Seismic Speed Vent Wheels 73mm x 54mm 77A set of 4. 53mm running surface, Offset bearing seat, Square outside edge, beveled inside edge. The 73mm by 54mm Seismic Speed Vent is molded around our proprietary weight-saving Energy Conversion (EC) hub - the first tall, wide hub seen in longboarding and still second-to-none. The 73mm diameter gives it the roll speed of a larger wheel, while the weight-saving hub adds the quickness and agility of a smaller wheel, as well as enhanced rebound. Combined with lips designed for pure grip, the Speed Vent stands in a class by itself.