What is a spool differential? Chris Harris talks about it to Norbert Singer at 10:30, of this video? How's this style differ from limited-slip, for instance? Why use spool?


Thanks!


https://www.youtube.com/watch?v=PZxC-knQmkM

 

Paging rockville. He may be the only person alive who understands how those things work. LOL.

But seriously, I read a Carol Smith book wherein he describes the way all of the different types of diffs function and the book has no pics. You might as well be explaining the color green to a blind person.

 

Thanks! From the conversation, seems that spool causes more understeer, but I guess gets more HP to the ground?

Differentials have always been black magic boxes, to me.

 

A spool is a solid diff. Like a welded diff. There is zero "differential" between the two wheels and they move the exact same (100% locked) all the time, acceleration & deceleration.

Aussie V8 Supercars ran spools, not sure if they still do. A proper torsen or Salisbury/clutch type diff, even a locker has more advantages over a spool.

 

How can a car with a spool diff turn?

Thanks!

 

Tire scrub. I once did a U-turn on pavement in a jeep while 4WD was accidentally left engaged. That felt...awkward. You could just feel something wasn't right.

 

Not very well at low speeds. On a track, the inside wheel is unloaded and the radius of a corner on a track is a lot larger than making a tight turn in a parking lot, so the tire scrubbing is less. There is no 'differential' between the tires, so there are compromises when setting up the suspension of a car that runs a spool. You can make it work; but there are better options.

 

Spool diff puts down more HP? More reliable?

 

Go drive a go-kart, thats a solid rear end. Braking and cornering are hilariously different than in a car with a proper differential. But it definitely has a hardcore feel to it

I have driven a few cars with a welded differential which is more or less the same thing, its f@#king brutal! But it outperforms an open differential when it comes to racing.