If there isn't enough sag in the rear suspension, the back of the bike sits up too high and makes the head tube angle too steep. That quickens the steering, couple that with the smaller front wheel, it can get unstable. Just set your sag correctly, and it's no big deal. Search the web for how to set the sag, it's easy. You want to set it at about 1/3 of the total rear wheel travel, pretty much the standard setting for dirt bikes. I only mentioned it because these bikes seem to come set up with too little sag for most riders.
The SF forks and shock have less travel. I wanted to use my bike off road with the S wheels, so I swapped the forks, shock, handlebars, cables, front fender, kickstand, etc.