[Doug Fattic]

Back to the OP’s question about which tire size to use and what affect that might have on handling. If my wife was small and just a normal recreational rider I would definitely choose 26” MTB size. My 1st concern would be that she has toe clearance unless she was an experienced cyclist that likes to ride at speed. That kind of rider is likely going slower and sometime may turn by turning her handlebar and if her foot hits the front wheel there is a good chance she is going down. If my wife hit the ground because her toe hit the front wheel, she would think I was an idiot for my frame/component choices for her bike.

Another advantage of smaller diameter wheels is the she will be seating closer to the ground for easier foot down at stops. In addition a lower bottom bracket height caused by smaller wheels gives better handling characteristics. Looking up the geometry of the 2016 Soma double cross I see that the BB drop is 66mm. Production frames have a higher bottom bracket drop just in case someone puts on longer cranks or likes to pedal through corners at speed. The point is that in this case choosing smaller wheels is a double advantage for both easier foot down and more stable handling with a lower bottom bracket height. Those factors would trump tire choices in my opinion. Decent enough tires can be found in whatever tire size is chosen.

If I was choosing which wheels to buy, I would plug in the numbers into BikeCad and see what tire (and crank length) options give me toe clearance. It is not smart to fail that minimum requirement. Just for grins I looked up the tire radius of a 26 X 1.5” tire. At 316mm, it is 9mm less that a 650b X 38mm tire that has a 325mm radius. Of course smaller width tires can be chosen in either tire sizes depending on where she will be mostly riding.

Since she is short she probably would benefit from 165mm cranks to help with toe clearance.

Just to understand where my opinions are coming from I’ve been a custom frame builder for over 40 years and a lot of my customers have been women that have had trouble getting properly fit on production made bicycles. The solution is often to design and make a frame with smaller wheels.