glye

Sounds sensible to me. In addition to the softer ride, the fatter tyres will also be more secure on gravel and bumpy roads. Depending on how much gravel you do, you could switch to Schwalbe Big Apple 50-355 which is even fatter than the original knobbies on the GT, it would be very smooth on paved roads, though you could lose a bit of grip on the worst paths. 50 grams more per tyre. Or you could go in the other direction: Schwalbe Marathon Racer 40-355 saves 125 grams per tyre, but you get less suspension and stability on gravel.

There are many ways of making the Birdy lighter, but once you have no mudguards and no rack, it gets more costly to lose weight. I'm not a weight weenie myself, but there are many here who know more about this. A carbon seatpost would have a decent effect, am I right?

glye

It is short, but perhaps not too short for mkatz. My calculator says this means 32 km/t at 80 pedal revolutions per minute, with those tyres. That's enough for a casual rider on flat ground and even slight downhill. Some older riders don't like that cadence. At 60 revs you get 24 km/t, still enough for casual riding on flat ground, but on any downhill you'll be coasting. Just putting the numbers out there. I have no idea how fast you like to ride, mkatz.
Also note that this gearing doesn't give you a very low gear either. If you're not very strong you may need to walk steeper hills, if you have them.

mkatz

80rpm is fine for me on the very rare occasion that I "need" to go "fast" (and 32KPH is fast enough). To be fair, when I rode motorcycles, nothing was fast enough.
On the other end, for riding uphill I would like a lower gear. As some of the components listed for the GT appear not to be particularly upscale (e.g. SRAM X5-A1 10speed derailleur), if compatible substitutes were available I'd be quite happy to purchase replacements to extend the lower end; of course, now I'm wondering how far I can extend the lower end (11 speed 9-36? 12 speed 9-42? Yes, this last thought might be kind of ridiculous ) Right now I'm perusing the Birdy "master thread" in an effort to gather thoughts about what upgrades/modifications might available. (I'm definitely compulsive that way.)

mkatz

The Big Apple suggest I particularly appreciate! I think I have no real need for knobbies. And I am a bit of a weight weenie, but look fore for saving a pound or three rather than an ounce.

gleearch

I'm curious. Instead of buying the 10spd GT and modifying it, would it make more sense to get the R11? It comes with a 53T chain ring, and a Shimano 11-28T cassette. The wheels and hubs are by Hubsmith. So it's a pretty speedy bike and it takes Schwalbe Kojaks 18 x 1.25. I don't think it's a stretch to switch to big apples with these rims. I know the bike costs more but by the time you spend modifying your bike, you might end up fairly close in price. Since the new R20 11spd is replacing the older model, some dealers are offering deals on them. The trick will be trying to get it shipped over, say from St. Kilda's in Australia. You would have to negotiate with them and see if they are willing to sell their limited stock of those bikes to the US.

Jipe

Kojak are not comfortable, aren't fast tires and are fragile, I definitely wouldn't recommend those tires.

The R11 comes with a 11-28 cassette so less low gear than the GT.

The only advantage is the 11s transmission and Hubsmith wheels for which there should exist a XDR hub body (the problem is where to find it outside Asia, I never saw it sold online) allowing 10-42 cassette for instance.

But the price difference is quite big. The chance to find a sale for the R11 seems to me low, there weren't so many R11 built.

glye

I have used the Sunrace 11-speed 9-36t cassette with a 45t chainwheel. This works, but I had to space the chainwheel out so the chainline was bad in lower gears. With 52t or bigger chainwheel this problem will be worse. With a 10-speed cassette it will be less bad since they extend less inwards than 11-speed mtb does. 11-speed road cassettes do not have this problem, but they don't come in 9-36t anyway, AFAIK. If you can find an 11-36 road (not mtb) cassette, that would improve your low gears without harming chainline much.

42t cassettes will also make chain rub worse, so chainline must be made even worse to compensate. This is sadly a general problem with the Birdy design: It's not made for big cassettes and/or big chainwheels. I needed the range of a 9-36t, but the Sunrace hub broke and I found the replacement was likely to break too, so I went for the Alfine 11 IHG instead. That solves the chainline / chain rub issues, at the cost of more weight and money.

Jipe

I do not agree with you: the Birdy could accept big chainwheel without the new chain tensionning arm around the chainwheel.

There are 9-32, 9-34 and 9-36 cassettes that fit on the 3gen Birdy but they require a SRAM XD ot XDR freewheel. Meaning that you need to change the rear wheel (or maybe find a Hubsmith XDR freewheel for the Birdy R11). If you do not need a longer gear, you can use a smaller chainwheel to have shorter gears (9-32 is 366% total range, 9-34 is 378 and 9-36 is 400%)
https://r2-bike.com/3T-Cassette-Bail...eed-9-32-teeth
https://r2-bike.com/LEONARDI-RACING-...ed-for-SRAM-XD
https://r2-bike.com/ETHIRTEEN-Casset...eed-9-34-teeth

glye

Ok, but not when combined with a big 11-speed mtb cassette, while also keeping a correct chainline. My 2018 Birdy with 11-speed 9-36t x 45t was not possible to set up with a correct chainline. A bigger chainwheel and a bigger cassette would only make this problem worse. If this works for anyone else, their frame is different from mine.
(With a small road cassette it may be fine. Big 10-speed mtb cassettes could perhaps also work.)

Jipe

What do you mean by chainline ?

Normally, the chainline is the distance between the chain and the center axle of the bike = center of the hub of the wheels.

Changing the size of the chainwheel doesn't change the chainline.

It seems to me that what you call chainline is the height of the upper part of the chain that could hit the right rear arm at the place where a protection is placed on it.

This could be a problem with huge cassettes with 42t till 50t biggest cog but not with 32t to 36t, R&M mount a 9-32 cassette and there is more space for a bigger cog. Changing from 10s to 11s doesn't really change the position of cassette.

But such a big cog is not really necessary with a small ETRTO 355 rear wheel.

glye

Chainline is how straight the chain runs between the front and rear sprockets, see https://www.sheldonbrown.com/chainline.html
If the chainline is bad, you get noise, high wear, and bad efficiency.

Not in itself. But on the Birdy, the problem is that the rear fork slopes outwards as you go up from the pivot point. That means if you have a small chainring placed as far inwards as it can go without chain rub, and replace it with a bigger chainring, you will get chain rub and you have to move the chainring outwards. And that changes the chainline.

Not what I mean. The problem is the part of the chainstay close to the suspension pivot.

Not with 11 speed mtb cassettes, unless one accepts a bad chainline. The inner cog position is different with mtb 10s and 11s, see below. 10s 36t might work, but 11s 36t does not, not on my Birdy at least. I know this, because I bought the 10s 9-32 Birdy and put an 11s 9-36 on it. I had to give it a bad chainline to avoid chainstay rubbing.

Not with road gearing, but with mtb cassettes it does affect the position of the inner cog. On 11s mtb cassettes the inner cog is more inwards than on 10s mtb. The cog is dished/"bent" inwards. This was done to allow putting one more cog on the same hub (Shimano) without making the cogs much narrower. (SRAM cogs are dished the same way, though their 11s cassettes are not 10s compatible.) You can see it here: https://www.bikerumor.com/ezoimgfmt/...=ng:webp/ngcb3

That depends on the chainring, the hils, the baggage, and the rider.

Jipe

As I wrote and as showed on the Sheldon Brown website, the chainline is the distance between the center of the bike and the chainring.




It doesn't change when you increase or decrease the chainring.

Most Birdy are factory equipped with a 52t chainring and the Birdy Touring has a 9-32 cassette.

I have a 52-39t front and -32 rear and there is space for more. I took 9-32 because my rear derailleur (Shimano Ultegra now) is limited to 32t rear.

The cassettes I have shown are all road cassettes including the 9-34 and 9-36, they fit on my rear wheel as my 9-32.

The Shimano XT M8000 11s is a kind of alien that was made to allow to move to 11s with 9-10s rear hub.

Shimano now moved to microspline with also cassettes starting at 10t.

glye

I'll try to explain again to help others from wasting their money.

"Chainline" has at least two meanings. Both meanings are common. Sheldon Brown uses both, on the page I linked to. I'll explain with examples:
1. "This bike has bad chainline" means: "The chain is not running straight between front and rear sprockets".
2. "The chainline on this bike is 42 mm" means: "The lateral centre of the chain is 42 mm from the lateral centre of the bike".

As I explained before, on the Birdy you will sometimes have to move the chainring outwards when you increase the chainring size, to avoid chainstay rubbing. This affects chainline.

I explained that with mtb cassettes, 10s and 11s has the inner cog in a different position - the chainline is different. It's more narrow on 11s, closer to the centre of the bike.
The Birdy Touring 2018 edition, which I have, originally has a Sunrace 10s 9-32 cassette, yes. I upgraded to the Sunrace 11s 9-36 cassette. This is an mtb cassette, meaning it uses mtb sprocket positioning. Which means in 1st gear, the chain is more inwards than on the original 10s. And that can lead to chainstay rubbing, as it did for me. To fix it, I had to move my single chainring outwards, which lead to a bad chainline. The chainring aligned with the 8th or 9th gear, which meant that in 1st gear the chainline was very bad (not straight). It worked, but not well.

The problem is not so much about the number of teeth on the 1st sprocket. It's mainly about the 1st sprocket position on 11/12-speed mtb cassettes, which is too narrow to work well on the Birdy.

I'll try to be as clear and specific as possible:
On the 2018 R&M Birdy Touring,
with a single chainring 45t or larger,
and using the Sunrace 11-speed 9-36 mtb cassette,
or any other 11 or 12 speed mtb spaced cassette 36t or larger,
it is not possible to achieve a good chainline (chainring aligned with 6t sprocket) because the chain will rub on the chainstay near the suspension pivot.

This I have verified in practical testing, not just theoretically. If you have a different result, then either you have a different bike, or a road cassette, or something else is different. If you managed to find a Sunrace 11s 9-36 cassette with road spacing, then good for you!

Jipe

OK, this is now clear.

The problem comes from all these Sunrace proprietary components used by Riese & Müller on the Birdy Touring: the Sunrace rear hub, the R&M mounted 10s 9-32t Sunrace cassette and your new the Sunrace 11s 9-36 cassette.

All this Sunrace system is proprietary to Sunrace including the hub and its freewheel (this is for me a major drawback because it forces you to use Sunrace components unless you change the rear hub).

All your observations are only valid with this Sunrace system which is used on only one Birdy model of Riese & Müller and no models of Pacific Cycles.

For the other rear hubs with other freewheel bodies, the situation is different.

For the mentioned Shimano 11s XT M8000, as said, it was made to be compatible with a 9s-10s freewheel but this happened only once, with the XT M8000 groupset. For the latest XT, Shimano moved to a new freewheel body called microspline. From your explanations, it seems to me that Sunrace used the same trick as Shimano to fit 11s on an existing 10s freewheel body. But this trick works only for MTB with cassettes with big last cogs it doesn't work for road for which cyclist want cassettes with small last cogs like 25t or 28t maximum. This trick isn't necessary for newly developed freewheel bodies like XD, XDR or microspline.

About my own experience, indeed, I use other components.

My Birdy was factory equipped with a hub with a standard Shimano/Sram 11s road freewheel and Shimano 11-28 11s road cassette (Pacific Cycles use the same transmission components on the Birdy R11, the only difference is that my Birdy was equipped with a front derailleur and compact 52-36 crank while the R20 has a single 52t).

I made a new set of wheels with a Hope road rear hub with a XDR freewheel on which I mounted a 11s 3T 9-32 XD cassette (XD cassettes can be mounted on a XDR freewheel, XDR means XDRoad).

What I observed is that both wheels have their cassette at the same position because there was no need to re-adjust the rear derailleur for the new wheel. The only thing I had to do is to increase the chain length by 2 links for the increase of the biggest cog from 28t to 32t.

The chainline didn't change at all.

This is also practical testing, not just theory.

The SRAM XD and XDR freewheel are now used by several companies as well for hubs as for cassettes and there are many manufacturers providing hubs and cassettes.

For the bigger XD cassettes with biggest cogs of 42t and above, as far as I know, they are unusable on the Birdy because they require a long cage derailleur unusable on small wheels like ETRTO 355.

glye

As expected, because you replaced a road cassette with another road cassette. They are made to be compatible, in the sense that a shimano standard road hub + cassette can be replaced with an XD road hub + cassette, as long as the axle standard is the same. The cassette spacing is the same for all/most 11s road cassettes.

Yes, the 3T 9-32 XD cassette is a road cassette. To quote Gerard Vroomen, co-owner/Head of Design 3T: "this is a road cassette for a road bike"
https://bikerumor.com/2017/08/31/eb1...roach-1x-road/
https://gerard.cc/

11s mtb cassetttes are a different story, see below.

No, it's not limited to Sunrace, it's a general issue for mtb 11 speed (not road). Yes, these Sunrace cassettes with 9t cogs only fit Sunrace hubs (except they may also be Capreo compatible, from what I hear). But the 11 speed mtb cog spacing they use is the same with Shimano and SRAM. The 1st cog is dished towards the spokes, which makes the cassette wider than the hub body would otherwise allow, wider than 10 speed mtb cassettes, and this moves the chainline inwards. This dishing can't be done with most road cassettes because the cogs are too small, but on mtb it's possible and a good idea in itself.

You can see the dishing in this picture (XD cassette): https://www.bikerumor.com/ezoimgfmt/...=ng:webp/ngcb3

"The cassette squeezes 11 gears in the space of 10 thanks to dished larger cogs that hug closer to the spokes."
https://bikerumor.com/2014/08/24/fir...n-bike-groups/

"Where their 11-speed road groups required a slightly wider freehub body, Shimano was able to squeeze 11 mountain bike gears into the space of 10 without making the gears any narrower thanks to the larger low cogs. Unlike a road cassette, the big cogs can be dished around the spokes since they sit out farther, so the freehub body and the hub spacing remain the same."
https://bikerumor.com/2014/04/11/fir...ed-mtb-groups/

The dishing can also be deduced from raw spacing data:
10 speed: Sprockets are placed at 3.95 mm spacing, with each sprocket being 1.6 mm thick.
11 speed: Sprockets are 1.6 mm thick, spaced at 3.74 mm (road), or 3.9 mm (MTB).
https://bike.bikegremlin.com/1232/bi...compatibility/
The 10s inner-to-outer cog tooth tip distance is 9 x 3.95 = 35.55 mm
On 11s the distance is 10 x 3.9 = 39.0
The 11 speed cassette is 3.45 mm wider. There is no room for it to expand towards the frame dropout, so it is dished towards the spokes. The chainline is moved inwards.

Again: The 1st cog on 11s mtb cassettes sits closer to the centerline than on 10s mtb. The chainline is different.

M8000 may be the only one from Shimano to this standard, but the same goes for all compatible 11s mtb cassettes: non-XD cassettes from SRAM, Sunrace, Microshift, and others.

I don't know if Microspline 11s is "wheel replacement compatible" with old Shimano HG 11s - if it is, it has the same spacing as mentioned above, and the same difference from 10 speed.

Jipe

This dishing is what I called a trick to fit 11s cassettes on a 10s freewheel body.

It was used for older standard of freewheel body.

It is not needed for the new types of freewheel bodies with 11s or 12s the first one being the Shimano 11s road freewheel body which is slightly wider than the previous Shimano 10s freewheel body (but with the same limitation of 11t for the smallest cog).

As also explained the dishing trick cannot be used for road cassette because cassettes like 11-23 or 11-25 must still remain possible for road bikes.

The XD freewheel body is wide enough for 11s without dishing, the XDR was introduced to allow 12s. To mount a XD cassette on a XDR freewheel body, a shim must be added just like when mounting a Shimano 10s cassette on a Shimano 11s road freewheel.

Now, as also said, these new huge cassettes are unusable for the Birdy due to the need of a long cage derailleur incompatible with small wheels like ETRTO 355, so for the Birdy, all this dishing story only apply to Sunrace, other recent MTB 11s cassettes are much too big.
And the new MTB standards like microspline use also a wider than 135mm OLD and therefore do not fit on the Birdy which has a 135mm rear OLD.

The Birdy, even if has full suspension and has a 135mm rear OLD, is a road bike made to use road components, not MTB components.

glye

Dishing is still used for at least 12 speed Microspline cassettes (see below) and SRAMs XD mtb cassettes. Here is the 11s XD 10-42, the dish is clearly visible:
https://www.bikerumor.com/ezoimgfmt/...=ng:webp/ngcb3

Dishing is a good idea for mtb. It's not just about fitting on older hub bodies. It also allows hub makers to maximise the flange-to-flange distance for a given hub width, which lets you build stronger wheels. Which is presumably why SRAM kept doing it for XD. It also looks like Shimano uses dishing for the new Microspline cassettes. Look at the third product image of this 12s cassette. The spider is mounted flush with the 2nd cog, while the 1st is bolted on outside of that, making it in effect dished further towards the spokes than the hub body allows in itself. With large cogs, dishing is good design.
https://www.bike24.com/p2271581.html?menu=1000,2,82

Not quite. To shift my 9-36 cassette I used an SRAM 11s derailer designed for 10-42 cassettes, it worked well enough apart from the chainline problem. So it is possible to use a 10-42 cassette on the Birdy, again apart from the chainline problem. 135 mm XD hubs exist. The derailer is long and gets close to the ground, yes, but works for paved roads. Going through rough gravel or grass with it would be a bad idea, though.

DT-Swiss has microspline conversion kits for some of their 135 mm quick release hubs, so it can be done easily enough.
https://www.dtswiss.com/en/support/c...-micro-spline/

To be exact, the Birdy is made to use typical 100/135 mm hubs, which exist for road, trekking and mtb. Wider hubs and through axle hubs, be they road or mtb, do not fit.

But yes, this is the issue I've been trying to get across: There are fitting issues with 11s mtb cassettes on the Birdy. But 10s mtb is fine. The chainlines are different.

Jipe

I haven't checked the XD 11s MTB cassette but what I can tell is that the XD body is wide enough to fit a 11s cassette without any dishing what wasn't the case of the 10s Shimano body used for the 11s XT M8000.

Latest SRAM MTB groupset are 12s and still use the XD body, so I guess that dishing is again needed. SRAM didn't move to XDR for 12s MTB, only for 12s road.

The latest MTB grouset from SRAM and also Shimano have cassettes going to 50t or 51t, do you think that it is still possible to mount their derailleur on a Birdy ETRTO 355 wheels without hitting the ground ?

If I understand well, you haven't mounted a 10-42 cassette ? When adjusting the rear derailleur for a 10-42 cassette the derailleur must go lower to keep the required space between the upper wheel of the derailleur and the biggest cog of the cassette, Even if the derailleur dosen't touch the ground with the 9-36 cassette, it will be even lower with a 10-42 cassette and could touch the ground.

glye

Road or mtb cassette? On 11s road the cogs are closer together, so the cassette is narrower. So 11s road might fit without dishing, while 11s mtb might not. That would explain why the SRAM 11s XD mtb is dished.

And 52t cassettes exist from other vendors. The most extreme I have seen is 9-52t, 578% range. I don't know if these can fit the Birdy. I haven't studied the derailers that can handle them. It might be getting so close to the ground that it depends on how fat the tyre is...

Not necessarily. It may not have to go any lower, due to the way these derailers are designed. In the picture below, the black dotted line for the X-Horizon is horisontal. This shows that the derailer body moves only horisontally. The distance between upper pulley and cog varies because of the large distance between the pulley and the rotation point of the tensioner arm. As the arm rotates forwards, the upper pulley moves downwards.



The difference in radius between 36t and 42t is 12 mm, so the upper pulley has to go 12 mm lower. When I set this up with my 9-36 cassette, I gave it the longest possible chain in order to improve shifting of the smallest cogs (pulley close to cogs). When on the 36t cog, the arm could still rotate forwards a good distance, which lowers the upper pulley. I think this is enough to give the required 12 mm extra clearance. If it isn't, it will be most of the way there, so only a few more mm needed. And on my setup, the lowest part of the arm had 3-4 cm ground clearance when vertical. Close, but workable. I haven't tried it, but I think the data shows it will work - apart from the chainline problem. Buyers beware, of course.

Jipe

To come back to the start of the discussion about the transmission, the gear range of the Birdy GT, it is interesting to note that all 3 models of Riese & Müller and all internal gear hubs of Pacific Cycles have longer ratio than the derailleur models of Pacific Cycles.

We already discussed the R&M Birdy touring that has 52x 9-32 which is 22% longer than the derailleur models of Pacific Cycles that have 52x11 as longest ratio. R&M choose this seldom seen and fully proprietary hub+cassette system to provide this longer ratio.

The Birdy Rohloff has 52x13, but the Rohloff multiply by 1.467 on 14th gear so equivalent to 52x (13/1.467) = 52x8.86

Last model of R&M, the Birdy City with a Nexus 8 and 52x16 but the Nexus multiply by 1.62 on its 8th gear so its equivalent to 52x(16/1.62) = 52x9.9

Then the Birdy Touring 3x8 of Pacific Cycles with 52x11-30 but on a Sturmey Archer CS-RF3 that multiply by 1.33 on its 3rd gear so equivalent to 52x(11/1.33) = 52x8.27

50PlusCycling

For those who haven’t read the entire thread, mounting 20” wheels on a Birdy is as easy as bolting them on. The only complication is that you need to move the brake pads outward, which means brakes with longer levers and more range for adjustment, or adapters which will move your brake arms upwards. These are bolt-on mods, and very inexpensive.

As for chain lines, these can be altered by changing the Q factor of the crankset. I had bought a Dura Ace 7800 crankset and front derailleur to run with an XTR 11 speed rear cassette and derailleur. I found that the chainrings were too close to the frame, and there was not enough clearance for the front derailleur cage to travel. A little scavenging and machining was necessary to make it work, and it worked nicely. However, with 11 speeds and an MTB cassette, a second chain ring on the front seemed redundant, so I removed the ring, derailleur, and shifter and am content to have an 11 speed bike.

As for Kojak tires, I went through two sets of them. With a properly set up suspension (adjusted for your weight and load), my Birdy was as smooth as if I ran wider tires. Where I live, gravel, dirt, and mud are nonexistent, but there are rough pavements, potholes, and road debris, the suspension soaks it all up. I now run Panasonic Minits Lite tires, which are very fast, and very light. I run them at 120 psi, and my Birdy rides softer than my road bikes. The Minits are more durable and longer-lasting than Kojaks.

Jipe

I agree with you, my Birdy has a compact crankset 52-36 and a 9-32 cassette and indeed, I almost never need the 36t chainring. I could as well remove this chainring + the front derailleur system and save weight.

I have minit lite PT tires in ETRTO 406 on another bike and they are good tires. The problem is to find them in ETRTO 355 for the Birdy, they seem only available in Japan and Singapore ?

glye

Yes, an odd choice, especially given the weakness of the hub, which I have written about before. I'm not exceptionally strong, or heavy, or careless, and I haven't geared it lower than 45 front / 36 rear, and still it broke. Since the 36t cassette is made by Sunrace themselves and fits only this hub, Sunrace can't claim they don't support it. I've broken two of these Sunrace hub bodies before I gave up. I can't believe this is just bad luck. So has R&M simply not tested it well? Sunrace is in Taiwan afaik and their local market has lots of small and light riders. Not so for R&M in Germany.

With gearing I care mainly about gearing range, and then adjust chainweel size to get the ratio I need. The 1x10 Touring model has 356% range, too low for me. Hence the upgrade to 11s 9-36 and 400% range, but then the hub broke. I could make an XD wheel and use a 10-42 cassette for 420% range, but then the chainline / chainstay clearance problems get even worse. I could go for a 2x crankset, but that has it's own problems. So I went for the Alfine 11 with 409% range. Enough range for me for this bike, no chainline problems, and half the cost of a Rohloff. R&M should offer this option. The Nexus 8 is only 306%, less than an 11-34 cassette.

The Sturmey Archer CS-RF3 is very interesting and was high on my list. It officially supports cassettes up to 9s 11-34 , which gives it 548% range! More than the Rohloff at 526%. When in 2nd gear of the hub, which you can be most of the time, it has the same efficiency as a pure derailer setup. This and the SRAM DualDrive seem to be good options for small wheel bikes. For larger wheel bikes the 11s and 12s options are now cheap enough and have enough range that I would prefer them in most cases.

glye

Yes. (For single chainrings it is easier and cheaper to use chainring spacers, and keep the Q as it is.) But for 1x11 or 1x12 with wide mtb cassettes and a reasonably sized chainweel, the frame makes it impossible to get a good chainline, at least on my 2018 R&M Birdy it is. So anyone thinking about that kind of setup should consider if they will be happy with the noise and wear you get from a bad chainline.

You seem happy with your setup, so I'm wondering if you have a Pacific Birdy? Maybe they have redesigned the frame to give it better clearance.

Jipe

I guess that R&M choose the Sunrace solution because there was no other solution to go under 11t at the time they designed the Birdy Touring. Other manufacturers like Moulton designed their own solution with proprietary hub and cassette.

The problem is that you cannot mount a chainring bigger than 55t or maybe 56t on the current Birdy models with the current chain tensionning arm. So the only solution to have longer gears is either a smaller than11t cog or an internal gear hub.

FYI, there are XD-XDR road cassettes up to 9-42 from E*THIRTEEN (XCX E*THIRTEEN cassettes seem to be road XD cassette, E*THIRTEEN is also the manufacturer of the 3T 9-32 cassette XD-XDR).

SRAM discontinued the Dual Drive several years ago, that's why several bike manufacturers using Dual Drive switched to the SA CS-RF3.

The choice between internal gear hub and derailleur is a question of taste, but its a fact that it isn't possible to switch gear while applying force on the pedals with the Alfine hubs what creates a lost of efficiency especially when shifting while riding uphill. The Rohloff allows to change gears while applying force on the pedal but the rotating grip becomes harder to turn.

The SA CS-RF3 add about 1kg (the naked hub without command and cables is 1090g) to the bike on top of the derailleur system, so not an option for people looking to a lightweight folder.