Alloy Wheel Information
What are alloy wheels?
Alloy wheels are automobile (Car, Motorcycle and Truck) wheels which are made from an alloy of aluminum or magnesium. These days aluminum is the major component of Alloy Composition. Alloy Wheels generally refer to wheels other than steel wheels.
Alloy wheel also come as OEM Fitment in some car models, and can be installed in almost all Cars in the market as an aftermarket upgrade.
Why change wheels?
The standard issue wheels on most cars are at best a compromise to keep the costs lower and maintain differentiation among different trim types. Ability to change wheels offers an opportunity to upgrade your car performance and aesthetics as per your choice.
Why change to alloy wheels - Engineers view:
- Lower Unsprung Weight : Smoother Ride
Alloy wheels are generally lighter for same size steel wheels while offering more structural strength. Lighter wheels improve handling by reducing unsprung mass, allowing suspension to follow the terrain more closely and thus improve grip.
In a vehicle with a suspension (Which means all cars and bikes), the unsprung weight (or the unsprung mass) is the mass of the suspension, wheels and other components directly connected to them, rather than supported by the suspension.
The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tyre compression, which induces a force on the unsprung weight. The unsprung weight then responds to this force with movement of its own. The amount of movement, for short bumps, is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip and more constant grip when tracking over an imperfect road.
For this reason, lighter wheels are sought especially for high-performance applications. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality and road noise are deteriorated. For longer bumps that the wheels follow, greater unsprung mass causes more energy to be absorbed by the wheels and makes the ride worse.
- Thermal Conductivity:
Aluminum Alloy used for wheels has superior thermal conductivity. (>150 watts per kelvin per meter) than Steel (45 watts per kelvin per meter). Better heat conduction helps dissipate heat from the brakes, which improves braking performance in more demanding driving conditions and reduces the chance of brake failure due to overheating. , It also reduces brake fading and helps prolong the tyre life.
- Corrosion Resistance:
Alloy wheels offer better corrosion resistance, do not rust internally like steel wheels and thus last the life of a vehicle.
- Structural Rigidity:
Alloy Wheels are stronger than Steel Wheels and resist deformations. This aspect makes them more suitable for modern tubeless tyres where bead seat retains its shape.
Why change to alloy wheels - Designers view:
- Improved Vehicle Aesthetics
Having designer Alloy Wheels is single significant upgrade that can enhance the look of a car and extend it a personality of its own. A normal stock car can look classy or modern with the appropriate alloy wheels.
- Wheel Upsizing and Lower profile Tyres:
Changing to a new set of bigger wheels allows to go for lower profile tyres which are definitely better looking than thicker OEM tyres that come as a standard fitment.
Do standard tyres fit on alloy wheels?
Yes, there is no requirement of special tyres to install alloy wheels. Standard tyres both Tubeless or Tube type fitted in the car or generally available in the market are perfectly compatible with the wheels.
How to Select Alloys Wheels for you Car?
- Alloy Wheel Diameter
A quick and easy way to find out the size of your wheel is to check the radius (R) of your tyre e.g. 205/45R15 tyre would indicate you have R15 = 15 inch tyre on your car. As a result of your tyre size, the diameter of your alloy wheel will be 15" also.
- Alloy Wheel Width
Your Car specifications shall mention width of the wheel, ie 14X5.5 , where 5.5 is the width of the wheel in inches.
On every alloy wheel the size will be stamped into the alloy wheel, this stamp can be on the outside but is usually stamped on the inside of the alloy wheel on the back of the spokes. For example, the stamp may read 15 x 7, 7 x 15, 15x7JJ etc. Every car is different, some cars have more space to fit larger alloy wheels than others. Most cars can take up to 17" alloy wheels without any problems and some cars can take up to 20" without any problems.
- Wheel PCD - Pitch Circle Diameter
The number of bolts used to install an alloy wheel varies from 3 to 8 studs depending on the car brand and car model. The pitch is the diameter of the circle that intersects the stud center. To fix alloy wheels correctly the same number of studs and the same pitch / PCD should be available.
- Wheel Offset
The wheel offset of a vehicle's wheel is the distance between the centerline of the wheel and the plane of the hub-mounting surface of the wheel. It can thus be either positive or negative, and is typically measured in millimeters. Offset has a significant effect on many elements of a vehicle's Suspension, including Suspension Geometry, clearance between the tyre and suspension elements, the scrub radius of the steering system, and visually, the width of the wheel faces relative to the car's bodywork.
Zero Offset - The plane of the hub mounting surface is even with the centerline of the wheel.
Positive Offset - The plane of the hub mounting surface is shifted from the centerline toward the front or outside of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
Negative Offset - The plane of the hub mounting surface is toward the back or brake side of the wheel's centerline.
"Deep dish" wheels typically have negative offset or a very low positive offset.
To maintain handling characteristics and avoid undue loads on bushings and ball joints, the car manufacturer's original offset should be maintained when choosing new wheels unless there are overriding clearance issues. Wheels are usually stamped with their offset using the German prefix "ET", meaning "Einpresstiefe" or, literally, "insertion depth". An example would be "ET45" for a 45mm offset.
How to Calculate the wheel offset?
First, measure the overall width of the wheel (remember, just because a wheel is 18x7.5, does not mean that the OVERALL width is 7.5". It means that the measurement between the outboard flange and the inboard flange is 7.5"). Next, divide that width of the wheel by two; this will give you the centerline of the wheel. Overall width/2 = Centerline.
After determining the centerline, measure from the hub-mounting surface of the hub to the edge of the inboard flange (if the wheel were laying flat on the ground - face up - your measurement would be from the ground to the hub-mounting surface). This is your back spacing. Back spacing - Centerline = Offset.
How to find wheel offset on an alloy wheel?
Stamped into the back of every alloy wheel will be the wheel offset. This is normally displayed as a number or a number with ET before it, e.g.: ET42, ET35, ET 3|8 below you can see some
pictures from different alloy wheels on how the alloy wheel offset is printed: