Terminology

[gribly]

1/2 the traction of both tires? That would be the full traction of one tire. If you would read and comprehend my post, and maybe look up static and kinetic friction if you're a little rusty on terminology, you would realise that I have nothing more to say. I don't know how else to explain it to you. And when one wheel is spinning, that does not mean that the other tire is not being driven, since both are still receiving the exact same amount of torque.

 

[gribly]

Oh, and if you jack a car in the air that has an open diff, and grab one tire while a friend hits the gas, you are going to lose an arm.

 

[--weezl--]

nope you're wrong, if that were the case we wouldn't need lockers and limited slip diffs... the purpose of a conventional limited slip is to increase the tolerance... if the traction is 50/50 wheel to wheel, they will both spin, but if it's say 60/40 (not taking resistance of the diff into account) then only one will spin, if enough torque is applied to spin it... a limited slip is to add a larger mid area (the resistance of the diff would probably work out to 60/40) but adding clutches will bring it down to 70/30 but even with a clutch l/s if you jack one wheel up, put it on a jack stand and spin the wheels, you are going to have one wheel spinning and one not... because one wheel being in the air does not fall into the 30/70 ratio or 20/80, or what ever it ends up being... you're 1/2 the traction of the other tire scenario is when you have a torque bias differential, or a torque sensing differential, like a torsen diff (like what's on my truck) in which case mine i think is 25/75 (1/4 traction on one vs the other) you're 1/2 traction scenario works out to 33/66 torque to keep it from spinning

and i am very sure a company (JTEKT Torsen North America, Inc. aka Zexel Torsen, Inc) did not invent a new style of differential, patent it, and market it to the big companies to add an additional 8% to the current diffs they have... audi uses torsens, the h1 uses a torsen diff, the ranger fx4 level II uses the torsen diff, some gm's use them... they also have a high bias diff, but i don't think anyone puts that in a vehicle stock...

 

[LearjetMinako]

What about the 4x4 SUV and crossovers that are FWD, then the rear differential is engaged to make it a 4wd?


.

Opps, I forgot about those.

 

[gribly]

nope you're wrong, if that were the case we wouldn't need lockers and limited slip diffs... the purpose of a conventional limited slip is to increase the tolerance... if the traction is 50/50 wheel to wheel, they will both spin, but if it's say 60/40 (not taking resistance of the diff into account) then only one will spin, if enough torque is applied to spin it... a limited slip is to add a larger mid area (the resistance of the diff would probably work out to 60/40) but adding clutches will bring it down to 70/30 but even with a clutch l/s if you jack one wheel up, put it on a jack stand and spin the wheels, you are going to have one wheel spinning and one not... because one wheel being in the air does not fall into the 30/70 ratio or 20/80, or what ever it ends up being... you're 1/2 the traction of the other tire scenario is when you have a torque bias differential, or a torque sensing differential, like a torsen diff (like what's on my truck) in which case mine i think is 25/75 (1/4 traction on one vs the other) you're 1/2 traction scenario works out to 33/66 torque to keep it from spinning

and i am very sure a company (JTEKT Torsen North America, Inc. aka Zexel Torsen, Inc) did not invent a new style of differential, patent it, and market it to the big companies to add an additional 8% to the current diffs they have... audi uses torsens, the h1 uses a torsen diff, the ranger fx4 level II uses the torsen diff, some gm's use them... they also have a high bias diff, but i don't think anyone puts that in a vehicle stock...

Open differentials always give equal torque to both tires. This is why when one of them loses traction, that tire is going to spin like crazy. Look at it this way - your truck is on a hill and one tire is on dirt and one is on ice. You go to hit the throttle and take off, but it spins one tire and slowly creeps forward - the amount of friction between the tire and the ice is going to cause only a small resistance, and the amount of torque that can be applied is very small. That amount of torque is exactly how much the tire on the dirt gets, which is why it does not spin, since there is not much torque going to it. Any extra throttle is going to go towards wheelspin since the coefficient of kinetic friction for that tire on ice is going to be MUCH less than the coefficient of static friction for the tire on dirt. That is why you have the torsen in your truck, it takes that amount of resistance from the tire that is on ice and spinning and multiplies it by whatever the coefficient is for that specific torsen unit, and that is how much torque the tire that has good traction gets, and the truck moves forward. In this instance, there is NOT an equal amount of torque going to both tires, it will be heavily biased towards the tire with traction. Take a torsen equipped truck and get one tire hanging in the air, and it will act almost like an open diff, since there is no resistance to multiply by the coefficient. It will rock a little more than if the diff was open since the weight of the tire will cause a momentary torque on the axle as it spins up, and the diff can multiply that and send it to the other tire, but it is only for a second as the tire spins up. This is why torsens suck for rock crawling and heavy off-roading but are excellent for a daily driver that will usually have all four tires on the ground.

Now, on the other hand, a locker will send up to 100% of available torque to one tire since both tires have to spin together. Make sense yet?

EDIT - Here is a neat trick you can do with a torsen due to the action I described earlier - when you get stuck, if only one back tire is spinning, you can apply light pressure to the brake and the tire that is not spinning will in turn receive more torque than it was before, even with the added resistance of the brake, and the resistance of the brakes on the side that is spinning will be multiplied through the torsen. It is just enough in some situations to get you out. This also can work with open and limited slips, but you have to get the tire spinning very quickly, and "pulse" the brake. It will jerk the tire that is not spinning just a little bit each time you pump the brake, and you can get moving again this way. Hard on equipment driving like that, though.

 

[gribly]

Here, read this thread, maybe it will help you learn a little more about differentials. Like it was said in there, the differential is an extremely misunderstood piece of equipment, so don't be embarassed for not knowing how they work.

http://therangerstation.com/forums/showthread.php?t=93157&highlight=differential

 

[88_Eddie]

if i'm reading this correctly, your mom is a woman. therefore, i think you could say 'gas cap' and there'd be a pretty good chance she also would not know what you were talking about

 

['99 EB Explorer]

When you really get down to it, 2WD is usually a lie. Most front or rear wheel drive vehicles are what I like to call "one wheeler peelers" anyway, unless locked in one way or another.

 

[--weezl--]

Open differentials always give equal torque to both tires. This is why when one of them loses traction, that tire is going to spin like crazy. Look at it this way - your truck is on a hill and one tire is on dirt and one is on ice. You go to hit the throttle and take off, but it spins one tire and slowly creeps forward - the amount of friction between the tire and the ice is going to cause only a small resistance, and the amount of torque that can be applied is very small. That amount of torque is exactly how much the tire on the dirt gets, which is why it does not spin, since there is not much torque going to it. Any extra throttle is going to go towards wheelspin since the coefficient of kinetic friction for that tire on ice is going to be MUCH less than the coefficient of static friction for the tire on dirt. That is why you have the torsen in your truck, it takes that amount of resistance from the tire that is on ice and spinning and multiplies it by whatever the coefficient is for that specific torsen unit, and that is how much torque the tire that has good traction gets, and the truck moves forward. In this instance, there is NOT an equal amount of torque going to both tires, it will be heavily biased towards the tire with traction. Take a torsen equipped truck and get one tire hanging in the air, and it will act almost like an open diff, since there is no resistance to multiply by the coefficient. It will rock a little more than if the diff was open since the weight of the tire will cause a momentary torque on the axle as it spins up, and the diff can multiply that and send it to the other tire, but it is only for a second as the tire spins up. This is why torsens suck for rock crawling and heavy off-roading but are excellent for a daily driver that will usually have all four tires on the ground.

Now, on the other hand, a locker will send up to 100% of available torque to one tire since both tires have to spin together. Make sense yet?

EDIT - Here is a neat trick you can do with a torsen due to the action I described earlier - when you get stuck, if only one back tire is spinning, you can apply light pressure to the brake and the tire that is not spinning will in turn receive more torque than it was before, even with the added resistance of the brake, and the resistance of the brakes on the side that is spinning will be multiplied through the torsen. It is just enough in some situations to get you out. This also can work with open and limited slips, but you have to get the tire spinning very quickly, and "pulse" the brake. It will jerk the tire that is not spinning just a little bit each time you pump the brake, and you can get moving again this way. Hard on equipment driving like that, though.

depends on how you look at torque, if you are spinning one tire, with an open differential, and your motor puts out 200ft/lbs, you are still potentially applying the full 200 ft/lbs (most likely not, but you can) however you aren't effectively transfering the full 200 ft/lbs (for arguments sake, that's what your motor puts out regardless of throttle position and RPM, if it's spinning the tires that's what's coming off the flywheel) isn't transfering the 200 ft/lbs to the ground, the wheel still has 200 ftlbs at it, but the ground is only receiving maybe 5... same with the other wheel... this is why if you are going up a hill, and one tire loses traction, you can actually slip back down the hill, even if it's not a steep incline, by your logic, the tire that's spinning forwards would be applying -5ftlbs of torque because it's going backwards... so yes, you are right in certain aspects, but the torque coming through the driveshaft is not being applied to the ground, which i think is where our disagreement is coming from... you can only really power one wheel, and that's the wheel with the least resistance, as we know, the laws of physics stipulates that all things, energy included will always take the path of least resistance, yes there will be some going to the slower wheel, but the amount is neglagable compared to the amount that is going to the other... if they are closer in resistance, you will see both spinning, but 9/10 times it won't be close enough, in a threshold situation...

as for the torsen and brakes, yes i have heard that, but only recently, and haven't had a chance to try that off road, i've also been told the best way to do it is to set the parking brake... something i wish that ford had done is either a) put traction control (usually individual corner braking to transfer torque) on the earlier years, or b) kept the level II with the torsen till traction control was on them... the torsen diff would work 10x better with tcs...

 

[gribly]

Err, if you're spinning your tires you are not putting the power to the ground, and you do not have your 200 ft lbs at the wheel. Same idea as taking a wrench and waving it around in the air, you are not doing anything. Plus, I have no idea how you think that sliding backwards while trying to spin the tires forwards creates any sort of negative torque, your driveshaft is still spinning in the same direction and the motor is still putting a torque on it to spin that direction.

What I think you are not understanding is that when the tire slips, only so much torque can be applied at it. Say that tire breaks static friction at 10ft lbs and can stay spinning with 6 ft lbs due to the lower kinetic friction. There is 6 ft lbs going through the axle shaft to that wheel. That same amount of torque is going to be transferred out the other side of the differential, so the tire with traction is only going to see 6 ft. lbs, and the driveshaft from the transfer case to the axle is only seeing a total of 12 ft lbs. This means that the tire with traction isn't really going to do much pushing forward, and you're going nowhere fast. Now say you apply more throttle to spin the tire faster - your kinetic friction is not going to change aside from the fact that you are heating up the tire and making it softer, giving a little bit more, and all that energy is going to go into increasing how fast that one tire without traction is going to spin. If you're sitting there bouncing off your rev limiter, and not moving due to no traction, you are NOT putting must torque at all through even the transmission.

And don't get me started on traction control and off-roading. Lockers man, lockers.

 

[--weezl--]

ok, take an electic motor, gear it properly so that it will spin at 50rpm with 100 ft/bs of torque, and not lose any speed when you put a load on it (with the motor running full out in both loaded and unloaded) the motor is supplying the full 100 ft/lbs when it's free wheeling, it's just not being utilized... you don't increase the amount of torque the motor has, just because you add resistance... that same torque is STILL at the wheel, it just doesn't get used...

 

[RatDog8o8]

.......I'm having severe physics class flashbacks........

 

['99 EB Explorer]

^+1 lol. It's making my head hurt!

 

[gribly]

ok, take an electic motor, gear it properly so that it will spin at 50rpm with 100 ft/bs of torque, and not lose any speed when you put a load on it (with the motor running full out in both loaded and unloaded) the motor is supplying the full 100 ft/lbs when it's free wheeling, it's just not being utilized... you don't increase the amount of torque the motor has, just because you add resistance... that same torque is STILL at the wheel, it just doesn't get used...

Take your same motor, just the way you described, and hook an ammeter up to it. It's not doing anything until you hook the load up to it. If there is no force there is no torque. How is that so hard to understand? Like I said before, it's like flailing a wrench around in the air in frustration, you are not doing anything. You're starting to enter into an area that my degree covers, FYI. The motor is capable of that torque, yes, but there is nothing to apply the torque onto, so it is just going to merrily spin there doing nothing and drawing very little current. As you add a load onto the motor, it will start to draw more current up to the motors limitations. As you get to the peak load the motor is capable of, it will start to slow a little, and as you add more load, it is going to slow down. As the motor slows down under overload, it is going to start putting out more torque up until the point you have added so much load that it trips the thermal overload and shuts off completely.

Refrigeration compressors, which are generally powered by electric motors are a great example of this. Take a fancier one from say, a rooftop unit, and some of those actually use solenoids to bypass cylinders and then drop out that cylinder when it's not required to save on electricity, since the amperage draw will drop. They do this instead of just running the whole compressor for a shorter period of time as it is much more efficient. This all happens with the same motor running at the same rpm.

 

[CHKNFKR]

Gribly's got you hands down weezl.