Anyone out there use this book? I am trying to understand the rules re roll cage tube sizes. Car is a 1967 Lotus Elan. Plan to use it in Street Class drag racing, sprints and hill climbs. It will be a hardtop. The regs seem to indicate that I can get away with just a hoop of 45mm diameter - 1.6.1 (c) My question is - I want to fit a full roll cage as we need to stiffen up the chassis, so does this have to also be 45mm diametrer or can I use 38mm as I am classing these tubes as optional?