I can respond to the grumpy reactionaries in the crowd.

It works.

650b tires ride like a dream. 650b offers a concept apparently alien to some of you.

...fun...

my wife loves hers, if I had the $$ I'd get one for myself.

alien??? do you mean a wheel to ride on?? a wheel with less than an inch difference diameter between it and a 26" rim? it works? the wheel works? it rolls?

or fun? yeah, fun on our bikes, it's real alien to those of us that have already been having fun on our bikes for decades.

put a rider on any slightly fat, street biased tire -doesn't matter what diameter rim - and send them out and man, that bike rides 'like a dream'

Fat is where it's at for 'rides like a dream'. 584c rim diameter, not so much.

So are we talking about mountain bikes ridden off road or other bikes ridden on pavement? Based on the OP, I thought we were talking about mountain bikes with fat tires. If so, the issue isn't comfort in the sense that a fat tire is going to help, the issue is a larger diameter tire is going to roll over obstacles easier. Obviously some folks have decided a 29" tire makes sense, I suppose the marketers are thinking maybe the folks who are resistant to going as big as 29" would be more likely to go to this new 27.5er thing. Silly, yes, but why do so many of you seem to be talking about this in regard to pavement riding? I agree, it's even more silly to add a new size for the pavement, but in regard to riding off road there's at least a functional difference worth noting (although I've obviously never ridden a "27.5er")-

So, how do you say this out loud then? "Twenty-seven-and-a-half-er"?

Well, yeah--and I admit to being a Grant fan, so I'm biased. But my wife had an old 700C Bridgestone roadie she almost never used because it "feels too nervous" (wouldn't fit tires bigger than 25mm). I had some long-reach brakes that fit it, and I had to replace her wheels anyway because I stole the rear for my singlespeed, so I converted her to 650 with some fat tires from Rivendell. I haven't ridden the bike (it's about 15cm too small for me), but she didn't like it before and loves it now.
Would it have been better for such a small frame to have been designed around 26-inch rims or had enough room for fatter 700s? Sure, but in the '80s they didn't do that.

I'm still bored. Where is my new stuff?

"Five eighty-four". Leave the neologisms to the marketards who think that not only do we need yet another wheel size but we also need yet another nonsense name for an old size.

Now do it in mud up a hill that is rut strewn from the rain and loose Rocks to boot- Find a 700c tyre for those conditions and see who is faster- Or a rock strewn downhill that a 26" wheel will just bounce off.

MTB wheels are strong- if not strong enough you get a stronger wheel. If the tyres are suitable for the conditions- then choose of of the 100's that are on the market already.

Can't see a necessity for a "NEW" wheel but then I also can't see a necessity for full suspension bikes either.

FWIW, I see certain advantages of 650b for touring/randonneuring bikes. It's a good way to get a fairly fat (30-40mm) tire without having to really jack the geometry around to make it fit. (650x38 ends up being essentially the same outer diameter as 700x23.)

The point has been made that 26" wheels would accomplish the same thing, and it would be a lot easier for tire manufacturers to tool up to make lightweight 26" road tires. On the surface, this would be true, but the reality is that the makers of 26" tires haven't done it, but the makers of 650b tires have, so there you go.

Just bought a 26" tire for a garage sale Schwinn Collegiate that fits the bill, an S-6 26 x 1 3/8" (37 x 597mm). Paid more for the tire, $13, than I did for the $10 bike. Any Schwinn dealer should have 'em. They've been around for a while. Around even longer are the tried and true EA-3 26" x 1 3/8 (37 x 590mm) that was/is standard for a zillion and one English (and some American) three speeds

Ah, but those really aren't lightweight tires. I'm talking about tires of construction essentially identical to racing tires, but wider.

Identical to racing tires?

Do you mean flimsier, less durable, more prone to flats, and much more expensive?

Yes. Also faster, lighter, more comfortable, and better feeling.

I can assume that this tire does not meet your particular requirements. If we all had the same set of requirements, 650b would indeed be a poor idea.

Faster is nice in theory; how much faster in fact? What is the trade off in comfort? See below.

Lighter? So what? See above.

Comfortable? Doubtful that any pair of high pressure "racing" tires will ever produce a ride as comfortable as lower pressure/wider tires on the same bike.

Better feeling? Maybe, especially if you can weigh them or read the brand name label while riding, otherwise see comments above.

According to recent testing by Bicycle Quarterly the difference between a heavily constructed tire like Rivendell's "nifty-swifty" and a lightly constructed tire like the Grand Bois "Cypres" could be as much as eight hours over the course of P-B-P, for a 150 watt rider. And for the most part, lightly constructed tires offer more comfort than heavier tires. Apparently the light sidewalls flex more and absorb more shock.

Weight by itself isn't terribly critical to me, but it is to other people. They key for me is that light weight seems to go hand-in-hand with low rolling resistance, which is important to me.

True, but I didn't say anything about high pressure racing tires. I said "tires of construction essentially identical to racing tires, but wider."

Have you ridden a wide tire of lightweight racing construction? I'd guess that you are basing your comments on preconceptions rather than personal experience. In my experience, wide, lightweight tires sound and feel absolutely wonderful, whether they are old Clement del Mundo tubulars or modern Grand Bois Cypres clinchers. Nothing else seems to match the feel of that kind of tire, and it's not a subtle thing. Compared to the Panaracer Col de Vie or Rivendell Ruffy-Tuffy -- both 28-30mm tires that I've used extensively -- a lightweight tire feels absolutely wonderful and is well worth the trade-offs in reliablility and longevity, to me.

Regardless, you seem to be arguing against a thing because it does not suit your needs, while seemingly believing that your needs are the only valid ones around. That you don't want a wide, lightweight, comfortable, "performance" tire (that admittedly isn't as durable as a heavier tire) doesn't mean that nobody else does, or that they should not exist.

why do you wrongfully assert "wide, lightweight, comfortable, performance" characteristics can only be built into a tire of 584c diameter????

What he said...

Since you're the OP, I'll ask you: what the heck does all this have to do with the link you posted in your original post? Those are mountain bike tires and rims. The only thing they have in common with a 650B pavement tire is the bead seat diameter. Is it a little silly that someone is now pushing for a "medium" (584) BSD for mountain bikes, to add to the already established "small" (559) and up-and-coming "large" (622)? I think yes, but the reason for it so far removed from what's been mostly discussed in this thread, I'm wondering what your original thoughts were in posting the link you did-

What he said.

Seriously, I think there's a strong case for 650b rando bikes. I don't know much of anything about mountain bikes, but from where I stand, 650b for the mountain bike doesn't seem to make much sense. (I'm open to education on the matter, though.)

I have not written or even implied that. In point of fact, I wrote "The point has been made that 26" wheels would accomplish the same thing, and it would be a lot easier for tire manufacturers to tool up to make lightweight 26" road tires. On the surface, this would be true, but the reality is that the makers of 26" tires haven't done it, but the makers of 650b tires have, so there you go."

The only even halfway rational opposition to 26" from 650b supporters that I have seen argues that 26" appears too small on "normal size" road bikes. IMO this vaguely true, but one has to look pretty closely and be fairly picky for it to be important. If the manufacturers wanted to turn out lightly constructed road tires for 26" I think they would function pretty much identically to lightly constructed road tires for 650b. But they haven't, so the rest is so much pontificating and theorizing.

I've ridden 26" (559) and 29" (622) mountain bike tires enough off road to have a clear idea of what the functional differences are for off road riding. Again, I'm talking about fat, off road tires that are at least 2" wide. Interestingly, the tires in the OP's link are 2.3" wide, which is a very fat tire indeed.

The whole point of 29" mountain bike tires is the abilility to roll over obstacles with less difficulty than with a smaller diameter tire. Just like if you were driving a 4wd truck off road, larger diameter tires will have an affect on how easy you drive over a big rock, for example.

But on a bike, it's not always better to have the bigger wheels; there are advantages, and there are disadvantages. In post #16, I gave real world examples of a couple of obstacles typically seen by mountain bikers, and I gave the reasons I'd rather have one size for one of the obstacles and the other size for the other.

Personally, I think having the choice of 26" or 29" is a good thing for mountain bikers, depending on their riding styles, the trails they ride, etc.; they've got a difference-making option there. But I also think adding another "standard" (584) into the mix is a very cumbersome idea. Just not enough difference, I don't think, to warrant the added headache of another bead seat diameter.

And based on the OP's original link, I don't think any of this has a darned thing to do with 650B tires that are designed for pavement riding-

Now that, there, makes no sense at all. Where are you going to find 650b tires when you're half way around the world?

BTW, I agree with the folks who claim the the 650b deal is promoted by people trying to make a profit by appealing to the snobbish "Look at me, I'm special because I use the same bead seat diameter as old French cyclotourists!" crowd.

That doesn't, however, detract from the point that 650b currently offers a rim/tire combo capable of things that no other currently available tire/rim combo is.

You mean the kind of "mainstream" cyclist who is concerned about the differences allegedly encountered over the course of P-B-P, for a 150 watt rider?

Or have experience with and love to discuss old Clement del Mundo tubulars, modern Grand Bois Cypres clinchers, Panaracer Col de Vie or Rivendell Ruffy-Tuffy tires? 650b tires seems just the thing for those folks.

I assume the market for this new tire size development is, and will remain, infinitesimal.

As has been pointed out, 650b is "just the thing" for folks who enjoy lightweight perfomance tires that offer a comfortable ride and don't require compromises like toe overlap.

As an aside, you seem quite upset over this "issue", and angry with folks who see the point in 650b while you do not. I can think of more important issues to get worked up over, myself, but to each his own.