TECH CORNER: All About Tires
The following article and images are by Bridgestone
Tire Tread Wear & Causes
As tires are used, it is normal for the tread to gradually become shallower and overall tire performance to change. In addition, irregular tread wear may occur for a variety of reasons that may lead you to have to replace a tire sooner rather than later. Regularly checking the tread depth and wear condition of each tire on your vehicle will not only let you know when it is time to replace a tire, it can also help you detect other needed maintenance and get the most value out of your vehicle and tires.
Why Tire Wear Matters:
Too little tire tread can create unsafe driving conditions. When tires can’t grip the road, a driver may lose control of his or her vehicle. When roads are wet or snowy, tire tread depth is very important. Anytime precipitation gets between your tires and the road, you need the tread to cut through it and maintain as much contact with the road surface as possible. The more shallow your tread, the more easily you may lose traction when driving in the wet or snow; reducing speed in those conditions helps you maintain grip.
What is the Minimum Tire Tread Depth?
In the United States, tire tread measurements are usually expressed in 32nds of an inch. For example, all-season passenger tires often have tread depths from 9/32-inch to 11/32-inch when new.
Most states have established a 2/32-inch minimum tread depth requirement, which require motorists to replace a tire when the tire wears down to that depth. Regardless of which state you live in, Bridgestone recommends that a tire be replaced when any portion of the tread is at 2/32-inch depth.
How do you know if you’ve reached the 2/32-inch threshold? Use the tire tread depth indicators found within the tread grooves. Every passenger, light truck, and medium truck tire has these indicators, also known as wear bars, at various places around the tire. Tread depth indicators are there so you can visually determine whether you have reached 2/32-inch in that groove without having to measure the depth with a tool. Replace any tire where the tread ribs become flush with the indicator bars.
Another method of evaluating tread depth gauge is the “penny test.” Place a penny, with Lincoln’s head upside down, into the groove between the tread ribs. If you cannot see the top of Lincoln’s head between the ribs, the tread is at least 2/32-inch deep at that location. If Abe’s whole head is visible at any groove location, you should replace that tire.
What Causes Early Wear Out or Irregular Tire Wear?
Just as vehicles, drivers, and driving habits are different from each other, not all tires are the same and they can wear at very different rates. For instance, high performance tires for sports cars wear more quickly than touring tires for a family sedan. However, a variety of factors can cause a tire to wear out sooner than expected, and/or cause it to wear irregularly and create noise or vibration. Two common causes of early tire wear out and irregular tire wear are improper inflation pressure and out-of-spec alignment conditions.
Tire Tread Wear Cause 1: Improper Inflation Pressure
When a tire is improperly inflated, there’s a good chance it will start to wear more rapidly and/or unevenly. Not only do vehicle manufacturers specify the inflation pressures for the front and rear tires to optimize performance for ride comfort, handling and fuel economy, they also take into consideration tire wear. Proper inflation pressure helps optimize distribution of vehicle load, acceleration, braking, and cornering forces in the tread. If the tire pressure is too low, or even too high, the contact patch of the tire tread is not optimized to handle the wide variety of jobs it is asked to do. Thus, different parts of the tread may be abraded away more quickly and/or irregularly.
Check the pressure in all of your tires, including the spare, every month. Also check it before going on a long trip or when you plan to carry extra load. You can find the vehicle manufacturer’s tire pressure specifications on a placard/label affixed to the driver’s door or along the door jam. You can also check your vehicle owner’s manual for tire pressure recommendations.
Tire Tread Wear Cause 2: Out-of-Spec Tire Alignment
Tire alignment, also known as wheel alignment, refers to the adjustment of the vehicle’s steering and suspension components – the system that connects and controls the motion of the wheels. It is not an adjustment of the tires or wheels themselves. The key to proper alignment is to adjust the angles of the tires and their contact with the road in accordance with the vehicle manufacturer’s specifications for parameters such as camber, toe, and caster.
Improper tire alignment can cause your tires to wear unevenly and prematurely. Common irregular tire tread wear conditions from improper alignment include the following:
Heel/toe tire wear: This happens when one side of the tread blocks is wearing faster than the other side circumferentially. When you run your hand over the tread blocks, they will feel like saw teeth. Heel/toe wear typically occurs in a shoulder rib and is often caused by excessive positive or negative toe.
Feather edge tire wear: Tires are “feathered” when the tread ribs are worn lower/smoother on one side and higher/sharper on the other. This is often caused by a combination of improper alignment settings, such as excessive toe and caster.
One-sided shoulder tire wear: This type of irregular tread wear means the inside or outside shoulder rib of the tread is significantly more worn than the other ribs. Also known as camber wear, excessive positive or negative camber often causes this type of wear.
The above article and images are by Bridgestone
Tire Pressure and Drag Racing
A lot goes into launching a race car. Suspension parts, geometry, weight distribution, power control, etc., all play a major part in moving the car out of the hole. One of the easiest things to control is tire pressure. However, there's a common misconception regarding low tire pressure. I'm sure the root of this comes from street racers attempting to make their DOT tires more like slicks. But when it comes to getting the quickest E.T., more tire pressure is better, to a point. The lower the tire pressure, the more a tire will give to conform to the pavement surface. Hence more friction; more friction = quicker 60-foot times. However, when a powerful drag car is equipped with slicks, side-wall wrinkle happens due to the amount of torque the car is placing on the tires. That wrinkle lost forward momentum, and therefore lost E.T. Each track will have it's own "sweet spot" for tire pressure, but the following steps will help you locate where to have your car's tire pressure.
Start low, keep increasing until there's spin. This technique will take a few test passes to get the right amount.
Start with a low amount of tire pressure. For slicks, this may be around 7 lbs of tire pressure.
Provided the rest of the car is set up correctly, you should plant the tires with no spin, and be on your way. However, to improve your 60-foot times, up the tire pressure by .5 increments and make a new test pass until you get tire spin.
Protip: A camcorder and slow motion can help spot tire spin. Once you have found where the car wants to spin the tires, back the pressure back down .5-1 lbs of pressure. Now you have set your tires to the optimal pressure!