What's With Tractor Wheel Sizes

[glennmac]

What\'s With Tractor Wheel Sizes

Why the schizophrenia in the way tractor wheels are sized and placed?

I was looking at an old Oliver at a dealer. The front wheels were miniature and only about 6 inches apart. They also seemed to be toed-in and cambered to an extreme degree. Right next to it was an old White with much larger front wheels spread apart almost as wide as the rears.

I assume these wheel size placements and sizes have something to do with farming applications and crop rows. I also assume that in the old days of no 4wd the idea was to have monster rear wheels for traction, leaving turning to be the only function of front wheels. But, still, why all the variations.

And, today, with 4wd being so prevalent, wouldn't it make sense for all four wheels to be the same size. There must be competing trade-offs and philosophies.

Glenn

 

[Bird]

Re: What\'s With Tractor Wheel Sizes

Glenn, I don't know all the answers, but the "tricycle" gear with either one front tire, or two right together used to be common. I'm not even sure anyone still makes anything like that now; don't think they do. But you're right about the big rear tires for traction, and the front ones only for steering and hold up a little weight. If you planted your rows the right distance apart, then for cultivating, your front wheels were between two rows and the rear ones were outside those same two rows. I think the main disadvantage of the tricycle gear is the same as with a kid's tricycle; they turn over too easily. Once in awhile you'll see a front end loader on an old tractor with tricycle gear, but not often; far too dangerous. So, I think that's the reason everyone went to the wide front ends. And if you look around, you'll find a number of the wide front ends that are adjustable; you can move the front wheels in or out to change the spacing. Neighbor's old 1755 Oliver has that feature.

So now we have the wide front ends; why not all four tires the same? Most of the big articulated all wheel drive tractors do have. I don't know the answer, but figure some implements might have to be redesigned, i.e., would there be enough clearance for the front end loader or would the bucket have to be farther forward and the boom arms and cylinders higher to clear the front tires? And the tractor would have to redesigned to sit level; couldn't put bigger wheels on the existing axle or it would look like it was running uphill all the time. How much would your visibility be reduced by the bigger tires and wheels on the front? And how much more would the bigger tires cost, both for the manufacturer and for the owner if he/she has to replace tires?

And now you just got me thinking and rambling, so I'll quit./w3tcompact/icons/wink.gif

Bird

 

[ERNIEB]

Re: What\'s With Tractor Wheel Sizes

Just to add a few comments to what Bird has said about tricycle tractors. Not only were the wheels spaced for rows, but extra cultivators could be added by a bar that was bolted right behind or beside the front wheels. That couldn't be done on a tractor with wider spaced wheels. And then there is the fact that a tricycle could turn on a dime, and give you some change. Which was important on the small acrage farms of days past. I suspect the passing of the small farm had as much to do with the passing of the tricycle as did it being dangerous.
There are probably a lot of odd reasons why companies chose the demensions of their tractors. I read somewhere that Henry Ford designed the demensions of the 9n based on how many he could load on to a rail car.
ErnieB

 

[Anonymous Poster]

Re: What\'s With Tractor Wheel Sizes

One of the main reasons why narrow front tractors were built was to cultivate crops for weed control. You had to be able to see the crop rows to do a good job of digging the weeds without killing the crop. Mid-mounted cultivators were often used for this.

Hardly anybody cultivates crops anymore. Now you spray the weeds.

Very large rear wheels also provide much better crop clearance under the rear axle.

 

[art]

Re: What\'s With Tractor Wheel Sizes

one of the main reasons for the narrow tires on the front was manuverability. Much like the early four wheel drives the old wide fronts used to take half the field to turn around. Even going back just 20 years of production todays four wheel drives turn tighter than those two wheel drives. Row crop work of cultivating is still a great way of helping sprays work better.

 

[W5FL]

Re: What\'s With Tractor Wheel Sizes

Glenn, Bird covered it pretty well. You will notice that most older tractors were designed to be the absolutely least expensive and simpliest and most reliable way to do things. Unfortunately, the tricycle front wheels are not very stable and not usable for loaders. Loaders also dictate that the front wheels be large enough to carry the heavy loads, but not so large as to move the loader any more in front of the tractor. Most tricycle wheel tractors did not have power steering either!

 

[patton]

Re: What\'s With Tractor Wheel Sizes

Regarding having all the tires the same size:
That is typically done with 4WD tractors (as opposed to MFWD), where the front tires provide almost as much tractive force as do the rears. Stearing would suffer if the tractor weren't articulated (hinged in the middle).

Big rear tires are needed to obtain clearance over the bulky final drives- no gears are needed on a 2WD (and the axle is commonly above the centerline of the tire), on an a MFWD, either a much lighter duty diff is used, or drop gearing can be used to keep the axle above the centerline.


Pat

 

[glennmac]

Re: What\'s With Tractor Wheel Sizes

Patton,

I am not familiar with the difference between 4wd and MFWD or what I have on my Kubota.

I wish my front wheels had as much flotation as my rears. With all the soft and muddy soil I have, it is the front tires that dig in and rut more than the rears even though the rears are filled with calcium chloride. It would be a much better flotation and traction situation.

I also don't understand the point about articulated bodies needed for steering. I mean, this is just my ignorance of tractor design.

 

[Bird]

Re: What\'s With Tractor Wheel Sizes

Glenn, I think Pat was talking about "full time" 4WD when he mentioned 4WD articulated tractors versus MFWD (mechanical front wheel drive) which is what we're accustomed to on our tractors.

Bird

 

[W5FL]

Re: What\'s With Tractor Wheel Sizes

Glenn,

Four wheel drive is same as MFWD which is just John Deere's marketing term for Mechanical Four Wheel Drive (as opposed to Hydraulic 4WD that was used at one time and still used on some vehicles). The reason they are articulated (pivot in the middle) is to make them turn faster. Although there is an articulated tractor, it is not a practical solution for most of us.

Size of tires is relative. My front wheels are 24 inch diameter and provide excellent flotation and traction with Ag Tires. Both Fronts and Rears are filled with antifreeze (non/toxic type). Front tires need to be as large as practical for loader work - you never see a tractor manufacturer show a tractor with a loader unless the tractor is 4WD. There is a very good reason for this. One is traction but a very important point is getting enough weigh supporting contact area for a loader with a heavy load. A loader with a heavy load transfers considerably more than the weight of the load to the front tires in addition to the tractor weight.

What kind of tires do you have. The Ags are designed to provide a lot of area on the ground and still allow the mud to be cleaned out of the tread to maintain traction. Turf and Industrial tires DO NOT do this well.

 

[RobertN]

Re: What\'s With Tractor Wheel Sizes

Part of it is $$$$$ On my 2wd Farmall, those smaller skinny front tires are like ~$60/ea, compared to $250/ea for the bigger rear tires.

Also, even with power steering, it would be harder to steer big tires on the fron of a tractor.

Larger front tiers would stick out further when you turn, ppossibly knocking around crops.

RobertN in Shingle Springs Calif

 

[patton]

Re: What\'s With Tractor Wheel Sizes

In the field of ag tractors, 4WD refers to a tractor that is full time 4WD and typically requires 4WD to acheve it's rated drawbar pull. A 4WD tractor is ballisted to put almost half it's weight on the front axle. Articulation is needed because a) the tractor is so damn big and b) the tractor is always in 4WD. You will see the same design in large loaders/intergrated tool carriers, while smaller 4WD loader-backhoes use the smaller front tires and part time four wheel drive like an equiivent farm tractor.

Front wheel assist, MFWD, part time 4WD, etc are designed to only be used ocasionally in 4WD, and a loss of turning radius is acceptable. Besides which, the tractors are fairly small and have a good turning radius to begin with.

They are ballisted heavier than 2WD, but not as heavy as 4 WD.

Pat

 

[RobertN]

Re: What\'s With Tractor Wheel Sizes

Gosh, I speel terribly! I gots to watch my posts beeter!

RobertN in Shingle Springs Calif

 

[thebonepile]

Re: Cultivating

Yes you are quite right, however, back in the older days before chemicals and super growing corn it was necessary to cultivate corn that was quite tall. With a wide front tractor the corn had to be able to go under the front axle without breaking off - so, once corn gets about waist high it is getting too big to go under the axles. However, with a narrow front tractor the lowest thing the corn had to go under was the rear axle, and you could cultivate corn almost shoulder high and still have it not break off.

As far as loaders, a narrow front can turn much better, but not worth a crap in the mud, and balance isn't as good, plus MFWD is not an option on narrow fronts

 

[thebonepile]

Re: What\'s With Tractor Wheel Sizes

the crop cultivating and price of the tractor were probably the main reasons for narrow front tractors (as everyone else says here)

I can put my two cents in.......

the narrow front wheels are cambered a lot to help clean mud out - as the wheels turn if mud gets stuck at the bottom as it goes up the back and the gap gets wider it will spin out.....

they turn much better than wide fronts, back in the older days of mowing hay with a sickle mower you could make tight perfect corners without missing a bit on every corner, plus implements weren't as big so it was nicer to turn sharper on the ends and get back going the other way easier..

Enough on that, now for the back tires......
tire companies have researched and found that a taller tire will transmit better and more traction to the ground - therefore, if you compare 2 ag tractors like a Allis wd45 to a big new John Deere (they now come with upto 46" tires) even if the weight, horsepower, everything else was identical, the one with taller tires would have better traction and power transfer to the ground. But there is a tradeoff, just like others mentioned in the post, would u like tires 8' tall on an 8n? and what about visibility, etc......plus on many MFWDs now - they size the front tires so the drivetrain/axle is centered on the tire - saves a lot on mechanical parts (compare modern things to Belarus' of a couple years back)

that's all for now.....

 

[Bird]

Re: What\'s With Tractor Wheel Sizes

<font color=blue>the narrow front wheels are cambered a lot to help clean mud out - as the wheels turn if mud gets stuck at the bottom as it goes up the back and the gap gets wider it will spin out</font color=blue>

Bonepile, that sounds perfectly logical to me, but sometimes the reality is different. I have a neighbor with an old Farmall with the narrow front end, and in this black clay in my area, it will just build up some much mud that the wheels quit turning. So what he has to do when he uses it in wet weather is take one front tire and wheel off and drive it with just one front wheel.

Bird

 

[Thomas]

Re: What\'s With Tractor Wheel Sizes

I agree about the narrow front end in turning sharp corner plus getting rid of the mud.
Pulling load of bale hay going down on a side hill I would rather have a wide front end,also travel down the road.

At one time one could purchase tire scapers for the narrow front ends to help keep the tire clean of mud and snow...wonder if they still sell them.

The tall the tire I feel less chance of getting stuck but one does make deeper ruts,plus the tall the tire for winter use w/good set of chains on can go about anywhere.

The down side of tall tires when one tire spins in mud and w/no fenders...arrrr. /w3tcompact/icons/crazy.gif

Even been going thru a field in high hay and have a narrow front end hit a chuck hole. /w3tcompact/icons/shocked.gif/w3tcompact/icons/crazy.gif/w3tcompact/icons/frown.gif


Thomas..NH /w3tcompact/icons/wink.gif