Four wheel drive question

[Paul Hearsey]

My neighbour has a new 94hp John Deere and the other day, when I mentioned I was shopping for tire chains for my 1986 30hp Kubota, he advised me to put chains only on the front, because they turn faster than the rear tires and will pull me out of trouble. I had never heard or thought of this, although I know my Ford Ranger pickup is set up like this. The truck manual warns of serious tire wear and possible drive train damage if I leave it in 4WD on dry pavement.

Is it true that all 4WD farm tractors are set up so that the front wheels turn slightly faster than the rear? When I questioned my neighbour, he said "Well, someone told me that a long time ago and I've always assumed it was true." What do you guys think of this. And if it IS true, how much faster is the front turning? Are we straining our tractors' drive trains by leaving it in 4WD year-round? And are chains best installed on the front only? (I don't think so because most of the weight is on the rear) I'm thinking about putting chains on all four wheels. Unless I shouldn't. My neighbour is about to drop some serious money on chains for his Deere and is as curious as me about this question. Any thoughts out there? Paul

 

[Jake Winn]

It is true with John Deere and Kubota tractors for sure, and Im sure that others are the same. While they are designed that way for a reason to help when pulling, if you are running in conditions that dont require the use of it, its advised to disengage it. This will help you turn shorter and cause less wear on the tires and drivetrain.

One thing to be aware of is when replacing tires, you have to keep the same ratio of tire size, otherwise something could get damaged. If you go to a larger tire in front for more floatation , it may be a larger diameter, causing the front to pull more. And the same if you went to a different rear tire. A good tire store should know these things.

 

[JDemaris]

Yes, it it supposed to be true - from the engineer's desk. I'm not how often it actually appears in reality. Not just with farm tractors but cars and trucks also. When Deere came out with it's 50 series 4WD tractors, they were all rated with a slighty faster front drive.

The front is always supposed to be pulling slightly, and never be pushed -for handling reasons. Thus the reason for the desired front drive to be .5% to 1% more aggressive then the rear drive. That is very hard to control since all it takes is a minor variation in tire-sizes to mess it up.

If you ever drove a 4WD car or truck with front wheels worn or too small in front that WERE being pushed by faster back tires - you'd notice real fast on ice, snow or mud. With slighty bigger fronts, it keeps pulling the vehicle whatever way the front wheels are pointing. Smaller in front 4WD ruins handling. If you've got used tires, always put the bigger-most unworn ones on the front - IF you ever do high speed driving in 4WD.

I don't know if that rule holds true anymore with computer-controlled AWD systems in cars. It was more of an issue with mechanical 4WD systems.

By the way, when John Deere came out with it's new 55 series of MFD tractors - what a mess. Somebody over in Germany over-did things a bit. Every new tractor we got in, for almost a year, had a 20% faster front then back. Tore up fields something awful. We had split every one and change gears under warranty.

As to tractors and wear? Seems a minor issue. Making many turns in 4WD on hard ground or pavement is more of a wear issue.

 

[Bob Bancroft]

Disclaimer: I don't have facts on this issue, just opinions!
I believe that most if not all Front Wheel Assist tractors have the front running just slightly faster than the rear. I see many where the fronts are weighted heavily, the rears are not, and they grind front tires off rapidly.
On my first FWA tractor purchase I weighed, read the book, calculated, and took 1000# off the front, and added 4000# to the rear. (200 HP tractor) I do only drawbar work with it- no mounted equip. I hear evidence that guys want to see the tractor jump when they punch that button. I don't. I want a little assist. I say if you want the front to pull so much- get an articulated tractor. I believe the axle ratios in my old Steiger were the same.

 

[buickanddeere]

Very true. I didn't get all four tires summer changed on the truck to winters.
Drove for a day with the new front pair or tires and worn out rear pair of tires.
Truck was spooky and darted for either ditch on every bump or snow/ice patch while in 4WD. When in 2WD the truck tracked straight.
If trying to save $$$ by using a 1/2 set of chains on only the front vs. only on the back. Then chains on the front will at least improve steering .
Better with chains on all four however.

 

[JDemaris]

I wonder how many people now-adays even know what chains are? I had to pull the FEDEX truck out of the snow here yesterday. He tried to come up my hill in a 2WD box-van, and didn't even have real snow tires, much less chains. I asked the guy about chains, and just got a blank look. He had NO idea what I was talking about. Not long ago, in bad areas - anybody with half-a-brain carried chains with them - in case of emergency.

In the Adirondacks, there are several public roads designated "with chains only" within certain dates. In theory, you can get a ticket if you get caught without them. It's a good law. Too many people get stuck, and then cry for help.

 

[buickanddeere]

Sad reflection of society as a whole today. Can't plan ahead, look out or look after themselves.
Just call and have somebody come and take care of them and their troubles.
If the van had dual rear it would be 4X more helpless.
For some reason tire chains faded out around here with the introduction of studded tires in the 1950's or so. Chains never made a comeback after studded tires were banned in the 1980's.
Maybe more of a mountain road type of application?
Then again a very very small part of the Canadian population lives outside of major urban cities. Rural and village populations barely show in statistics.
The winter tire with the mountain and snowflake symbol should mandated by law here as it is in Quebec.

 

[JDemaris]

Some of the roads I drive in the Adirondacks kind of feel like I'm going back in time. I like it. Still a few corduroy roads around. Amazing how long they've lasted. Also some that end at beaver ponds with no way to cross without a boat. Several roads with signs reading " tire chains required after Nov 15", etc.

On the other hand, some jerk runs his car off the Northway in the middle of the winter, dies from the cold (and lack of a winter coat) - and all of a sudden - the entire Adirondack Park needs cell phone towers and service? So, now, NOT having cell phone service is a life-hazard?? I wonder how many have died since they take more chances BECAUSE of cell phones - and/or could NOT find a hard-wired pay phone to use.

 

[JDemaris]

I looked at some of my spec-sheets. Deere used mechanical front drives that run 1% to 5% faster then the rear on tractors.

Cars and trucks run from 0% to 1%

 

[Stuart]

Yeah running your tractor around in 4wd all the time on pavement or hard ground is hard on it. Our neighbor has a large 500 cow dairy and the two tractors on his TMR mixers are MFWD and he puts chains on the front of them. He is also pulling 40,000lbs around to so maybe he doesnt get as much traction with the tounge weight he has. I would put chains on the front of a truck unless I had to because the front axle is not as strong as the back axle. Sometimes you have to because of conditions. Other reasons for putting the chains on the front of a MFWD tractor is that certain designs of chains are hard on tires and front tires are alot cheaper than rears. Just paid $3200 for a set of 18.4-46 tires last summer.

 

[dan_41jdh]

Back in my high school days (about a million years ago), there were several times when several of us boys helped the driver put chains on the school bus after he got stuck in the snow. You won"t see that happening today.... Either school would be cancelled due to the slightest weather disturbance, or the driver would radio in for help if he actually got into trouble.

It"s been thirty years since we travelled occasionally across Donner Pass in California where chain laws are aggressively enforced with inspection stations as you approach the summit. If you have a vehicle that requires chains, you either have chains installed, or you are required to turn around.

Felt sorry for the truckers with double-bottom trailers who not only had to chain up the driving axles on their tractors, but had to chain up an axle on each trailer, also - in a snowstorm, typically.
California Chain requirements pdf

 

[Paul Hearsey]

Guys, great answers! Thanks especially to JDemaris for looking up the specs. Here's a clarification regarding pickup trucks, courtesy Wikipedia: generally, the front and rear axles turn at the same speed and 4WD works just fine, even on dry pavement as long as you don't do anything but drive in a straight line. As soon as you start to turn, the front wheels must travel a greater distance and therefore speed up, relative to the rear wheels. The front wheels will slip, grab, slip, grab... causing a hopping kind of action. Hell on the tires and drivetrain damage can eventually occur. That's why almost all pickup trucks are called 'part-time 4WD'.

Serious off-road vehicles and most All Wheel Drive (AWD) vehicles have a THIRD differential, called a center diff, that allows the front and rear axles to rotate at any speed they wish. Four wheel drive can then be used anywhere, anytime. I believe all 4WD construction equipment, backhoes, skidders etc. work something like this.

Farm tractors: well, I THINK there is generally no center diff, because manufacturers figure slippage between tires and soft ground will take of the problem. Having the front turn a bit faster makes sense from a steering -control point of view. I do agree that MAYBE we should be using 4WD only when conditions call for it. By

By the way, the rear tires on my Kubota ARE one size bigger than the manual suggests! Hmmmm...... sure glad I posted this question today before I broke something expensive! Paul

 

[Bob]

Just dealt with a 1985 Dorf F-150.

Front ratio 3.07, rear ratio 3.08.

 

[Mike M]

I have seen several UPS trucks here in Ohio with tire chains wrapped around the seat post. So they at least had some on board.
I don't think they were used much ?

 

[The Dukester]

Well, with all the lawsuits going on today I can see where it just isn't worth the risk of having an accident and/or someone hurt trying to help a schoolbus driver get chains mounted. It just isn't all that necessary to try to make a bus route with the roads slippery and maybe all the boys having to get out and push on the stuck bus like we did back in the '40's and '50's when I went to school. The fact that many of the drivers are women makes a difference too (sorry girls, but it's true).
As far as the chain laws in western states, it's a darned good thing, you aren't gonna climb some of those long treks up the mountain passes without 'em and there's too much danger if you go off the road. I lived there a lotta years and saw some scary things on the highways in the winter going to Reno or Stateline to "pull levers" or shoot dice for a weekend. Tobogganing was my "Waterloo"...I broke my left femur bone into seven major fragments on a steep little slope near Long Barn on California 108 just above Sonora showing off my "midweat country boy skills". 51 days in the hospital in a traction frame bed is a hard lesson.

 

[Dean Barker]

At Oliver and White Farm Equipment, we wanted the front tires to turn from 0% to 5% faster than the rear tires. Sometimes we would have to accept a negative 3% up to 10% faster for the front wheels. The front tires on a fwa tractor always wear faster, so they tend to approach a 0% lead if the designed lead was 0% to 5% or more. Hope this helps.

 

[Anonymous-0]

FWA is very common over here . The fronts should have a ground speed about 1 to 5 % more than the rears . This is called the lead ( as in leed ) and is to help keep them straight , and to allow partly for steering , where the fronts obviously take a wider turn . The reason the fronts wear quicker is mostly down to them being smaller than the rears , and so have to turn quicker .

 

[JDemaris]

In my area, UPS drivers do much better then FEDEX, with rural deliveries. UPS has actual employess and owns its own trucks. FEDEX uses many fly-by-night sub-contractors who drive Budget Rental box-trucks.

That being said, UPS is changing too, as the old drivers retire and new guys take over the routes. When I drove a truck (garbage and heavy equipment hauler) we had to carry chains and tire irons. That was 30-40 years ago. If we got stuck, we got out and put the chains on. If we got a flat, we often had to fix ourself if in a rural area. But that was when the trucks had split-rims.

 

[Anonymous-0]

Yes, most 4wd systems are geared slightly "faster" on the front, even in pickups - 4.09 gear in front vs. 4.10 gear in back, etc. This is because the front end has to travel faster in turns, to avoid drivetrain binding. The "serious wear" on tires and powertrains would take many miles/hours of operation on hard surfaces with excellent traction travelling in a straight line. That said, it is definitely best to engage 4wd only when necessary, which is why Deere went to an "auto" mode on it's MFWD systems in the bigger tractors back in the day. In "auto", the MFWD kicks out at speeds above 8 mph.

 

[Farmer Devin]

We always recommend a single pair only on 4wd tractors because "something has to give and you don't want it to be your drivetrain." Personally, I'd put chains on the rears. They are your primary traction source.

On the Belarus I had, (note past tense) The fronts were geared slower than the rears. Bought it with 300 hours and the tires were nearly new.

Devin