Tractor Traction

Contributed Article

Putting Horsepower to the Ground
(Tractor Traction)

Some folks may look at a vintage tractor and assume that, because it has massive lugs on the rear tires and is mostly cast iron or heavy steel, it shouldn't need more weight to get the necessary traction. This would be true if your tractor were simply transportation. That is to say if it merely had to drive from one place to another like an automobile or truck, the weight and tire tread would be sufficient to drive through the deepest mud and softest soil imaginable and even 24 inches of snow wouldn't stop it. The difference between a transportation vehicle and a tractor is that when a tractor is moving, it has to do additional work beyond moving itself and a rolling load. If the primary purpose of your tractor is to use, say, a post hole digger, it may be one of those exceptions. Putting this type of use aside, for most tractors, the work will involve pulling a resistant and occasionally stubborn load.

Our first bout with traction problems came when cultivating with our Massey-Harris Pony. Up till then, this tractor had been running a corn grinder and pulling a trailer. It had new unfilled rear tires and no wheel weights. The garden was already sprouting when we hooked up the mid-mount shovel cultivators to the Pony. The seed bed was soft enough that the rear end would spin and slowly work its way to the downhill side of the gardens slight incline. From this, we learned our lesson since the tendency to side slip actually cultivated out many new corn plants.

The problem with traction boils down to two principles. The first principle is that some loads, such as front mount implements, cause a weight shift from the normally heavy rear driving wheels to the front. Many people are shocked by how little they can push with a front blade before the rear wheels just start spinning. This is why wheel tractors make such unwilling bulldozers. An extreme example of this load shift is with a loader. Imagine moving around the corral, scooping up massive piles of slippery manure mixed with mud. You can envision the load causing the entire tractor to act as if it were a weight scale, removing the weight from the rear wheels as the loader rises. Now if you have to go up a muddy incline to where you will dump the load, it becomes apparent why extra weight is needed.

The second principle is simply that some implements can generate a surprisingly massive drag on the rear end. Heavy tillage implements are good examples of this. Implements such as plows, subsoilers, ditchers and back or box blades. The tractor makers, based on the work of Harry Ferguson, had a plan that partially addressed this and by the 1950s, most had implemented the scheme. Manufacturers used the weight of mounted heavy tillage implements (such as plows) as a method of transferring weight back onto the rear wheels. This was done by hydraulically lifting the implement (almost imperceptibly to the operator) when forward motion was impeded. This helped, but did not make having basically good traction obsolete. If the wheel-slip starts prematurely, the weight transfer effect starts too early with the end result being the implement barely gets in the ground before it starts to bob back out. This condition results in a inconsistent job. If we use a plow as an example, your field would be deeply tilled in some areas and barely scratched in others. Having sufficient rear wheel weight and traction to start with, will result in a smoother and more consistent job.

There are two methods of obtaining sufficient rear wheel weight. The first is the time-honored tradition of filling the rear wheels with Calcium Chloride solution. This is a non-freezing liquid solution. By putting it inside your inner-tube, the weight is carried as low as possible which is good for the tractor, traction and safety. Unfortunately, once you fill the rear tires, you must watch carefully for leaks and attend to them immediately. I once spilled a small amount on the painted bumper of my truck when loading a leaking rear wheel. It was completely rusted in two-days. When this solution comes in direct contact with metal, a highly destructive process begins immediately and if left unattended, will destroy rims, hubs and whatever else it touches very quickly. Because of this and more serious safety concerns, filling and caring for your wheels is a job for your tire store unless you have a backhoe or very large loader (on a separate tractor). Lifting a filled wheel into your pickup bed is an operation that when done without equipment is reminiscent of building the pyramids. The only safe way to deal with a tire that is filled is to leave it on the tractor and have your tire company bring their rig out. They will drain it, remove and fix the tire, and refill it. Surprisingly it costs only a little extra to have them come out and it could save you some real headaches. If you have ever seen a large filled tire fall over, it will make the above believable to you.

The second way to get necessary weight on the rear wheels is through the use of cast-iron wheel weights. These come in two styles, one piece and multi-piece. A one piece wheel weight is simply a large round piece of cast iron that will bolt to the rim. On some machines you can add more than one to each side to gain even more weight. The real disadvantage of one-piece wheel weights is that they are heavy and unwieldy and thus difficult to mount and unmount. To overcome this problem, manufacturers cast wheel weights in many smaller sections or wedges that when installed would all add up to even more weight than a one-piece weight but individually were not as heavy. Generally it is easier to find one-piece that will fit your rims since they don't necessarily have to have been made specifically for your tractor to fit. With multi-piece weights, you are best off locating original equipment weights.

What is the downside of adding weight to your tractor? Nearly every manufacturer recommends removal of weight when it is not needed. There are two reasons. The most serious downside is that once equipped with better traction, the conditions where the tractor may have experienced wheel spin, can then cause backflip (which most frequently results in death). Basic tractor safety states that you should never pull loads that are or can become immovable (this includes any skidding or dragging) or maneuver the tractor where it can contact immovable objects (such as stumps, trees and buildings). The better the traction the more the danger of backflip!

The second downside is that some parts will wear out sooner. The excess weight puts significantly more stress on nearly every component, especially bearings and bushings related to the drivetrain. Though not fun, removing some or all wheel weights during times when the tractor is not needed for heavy pulling, snow plowing or loader work is a good idea. For those with the equipment to safely deal with filled tires, the best bet is to have two sets of rims, one set filled and one empty. I have found that I need the weight for nearly every job I need a tractor for and leave weights and filled tires on at all times. I presume that the price for this will be realized someday in replacement of bearings or axle components.

Not all tractors were designed to have extra weight added so be sure that you read up on your specific model to see what the manufacturer recommended. If it does appear that it was, consult your local tire store and see if they offer a service for filling and draining. For sources of wheel weights, check with your local scrap yard.

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