What do these mean

[Soundguy]

Wasn't even 50' for me.. I use dto own a 4wd tractor.. it started to stick and by going to 4wd I got it another 10'.. almost too far for the tow strap to reach me.

I traded the 4wd after that... I can get stuck in 2wd just as easy..

soundguy

 

[MossRoad]

Alright.. I see you went the back door secret route ....

soundguy

Hahahahahaaaa!!!! Pretty funny stuff here, that's for sure!

His explanation was perfect. The problem is, many folks couldn't grab the concept until it was expanded a bit more. I am one of those folks. This line explains it the best for me...

If the free wheel has no resistance, it therefore is supplying no force, the restricted wheel is applying the same force. NONE.

 

[MossRoad]

Wasn't even 50' for me.. I use dto own a 4wd tractor.. it started to stick and by going to 4wd I got it another 10'.. almost too far for the tow strap to reach me.

I traded the 4wd after that... I can get stuck in 2wd just as easy..

soundguy

4WD works well on wet slippery soil, grassy slopes, leaf covered forest floors, etc... I've been plenty of places in 4 that I could not go into with 2.

 

[Harry c]

Hey Soundguy,
First: You're right, I am a Mechanical Engineer. Second: You're wrong, I have no desire nor reason to try to exhibit my "hat size..." I'm pretty much a down to earth guy.

I was just trying to offer a fairly complete explanation of a commonly misunderstood situation. I really don't know how to describe the process much more simply. If it were really simple it would not be so widely misunderstood. Maybe next time I'll sub the word "push" for the word "force" if that seems to hang someone up.

Sorry if I confused anyone, but I'll bet that almost everyone that has read this thread has a better understanding of the 1wd/ 2wd/3wd/4wd principles!

 

[wolc123]

I have often heard the argument that 4wd will just get you stuck deeper. That is pure nonsence. I struggled for many years with 2wd tractors. My farm is all dark, mucky bottomland soil that takes a long time to dry in the spring. On average, I got 2wd tractors stuck about (3) times a season. There is only so much time in the spring and sometimes I had to take risks to get the crop in. I would always use my second largest 2wd for the risky operations so I could yank it out with the big one when necessary. In the (3) seasons I have had 4wd I have not come close to getting stuck a single time. I have also rarely witnessed any wheelspin despite heavy drawbar loads. Fuel economy is up by nearly 50%, just in the nick of time with the cost of diesel these days. A fwd tractor with r1's has such good traction that I am unable to imagine any situation where a sane, experienced operator could get one stuck. If anyone is aware of such a situation, please tell us about it.

 

[David Cockey]

Soundguy is definately right on this one. Think oif a 2 WD car. How many times have you seen one with one wheel on ice and the other on dry pavement where the one or ice or snow just spins and the car does not move. If there was any torque being applied to the opposite wheel the car would definately move. Limited slip differentials overcome this problem. somewhat

Andy

Small is not zero.

With a standard differential the torque at both wheels is equal. That is inherent in the differential mechanism.

If one wheel is on ice and the other on dry pavement with a standard open differential, the torque to the wheel on dry pavement will be the same as the torque needed to spin the wheel on ice. If the car just sits there then the combined torque of the two wheels isn't enough to overcome the resistance to moving the vehicle.

Ice and snow get really slippery when there is layer of water on top, such as generated by a spinning tire. In technical terms the coefficient of friction can be .001 or lower or around 1% of the traction available on dry pavement. That small amount of force at both the wheel on ice and the wheel on dry pavement frequently isn't enough to move the vehicle.

If the differential is locked in the situation above the wheels have to move at the same speed. In that case (assuming there is much more torque needed to spin the wheel on ice) the torque to the wheel on ice will be limited by the traction available at that wheel. The torque to the wheel on dry pavement will either be the remaining torque available, or if sufficiently large to spin the wheel on drive pavement then it will be the torque needed to spin the wheel.

A limited slip differential acts somewhere between open and locked differentials. If the speed difference between the wheels is small then the torque to either wheel will be about the same. As the speed differnence increases the torque difference across the differential can increase.

Yes, I'm a mechanical engineer who happens to work in the auto industry and has delt with traction issues. I live in Michigan and have had done a lot of traction "testing" recently with snow and ice covered driveways and roads. It's interesting going up or down an 8% grade when the road is covered with glare ice with out chains, even with 4wd and a locking rear differential.

 

[Soundguy]

4WD works well on wet slippery soil, grassy slopes, leaf covered forest floors, etc... I've been plenty of places in 4 that I could not go into with 2.

Lucky for me I'm on pancake flat land with no trees or leaves except inthe margins of the property.. no slopes.. the 2wd makes sense for me... more hp and other things I can use.. vs the 4wd which wasn't much of a premium to me.

soundguy

 

[Soundguy]

It's funny... after 'that' post I was 99.7% sure you were a mech/eng. Most of my buddies are eng's.. some elec.. some mech.. some computer, and a couple of us are civils. I still remember the joke that always went around... civil's build targets.. mech's build the things that shoot the targets. Strangly enough in our small group anyway.. everyone gets along good.. but it's the civil and mech's that always have the most friction..... might be because 'small' for us is probably a 'tenth'.. where small for you guys is probably a thousandth...

seriously though.. good conversation.

soundguy

Hey Soundguy,
First: You're right, I am a Mechanical Engineer. Second: You're wrong, I have no desire nor reason to try to exhibit my "hat size..." I'm pretty much a down to earth guy.
s!