Roller coasters use special grease on their wheels and tracks that must stay slippery through rain, blazing sun, and temperature swings of 50°C or more, while never becoming so slick that it affects braking safety. The wheel bearings on a single coaster train can experience forces over 4G during loops and turns, requiring lubricants tough enough to protect metal under pressure equivalent to an elephant standing on a quarter. Maintenance crews apply fresh grease to hundreds of wheel assemblies every single day at busy theme parks, because dried-out lubricant creates that distinctive screaming sound riders sometimes hear. Modern coaster greases use synthetic formulas with tackifiers—sticky additives that make the grease cling to fast-spinning wheels even when centrifugal force tries to fling it away at speeds exceeding 100 mph.