The belief that you waste energy bouncing around on a sprung Brooks is a myth. Well, except for maybe the very largest models. The springs on a B66/67 measure .092" and are quite stiff. There is no noticeable rocking. You have it right - they only really react when needed.

The Champin Flyer (a sprung B17) springs are also .092" and will be firm. I don't know what the thickness is on the B72. I have never been able to figure out what that spring design does. It appears to be a type of torsion bar setup.

The rear two springs on the B73 measure .084 and are alot more supple. I have switched out the springs on my two B67's for the lighter one off B73's. Much nicer ride, and still no bounce or rocking.

B17's are not sprung. They have alot of adherents. My first B17 was not working for me, but I persevered and got another one for my new bike and it has been great.

Breaking them in is an over-rated experience for me. The B67's were perfect the first day and only get better. The B17 is still, after 850, not giving in. One tough mold. I have to deduce that it's the road bike position that keeps my weight off it. Comfortable, though.

My next Brooks will be a Champion Flyer for my tour bike.