The Grimlock Rotary Forged? Wheel is manufactured using a highly advanced production technique called Rotary Forging. The rim of the wheels is forged at high pressure while the wheel is spun at high speed. This alters the molecular structure and enhances the strength of the alloy. The benefit is a much lighter weight than a regular cast wheel. Most importantly, the weight saving is in the outer rim of the wheel which dramatically reduces rotational mass and enhances vehicle performance.