What is a spool rear end?

A spool rear end is a type of differential used in vehicles, particularly in racing and high-performance applications. Unlike a traditional differential, which allows for some wheel slip during turns by letting the wheels rotate at different speeds, a spool locks both wheels together, ensuring they spin at the same rate. This provides maximum traction and stability but can make turning more challenging, as both wheels must rotate in unison. Spools are favored in drag racing and certain motorsports where straight-line acceleration is prioritized over cornering agility.