I presume that 27.5 would get some momentum from the 29er hype while it fills up the gaps that 29er lacks. Not to mention that it would be so much weenier than the brick big wheels.
The idea that the 27.5 wheels could possibily fit on the fork and the frame of the 26" sound exciting and seem like a cheap switch over to have a try.
All you need is new rims , Stan already has its range of 650s, and tires, Racing Ralphs are already in.
Currently I am very curious anyone has been riding one ?

just orderd the stuff to make them

I wouldn't mind a 650b AM fullsuspension bike. For XC I'm going to keep on riding my 29'ers as I have been doing in five years.

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My blaaaack Tarmac SL4

My dad has been running 650b for a few months now, and he seems to really love it! While I love the idea, I need something with burlier sidewalls than a Rocket Ron, but something that rolls faster than the other more burly 650b tires.

My guess is that for all but the most hardcore XC racers who need the lowest positions, 27.5 hardtails will be pretty niche. Could see people going with them more commonly on full suspension bikes, with short travel ones being the rarities while ones with medium travel possibly becoming pretty popular.

The full suspension bikes I've ridden with anything more than about 110-120mm travel have all felt pretty sluggish. I could see something like a Stumpjumper FSR/ Fuel EX/ Blur LT being pretty fun.

My wife has been riding 650B on her single speed MTB for a couple years now, she loves them. It's a Surly 1x1 (with the old non sue corrected fork, so the position is really low in the front). I think those bikes were pretty much made for 650B!

Stan's rims (old 355 setup) to King hubs. She's ran the Racing Ralphs and the Pacenti tires as well. Great overall bike. It served as a stepping stone for her to move to 29" wheels for her XC race bike this season (S-works HT). I think if a high end 650B race bike was available at the time, she would have gotten one instead of the 29er. 650B wouldn't clear her 26" S-works HT from last year (we tried!)

It's all about the tire and wheel options available. Things are already looking good, with many companies finding it to be a good time to introduce some 650b parts to market--someone needs to be the first to invest heavily into it, with others likely jumping on board, once the good word has spread about 650b, to cash in on the "trend" (which will likely coexist with the 29er and 26", only taking a fraction of the market share, but not replacing either). I personally want a 29er front (120mm travel) and 650b rear (130-140mm travel) design that works well, but I see more refinements every year, which keep me from buying right away.

On similar note, I wonder when 120mm travel becomes a norm for "XC" (or trail, whatever you want to call it), when sub 2kg/4.5lb carbon FS XC/trail frames are a norm, when Lefty becomes more refined to show up on more bikes (with more travel on 29ers), when carbon rims become cheaper and more common...

I've heard SRAM will have some offerings in 2013, not sure if that just means wheels or if Rock Shox will be making forks in the new size.

I would love a 650b 5" bike w/ AM geometry.

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Rapha cycling's Ed Hardy

Thought I would chime in with a photo of my rig.
I had tested out a friends set of Blunt low dollar stock wheels (about 2000gr) and his Neo moto Pancenti tires.
He didn't have them set up tubeless either.
I added some heavy old back up skewers, some older heavy rotors and my XX cassette.
I went to a popular local 25 mile loop twice, I ride regularly and raced on a bunch and then tested it out on a smaller fast 6 mile loop and a longer local 20 mile trail. I was sold. The wheels allow the bike to handle chatter bumps way faster, smoother, the bike is more stable at higher speeds on the trail, it handles roots, rocks and obstacles way better. I spend less time thinking about my lines and more time focusing
on how much faster I can push the bike. It raised up my BB and cranks now, so I can pedal through more turns and over more roots. I was up one gear higher on the cassette, while riding my popular trails. The bike was still light and quick enough to whip around and flick down sweeping trail sections with trees. I was quicker to get going from a stand still and quicker up short steep uphill sections than my fast friends on 29er bikes - HT and Full Susp. I was able to lean the bike, even with the tubed tires, further over than I have ever had it and pushed the bike into turns and sections of the 25 mile trail, where I had never before. Confidence!
Hence the newly built race Stans 650b rims with the sweet race light DT240 disc hubs.
The wheels weighed in around 1500 grams, the tires are Neo Motos with paint pen covering the logos, since my team is sponsored by
another tire manufacture. These neo's are right about 500 grams give or take 10g. I would like to try the Schwalbe Racing Ralph 650B Tires though, as they seem to be just a little more narrow.
I have them set up tubeless with Stans and stans tape.
The bike is about 22 1/2 lbs

love mine. stiff light and pick up speed faster then a 29 and roles over stuff better then a 26. im running mine in a cannondale scalpel.

Is that an Epic 650b?

650b is definitely catching on. Might be popular FS offering for the 29" XC crowd.