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  Glossary

Backspacing – isalso called rear spacing, it is the distance from the mounting pad to the back edge of the rim. This is different than wheel offset.

 

Bolt Pattern – is the arrangement of the bolt holes on a wheel. The bolt pattern or bolt circle is the diameter of an imaginary circle (P.C.D) formed by the centers of the wheel lugs. Most bolt patterns are represented in the following manner: 100 x 4H or 4/100. The "100" indicates the diameter of the bolt circle measured in millimeters. The “4” indicates the number of lug holes. Bolt patterns can be 4, 5, 6, 8, or 10 lug holes. However, tuner applications are typically 4 or 5 lugs. Bolt patterns are measured in both inches and millimeters. Thus, a wheel with 5 lug holes and a diameter of 114.3 mm can be referred to as either 5 x 114.3 or 5 x 4.5. 1 inch is equivalent to 25.4 mm.

 

Cast Wheels – is the most common type of aluminum wheel. Casting is a relatively inexpensive way to produce quality alloy wheels. The casting of wheels is the process of getting molten aluminum inside a mold to form a wheel. There are two methods used to produce cast wheels, gravity casting and low pressure casting.

 

Casting, Gravity – is the process of pouring molten aluminum into a mold utilizing the earth’s gravity to fill the mold while it cooled. Gravity casting is one of the most economical methods to manufacture alloy wheels if reducing weight is not a primary concern. Since the process relies on the earth’s gravity to fill the mold, the aluminum is not as densely packed in the mold as the low pressure casting. Generally speaking, gravity cast wheels will have to be made heavier in order to achieve the desired strength.

 

Casting, Low Pressureisthe process of the molten aluminum drawn up into the mold using a high-pressure vacuum. Low pressure casting allows the molten aluminum to move quicker into the mold thus produces a finished product that is denser with less trapped air than gravity cast wheels. Although low pressure cast wheels are stronger and less porous than gravity cast wheels, the production cost is significantly higher.

 

Center bore – is the size of the machined hole on the back of the wheel that centers it properly on the hub of the car. Center bores are measured in inches or mm. When the wheel is perfectly positioned with its center bore matching the hub or becomes hub centric, the chance of vibration is minimized. Sometimes hub rings may be required to be placed in the back of the wheels for them to become hub centric and thus reduce the risk of vibration while driving.

Forged Wheels, Fully– is c onsidered the best wheel manufacturing technique. Forging allows for the compression of an aluminum billet (one solid piece of aluminum) into an aluminum wheel using over 8000 tons or 16 million pounds of pressure combined with heat. Forging produces a wheel that is both stronger and lighter then the standard low pressure aluminum wheel. The costs of tooling, technology, development and equipment make this type of wheel very exclusive and usually demand a high price in the aftermarket.

 

Forged Wheels, Semi-Solid – is a process which the aluminum billet is heated to an almost liquid state and then it is forced into a mold at a very high rate. The finished product offers mechanical properties very similar to the fully forged wheel but without its high production and tooling costs. Although semi-solid wheel may offer an excellent value to many consumers, fully forged wheel remains the ultimate wheel in the market.

 

Hub Centric – is a wheel with a center bore made to match up with a vehicle's hub diameter.

 

Hub Centric Rings (Hub Rings or Spacers) – is the hard plastic or aluminum rings mounted on a vehicle's hub before the wheel. Without hub rings, there is a possibility of getting a vibration even if the wheel & tire assembly is perfectly balanced.

 

Load Index – indicates the maximum weight that each tire is able to support.



Negative Offset – is the mounting surface of the wheel is behind the true centerline of the rim/tire assembly. This will cause the tire to stick out away from the vehicle. Many powerful rear-wheel drive cars often have wheels with negative offset.

 

Offset – is the distance from the mounting surface of the wheel to the true centerline of the rim. Offset is usually stamped or engraved into the wheel and is measured in millimeters of 'ET' [ET is the short form of the German word 'Einpresstiefe' which literally translates as 'insertion depth.'

 

P.C.D – abbreviates for 'pitch circle diameter' and is the diameter of a circle drawn through the centre of your wheel's bolt holes. P.C.D is measured in millimeters.

 

P-Metric System – is a system for specifying tire sizes using the tread width (millimeters), the aspect ratio, type or tire construction and the rim diameter (inches). The sizes are written as such: P215/65R15 89H.

    P225/65R16 92V

  • The "P" stands for "P-Metric" or "Passenger". This means that it is a North American tire sizing designation. European tires typically don't have the "P" attached to the size. Tires with higher ply ratings will generally start with "LT" which stands for "Light Truck". This indicates the tire is an LT metric and will always have a Load Range indicated. It is important to note this for vehicles that call for LT metric tires. Never substitute a P metric tire for an LT metric tire, even if all the other dimensions are the same.

  • The "225" is the width of a tire, also known as the "section width". This is the width of the tire in millimeters at its widest point from sidewall to sidewall when mounted on the recommended rim width. The actual tire width can vary depending on the rim width it is mounted on.

  • The "65"is known as the Aspect Ratio. It is calculated by dividing the section height by the section width and multiplying by 100. (In this example, the sidewall will be 65% of 225)

  • The "R" stands for Radial, meaning it has a radial construction. Radial tires have ply cords that extend to the beads and are laid at 90 degrees to the centerline of the tread, the carcass being stabilized by a circumferential belt. Other possibilities include "B" for belted construction and "D" for diagonal construction.

  • The "16" stands for the diameter of the wheel in inches. This is the exact size that this tire will fit.

  • The "92" is the load index.

  • The "V" is the speed symbol.

Plus Sizing – is the change of the original stock tire size of your vehicle to a different size. Plus sizing your wheel & tire combination was designed to enhance vehicle performance and looks by allowing fitment of larger diameter rims and lower profile tires. The theory is that while making these changes, you keep the overall tire diameter within 3% of the original equipment tires. This is important because larger variances can cause problems with transmission shift points which can decrease fuel mileage. It can also confuse braking system computers which can even lead to braking failure. Plus-Sizing or Up-Stepping are two terms given to the practice of increasing the diameter of your wheels whilst simultaneously reducing the profile of your tires to keep the overall rolling radius the same.

    Plus One:
    Increase section width by 10mm
    Decrease aspect ratio by 10 points
    Increase rim diameter by 1 inch

    Plus Two:
    Increase section width by 20mm
    Decrease aspect ratio by 20 points
    Increase rim diameter by 2 inches.

Positive Offset is the mounting surface of the wheel is positioned in front of the true centerline of the rim/tire assembly. Most front wheel drive vehicles have positive offset wheels.

Speed Rating is a measurement of the top safe speed the tire can carry a load under specified conditions. A higher rated tire will give you better traction and steering control response.

Speed Rating

Miles/Hour

Kilometer/Hour

Q

99

160

S

112

180

T

118

190

U

124

200

H

130

210

V

149

240

W

168

270

Y

186

300

Z

Open ended

Open ended

Zero Offset – is the way the wheels have their mounting face even with the centerline of the wheel.

 

  Wheel Care Tips

It is important to keep your wheels clean at all times. The brakes on the car will cause the wheels to heat up, and this heat in turn can cause any dirt or brake dust to sap into the clear coat. If this happens, there's not a lot you can do besides having the wheels refinished. Protect your investment and keep your wheels clean!

Below are some simple instructions on how take care of your wheels:

  • Do not use household cleaners or other detergents to clean your wheels. The best wheel cleaning solution is a mild soap and water solution (what ever you would trust on the paint of your car).   Clean with a soft, un-abrasive cloth. Only on polished wheels can you use aluminum wheel polish. If you use this polish on chrome, painted, or clear coated wheels, you will only scratch or dull the finish.
  • Do not use steam cleaner in an automatic car wash.
  • Do not use any tire cleaners on your wheels.
  • Clean wheels when they are cool. Heat can affect the soap, causing it to dry on the wheel and become difficult to rinse off.
  • Clean one wheel at a time. This also prevents the soap from drying on to the wheel.
  • After the wheels are clean and dry, apply a coat of soft paste style wax to them. This will create a moisture barrier and help ensure the finish lasts as long as possible.

Before you fit your wheels, give them several coats of good quality car polish back and front. This will help prevent the road salt, brake dust and dirt 'keying' to the surface on first use. Be sure to treat the surface of your alloys as well, if not better, than you would your paintwork. Remember, you've spent a small fortune of your alloys and they're going to be subject to the harshest conditions of just about any part of the car!

Frequent washing with mildly soapy warm water [having hosed all the loose abrasive grit off first] is the best way to keep wheels clean. Never use abrasive cleansers, electric buffers or wire wool pads on your wheels. Where possible let your wheels cool thoroughly before cleaning them and avoid car-wash wheel-cleaners at all times.