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As I learn more about LSD, I wonder why do manufacturers even bother installing open diff? Or is it one of those situation like how FWD is cheaper than RWD and thats why they choose it? Unless I missed something over the many threads on here, I do not see any advantage that open has over lsd so thats why it had me thinking this.
To aim the engine power at the wheels
To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)
An LSD isn't needed for a daily driver, and if it was then it wouldn't cost extra to have it come with a stock car. In order for a differential to work it only needs to be specific to one tire, so the automotive industry found one more item that they can sell as an aftermarket product for money, or sell the car with it for extra money because it isn't something that is needed in order for it to complete it's task in making the vehicle move.
I wish I could better explain the answer you are looking for, but I am just giving a guess at why vehicles usually come stock with an open differential instead of an LSD.
To aim the engine power at the wheels
To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)
An LSD isn't needed for a daily driver, and if it was then it wouldn't cost extra to have it come with a stock car. In order for a differential to work it only needs to be specific to one tire, so the automotive industry found one more item that they can sell as an aftermarket product for money, or sell the car with it for extra money because it isn't something that is needed in order for it to complete it's task in making the vehicle move.
I wish I could better explain the answer you are looking for, but I am just giving a guess at why vehicles usually come stock with an open differential instead of an LSD.
I for one dont understand open diff. myself cuz i hear its 2wd but yet only 1 wheel spins how can u say its 2wd when only 1 wheel turns?
The way that I have learned is that with open end both wheeles spin but they spin freely not together. So whichever wheel doesn't have traction will spin and the one that does will proppel the car forward. Pretty much if the cars back wheels are on ice then both wil spin but if 1 is on ice then that one will spina nd the other one will move the car forward. Like I said thats how I have learned it works. And then as you know with lsd it locks the wheels together so that they spin the same so if one is on ice and the other isn't it will lock the wheels together and so the one on ce will spin the same speed as the one not on ice.
Brian is pretty much correct in his understanding on Open Diff. Both wheels spin, just at different speeds.
Say you are turning a corner, the outside wheel is going to make up for the further distance it has to travel and be the faster spinning wheel of the two rear wheels, as for the inner wheel it will slow down due to it not having to go as far to get around the curve.
By the way, FWD is not simply cheaper (or even much cheaper, the CV joints add a lot of cost). It gives more space for passengers/luggage, and is vastly superior in bad weather, particularly snow. The transverse engine adds a bit of safety.
It really is a much better idea for a practical passenger car. The exception is a high horsepower car where torque steer is too big a problem, or a sports car. Although some small well designed FWD cars are pretty good sports cars, too.
Brian is pretty much correct in his understanding on Open Diff. Both wheels spin, just at different speeds.
Say you are turning a corner, the outside wheel is going to make up for the further distance it has to travel and be the faster spinning wheel of the two rear wheels, as for the inner wheel it will slow down due to it not having to go as far to get around the curve.
ok so if i was to jack the back of the car up with both rear wheels off the ground both wheels would turn? right?
Great question. Some LSDs require some traction on one wheel to generate the force to lock them up. Works fine in practice, not so good with your experiment.
The diff has nothing to do with gas mileage. Gears have to do with gas mileage.
Its a cost issue. Open diffs are cheaper to produce so they were put in the non-performance factory cars...the fbody v6's. Hence why they call it the "Y87 Performance Package" which comes with LSD.
An LSD, or especially an automatic torque biasing differential (Torsen or Quaife units), actually affect how a car handles compared to an open differential. With an open differential, if you get a tire in the air then all the power goes to the unloaded tire and it will be the only one that will be 'driving' the car - the one on the ground will do nothing to move the vehicle. Which is why you don't want to offroad with an open differential - get stuck with a tire in the air and you are not going anywhere as all the power is going to the tire with no grip. With an LSD or torque biasing differential basically all the power would be going to the wheel with grip on the ground, not the one in the air.
Automatic torque biasing differentials give more power to the tire with more grip, and once the grip has been exceeded the opposite tire now will be having more power transferred to it - hence the automatic torque biasing. Open differential differentials are "safer" for a daily driver in the sense that once a tire loses grip you will essentially be coasting down in a stable manner until grip is regained. With an automatic torque biasing differential the rear end is constantly changing grip based on available traction from side to side and won't be as stable for the average Joe driver if he/she doesn't realize what is going on. That is probably the main reason open differentials are standard on a daily driver vehicle.
An LSD is not like an automatic torque biasing differential though because it doesn't transfer more power to the tire with more grip. It senses the loss of traction and compensates via diverting power from that tire to the one with more grip. So instead of sensing a torque bias and constantly giving more power to whichever tire has more grip like an ATB, a LSD differential is constantly sensing wheel slip and diverting power away from that tire. Basically it functions in principle like an ABS system...
Forget an LSD differential, the ATB differential is what you really want for cornering grip and handling ability. A LSD differential works from wheel slip, meaning it doesn't really start working until a tire has lost grip. The ATB differential is constantly biasing the grip available in an effort to maintain maximum grip... big difference.
if you jack your car up, place it in neutral and you have a open diff, both wheels will spin however in the opposite direction. If you have a posi, they both spin in the same direction. Most posi units use a series of clutches to lock/unlock both wheels. The posi unit requires more effort to turn the tires because there is some preload built in. Posi units are significantly more expensive than standard differentials so that is why they are optional on certain vehicles.
Front wheel drive is much better in snow since pulling is easier than pushing. Rear wheel drive is better in a performance application such as drag racing. when you floor your car, the weight transfers to the rear of the car improving traction.
Crap...now i'm slightly confused. Ok, so since I peeled out and only the right side leaves a skidmark, that means i have an open differential correct? And if I get an LSD it would leave both skidmarks (providing i have the power to pel out...)? i know about posi-traction, but tha'ts bout it.
ok so if i was to jack the back of the car up with both rear wheels off the ground both wheels would turn? right?
This happened to me and Technically yes but one tire was moving 60MPH and one was moving maybe 2MPH.
O and in case you dont know it, don't put a donut tire on a a rear tire with LSD, you will no longer have LSD. This happened to me after owning my car for about 6 months, and now I can only do the one wheel spin. Just something else I need to fix....
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So whats the point of open diff anyways then?
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