Hamilton's Ultralast Wheels - Quick Ship May 18, 2009 The new Ultralast Wheel possesses "off the chart" performance characteristics- specifically in the areas of thermal retention and rollability. Heat buildup in polyurethane, due to high loads or continuous duty applications, is the most common cause for material breakdown over the life of the wheel. Ultralast polyurethane operates much cooler under load and at higher speeds compared to most other urethanes. The result is a simply superior dynamic performance and a longer service life.