Originally Posted by
Chaz955i
A spool essentially locks the axles together so they will turn at the same rate. A gear differential or any differential for that matter will allow the axles to turn at different speeds. Think about when turning, the outside wheel follows a larger arc than the inside wheel. The differential allows the outside axle to turn at a faster rate than the inside so both wheels can go through the turn without binding up. A spool does not. Both work but some prefer the feel of one over the other.
OK, in my old timer parlance I would call a "spool" a "posi", as in Posi-traction. Typically with real cars, a posi is good for drag racing and four wheel drive and for acceleration, but can be hard on larger tires on high grip surfaces. Where does the word "spool" come from in this term?