Hi guys. Fred's got it pretty much covered.
A lot of large new tractors are 4, 6 or 8-wheel drive (4 driving axles with 1 or 2 wheels each). On that type, they're all the same size.
The smaller 2WD ones are still all-terrain devices, and therefore need both the 'floatation' effect and the massive lugs. The large area of weight distribution aids in staying on top of mud and soft soil, so as to avoid either getting stuck or causing too much disruption of the ground. While spreading fertilizer, for instance, you don't want to be digging up the crop as you go. As mentioned, most of the weight of a tractor is on the back, so the thin wheels up front don't cause a lot of damage.
I don't know if anyone still makes them, but some of the older jobbies from when I was a kid were almost tricycles. The two front wheels were only a foot or so apart and had massive camber so they formed a downward-facing 'V'.
Quite true, sree, but they're in a different class. Generally speaking, they're used in mining or construction rather than farm-like conditions. Also, most of them do in fact have the same size of tires all around and the engine and ballast weights are in the back to offset the load.
If you mean the type that are sometimes attached to farm tractors, they don't carry a really significant amount of weight, and are usually only fully loaded when on hard ground. The lifting ability is based upon the centre of mass of the tractor rather than the strength of the hydraulics. If you try to pick up too much, the C of M will be ahead of the front wheels and the tractor will 'nose over'.
in reply to danger's comment about the "tricycle" tractors
no one makes them anymore since they would tip over really easily
i used one growing up , it is a Farmall M
the advtange of it though is that it can turn a really sharp radius when you brake only one tire at a time
Hi Brewski. Now I know why Cat was so eager to snap you up from uni. :rofl:
Right, Shawn... Farmall. I'd forgotten that brand entirely; was thinking of the little grey Ford. And ours did flop over a couple of times. It also, if I recall, had a tendency to pull wheelies if the plow hit a rock. Not much weight in the front end of one of those things.
When you see the near tri-cycle tractors race, its even better. Its all about how slow you can go, last to cross the finish line wins! Not as common anymore, but will still happen at a rural fair near July 4th in the midwest.
They really do allow for an incredible turning circle with one rear brake locked. It makes backing up trailers incredibly easy around bends or obstacles. On our farms, we had many Farmalls (I think they later became part of Case-IH) with a "B", "H", W4 and W6. Like the original Jeep, these tractors were designed in an era of easy serviceability by near anyone and incredible durability as an integral part of the DNA.
The ROPS (Roll Over Protection Structure) is sometimes adopted to older tractors, its a big roll bar near the seat, but cost and pride and lack of seat belts mean they are generally only on tractors where they were required for manufacture.
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