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.