Some wobble can be normal for the Halfbike after a certain speed - with practice you'll get better at controling it. However you can definitely minimize it by making sure both tires have equal pressure. Also, If the silver nut is not screwed on properly your tires might wobble. Tighten carefully, as overdoing it can lock the bearings thus preventing the tires' free rotation. We suggest that you tighten the nut well at 1st - until it starts to block the wheel and then make a quarter revolution backwards to loosen it slightly.