The same hollow core technology that produced tremendous speed, control and stability in our infamous JUKE wheels now powers the new BOOM HP (High-Performance) derby wheels.The new flat face, set back hollow cap with 5mm LiP and stronger core construction, combined with Atom's most amazing derby formula ever, makes BOOM extremely fast, light weight forgiving and diverse wheel ever...an entirely new kind of speed. control slide (grip when you need want it and slide when you need to) absolute best wheel for all cement surfaces hands down light weight (nylon__82g.___)(alloy___86g.__). speed with control super ball rebound super tuff "guarantee" skater satisfaction guarantee Firm: recommended for all slick surfaces but also has slide capabilities for plow stops. XFirm: recommended for surfaces with more grip but skaters looking for additional roll with grip and a controlled slide. XXFirm: recommended for grippy surfaces, skaters wanting maximum roll with controlled slide on sticky surfaces.