its surely possible to make a lightweight 16" Brompton with disc brakes but it will cost (much) more than 1800€.

Cheap, Strong, Light

You can have any two you want.

A Shimano Nexus/Alfine adds about 700g when retroffiting a six-speeder

How much heavier are hybrid brakes + disks compared to Brompton's road calipers?

Replacing the square taper BB with a hollowtech BB, the pedals and the saddle with lighter parts wouldn't cost much considering Brompton sells ten's of thousands of bikes a year. And possibly the steel seatpost with a titanium part.

Wouldn't that stick to the ~1,800€$ the six-speed C line currently sells for?

--
Edit: The Nexus SG-C6001-8R is announced for 1735g while the — disk only, but it can be used with rim brakes — Alfine SG-S7001-8 is said to weigh 1670g.
--
Edit: With this "Driveline-crank for road Birdy Brompton, 5holes, 130bcd 170mm", the crank is announced for 680g while its BB is 90g — as a reference, the Shimano BB-UN55 118x68mm is 300g.

Brompton choose hydraulic disc brakes for the G-line, not mechanical nor hybrid, that work pretty well.

Riese & Müller mount Shimano hydraulic disc brakes on the Birdy 3 since many years without encountering any reliability issue.

Why do you want hybrid disc brakes while hydraulic work better, cost less and can weight less?

Remember the 1,800€ mark for which the C line currently sells over here

The goal of this thread is to see if Brompton could offer an alternative C line with disk brakes and a gear hub that provides the same range as the six-speed transmission — since S-A seems to phase out its 8s hub, which is heavier and crap anyway, that leaves Shimano.

There's a shop in Scotland that makes/made new rear swinging triangles for Bromptons that would fit Shimano Alfine 11 if I recall correctly (wider O.L.D. spacing), but that new triangle was handemade and cost a bunch, not including the new hub. Alfine 11 was not really designed for 16"/349, but with the right chainring and cog (or cog-belt drive, even better), I think the gearing could be correct. My concern (not yet validated) is that Alfine 11 I think uses roller (sprag) clutches instead of ratchets, and I don't know if they slip under standing climbing, nor the durability of them.

IMO, any IGH you get now, should be one with oil lube (not grease which requires a teardown, clean, lube, assembly) with easy drain and refill, and good seals to hold the oil and keep water out. With regular at-home lube replacement, that should go a long way toward avoiding a full teardown, cleaning, and relube of the hub, which saves big bucks annually.

From the factory, I think Brompton could offer a good IGH with belt drive at reasonable cost, but for the belt, you'd need a removeable drive-side dropout to get the belt on. Disc brakes should not be a challenge.

I know Kinetics, but there's no way that Brompton would cost 1,800€ like the C line.

The Alfine 11 costs almost three times more, and an Alfine 8 provides enough range anyway — even a bit more than the 3*2 transmission.

The goal is only to compensate the ~700g added by an Alfine/Nexus 8 hub and ?g by the hybride/hydraulic disk brakes while remaining in the same price zone.

Well, that kind of weight savings is going to cost. But equally important, if you can save that weight for the IGH and disc setup, you could also save that weight for the standard setup and have a lighter bike.

It's like when I talk to people about the failings of the F-35 fighter:
Me: It's not as agile as an F-16 or F-15, so same for our adversaries with generation 4 and 4.5 fighters.
Them: Doesn't matter, because it has helmet-cued off-bore sighting.
Me: Yeah, if that means it doesn't need agility, then why not mount the same system on a cargo plane? One answer is that missiles can follow off-bore sighting, but bullets from the guns can't. So agility matters.

My point being, any advancement as an "offset" for a disadvantage, can also be applied to the non-disadvantaged, resulting in superiority.

For the Brompton, maybe the lowest weight does not matter as long as it is below the threshold maximum weight for carrying frequently with ease. Decide what that is for you, and you have your target weight.

I agree: an IGH like the Nexus 8 increases the weight and doesn't provide a wide enough gear inch range (Brompton moved to the 3x4 = 12s to increase the range of the 2x3=6s).

A good derailleur+cassette like on the Birdy Touring costs less, weight less and provide a wider gear inch range.

Another concern is the torque limit of the hub.
VERY Small wheel + heavy rider might exceed the torque limit.

Obviously, check the documentation before install.

I think you might have that backwards, but I could be wrong. Smaller wheel radius means a smaller torque arm, through which the same ground thrust acts, so actually smaller torque that the hub needs to output to provide the same thrust/acceleration. However, smaller wheels are inherently lower geared, which means you might need to run in a higher gear to get the same speed, and I don't know if all the gears can take the same input torque. Plus also, you sometimes don't have a tall enough high gear. So I'm not certain I'm correct, but maybe. Rider weight is always a factor, but the smaller wheels may help offset. Always good to check and calculate, compare to hub maker specs, being careful to know which specs are independent of tire size, and which are parameters based on a certain tire size.