About the 77mm:The 77mm by 55mm Seismic Speed Vent is molded around our 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 Speed Vent is utterly unique among high-end wheels. Breakthrough performance for longboarding, downhill, GS, and even Hybrid slalom.Clear Orange - 75aClear Blue - 79aClear Purple - 83aAbout the 85mm:The very fastest wheel in the world - used by Joel King of England to set a Guinness World Record of 114.7 mph on a jet-powered luge! The 85mm by 52mm Seismic Speed Vent is molded around our proprietary weight-saving Energy Conversion Core - possibly the raciest, sexiest core on the market. The 85mm 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 Speed Vent is utterly unique among high-end wheels. Breakthrough performance for longboarding, downhill, GS, and even Hybrid slalom.Clear Blue - 75aClear Purple - 79a