Differentials

I've been doing a lot of research on differentials lately; simply because my FWD car is making me sick of never having traction. So here I go looking for the differences in RWD. I still don't have the best idea about the difference between Open and Limited-Slip. The technology and mechanics are explained all over the web, but what they mean to the driver is hardly explained in "Lame-man Terms".

My first wonder being the pictures I see of the Chrysler 300C SRT8, the Dodge Charger SRT8, and other muscular cars with Open diffs doing burnouts with smoke coming from both rear tires.... How does that happen? My car has an open diff, and all it does (with the Traction Control off) is send power to the one drive wheel, and it hops while it strains to get grip. I thought that in an Open Diff, only the one drive wheel gets the torque?

Then I drive an 06 Ponty GTO, and I can leave twin sh*ttys all over the place with the LSD on it's axle....that makes sense....but how do you smoke BOTH tires with an open diff? Geez, all those high-powered BMWs, AMG Benzs', etc. mostly have open diffs. How can a 604 HP MB SL65 AMG get all that torque to the tarmac with an open diff?

Someone please explain it to me like I'm dumb... Wait....more like I'm retarded, I guess.

well, i have wondered this question myself many times before and i think it has something to do with how much power the engine is putting out. as my neighbor explained it, apparently if you have enough power, the car will spin both tires even with an open diff... although likely the rear right one will be longer since as you gain speed, its harder to keep em both spinning without a posi unit of some kind... it might look like this.... i think lol

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In an open diff, if both wheels have equal or nearly equal traction, they both will spin equally.

The images of one wheel spinning comes mostly from live- axle RWD cars.
Old style live axle (a solid axle, like in good old American cars) will twist when power is applied. This twisting effect reduces the down force (weight) on the right (passenger side) rear tire and increases the downforce on the left rear.
This effectively reduces the right rear wheel traction and increases that of the left rear.
Apply enough power and the right rear will almost always go up in smoke.

All those open diff cars mentioned in the first post have independent rear suspension. There is very little or no load change on the tires due to twisting and usually spin both wheels equally.

Good answer Magi-Rat--it's interesting to note that the antics of a live rear axle still overpower the effect of the engine torque twisting the entire car over to the right, which might seem to ADD traction to the right rear, but...
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Your research on diffs is a start, but the problem with your car is terminal and beyond your control ;)
FWD cars by their nature are not suited to putting a lot of HP to the ground well. The mechanical layout of FWD, (namely forward weight bias, and the engine weight over the driving wheels) that work so well at very low levels of traction, like snow, work against you when the available traction is high, a least compared to a RWD car.
When you let the clutch out in first gear in any car, the weight shifts aft. This removes weight off the front tires and adds weight to the rear tires. In a FWD car this subtraction of weight means less available front tire grip. The same situation occurs with a RWD car. Except that the weight added to the rear driving tires helps traction.
Mind you this is all theoretical (everthing else being equal sort of thing), and your car can probably still holeshot a stock '65 Mustang. Probably not in the rain going uphill 'tho...
I would guess that your particular problem of one wheel doing all the spinning might be that your car has considerably more weight on one side than the other, or a mechanical problem.
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The really fast cars have RWD and use the laws of physics to their advantage.
FWD cars--don't.

Okay, thanks for the input.... And that leads me to my next question... Can you "drift" with a RWD open differential? Say an SRT8 Charger or SRT8 300C? How about a BMW 550i (360HP/360TQ/3800lbs.), or a Merc-Benz C55 AMG? Those are all high-powered RWD open diff cars with independent suspension....which I now know that can do two-wheel burnouts, but can they drift just like a limited-slip diff can?

Not as effectively, but yes. In a turn where you are maxing the cornering forces, a good stab of the throttle usually breaks the inner tire loose which causes it to give up what little traction it had. That plus the extra forward force tend to push the car into oversteer.

if you've got a cheap car you don't care about and want to drift it you can weld the diff solid - 50/50 torque split.

In an open diff, if both wheels have equal or nearly equal traction, they both will spin equally...........
...All those open diff cars mentioned in the first post have independent rear suspension. There is very little or no load change on the tires due to twisting and usually spin both wheels equally.



Interesting side note, based soley on my experiance-
Iv owned 2 RWD cars, with independant rear ends, that would only ever spin one rear wheel. Didn't matter what the road surface was like, or how I was motivating the loss of traction, they would only ever spin one rear wheel.
But, Im now on my 2nd FWD car that will happily spin both wheels.
The two RWD cars had centraly mounted drivelines, and equal length axle's, while the FWD cars have off centre engines, but the intermediate shafts to the axles are equal length.

These are the unusual exceptions though, the RWD cars most likely only spun one wheel because of thier older suspension designs, by a manufactor who pioneered IRS (in the 50s), and which lacked even simple anti-roll bars, making it easy to achieve an un-equal distribution of power.
The FWD cars are much more modern, and from a manufactor who has a history of building some of the worlds best FWD chassis's.

On an open differential there is nothing there to "grab" the axle once it starts slipping, The spider gears inside the housing just start spinning around the differential like your were making a turn. When you make a turn the outside tire has to travel a larger distance then the inside tire. If the axles did not spin a two different speeds you can not make a turn. Open differentials are easier and cheaper to make then a limited slip differential. In a limited slip or posi whatever they call it, a set of clutches or cones with grooves engage and "grab" the axle that is not spinning and turns both axles at the same speed it takes a second for the limited slip to grab hence the name "LIMITED SLIP". There is also something called a Locker Differential this type has a wratchet inside of it. When you give it torque it locks like your wratchet wrench and both axles are one. They also have the "Poor Man's Posi" where you take a welder and weld you spider gears together and it forces the differential to rotate in other words locking your axles together. Or you can buy a mini spool that gets rid of you differential and spiders and has a slot for both axles to slide in between your ring gear. Thats why you have your "One Tire Fire"

Also what happens is what Magic Rat said kinda. Since the pinion is under the ring on most setups like old muscle cars, when you give the rear end lots of torque it will twist but not side to side. The differential forces the rear suspension UP as the whole housing and axles twist downward into the ground. This is bad it can cause something called wheel hop. One way to stop wheel hop is by staggering you shock absorbers or by getting traction bars. A traction bar is put under the axle to keep it from making the rear suspension move up by not letting it twist down.