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- April 16, 2002
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- Year, Model & Trim Level
- 93 4 dr 4x4 manual XL.
Hi, got this from another site when I was asking about differentials and lockers and such. Was a little of a simple explanation, but it would be helpul for someone who is new to this stuff.
When going around a corner, the outside wheel always travels farther than the inside wheel (circles of different diameters have different circumferences). Since both wheels are attached to the same vehicle, it is obvious that for this to happen, the outside wheel must therefore also travel FASTER than the inside wheel.
The standard open differential and the limited slip (what most auto makers offer as a traction-adding device) allow the outside wheel to be driven (by the engine) faster through a turn than the inside wheel. This makes for a smooth driving vehicle with no binding of the drivetrain or scrubbing of the tires. There is no hopping or chirping of tires which was common with early automobiles that did not have a differential. BTW, that's why it's called a differential, it allows for different speeds between the two wheels.
The problem with these differentials is that they operate by balancing the torque load on both wheels. That is fine when both wheels have the same traction (and therefore the torque loads have the same resistance at each wheel). But when one wheel has less traction than the other (ie: it's on ice, snow, mud, sand, or even in the air) then very little torque load can be applied to it because there is very little resistance. And because the differential wants to balance the load, BOTH tires end up with very little applied torque. That's why you end up seeing the wheel with the least traction spinning: it's spinning because it requires very little torque. On the other hand, the wheel with the good traction can't even turn because the torque is too low.
Limited slip differentials try to get around this problem by biasing the torque so that it gives a greater percentage of available torque to the non-spinning wheel. In other words, it doesn't balance the torque, it biases it to the wheel with the greater resistance or traction. In many cases, this is all you need (ie: snow covered streets, wet pavement and dirt roads). But when you're on the rocks or you're going uphill on a rutted road, a percentage of a small amount of torque just isn't going to cut it. That's when you need a locker or spool.
A spool is the exact opposite of a differential. It allows absolutely no speed difference between left and right wheels. They are permanently locked together. No matter what the traction conditions, the engine will always drive both wheels. This provides an enormous advantage on difficult terrain. The problem is that it is horrible on the street because there will be driveline stress and increased tire wear whenever you drive around corners. On the dirt, it's not too bad since the wheels can slip but on the street the traction is too good. The tires will chirp and possibly hop. Some people use spools on the street but they're a distinct minority and I'd discourage it.
ARB, OxLocker and some other manufacturers make a combination differential/spool that let's you choose in which mode it should operate. These are often referred to as manual lockers. For the street, you can turn the spool off so it will operate like a regular open differential. Off-road, you can turn the spool on for maximum performance. No downsides except for the price and difficulty of installation.
The locker, it is often confused with a limited slip, is a kind of automatic spool. They are oftened referred to as automatic lockers. Its default state is to lock (hence the name) left and right wheels together like a spool. In this mode it operates just like a spool. But when going around corners, it allows the outside wheel to disengage from the inside wheel and turn faster by allowing it to be driven by the ground (as opposed to being driven by the engine). It accomplishes this by a ratcheting mechanism. Once the vehicle exits the turn and drives in a straight line, both wheels lock together again. It is this locking/unlocking action that is the locker's source of advantage and disadvantage. It's advantage is that it doesn't result in the driveline stress or tire wear common to spools. It's disadvantage is that the point of locking/unlocking results in sudden over- and under-steer which is particularly pronounced on sweeping turns (as opposed to sharp turns). It's enough of an annoyance and disturbance that some people would prefer the more predictable manners of a limited slip or a spool. But there are lots of other fourwheelers who have learned to live with the locker's quirks.
On ice and snow, the spool and locker are probably the worse choices for highway driving because if they spin, both wheels will spin which greatly reduces your ability to maneuver. With a limited slip or open diff, generally only one wheel with spin, allowing the other to help track the vehicle in a straight line. A manual locker would also be a good choice for snow/ice-covered roads because you can choose how it should operate. Having said that, there are many people who drive their automatic locker-equipped vehicles on icy roads on a regular basis. It all depends on your comfort level.
...lars
When going around a corner, the outside wheel always travels farther than the inside wheel (circles of different diameters have different circumferences). Since both wheels are attached to the same vehicle, it is obvious that for this to happen, the outside wheel must therefore also travel FASTER than the inside wheel.
The standard open differential and the limited slip (what most auto makers offer as a traction-adding device) allow the outside wheel to be driven (by the engine) faster through a turn than the inside wheel. This makes for a smooth driving vehicle with no binding of the drivetrain or scrubbing of the tires. There is no hopping or chirping of tires which was common with early automobiles that did not have a differential. BTW, that's why it's called a differential, it allows for different speeds between the two wheels.
The problem with these differentials is that they operate by balancing the torque load on both wheels. That is fine when both wheels have the same traction (and therefore the torque loads have the same resistance at each wheel). But when one wheel has less traction than the other (ie: it's on ice, snow, mud, sand, or even in the air) then very little torque load can be applied to it because there is very little resistance. And because the differential wants to balance the load, BOTH tires end up with very little applied torque. That's why you end up seeing the wheel with the least traction spinning: it's spinning because it requires very little torque. On the other hand, the wheel with the good traction can't even turn because the torque is too low.
Limited slip differentials try to get around this problem by biasing the torque so that it gives a greater percentage of available torque to the non-spinning wheel. In other words, it doesn't balance the torque, it biases it to the wheel with the greater resistance or traction. In many cases, this is all you need (ie: snow covered streets, wet pavement and dirt roads). But when you're on the rocks or you're going uphill on a rutted road, a percentage of a small amount of torque just isn't going to cut it. That's when you need a locker or spool.
A spool is the exact opposite of a differential. It allows absolutely no speed difference between left and right wheels. They are permanently locked together. No matter what the traction conditions, the engine will always drive both wheels. This provides an enormous advantage on difficult terrain. The problem is that it is horrible on the street because there will be driveline stress and increased tire wear whenever you drive around corners. On the dirt, it's not too bad since the wheels can slip but on the street the traction is too good. The tires will chirp and possibly hop. Some people use spools on the street but they're a distinct minority and I'd discourage it.
ARB, OxLocker and some other manufacturers make a combination differential/spool that let's you choose in which mode it should operate. These are often referred to as manual lockers. For the street, you can turn the spool off so it will operate like a regular open differential. Off-road, you can turn the spool on for maximum performance. No downsides except for the price and difficulty of installation.
The locker, it is often confused with a limited slip, is a kind of automatic spool. They are oftened referred to as automatic lockers. Its default state is to lock (hence the name) left and right wheels together like a spool. In this mode it operates just like a spool. But when going around corners, it allows the outside wheel to disengage from the inside wheel and turn faster by allowing it to be driven by the ground (as opposed to being driven by the engine). It accomplishes this by a ratcheting mechanism. Once the vehicle exits the turn and drives in a straight line, both wheels lock together again. It is this locking/unlocking action that is the locker's source of advantage and disadvantage. It's advantage is that it doesn't result in the driveline stress or tire wear common to spools. It's disadvantage is that the point of locking/unlocking results in sudden over- and under-steer which is particularly pronounced on sweeping turns (as opposed to sharp turns). It's enough of an annoyance and disturbance that some people would prefer the more predictable manners of a limited slip or a spool. But there are lots of other fourwheelers who have learned to live with the locker's quirks.
On ice and snow, the spool and locker are probably the worse choices for highway driving because if they spin, both wheels will spin which greatly reduces your ability to maneuver. With a limited slip or open diff, generally only one wheel with spin, allowing the other to help track the vehicle in a straight line. A manual locker would also be a good choice for snow/ice-covered roads because you can choose how it should operate. Having said that, there are many people who drive their automatic locker-equipped vehicles on icy roads on a regular basis. It all depends on your comfort level.
...lars
