Seismic Speed Vent Wheels 77mm x 55mm 77A set of 4. 54mm running surface, Offset bearing seat, Square outside edge, beveled inside edge. The 77mm by 55mm 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 77mm diameter gives it the roll speed of a downhill 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.