1st Time in 4 Wheel Drive (Snow Baby!)
12-27-2004, 09:52 PM
#31
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fredbert....
Hah!!! I got you repeating what I said to the tee! Here's what you said...
"If you stop one wheel, the other will go twice as fast. v8440's "free-wheeling" test is entirely consistent with this. The small torque he resisted to keep one wheel from rotating came from friction in the rotating gears and bearings on the other side of the axle."
And here is what I said....
"One tire is on ice and the other tire is on dry pavement. With the vehicle stationary and power applied the tire on the ice will spin and the tire on the pavement will remain at rest. The only torque that is being applied to the ground by the tire at rest is the amount of torque that it is required to rotate the spider gears inside their carrier. And this torque is very minimal after the differential has reached a steady state operation. This is why a person is able to hold a vehicles tire stationary while the other tire spins (don't try this with limited slip!)."
You know we are getting somewhere in this spirited discussion when we start saying the same stuff and still think we have different viewpoints! I fully agree that a diff transfers torque. Sometimes the right wheel may have 60% of the torque and the left 40%. Sometimes it is 50/50. And yes folks....sometimes it is 99.5%/0.5%. This situation, in the "real tires spining on the ice world", torque is transferred 100% to the wheel that slips. Theoretical and common sense always have to work together.
Ya know fredbert.... you may not be the only mechanical engineer that hangs out here.
By the way 2wd Diesel Duallys are very cool!!!! But I gotta go through mud at the farm pulling trailers with tractors on them. So I gotta have that 4 wheel drive!
Hah!!! I got you repeating what I said to the tee! Here's what you said...
"If you stop one wheel, the other will go twice as fast. v8440's "free-wheeling" test is entirely consistent with this. The small torque he resisted to keep one wheel from rotating came from friction in the rotating gears and bearings on the other side of the axle."
And here is what I said....
"One tire is on ice and the other tire is on dry pavement. With the vehicle stationary and power applied the tire on the ice will spin and the tire on the pavement will remain at rest. The only torque that is being applied to the ground by the tire at rest is the amount of torque that it is required to rotate the spider gears inside their carrier. And this torque is very minimal after the differential has reached a steady state operation. This is why a person is able to hold a vehicles tire stationary while the other tire spins (don't try this with limited slip!)."
You know we are getting somewhere in this spirited discussion when we start saying the same stuff and still think we have different viewpoints! I fully agree that a diff transfers torque. Sometimes the right wheel may have 60% of the torque and the left 40%. Sometimes it is 50/50. And yes folks....sometimes it is 99.5%/0.5%. This situation, in the "real tires spining on the ice world", torque is transferred 100% to the wheel that slips. Theoretical and common sense always have to work together.
Ya know fredbert.... you may not be the only mechanical engineer that hangs out here.
By the way 2wd Diesel Duallys are very cool!!!! But I gotta go through mud at the farm pulling trailers with tractors on them. So I gotta have that 4 wheel drive!
12-27-2004, 09:55 PM
#32
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Originally posted by t-7 firefighter
Wow!
you guys are hurtin my head.
Wow!
you guys are hurtin my head.
Sorry for the headache. We are just having a little technical discussion amoung friends! We will all see eye to eye eventually!
Thanks for posting the pics of your topper. That truck is very impressive!
12-27-2004, 10:11 PM
#33
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Originally posted by PapaPerk
Britt...
Sorry for the headache. We are just having a little technical discussion amoung friends! We will all see eye to eye eventually!
Thanks for posting the pics of your topper. That truck is very impressive!
Britt...
Sorry for the headache. We are just having a little technical discussion amoung friends! We will all see eye to eye eventually!
Thanks for posting the pics of your topper. That truck is very impressive!
no problem... took an asprin and i'm better now.
hope the pictures helped you some. i have been really happy with mine.
thank you for the compliment.
britt
12-27-2004, 11:30 PM
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Good discussion the real world is wear it all counts. I've seen sometimes when a truck with an open differential would go where a "possy" won't with both tires spinning there is nothing to keep the vehicle strait. You can end up sideways in a hurry! I use 4wd almost everyday and even with open differentials would not be with out it!!!!!!!!
the real world is wear it all counts. I've seen sometimes when a truck with an open differential would go where a "possy" won't with both tires spinning there is nothing to keep the vehicle strait. You can end up sideways in a hurry! I use 4wd almost everyday and even with open differentials would not be with out it!!!!!!!!
12-28-2004, 02:32 AM
#35
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Papa Perk,
Your examples of a spinning tire on ice do not make sense. Faster spinning does not mean more torque transmitted to the ground and it does not mean the spinning tire is transmitting all or the majority of the torque to the ground. The stopped wheel does not somehow trigger all the torque through the spider gears. It's time to do a little more research if you want to understand the system. Speed and torque are two different things.
It's a very simple design principal of the open differential to equally distribute torque too both wheels. Don't take my word for it (I know you won't), but do your own research beyond just justifying a common myth. That's how "engineers" solve problems. Follow the facts and do the research. If all we did was come up with formulas to satisfy first impressions we'd never get anywhere.
Wetspirit
Your examples of a spinning tire on ice do not make sense. Faster spinning does not mean more torque transmitted to the ground and it does not mean the spinning tire is transmitting all or the majority of the torque to the ground. The stopped wheel does not somehow trigger all the torque through the spider gears. It's time to do a little more research if you want to understand the system. Speed and torque are two different things.
It's a very simple design principal of the open differential to equally distribute torque too both wheels. Don't take my word for it (I know you won't), but do your own research beyond just justifying a common myth. That's how "engineers" solve problems. Follow the facts and do the research. If all we did was come up with formulas to satisfy first impressions we'd never get anywhere.
Wetspirit
12-28-2004, 11:25 AM
#36
From what I've been able to figure out:
1. A limited slip works well on mixed traction surfaces as it will transfer a portion of available torque to the wheel that appears to be slipping. A limitation of the general design is that it can only transfer a percentage of torque, so if you're on a uniformly slick surface or especially an uneven surface with a wheel off of the ground, it will transfer a percentage of zero, which is still zero. Some hard core off roaders test traction on a ramp which represents an uneven surface, and vehicles with limited slip axles just stop. Specific designs seem to vary the amount of torque transferred, 'bias' I think it's called, and an agrressive 'high bias' limited slip can create problems on uniformly slick surfaces as it will transfer a lot of torque to a wheel with marginal traction, possibly breaking the rear end loose. Lower bias designs act more and more like an open diff on uniformly slick sufraces, with a tradeoff of less traction on some surfaces.
2. An unselectable locker will provide traction on the ramp described above as once engaged torque is evenly transferred to both wheels, with no differential action. Tires chirping on corners or a bit of hop with high traction tires are symptoms, as well as the rear end breaking loose on uniformly slick surfaces.
3. An open diff will get you stuck if a front and rear wheel start spinning, but from what I understand it's the safer option on uniformly slick surfaces, as instead of breaking loose you just get stuck. You need to pay more attention to tire choice and possibly need to carry chains.
I would prefer having a selectable locker with an open diff, and use it when needed just like I use 4wd.
1. A limited slip works well on mixed traction surfaces as it will transfer a portion of available torque to the wheel that appears to be slipping. A limitation of the general design is that it can only transfer a percentage of torque, so if you're on a uniformly slick surface or especially an uneven surface with a wheel off of the ground, it will transfer a percentage of zero, which is still zero. Some hard core off roaders test traction on a ramp which represents an uneven surface, and vehicles with limited slip axles just stop. Specific designs seem to vary the amount of torque transferred, 'bias' I think it's called, and an agrressive 'high bias' limited slip can create problems on uniformly slick surfaces as it will transfer a lot of torque to a wheel with marginal traction, possibly breaking the rear end loose. Lower bias designs act more and more like an open diff on uniformly slick sufraces, with a tradeoff of less traction on some surfaces.
2. An unselectable locker will provide traction on the ramp described above as once engaged torque is evenly transferred to both wheels, with no differential action. Tires chirping on corners or a bit of hop with high traction tires are symptoms, as well as the rear end breaking loose on uniformly slick surfaces.
3. An open diff will get you stuck if a front and rear wheel start spinning, but from what I understand it's the safer option on uniformly slick surfaces, as instead of breaking loose you just get stuck. You need to pay more attention to tire choice and possibly need to carry chains.
I would prefer having a selectable locker with an open diff, and use it when needed just like I use 4wd.
12-28-2004, 11:36 AM
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Wetspirit...
My examples of the tires on ice makes perfect sense. It is the same thing as puting the vehicle on a jack stand and holding one tire while the other turns freely. Virtually all torque is transfered to the wheel that is spinning. The only force required to hold the tire stationary with your hands is the firction force required to rotate the spider gears. This force is almost zero after the diff. has reached a steady state of operation. So real world torque transfered (yes...by the spider gears) is 100%. Fredbert and I both agree on this. At least I think he does because that is what he said in his last post.
I am not even responding to the "that's how "engineers" solve problems" comments. Give me a break.
Since you are big on facts..where are yours?
All of my comments are in fun by the way. 
My examples of the tires on ice makes perfect sense. It is the same thing as puting the vehicle on a jack stand and holding one tire while the other turns freely. Virtually all torque is transfered to the wheel that is spinning. The only force required to hold the tire stationary with your hands is the firction force required to rotate the spider gears. This force is almost zero after the diff. has reached a steady state of operation. So real world torque transfered (yes...by the spider gears) is 100%. Fredbert and I both agree on this. At least I think he does because that is what he said in his last post.
I am not even responding to the "that's how "engineers" solve problems" comments. Give me a break.
Since you are big on facts..where are yours?
All of my comments are in fun by the way.
12-28-2004, 12:48 PM
#38
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Papa Perk,
Using your example of a vehicle on a jack and both wheels off the ground with an open diff. Of course you can hold one wheel with your hands while the other spins. An insignificant amount of torque is being transmitted through the system. Gear loss, seal and bearing friction. No big deal. It's easy to hold one wheel, we agree on that. Now begin to add resistance to the spinning wheel. Have a friend use a 2X4 and pry gently against the spinning wheel as you hold the other one by hand. As friction is added to the spinning wheel it becomes progressively harder and harder to hold the stationary wheel by hand. Why? Because of the equal torque delivery of a differential. Now you are simulating one wheel on ice and the other on pavement. The wheel on ice spins with some resistance against the ice and the other is held statioary on dry pavement. The forward driving force is dependent on how much friction the wheel with the least traction has. Again, this is basic differential theory, torque equal at varying speeds. Torque is always equal regardless of speed. Both wheels on dry pavement, vehicle going straight. Torque equal. One wheel on ice, the other on pavement. Torque equal. The reason we get stuck in that situation is because the wheel with the least traction limits the overall torque delivery. But they are both putting down the same driving force.
Again, I ecourage you to do a little more research with a source you think is credible. I think the differential is one of the most creative inventions there is! It's so useful, there are so many of them, we all use them, it's simple, and it is still so misunderstood. How cool is that!
Wetspirit
Using your example of a vehicle on a jack and both wheels off the ground with an open diff. Of course you can hold one wheel with your hands while the other spins. An insignificant amount of torque is being transmitted through the system. Gear loss, seal and bearing friction. No big deal. It's easy to hold one wheel, we agree on that. Now begin to add resistance to the spinning wheel. Have a friend use a 2X4 and pry gently against the spinning wheel as you hold the other one by hand. As friction is added to the spinning wheel it becomes progressively harder and harder to hold the stationary wheel by hand. Why? Because of the equal torque delivery of a differential. Now you are simulating one wheel on ice and the other on pavement. The wheel on ice spins with some resistance against the ice and the other is held statioary on dry pavement. The forward driving force is dependent on how much friction the wheel with the least traction has. Again, this is basic differential theory, torque equal at varying speeds. Torque is always equal regardless of speed. Both wheels on dry pavement, vehicle going straight. Torque equal. One wheel on ice, the other on pavement. Torque equal. The reason we get stuck in that situation is because the wheel with the least traction limits the overall torque delivery. But they are both putting down the same driving force.
Again, I ecourage you to do a little more research with a source you think is credible. I think the differential is one of the most creative inventions there is! It's so useful, there are so many of them, we all use them, it's simple, and it is still so misunderstood. How cool is that!
Wetspirit
12-28-2004, 12:54 PM
#39
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[QUOTE]Originally posted by PapaPerk
[B]fredbert....
And here is what I said....
Ya know fredbert.... you may not be the only mechanical engineer that hangs out here.
[B]fredbert....
And here is what I said....
Ya know fredbert.... you may not be the only mechanical engineer that hangs out here.
12-28-2004, 06:27 PM
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Here is a good read on the open differential and how the Torsen works. (what you have if you have anti-spin)
http://www.sonic.net/garyg/zonc/Tech...ferential.html
http://www.sonic.net/garyg/zonc/Tech...ferential.html
12-28-2004, 09:40 PM
#42
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Wetspirit...
I said it once and I will say it again....
"I fully agree that a diff transfers torque. Sometimes the right wheel may have 60% of the torque and the left 40%. Sometimes it is 50/50. And yes folks....sometimes it is 99.5%/0.5%. This situation, in the "real tires spining on the ice world", torque is transferred 100% to the wheel that slips. Theoretical and common sense always have to work together"
Now aren't we really saying the same thing? Huh....???
Sticking a 2 x 4 on the tire that is spinning changes our situation. The discussion pertained to a tire on ice (low friction) and a tire on pavement (high friction). If we start adding load to the tire that is spinning. The tire is less likely to spin. After all that is how the limited slips work in the first place!!! But they use clutches, ratchets, or helical gearing....not 2 x 4's.
The vehicle's torque transferred to the ground is limited by the traction of the tires to the ground. That is where the torque = force x distance formula comes in. And force at the tire = (friction coeffiecent of rubber on ice) x normal force. Of course as you said before I am probably making up some B.S. (in engineering) equations to support my "opinion".
I said it once and I will say it again....
"I fully agree that a diff transfers torque. Sometimes the right wheel may have 60% of the torque and the left 40%. Sometimes it is 50/50. And yes folks....sometimes it is 99.5%/0.5%. This situation, in the "real tires spining on the ice world", torque is transferred 100% to the wheel that slips. Theoretical and common sense always have to work together"
Now aren't we really saying the same thing? Huh....???
Sticking a 2 x 4 on the tire that is spinning changes our situation. The discussion pertained to a tire on ice (low friction) and a tire on pavement (high friction). If we start adding load to the tire that is spinning. The tire is less likely to spin. After all that is how the limited slips work in the first place!!! But they use clutches, ratchets, or helical gearing....not 2 x 4's.
The vehicle's torque transferred to the ground is limited by the traction of the tires to the ground. That is where the torque = force x distance formula comes in. And force at the tire = (friction coeffiecent of rubber on ice) x normal force. Of course as you said before I am probably making up some B.S. (in engineering) equations to support my "opinion".
12-29-2004, 09:26 AM
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Originally posted by BIGBADBOB
Just ordered new decals for my Dodge 3X4 Sorry just slipped out Yup its 4X4 till ya get stuck
Just ordered new decals for my Dodge 3X4
Sorry just slipped out Yup its 4X4 till ya get stuck
could you order me a set while your at it?
just kidding guys.
britt
12-29-2004, 12:47 PM
#45
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I see what wetspirit is saying. I think he may be right. I didn't realize before that in my example of a car on jackstands, the spinning wheel does not necessarily account for any large amount of torque. I was automatically interpreting the high speed of the wheel I was not holding to mean that lots of torque was being applied to that side. That is not necessarily true, since there's almost no resistance to that wheel turning. There does not have to be much torque at all present if one of the wheels is free to spin. That being the case, you can hold one of the wheels still easily. What a limited slip does is attempt to hold wheel SPEED equal, even if that means applying different amounts of torque to achieve this. Makes sense to me now, and fits all the examples we've given in this thread.