⚙️ Spool
A locked (non-differential) axle where both wheels are forced to spin at exactly the same speed — used in some racing classes for maximum forward bite through corners.
What it actually does
A spool is a solid front "differential" that does not differentiate at all — both front wheels are locked together permanently. It sounds crude, and it is the standard choice in several racing classes because it delivers utterly predictable corner-exit drive.
In practice
With both wheels locked, power goes down evenly and the car pulls straight out of corners without the inside wheel spinning away. The cost is steering: a spool makes the car harder to turn at low speed, and it puts noticeably more strain on front driveshafts and outdrives.
Worth knowing
A spool is not a bashing upgrade. On loose surfaces and tight turns the reduced steering and extra driveline shock cause more problems than the traction gain solves.