Tractor Wheel Size

Because the loads they support are heavier. Pleas do the arithmetic.

What kind of tractor?

If you are referring to farm equipment, generally the driving wheels are the larger due to the increased surface area, traction and buoyancy on soft earth afforded by the large diameter. The track width and general form factor of these machines is generally dictated by their intended function in the field (something to do with the spacing of crop rows for farm tractors). The front wheels of farm tractors and backhoes often only give a moderate influence over the direction of travel on loose surfaces and serve mostly to keep the front end from falling on the ground. The driving wheels are able to be individually braked to assist steering or the differential can be locked to increase pulling traction. The large high profile tires also provide some protection against surface irregularities and sharp stuff that might peel a smaller tire off the rim.

In general, the big tires are the ones that do most of the work on the machine.

long ago we filled the back wheels with some water to increase further increase the grip.

Not just plain water, but stuff called "calcium" which was even heavier (I think it was a calcium chloride solution, but I'm not a farmer). This often led to corrosion of the rims.

Off topic, but remember that we should admire farmers. They have a huge investment in land and equipment, and gamble with the weather every year.

It was indeed calcium chloride added to the water. And it was nasty stuff.

Still is.

the bigger the wheel

Find a photo of some of the old steam traction engines. On some of them the rear drive wheels were 8 feet tall and quite wide. Even smaller ones were probably a foot wide.

Soil compaction and implement mass and/or down-force - could be added to the two GA's above.

And the large diameter wheel adds to the Gear ratio...

dang...in West Virginia we been puttin them big tires on the left side and the little ones on the right side so we could plow the hill without tippin over.....

Well, We did the same.

Problem was when we needed to turn back.

Please enlighten us: How did you solve the problem?

We never turned back,just plowed clockwise all the way around the mountain in a spiral.When we got to the top,we swapped wheels to come back down.

Of course,there were always a few oddballs that plowed counter clockwise.

you just always drive the same direction around the hill! ;-)

Yeah! And the downhill ham was always bigger than the uphill ham on hogs.Had to plant watermelons next to a fence to keep them from rolling downhill,but they sure wuz easy to load...just pick up the fence and they rolled right into the wagon.

As my ole pappy used to say,"The first liar ain't got a chance."

"They are marvelous little machines and tremendously useful for small and medium jobs on the farm."

Yeah, didn't express that last part too clearly, did I? I was thinking of smaller farm tractors that are 4WD and allow small time and hobby farmers to have the power of much larger older 2WD tractors. But you're right, those big rigs are incredible, too. Interesting that even when they are tracked, the rear wheel is larger. I wonder if that's design inertia or aesthetics?

"Big rigs" tend to be about 'compaction' that go's with the mass to have the grip, to do the pull. Compaction is a big issue in broad-acre.

"even when they are tracked, the rear wheel is larger"

You can still lift the front on torque, so the bigger rear gives more 'latitude' and a lesser 'divot' to climb out of - so I'd say 'by design' - as implement 'tow height' (parallel links pivot height) sets your basic criteria/moment.

This 'height', so implement geometry; is an issue with "mountain dozer's" in steep terrain, such as vineyards in Europe.

But you are right, the likes of these are extremely handy workhorses.

Every farm should have one

Dear Mr. SPradhan,

The Tractor moves in a slow speed, NOT LIKE OTHER VEHICLES. For a given HORSE POWR Lower Speed means the TORQUE WILL BE HIGH.

If the wheel is smaller, on account of the HIGH TORQUE, the FORCE will be higher but the grip on the surface will be poor and hence the wheel tends to slip. In order to have a better grip wheel is of bigger size.

DHAYANANDHAN.S, INDIA

First of all ,what is the use of a tractor?.The big wheels are meant cater for pulling stability ,and load management.A tractor is not a racecar that banks on speed ,it banks onpower,thats why they dont exceed 100km per hour.