Front wheels spinning in 4WD. Normal?

[sevilla]

Thank you very much for the informations. Helpful as usual.

 

[SPYDERLK]

In 2wd your tractor is actually 1wd and the rear wheel with least traction will spin.

In 2wd with the diff lock engaged your tractor is actually 2wd with both rear wheels pulling together.

In 4wd your tractor is actually 2wd and the rear wheel and front wheel with least traction will spin.

In 4wd with diff lock engaged your tractor is actually 3wd with both rear wheels pulling together and the front wheel with least traction will spin.

As GW pointed out, the only exception would be a tractor with a front diff lock mechanism of some sort and it would then have true 4wd. I didn't think any tractors were so equipped, but GW educated me on that a while back!!

Not really. Like you say the wheel with the least traction will spin, however the non spinning wheel is providing about equal thrust as the spinning wheel. Both wheels are driving, but youre only getting 2x the thrust of the one with least traction. Not 1 [or 3] wd.
larry

 

[gwdixon]

Not really. Like you say the wheel with the least traction will spin, however the non spinning wheel is providing about equal thrust as the spinning wheel. Both wheels are driving, but youre only getting 2x the thrust of the one with least traction. Not 1 [or 3] wd.
larry

Whaaat? Then why don't you go anywhere when a wheel is spinning in 2WD? And why do you go somewhere when the diff lock is engaged (or at least two rear wheels spin)?

 

[RickB]

Locking hubs allow the hubs to be disconnected from the axle shafts on an axle assembly. This is done in passenger vehicles to allow more efficient operation in 2wd by reducing parasitic drag from spinning the front portion of the drivetrain.

Manual or automatic locking differentials force both wheels on an axle assembly to turn at the same rate to enhance traction.

Limited slip differentials (positraction, trac-lok, M7040, etc) use friction discs or such in the differential to bias some torque to the wheel that is slipping.

The front LSD is one of the things I envy about the bigger M series Kubota guys.

But many New Holland utility size and larger tractors are available with locking front and rear differentials. THAT'S 4WD.

 

[SPYDERLK]

Whaaat? Then why don't you go anywhere when a wheel is spinning in 2WD? And why do you go somewhere when the diff lock is engaged (or at least two rear wheels spin)?

because twice the thrust of the spinning wheel is not as much as the thrust of the spinning wheel added to what you can get from the wheel with good traction if you force it to turn too using the d/l.
larry

 

[gwdixon]

because twice the thrust of the spinning wheel is not as much as the thrust of the spinning wheel added to what you can get from the wheel with good traction if you force it to turn too using the d/l.
larry

Maybe I just don't understand the physics of it or perhaps the English language. Anybody out there that can explain this phenomenon in intelligible terms?

I get it that all the engine torque is applied to one spinning wheel and using the differential lock divides the torque and applies it to two wheels for the purpose of applying the torque to increased ground contact (the second wheel). As the number of driven wheels increases the torque is not greater but rather divided amongst the driven wheels.

 

[Stradbash]

Perhaps reading this Wikipedia article;

http://tinyurl.com/3xlwum

Will help folks understand what is going on when a wheel slips on your tractor or your "friends" jack one of the driving wheels of your car off the ground while you're getting married...

 

[radioman]

go here - About.com: http://www.howstuffworks.com/four-wheel-drive.htm and click play on the 4 wheel drive demo. I saw this article a few years ago and it really opened my eyes how 4 wheel drive really works and explains why 4 wheel drive really gets stuck unless it has a locking diff.

 

[ovrszd]

I knew my explanation would stir the techno guys!!!

End result, when my vehicle isn't moving and three tires are spinning while one sits and watches, in my Redneck eyes, I am in 3WD. A physics book laying on the seat next to me doesn't change that, only the flip of the locker switch causes forward movement. Call it what you want. I call it 3WD

 

[gwdixon]

go here - About.com: http://www.howstuffworks.com/four-wheel-drive.htm and click play on the 4 wheel drive demo. I saw this article a few years ago and it really opened my eyes how 4 wheel drive really works and explains why 4 wheel drive really gets stuck unless it has a locking diff.

This link above was informative but confirmed what I understand about 4WD. It doesn't clarify the post by Spyderlk.

To ovrszd: In the usual circumstance the second front tire won't spin (or have traction, or have torque applied, or whatever) unless a locking differential in front is part of the system. I agree, most 4WD systems engage three wheels at best. The front tire with the least traction spins. If it happens to grab then the other tire could lose traction and be the one to spin. In a convoluted way, all four tires could at some time or another be driven - thus 4WD.