Seismic Wheels - Speed Vent 73mm x 54mm - 76a - Orange. The 73mm Speed Vent is molded around Seismic's proprietary weight-saving Energy Conversion Core ? possibly the raciest, sexiest core on the market. The 73mm diameter gives it the roll speed of a larger wheel, while the weight-saving core adds the quickness and agility of a smaller wheel, as well as enhanced rebound. Combined with lips designed for pure grip, the 73mm Speed Vent is utterly unique among high-end wheels. Breakthrough performance for longboarding, downhill, GS, and Hybrid slalom.