Undercar: The Science Behind Traction And Braking
We all know to check the owners manual to find out which weight oil should be used in the engine of a vehicle, and also generally know to only use motor oils with American Petroleum Institute Certification, designated by the starburst displayed clearly on the container, in most vehicles. But what really is the difference between a SAE 10W-30 and a SAE 10W-40, or for that case, SAE 0W-20 motor oil?
To better understand the numerical code used, a brief explanation is in order. When referencing motor oil weight, you are actually referring to the viscosity grade or the tendency of a liquid to flow slowly or quickly. The Society of Automotive Engineers (SAE) developed a grading system to designate the viscosity level of single grade and multigrade motor oils.
In single grade oils, the lower the number, the better it flows at cold temperatures. Likewise, the higher the number, the thicker the oil. In regard to multigrade oils, the first number in the code, such as 10W in SAE 10W-30, means that the oil can still be pumped by the engine at a temperature as low as a single grade 10W oil. A 5W, like in SAE 5W-30, can be pumped at an even lower temperature, and a 0W, like in SAE 0W-30, will pump at the lowest tested temperatures. The W in the designation is commonly thought to represent weight, but in fact stands for Winter. The second number, 30, indicates how well the oil will flow when heated to 100C/212F or higher.
As engines have become more technologically advanced, engine clearance levels and viscosity grade recommendations may have been reduced, hence the reason your father swore by SAE 20W-50 and your engine calls for SAE 5W-30. If a thicker oil is used in some of todays high-tech, small clearance engines, oil pressure may increase, but the possibility of improper lubrication can result if the oil can not adequately flow through the engine.
Engine manufacturers carefully select the recommended motor oil viscosity grade for each specific engine, which is why the owners manual recommended viscosity should always be used.
Courtesy of Quaker State
Steering Truck Drivers in the Right Direction
Steer tires typically receive a lot of attention from drivers. These tires usually carry more load than any other tire on the vehicle. An individual drive or trailer tire may carry less than 4,500 lbs., while a steer tire is usually asked to carry 5,000 to 6,000 lbs. While the steer tire has to be strong enough to carry the weight, it also has to be tough enough to handle scrubbing. Every time the driver turns the wheel, the steer tires encounter significant lateral forces as they fight the tendency of the trucks tandem rear axles to go straight ahead. These forces are at their greatest during hard cornering or in an emergency turning maneuver.
Rubbing the Wrong Way
Side forces away from the direction of the turn cause scrubbing across the tread surface, which leads to rapid tread wear, particularly on the outer rib. Since drivers tend to turn more sharply to the left (sight side) rather than to the right (blind side), the right steer tire tends to get scrubbed the most.
Setback front axles, typically 13 inches to 15 inches back from the standard position, are designed to improve weight distribution as well as the trucks turning circle. But, that also increases side forces on tires during turns.
One H-D truck tire manufacturer said their studies have shown that tires on a tractor with a 140-inch wheelbase must generate about 65 percent more cornering force to slide the tandem drive axles around a corner than steers on a 210-inch wheelbase tractor.
The setback axles also incorporate increased wheel cut angles, which add to steer tire scrubbing when turning. For many years, the standard industry wheel cut angles have been between 32 and 34 degrees. Setback axles are typically at 42 to 44 degrees. While side forces on steer tires can accelerate tread wear, higher loads on steer tires can actually help even tread wear by providing a larger, squarer footprint where the tire contacts the road surface.
The tiremaker also said tests have shown that vehicles with lightly loaded steer axles (10,000 lbs. or less) are more prone to irregular steer tire wear than those with heavily loaded front ends. With light loads, the tires contact area is quite long in the area of the center tread rib and much shorter toward the shoulder rib. Since the footprint is uneven, there is more scrubbing and wearing away of the shoulder rib.
It should come as no surprise that the most frequent steer tire problem is fast shoulder wear, which can lead to cupping and early removal of the tire. Instead of running steer tires down to 6/32 of remaining non-skid, and more than 100,000 miles before removal, you might get only 70,000 miles out of them before you have to remove them for worn shoulders, while the center portion of the tread may have more than 10/32 of remaining non-skid. Two other significant threats to steer tire performance are misalignment, which results in uneven wear, and under inflation, which causes excessive casing heat, thus reducing the tire’s retreadability or possibly leading to something far more serious: an on-road failure. Unlike a failure on one of a pair of dual tires, there is no support when a steer tire fails, and the driver may struggle to keep control of the vehicle.
The bottom line if you service these rigs is to install quality steer tires.
Educating Future Service Professionals on Ride Control
The Tenneco Technology Tour including the Monroe Ride & Drive training experience will visit more than 30 cities in North America during 2007 to help thousands of automotive service professionals and future technicians explore premium ride control products. Designed to explore the advantages of premium ride control technologies for domestic and import vehicles, the new Tenneco Technology Tour is expected to attract more than 5,500 professional technicians throughout 2007 for in-depth technical training and ride control test drives.
The Technology Tour is a conduit for Monroe to educate current and tomorrows technicians about the true performance differences of its premium products. A ride and drive experience is a hands-on illustration of our ride control technologies. The Tour also gives techs a wider perspective of Tennecos broadmarket and specialty products.
The Technology Tour gives technicians an opportunity to compare the steering, stopping and stability characteristics of vehicles featuring worn original equipment ride control components and identical models equipped with premium Monroe replacement products.
This years Ride & Drive fleet features 2003 BMW 325i and other popular domestic and import vehicles. The Tours ASE-certified instructor will then help participants learn how to better communicate the need for ride control and brake replacement to vehicle owners.
For more information regarding the Tenneco Technology Tour, or for instructors interested in signing up their class to attend an upcoming Ride & Drive session, contact T.J. Fontana, manager of training and operations at Tenneco at 800-843-4169, ext. 8072.