MAK

These guys put out informative and seemingly well researched videos.

One of the comments mentions a do it yourself double chainring he uses without a shifter. A response suggests that you nudge with your foot to the smaller ring (dangerous?) and getting off the bike and using your hands to go back to the larger ring. That seems to ruin any ride IMO.

Jipe

Proposing a 3x4s transmission with an old, slow, low efficiency IGH in 2024, crap !

Lightweight Brompton deserve an efficient, lightweight transmission with a good 11s derailleur and a 9-32 or 9-34 or 9-38 cassette like on the Birdy Touring.

CrimsonEclipse

"Assist ratio" ?!

(dons boots)

The BSometer pegged at 11!!

I've been steadily losing respect for Brompton for a while now, but not I just can't take them seriously.

Winfried

What's the biggest cassette currently available for Brompton? 7-speed?

With a dual 50/34 chainring, a 11-28 cassette would provide 1.61 - 6.05m meters development and make for an efficient touring solution.

Jipe

1.61m is nice, it allows to climb steep hills.

But 6.05m is much too short to ride at high speed on flat roads.

For me to have be able to ride from steep hills to high speed on flat roads, 1.6m to 8.0m is needed. 2m to 7.5m could be OK.

Fentuz

That the sort of range I use in Cylcocross and on the road, @ speed, I have to @ 100rpm to get to "normal" speed. On my 20", I run a 53-39 and it is OK in town with a 11-34 cassette (I prefer 11-28 but Wife needs range).
With a 16" wheel, I would at least try a 56/44 setup, the 56T would be equivalent to a 32T on a 700C bike.

silverx

wah i thought 12 x1 but 4 x 3
ok n skip

Schwinnsta

I think it makes sense. They have all the parts to it already. But I think it makes more sense for them to do a 20-inch version with standard 10 to 12 speed. For me personally, and many would disagree, they should have gone with 18-inch 355 from the git-go.

Jipe

The issue is not ETRTO349 or ETRTO355, there is only 6mm difference !

The issue is the tire clearance on the Brompton frame that limit the tire width to about 37mm (no space in tire width and tire height to go beyond 37mm). .

If there was more space, asking Schwalbe to make for instance a Big Apple 50x349 or Continental to make an Contact Urban 50x349 is not a problem.

tcs

The expected use envelope is the regular gear range is normally adequate, but when you get to the bottom of Hardknott Pass you nudge the chain down onto the smaller chainring. At the top of the pass you place the chain back on the large chainring as you stop to catch your breath, drink some water, take a congratulatory picture and nibble chocolate.

tcs

Instrumented tests I've read indicate 9-10-11T derailleur cogs are less efficient than old, slow, inefficient 3-speed IGHs.

FWIW, I haven't seen a post from anyone on the Brompton Touring Facebook Group who has modified their wide-range Brompton in the IGH+Derailleur hybrid-gearing way the factory is rumored to be doing it. Those who modified their Bromptons for wider range gearing go with Kinetics wide rear triangles and Afline 11 or Rohloff 14 IGHs (typically with disc brake).

Trifolds from other manufacturers have either Shimano 8-speed IGHs or 5-, 6-, 7-, or 9-speed derailleur systems, a few 2X with front derailleurs. Interesting direction for the Brompton factory. Perhaps they are trying to maintain their 'fold in any gear' capability.

Schwinnsta

I meant to imply that when I said if had been designed around a 355. At the time, narrow tires were thought to be faster.

2_i 

I tour in this fashion, and it is great.

Winfried

I use a derailleur, but if you don't need to switch between the two chainrings often, you can do without.

Winfried

With the smaller on the outside and some practise, it might even be possible to move the chain from the smaller back to the bigger ring.

Duragrouch

Wow, that looks like a superior gear calculator than on Sheldon Brown. Still haven't totally grocked it, and I'm an engineer. Trying to grasp the above in gear inches, changed units to that, but didn't display.

I have almost that exact setup, 50/34 x 11-30, but on 20"/406 1.75"/44 tires, which gives me 21-85 gear inches. I don't need taller, but would like a bit shorter than 21 (without sacrificing the 85, that is minimum for me) if I tour with loads, on hills too long to just climb when standing.

I think a Brompton style frame, with 20"/406 wheels, on paper should only be about 2"/50mm bigger in each direction, still quite compact, but be superior in every way; better ride, no need for IGH so lighter and capable of field repair, lower maintenance costs, and much wider choice of tire sizes available.

Winfried

To add/move/remove chainrings and cogs, just use the mouse to move them in the section above. For the settings, use the Gears, Tire Size, and Display settings.

For shorter gear inches, a cassette with a 34 or 36 smallest cog.

Duragrouch

Nice video; concise, to the point.

A 400% drivetrain on a Brompton would be great, 400% is my minimum need. I think the IGH setup indicated is set too high, should be set for a 20 gear inch low and not 30, sacrificing some top-end, but above 85 is just not needed on a tourer. That said, the dual-chainring setup they theorized, would be superior, in my opinion, especially for touring, with wider gear range, easily field repairable, lighter, more durable (especially with touring loads). Choice of which, as asked? This is easy to offer both. However, note: In for a pence, in for a pound; With an external derailleur with 4 cogs and 3 speed IGH, you have the disadvantages of a derailleur, but lack the advantages, as you ***still have an IGH that you are dragging around with it***. Either do an all-internal Rohloff 14 (expensive!), or just go all external gearing, 8 or 9 cogs in back (with a standard 135mm dropout, folks), double crank in front, and be done with it.

People should pay me for such good advice.

Winfried

An enlarged/replaced 135mm OLD triangle to use a wider cassette + double chainring in the front is a good solution for touring. Light, efficient, with a wide gear range.

Too bad Brompton still doesn't offer a 135mm triangle as an option.

Duragrouch

I think the standard triangle is what, 110mm? I don't think 25mm wider would affect folding, as the rear triangle does not pass the top tube, only under, and 12.5mm per side should not be too much problem for the folded parts on the drive side.

I met someone with a Brompton with a Schlumpf drive, but I'd still like the simplicity of a double crank. 1X systems are nice, no duplicate gears, but difficult packaging on a 406 wheel, much less a 349, the rear derailleur is gonna drag on the ground. Plus I hate that the cassettes are riveted together for lateral stiffness on the big cogs, that makes cleaning a real pain.

Winfried

Brompton uses 112mm.

Cold-setting the triangle doesn't affect the fold, but it must be done properly — the right stay is slightly more curved outward, so the ratio must be preserved when pulling the stays (wrong way to do it).

It'd just be a lot easier if Brompton simply sold it as an option. No need for DIY.

I don't know much about derailleurs, but maybe one with a short cage (what's the widest cassette they can take?) + dual crankset in the front would offer a wide enough gear range for touring.

Jipe

First, enlarging the rear triangle to 135mm doesn't affect the fold, the bike folds as usual and the folding width is the same.

With a special jig as done by Kinetics Glasgow, it can be perfect also for the Brompton titanium rear triangle. This was done for me by Kinetics and I mounted a Rohloff hub, its the perfect gearing with a range from 1.54m to 8.11m (19” to 102”).

For a derailleur solution, on the Birdy with about the same wheel size, its possible to use a medium cage derailleur (i.e. without risks to damage it) like the Shimano Ultegra RD-R8000GS that support cogs up to 34t.

With a 9-34t 11s cassette (what is also mounted on the superlight Helix), the range is 378%, with a 50t chainring its a good gear inch range for most cases even steep hills (I have a double 52-36t chainring with a 9-32t 11s cassette on my titanium Birdy and I almost never need the 36t chainring).
The 35x349 wheels of the Brompton are slightly smaller that the 40x355 wheels of the Birdy Touring (my titanium Birdy was factory equipped with even smaller wheels of 32x355 due to Kojak tires that have a theoretical overall diameter identical to the one of the Brompton).

There is also a 9-39t 11s cassette that provides a slightly wider gear inch range (433%) than the 12s 3x4s Brompton solution but requires a long cage derailleur like the 10s RD-T610-SGS mounted by Riese & Müller on the Birdy Touring (which is also compatible with 40x355 wheels without risks of damage).

These 9-34t and 9-39t are high quality, lightweight cassettes, the RD-R8000GS Ultegra is a lightweight derailleur, the 11s derailleur solution weight much less than the BWR+4s derailleur solution of Brompton and is much more efficient (even on the 9t cog because the efficiency of the BWR on the 1st and 3rd gears isn't good due to the relatively big reduction/multiplication ratio).

Schwinnsta

Can you back this up with any data? I think the efficiency is similar to their standard 3-speed, I can't remember the number. One of the reasons for going with the unusual gear change system that they have, was that having a 3 speed IGH was more efficient than one with a higher number of gears.

Jipe

Its a well known issue of this type of design: everything else remaining the same, a bigger ratio between the input rotational speed and output rotational speed (it can be a reduction or multiplication) reduces the efficiency.

There are no measurements for the BWR vs. the BSR because the BWR is a proprietary IGH made for Brompton but you have exactly he same effect for the Schlumpf: the Schlumpf Mountain Drive and High Speed Drive with a 2.5 ratio have a significantly lower efficiency than the Speed Drive with a 1.65 ratio.

More speed doesn't necessarily mean less efficiency, it depends of he IGH design, the 14s (actually 2x7s) Rohloff has a better efficiency than all other IGH with less speed.

tcs

Yes, but the claim was the BWR+derailleur with 11T sprocket was less efficient than a derailleur with a 9T or 10T sprocket. Tests? Data?