Originally Posted by cyclezen

given the bike was designed/spec'd for 650B x2.1 (=53.3mm) or 700c x 37/38 (from website); going to a 650B x 28 would be a very significant drop in bike height.
And maybe not a desirable drop in BB ...
quick calc ... the difference between a 650B x2.1 and a 650B x 28mm wheel/tire combo is 2.75 cm !!! over an inch lower...
quite a long drop... and given the propensity for putting longer cranks on gravel and mtb type bikes... pedal strikes would certainly be more likely with the 650b x 28, would not be my choice.
AND, the bike handling will suffer also... dropping the wheel size significantly affects 'trail', in a negative fashion (assuming the bike geo design for the larger wheels gives a good balance of steering quickness and 'stability' in straight running) - would be quite a bit more handful on speedy downhill descents.
whereas ...
a 650b x 2.1 compared to a 700c x 28 : 700 x 28 is only 7mm lower... and if a 32 mm is used then the difference is only 3 1/2 mm lower...
I would opt for getting a 700c wheelset and use 32mm, to keep the handling as close to 'optimum' as possible. Pedal strikes don;t bug me as much as a spooky descent... Wheel shimmy on short trail geo is very possible as you go further over 30 mph... my experience... (happens also on steep head angle design - 74+ - which don;t compensate with more trail...)
Ride On
Yuri