This used to be the gospel and many still believe it. But several belt bikes are now being offered with variable chainstay length and a belt tensioner, with "back-bending" of the belt. R&M makes them, and there are also some offroad bikes. I'd definitely like a belt for my Alfine 11 Birdy. (Now I use a chain and chain wax for cleanliness, which works, but must be applied frequently.)

Some factors I think are preventing a belt Birdy:
- R&M don't seem interested in developing the Birdy further, with their massive focus on mid-drive ebikes. Pacific focuses more on lower price models, and have licensing limitations.
- Belts require a straight beltline. The Birdy suspension pivot is slanted, so as the suspension moves the beltline changes, and the rear & crank axles change from parallell to non-parallell. The deviations are small, but perhaps enough to either cause problems or keep R&M from wanting to experiment with it.
- As you say, a belt tensioner that works when folding, and also when riding, can be difficult to design. I guess it needs to be quite strong and stiff.

The same folding problem happens as shown on the picture when the chain is not on the smallest cog.

Can you check if its not the chain on the cog that prevent to fold enough ?

For the belt tensionning while folding, Kinetics makes Brompton with belt drive and use a modified Brompton tensionner. I always wonder if such a system provides enough tensionning for a belt ?

Do you have any detail on this? Anecdote: My 4 years old gates belt drive mid-motor ebike with nuvinci has passed 14 000 km now, with no sign of belt damage/wear, and no cleaning done. Ridden year round in sun/rain/snow. I don't know how long it will last, but even if it suddenly snaps tomorrow I'll be happy with it.

Maybe true for most of the riders that use belts. But for a strong enough rider, belts are more efficient than chains. I don't recall the exact wattage point where the belt wins, but it's been measured thoroughly. Of course in muddy/dusty MTB use, or with poorly maintained rusty chains, belts can win even with quite low wattage, I'm sure. Belts are an excellent option for the right uses.

For the Birdy, yes, because of the slanted pivot axle and the folding limitations. But variable chainstay length and belt tensioning in general is no longer a dealbreaker with belts, several manufacturers make such bikes now including R&M.

This is no longer true, I think. For sure the NuVinci / Enviolo can shift with power (though I would only recommend this hub for ebikes because of its low efficiency). And there are several new-ish options now like the Kindernay and the 3x3, made for MTB and/or ebike use. Are we sure those can't be shifted with power?

Anyway this shift-with-power thing is overrated, I think. With derailers it accellerates cassette/chain wear, so there's a benefit to reducing power anyway. Those who haven't tried IHG's may think the issue slows down shifting, but I'd say that's not generally the case. My Alfine 11 shifts instantly, always, and I don't have to stop pedaling, just reduce pedal speed. With derailers the shift speed depends on how fast the wheel/cranks are rotating. If climbing a tough hill in the 2nd lowest gear and I need to shift down, that shift can be very slow, while at high speed the shift is quick. (I ride with chains, belts, derailers, Alfine 11, Nuvinci, and Sturmey-Archer 5-speed. Each of those systems are excellent for their uses.)

Interesting option. It looks like they use a belt snubber. With that they can get away with less tension.

https://cimg6.ibsrv.net/gimg/bikefor...1c41c7200.jpeg

This is an 11~36 with GS derailleur. I used to run an XT SGS derailleur and 18” wheels, and was always bashing the derailleur. I swapped to 20” wheels and the GS derailleur and no more bashing. The bike doesn’t fold quite as tightly as before, but still fits in a Birdy bag.

Makes sense.

What's the biggest tire size that can be fitted on a Birdy with a 406 rim?

35x406 without mudguards (Continental Contact Urban 32x406 on 25mm inside rims = 35mm measured width).

Pacific Cycles deliver the R20 11SP with Panaracer Minits Tough 32x406.

I didn't had any folding issue but it was with the Titanium Birdy, not Birdy III. It might be different with a Birdy III but I doubt about it because the overall wheel size isn't much bigger in 35x406 than in 50x355 which is the standard wheel size of the Rohloff Birdy III.
Below a picture of the folded Ti Birdy with the 32x406 Continental Contact Urban tires (and a custom carbon front mudguard+Ridea rear mudguard and easy wheels):
https://cimg1.ibsrv.net/gimg/bikefor...46bf9638cf.jpg

I figured out the problem. Chain tensioner was hitting the frame as it wasn’t installed correctly (too forward).


https://cimg0.ibsrv.net/gimg/bikefor...0e5489766.jpeg

repositioned it to face down when unfolded and now all is well. Since rear wheel folds further up fold became much smaller as front wheel spindle now goes fully underneath the derailleur. Unbelievable how much difference it made.

Is this much chain slack and position of tensioner when folded normal?


https://cimg5.ibsrv.net/gimg/bikefor...65fabc530.jpeg

No, its too much slack.

Do you have a picture including the rear derailleur when folded ?

The chain isn't the original one, could it be that its too long, longer than the factory chain was?

The Birdy can benefit from a bit shorter chain than is common/advised on other bikes, so no wonder if the bikeshop made it too long. I have it rather short on mine since the Alfine chain tensioner isn't very long, to avoid it getting slack when folding.

https://cimg7.ibsrv.net/gimg/bikefor...710a52295.jpeg

Donno about chain length

The derailleur cage is completely folded which is OK.

I really think that the chain is too long for the Birdy.

If you still have the original chain, you can count the number of links of both chains.

Since, if I understand well, you now have a 11-32t cassette, the new chain doesn't need to be longer than the old one made for the original 9-32t cassette (for the first tested 11-36t cassette, it was probably 2 links longer).

Millennium pink
 

I have a millennium pink bd-1 and need a headset for it. Can’t find any information or numbers or sizes from searching and the local folding bike shop proved clueless too. Any got answers?

If that brings you nowhere, you could contact R&M (or Pacific) directly.
https://www.r-m.de/en-gb/contact/

It’s normal.

5nm according to an old official manual. New manual didn't include the torque specification for these two screws. There is a picture circulating among the community that says 6 to 8 nm, which isn't correct. Becarefull not to over torque these two screws.

Thanks for the info BabyCowHK , appreciate it.

Ok guys, chainrings received and installed. 53/39. On direct swap when on 39 chainring and biggest cog (32t) chain was rubbing against the fork, so had to add spacer taken from left side to drive side of the crank, so Q factor hasn’t changed. This way it’s now two spacers on the right side of the crank. While chain is not rubbing, when on 39 and 32t cog rear derailleur cage was slightly touching Big Apple tires. Those are wider than standard so I guess it’s normal. My mechanic adjusted the wheel spokes a little so the wheel was offset left for a mm or so, now derailleur cage while very close is not rubbing against the tire. Drive tested the bike and everything seems to be normal. 39 chainring on 32t cog is insane, bike can climb walls. Now will need to wait for derailleur adaptor and my drivetrain upgrade will be complete.


https://cimg6.ibsrv.net/gimg/bikefor...eb22d114d.jpeg

On my Birdy also with Big Apple, the Shimano Ultegra RD-R8000GS is very close to the tire on the biggest cog but doesn't rub.

The difference with your Birdy is as you know that I have an 11s XD cassette on a XDR rear hub with the needed spacer to mount a XD cassette on it.

Jipe it was really really close to the tire and was touching it. Would probably be solved by increasing tire pressure a little but my mechanic decided to be safe and shifted the rim a little.

Do you think Saint derailleur will be a good idea for my setup and avoid the cage being so close to the tire and ground? Hope it will not affect the fold much.

Saint is made for single chainrings, it will be too short for 2x. It has listed capacity of 25t. With 11-32 cassette that's 21t capacity consumed, leaving you only 4t left for the front. But you have 14t difference on the front, for a total of 35t. Shimano is very conservative in their numbers, but going 10t above what they recommend doesn't sound good.

Of course if you never crosschain it can work. But if you for example can only use 5 cassette cogs with each front chainring, that means shifting the front more often. That gets annoying pretty quick. I have experience with this, on a 3x setup where a medium derailer was the only possible option due to major tire rub. Front shifts must be done very often.

Well I noticed that when the chain is on 53 chainring and 32t cog the chain will rub the fork ever so slightly. The shiny cover to be precise. Barely audible/noticeable. I think it’s because there are two spacers on the drive side so chain light is shifted. It’s actually fine as the idea would be to not use any of 2 chainrings all the way but say for 8 speeds avoiding last two. But still, bike was perfectly fine on 39t chainring throughout full range on the cassette and was also fine on 53. So I’m happy with results, I can skip using last two biggest cogs with 53t and switch to 39t instead.

I do not think that any derailleur will have a cage so short that it doesn't come besides the tire with ETRTO355 wheels.

With the Shimano RD-R8000GS that according to Shimano goes up to 34t and from testes goes up to 36t, there is no problem of rubbing.

But it also depend of the chain length. The chain must be adjusted to be just long enough to accept the combination biggest chainring+biggest cog, in my case its 50x34. The critical condition for rubbing is the chain on the biggest cog, as soon as its on another cog, the chain moves outward the derailleur cage isn't close to the tire anymore.

https://cimg7.ibsrv.net/gimg/bikefor...ee115ca088.jpg
AS can be seen with my chain length adjustment and this mid cage derailleur, when the chain is on the biggest cogs, the derailleur cage comes just above the place where the tire is the widest.

Have just received Trigo adaptor for Brompton carrier block. There were no indications on what max torque to apply so I went for 5nm max. It didn’t make the ends meet but is pretty snug. Maybe I should keep screwing it in till both ends meet?

Fits fine, doesn’t interfere with front wheel release while full turn. Also fine with my comfort stem. For 20 degrees sports stem I’d suggest to go with inclined version which I think Jipe uses as it would definitely interfere with any big bags used. I had to push front light forward as it did interfere in it’s current position.


https://cimg6.ibsrv.net/gimg/bikefor...bac679bcf.jpeg

So you were right about the chain length. I replaced the old one which was under heavy load the whole time while I was on tours. I tried 50KM with a new chain and the shifting has improved.

I wander what’s this thing?


https://cimg0.ibsrv.net/gimg/bikefor...4f0e4ba5c.jpeg