A vast majority of folders have poor riding dynamics. They make you sit upright where most of the weight falls on rear wheel, not to mention such a riding position takes away the suspension effect of weighted arms. They compensate for this by adding a rear suspension, making the bike rear heavy, complicated and prone to bobbing (not to mention loss of pedalling efficiency). I have only ridden 20 inch bikes and they are smooth enough that you don't need any suspension as long as some weight is distributed on the front wheel.