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I took some pictures and I thought you might wish to see them. 26" Pike (150mm travel) with a 650b wheel / tyre. I'd call that useable.
Wheel is Sram Rail 50 with a High roller 2 2.35.
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More pics
As an aside, the rear 650B wheel fits comfortably in the (Medium Transition Covert) frame, but does slightly bottom out on the seat tube as shown in the last picture. But then I'm pretty sure the Yeti SB66 does that anyway, so no biggie.
That's only good for dry almost no mud clearance, also no chance to fit bigger tyres like Schwalbe or 2.4/2.5 Maxxis.
Have you let all the air out the fork and compressed it all the way to see if the tyre hits the underside of the crown?
Personally, with the limited tyre choice given the tight clearance, Id prefer to run 26" with the tyres I wanted
Admittedly, I didn't check for bottom out on the crown. And yes, you would be limited for tyre choice.
I personally think that trying to shoehorn 650b wheels into a 26" frameset is a mug's game. But some people want to know this sort of stuff.
Wow!
Wouldn't be me..
If you pick up a stone in the tread it'll mark the brace big time, although the 650B version of the Pike has barely any more clearance.
Wouldn't want to land hard on that!