Performance Chips Glossary

Aspect Ratio

In tire lingo, aspect ratio is the proportion of size between tire width and sidewall height. When you look at the string of numbers stamped into the side of your tire, the aspect ratio is the 2nd number, following the tire's width.

Combustion

Burning of the air/fuel mixture in the combustion chamber that generates the energy necessary to run your engine. The mini-explosion in a combustion engine is triggered by a spark from the spark plugs that's added to the compressed air/fuel mixture at the top of the piston cycle. Timing and a proper air/fuel ratio are critical to the power gained during combustion.

Detonation

Essentially, detonation is uncontrolled combustion. In other words, if your cylinder fires when it should not be firing, you have a detonation problem. During engine combustion, air and fuel mix together and are ignited by the spark plug, producing the driving energy behind your vehicle. This ignition should only happen once every cycle. However, if there is too much heat or pressure in your cylinders, or if your air/fuel ratio is too rich, your engine may experience detonation, or multiple ignitions during a single cycle.

Diagnostic Trouble Codes (DTC)

A DTC is a 5 digit alphanumeric code that your onboard diagnostic computer generates when it senses a problem. In order to view these codes, you need to plug either a mechanic's code reader or a power programmer into your OBD-II port, which can be found right below your dashboard.

Diameter

A straight line segment that passes through the center of a circle or sphere and connects two opposite points. Mathematically, the diameter of a circle is expressed as 2r, with "r" representing the radius of the circle or sphere.

Load Index

A tire's load index indicates its maximum load-carrying capacity when fully inflated. All tires are rated on a scale that ranges from 0 (99 lbs. per tire) all the way to 150 (7385 lbs. per tire). If a vehicle has four tires that all have a load index of 99, then each tire can safely bear 1709 lbs. of weight, and all four tires together can support 6836 lbs. of weight. The load index is always embossed into the side of your tires, and it's the last number before the speed rating letter.

Magnuson-Moss Warranty Act

Legally, a vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part unless they can prove that the aftermarket part caused or contributed to the failure in the vehicle. If your vehicle manufacturer fails to honor emission/warranty claims, contact EPA at (202) 260-2080 or www.epa.gov. If federal warranty protection is denied, contact the FTC at (202) 326-3128 or www.ftc.gov.

OBD-II Port

Short for OnBoard Diagnostics, an OBD-II is the computer system in your vehicle that monitors and controls your engine, transmission, and other vital parts. These onboard computers have a port that you can tap into to troubleshoot engine issues as well as reprogram the system's performance level. All vehicles produced after 1996 are mandated by law to be equipped with an OBD-II port for greater control over exhaust emissions.

Octane

Octane is a flammable liquid hydrocarbon that is found in petroleum fuels. The level of octane in your fuel has a direct correlation to how well your engine resists detonation. Low octane petrol converts combustion into heat more than energy, and that added heat in your cylinders can cause premature combustion, also called detonation. Higher octane fuels generate more power and less heat, which makes your engine run cleaner, more efficiently, and more powerfully.

Speed Rating

Tires are built to be driven within a specific speed range. If they are pushed beyond their top-rated speed, they become unstable and dangerous. Therefore, a uniform notational system was devised to clearly state a tire's maximum speed range. The speed rating is indicated by a letter, the last character in a long string of numbers and letters that are embossed on the side of your tire.