Do any tractors have true 4wd? Seem like they always call the powered front driveline something else. Is that branding or some other reason? Do any have front and read wheels that spin at the same speed or is that all part of the issue?
4wd?
- Thread starter Surgeon
- Start date
- Views: 8609
The big ag tractors have true 4wd while the smaller ones have front wheel assist. On them the front wheels turn slightly faster than the rears when engaged. This is why the manual will say to not drive in 4wd on hard surfaces.
brain55
Veteran Member
Not sure exactly what the question was I think there are a couple in there. Yes, there are true 4wd tractors. You probably won't find it in CUT's, rear diffs will be open carriers w/diff lock and fronts will be open carriers also meaning in limited traction situations you will likely at the most have 3wd. As you get into larger machines you will start to see limited slip diffs in the front, I have even seen mechanical diff locks in the front.
Now as far as wheel speed front and rear with different size tires front and rear there will only be a small window where speeds are matched because of tire wear and varying inflation pressures. The factory tries to match it as close as the can with gear ratios that is why they don't recommend using 4wd on hard surfaces.
Now as far as wheel speed front and rear with different size tires front and rear there will only be a small window where speeds are matched because of tire wear and varying inflation pressures. The factory tries to match it as close as the can with gear ratios that is why they don't recommend using 4wd on hard surfaces.
Opti-Mist
Platinum Member
Generally speaking, the equal sized front and rear wheels would be 4WD while the unequal sized (front being smaller) is Front Wheel Assist. In the latter case the front wheels tend to turn just a bit (5%) faster than the rears by design.
I watched a friend in his Jeep Rubicon lock his diffs and pull out a neighbor's Kubota that I could have never budged with my MFWD tractor despite my tractor weighing more and having chains. He told me that my front end would always spin and break through because I only have 3wd and the front spins faster than the rear. ...so I was thinking about it (it was bugging me) and knew someone here would know the answer.
scrappy isb67
Gold Member
they are ALL MFWD (Mechanical Front Wheel Drive) doesn't matter if it is a 1023e all the way thru the 8r series. and unless the tractor has all 4 tires the same size( a 9r series), there will always be a slight overdrive to the frontend. the major difference is the open diffs on the front of the little ones vs lockers/limited slip diffs in the big ones. even some of the bigger 4wd (equally sized tires) have some gear lead in the frontaxle.
We have two different 4WD tractors- I have a Kubota B7100, and my father has a NH3930. The front tires do not lead, or rotate faster, than the rear tires. If they did, you would get tension even when going in a straight line, and either the front tires would spin, or the rears would drag. Neither does this. I don't know where you get your information that the front tires lead by a percentage, but it is due only to a difference in tire sizes- where there is a discrepency in the ratios, say due to under or overinflated tires. Again, the difference in rotational speed would manifest itself, especially the farther you travel and/or faster you travel. The only way it would be possible is if there is a differential in the transfer transmission, which would absorb the difference. Neither of ours do. Simply, 4WD is a 100% mechanical link up of the rear and front axle. Regardless of the terminology, both of our tractors, and any other 4WD tractor that I have had experience with, was a 100% mechanical link-up 4WD. Backhoes, articulated tractors and wheel loaders, telehandlers, etc. all work in the same way- many of them can't even be disengaged from 4WD.
The tension that is generated by a 4WD tractor is not from a difference in rotational speed between the front and rear, but a difference in the turning arc. Because the front tires turn left and right, they follow a different length arc in a turn than the back tires. A difference in distance travel when the front and rear tires are turning will cause a mechanical bind, because they are 100% mechanically linked.
And, a 4WD tractor is exactly that-4WD. There are differentials in the front and rear, for a good reason. These differentials allow traction to be lost on the tire with the least traction, because of the differential action. If the two tires have the same amount of traction, both will spin. The same for the front. So, on a vehicle, whether tractor, or atv, or truck, or whatever, if it is 4WD with no locking differentials, all 4 tires will direct power to the ground unless there is unequal traction. Then, you have a 2 or 3WD vehicle. The only way to overcome that, as mentioned with the Rubicon Jeep, is to have differentials that lock. Most 4WD tractors have a locking rear, but not a front. If they were both locked permanently, it would be a nightmare to drive. I would imagine that manufacturers haven't addressed and started offering locking front differentials on tractors is the lack of need- most of the time, traditional 4WD is more than enough. It keeps costs down, and simplifies things. I understand that some large tractors have the option, but I'm not familiar with it on smaller tractors. I haven't found it to be necessary on either of your tractors. Traditional 4WD with a locking rear has been more than enough. We aren't rock crawling with them- 3 and 4WD has done the job well.
The tension that is generated by a 4WD tractor is not from a difference in rotational speed between the front and rear, but a difference in the turning arc. Because the front tires turn left and right, they follow a different length arc in a turn than the back tires. A difference in distance travel when the front and rear tires are turning will cause a mechanical bind, because they are 100% mechanically linked.
And, a 4WD tractor is exactly that-4WD. There are differentials in the front and rear, for a good reason. These differentials allow traction to be lost on the tire with the least traction, because of the differential action. If the two tires have the same amount of traction, both will spin. The same for the front. So, on a vehicle, whether tractor, or atv, or truck, or whatever, if it is 4WD with no locking differentials, all 4 tires will direct power to the ground unless there is unequal traction. Then, you have a 2 or 3WD vehicle. The only way to overcome that, as mentioned with the Rubicon Jeep, is to have differentials that lock. Most 4WD tractors have a locking rear, but not a front. If they were both locked permanently, it would be a nightmare to drive. I would imagine that manufacturers haven't addressed and started offering locking front differentials on tractors is the lack of need- most of the time, traditional 4WD is more than enough. It keeps costs down, and simplifies things. I understand that some large tractors have the option, but I'm not familiar with it on smaller tractors. I haven't found it to be necessary on either of your tractors. Traditional 4WD with a locking rear has been more than enough. We aren't rock crawling with them- 3 and 4WD has done the job well.
brain55
Veteran Member
Thanks Hodge, you said more eloquently what I wanted to say.
Buckgnarly
Platinum Member
The 4:1 low ranger transfer case did not hurt in this case....I have a Rubicon, and when both axles are locked and in low, that thing can PULL like no other!
LD1
Epic Contributor
Some mis-information in this thread I'll try to clear up :mur:
First, On tractors that have smaller front tires (that I am aware of), there is INDEED a lead percentage built into the system. And YES that makes the front tires slip a little. Just the way it is. I dont know where you are getting YOUR info from, but that is the way it is and is common knowledge amung 4wd tractor owners.
Second thing, it dont matter WHAT you call it, cause there is nothing set in stone. So MFWD, 4wd, AWD, front-wheed assist, etc are ALL used interchangebly.
Third, if you have one of the above mentioned 4wd, mfwd, etc. Tractors, and it has open differentials in front and rear, it is STILL 4WD. NOT 2WD or 3WD. That is incorrect termonology. IT is 4wd because ALL 4 wheels are STILL trying to drive the tractor. Sure, there is a time where a wheel or two may just sit and spin, BUT it is STILL trying to DRIVE the tractor. In an open differential, ALL wheels are attempting to move the vehichle with the EXACT same torque. IE: open diff means EQUAL TORQUE and UNEQUAL SPEED. But STILL, you have ALL 4 wheels trying to drive the machine with the EXACT SAME amount of force.
First, On tractors that have smaller front tires (that I am aware of), there is INDEED a lead percentage built into the system. And YES that makes the front tires slip a little. Just the way it is. I dont know where you are getting YOUR info from, but that is the way it is and is common knowledge amung 4wd tractor owners.
Second thing, it dont matter WHAT you call it, cause there is nothing set in stone. So MFWD, 4wd, AWD, front-wheed assist, etc are ALL used interchangebly.
Third, if you have one of the above mentioned 4wd, mfwd, etc. Tractors, and it has open differentials in front and rear, it is STILL 4WD. NOT 2WD or 3WD. That is incorrect termonology. IT is 4wd because ALL 4 wheels are STILL trying to drive the tractor. Sure, there is a time where a wheel or two may just sit and spin, BUT it is STILL trying to DRIVE the tractor. In an open differential, ALL wheels are attempting to move the vehichle with the EXACT same torque. IE: open diff means EQUAL TORQUE and UNEQUAL SPEED. But STILL, you have ALL 4 wheels trying to drive the machine with the EXACT SAME amount of force.
