Wheel bearings are often overlooked, yet their importance is undeniably the primary reason your rig is able to move at all. Even though the Wheel bearing's job in life is of the utmost importance, their actual formidability is not as critical as one might think. Even though the bearing has the sole task of keeping the entire vehicle's weight rolling effortlessly down the road, the bearing's surrounding components have more to do with it from crashing to the ground, than the bearing itself. Even so, there are some important aspects and guidelines to follow in order to get the most out of your wheel bearings.

Many times you hear statements that "moving the tire outwards from the bearing (such as in a reversed or wider rim such as in a wider tire) will cause premature bearing failure." While this statement may be "technically" true, it is realistically untrue. A standard automotive wheel bearing under pristine conditions (flat interstate driving, unloaded, no bumps in the road, etc.) is designed to last 300,000 miles. Under the same conditions, a wider, reversed rim with a larger tire might get 250,000 miles. Point is, there will undoubtedly be other factors that will end the bearing's life before increased loads will, such as lack of maintenance, improper lubrication and contaminants. So, generally speaking, saying that "a larger wheel/tire will wear out a wheel bearing faster" would be similar in saying, "smoking one cigarette will shorten your life." While both statements might be technically true, realistically, they would be immeasurable due to all the other factors that can affect the end result.

Does this mean you can slam on the largest tire you can find and have at 'er without a worry? Hardly. The forces that be are magnified exponentially as you increase the abuse the suspension might see. In order of attrition, those forces include hauling weight, cornering G-forces, Increased Articulation, Rough Terrain, and becoming Airborne. And even through all this, it's not necessarily the Wheel Bearing that will be the weak link, it will usually be the surrounding components, such as the spindle, knuckle, ball joints, axle tube, etc.

In the illustration to the left, the above full reversed offset wheel has a 6 inch offset from the axle connection point to the outside of the tire. The forces at work proved the leverage equivalent to that of a 6 inch lever at the outside of the tire. The diameter of the tire also increases lateral leverages when being subjected to side loads, such as sliding sideways into a curb. There the leverage is equivalent to half of the tire's diameter, which in this case is 15 inches. The tire and rim combination on the lower left illustration depict a tire twice as wide as above example. The outside leverage is equivalent to that of a 12 inch lever at the outside of the tire, almost double that of the top version. HOWEVER, those forces will only be seen when the very outside, and ONLY the outside of the tire is subjected to a force differential. Otherwise, the inside of the tire will begin taking the brunt of the load first, since it has not changed in this illustration. The load will be distributed over more of the tire's width, but not equally, as shown in the example below.

As another example, the illustration to the right shows how a typical dually style tire distributes the load to the axle. Even though the outer edge of the outside tire doubles the width of the leverage potential on the axle connection point, the actual load center is only moved outwards by half of that distance. This represents the typical forces exerted on the connection point while driving down a road. The "leverage potential" on the other hand "increases" as the contact point hits the tire further and further out. This would represent uneven terrain, rocks, etc.

In other words, in average road driving conditions, the axle sees very little increased leverage beyond that of the road contact point of the inner most part of the tire, with less concern to how many tires or how wide they are. However, on uneven terrain the connection point will only see the force of the leverage multiplication calculated at where the obstacle impacts the tire's width, regardless of where the inner most part of the tire was supported at the time.

Even if the leverage forces are amplified by larger tires and wider or offset wheels, the wheel bearing itself is usually not the first point of failure. There are other concerns that would probably fail first, as represented in the chart to the left. Rarely do you see a wheel bearing mechanically fail due to load or stress of a wider, larger tire and/or rim. Rather than cracking or breaking, the most common bearing failure seen is due to a lack of lubrication as a "result" of the increased loads. This isn't necessarily a bearing problem, but a lubrication concern. Increased loads on smaller than adequate bearings for a particular modified application can elevate heat production in the bearing, thus will result in a lack of lubrication. Premium lubricants, greases and additives coupled with religious maintenance regiments and proper assembly specification will virtually eliminate bearing failure in the scenarios above.

Never over grease the bearings. Old wives tales say that "the extra grease will flow into the bearing if it gets hot." However, if the bearing is getting hot in the first place, it's probably already too late. Excessive grease can prevent the bearing grease from cooling itself, besides being a real pain to clean out when performing preventive maintenance. Clean and pack the bearing sufficiently with an ultra-high quality synthetic grease, and then lightly coat the bearing with about a 3/16" thick layer of grease and install it. Nothing more.

Keep in mind, that while setting the bearing adjustment, there needs to be approximately .002" clearance between the bearing and the race to insure the grease does not get scraped off the surface, thus causing a lack of lubrication and inevitable bearing failure. Since the bearing needle angle is approximately at a shallow 20 degree pitch, this equates to the commonly stated instructions of turning the bearing lock nut out 1/4 turn after fully seating the bearing at zero lash. Periodical maintenance to insure this critical clearance is demanded to guarantee reliable operation.