The edging length needed depends on the amount of  protection needed. Most riders want the best capsule possible under all wind conditions.  To do this it it best to run the edging down the sides as far as possible. This extra coverage helps keep the capsule comfortable in cross winds and dryer while riding in the rain. Besides this, it also looks more finished. Tip: Never stop at a corner… for grip strength the edging needs at least 4 inches (10 cm) of relatively straight area when ending.  Here is a video to help.