Seismic Wheels - Speed Vent 77mm x 55mm- 77A - Orange. The 77mm Speed Vent is molded around Seismic's proprietary weight-saving Energy Conversion Core ? possibly the raciest, sexiest core on the market. The 77mm diameter gives it the roll speed of a downhill 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 77mm Speed Vent is utterly unique among high-end wheels. Breakthrough performance for longboarding, downhill, GS, and even Hybrid slalom.