spool rear ends advantage

[Brandon505]

why do drag cars use a spool rear end? what kind of advantage over a regular differential do they have?

[Dave B.]

In a 'regular' differential, the two axles are 'connected' by spider gears. These give the rear end the 'differential' action - allowing the rear wheels to rotate at slightly different speeds in turns. Power is transmitted to the side with the least resistance.

A spool is a solid casting or forging. Both axles turn at exactly the same speed. There's almost nothing to break in a spool, plus, power is transmitted evenly to both sides - so they are favored by drag racers. The downside is that the car is VERY difficult to turn. In a sharp corner, you can feel the rear end 'twitching' when the inside tire wants to turn fewer RPM than the outside one.

SL

[Brandon505]

you only told me things i already know, you didn't answer my question. In regular differentials when your driving straight, the pinion gears turn the side gears all as one unit, and the power is distributed evenly also, so it seems to me that the only difference between drag racers using a spool rear end and a regular diff, is that their gonna wear tires out faster at the end of the track when they turn.

[Crvett69]

on normal rear ends the wheel that has the worst traction gets the most power, thats why on most cars one tires will spin and the other one not turn when they get stuck. with spools both will spin no matter what. will be no slippage or spider gears or posi clutches to break if car makes more power than the rear axle can handle but on the street the cops will follow you around and give you tickets when the tires chirp going around corners

[Dave B.]

Originally Posted by Brandon505

you only told me things i already know, you didn't answer my question.

I DID answer your question - you just weren't willing to question what you thought you knew. If you stare at a computer screen long enough, you may figure out how all this works, but...

My advice to you is to do what I did at 13 - find a racing team operating on a shoestring and volunteer to be their gopher. Get your hands dirty, fetch some wrenches, clean a few hundred parts, watch what falls into the pan after something goes BANG! Then you won't have to rely on 0s and 1s for your answers.

SL

[Brandon505]

maybe id let them be my gophers lol

[DavidJohnson12]

At the same time, differential helps in maintaining equal speed of the wheels when the car is going straight.

[Black Lotus]

Originally Posted by DavidJohnson12

At the same time, differential helps in maintaining equal speed of the wheels when the car is going straight.

You mean-- a non-spool diff helps the car keep going straight when the tires are a slightly different size and running at a slightly different speed....
A spool diff with different size tires would try to turn the car in the direction of the smaller diameter tire.
I knew fellow with a locked rear end (spool, really), high power per pound, autocross car, and in the wet it was almost undrivable, as the car would try to spin whenever there was a difference in traction.
But really , if you want to absolutely get all the power to the ground that you possibly can, a spool is the way to go.