forward if you furl
To find the correct place of the cars with full headsail (which is your starting point)you should go on a close reach and ensure your tell-tales flow evenly -which means you have the correct trim. Then bear away slightly: if the lower tell-tales break first, your car is too far forward, if the upper tell-tale breaks first, your car is too far aft. They should break simultaneously. You then do the same thing at various stages of furling, but it will be less accurate,because the sail-shape is being distorted (but you can try it out with a storm-jib). I have found that when wind suddenly increases so as to require furling, the best method is to furl, push the car of the lazy sheet forward to its pre-determined place (as above -I have three 'standard' positions) tack, and then push the other car forward. Moving a car forward under load in my experience doesn't work.