Is there any reason a 29er or 29/27.5 mullet wouldn't work on a small frame? I'm mulling over the possibility of building a fairly burly bike for use by my BIL/eldest son. BIL is ~5' 5" and son will be catching up soon enough so I'm looking at a small frame. The parts bin has a 140mm 29er fork plus wheelset and brakes, controls, etc., I'm just after a frame and I'm wondering if it might be worth selling/swapping the 29er parts for 27.5 and going that route instead.
Any suggestions?
Depends if the frame is designed for mullet, if not, it's likely to be very unbalanced.
Also be aware that mulleting a bike will reduce the reach somewhat. Depending on the reach of the frame, it could be worth sizing up (unless standover is an issue).
I tried this on my nukeproof Reactor 290. Installing a 27.5" rear wheel & changing the flip chip to high mode. Was great but a little short.