A customization system for an article of footwear is disclosed. The customization system comprises an insert system. The insert system includes an insert and a heel member. Both the insert and the heel member may be interchangeable, allowing the user to modify the article of footwear to provide a customized fit or performance optimization. An article of footwear may also include a full length composite plate to be used as part of an outsole assembly. The full length composite plate may comprise a composite material that has a certain percent elongation, and can include a heel cup for heel stability and improved traction.