What is an Alloy Wheel?
Until recently, the wheels fitted by most manufacturers to their every-day cars have been "steel wheels" Steel wheels are more resilient to damage, and are considerably cheaper to fit. Unfortunately they are almost always heavier, less attractive and smaller in both diameter and width than alloy wheels.
The term alloy wheels is usually given to wheels 'cast' from a mixture of aluminum which is light weight and great at dissipating heat and small amounts of more rigid metals whose presence in the 'mix' provides rigidity and helps prevent cracks propagating. What are the benefits of fitting Alloy Wheels to your car?
In general, alloy wheels are lighter, more attractive, and better at dissipating brake heat that their steel counterparts. They tend to be available in standardised sizes which means competition amongst tyre vendors giving low prices and good availability!
Fitting alloy wheels normally reduces your car's unsprung weight - in layman's terms this means a reduction in rotating mass at the ends of your suspension components, giving you improved steering feel and greater braking response. What does Offset mean?
Offset is the distance between the hub mounting face at the back of the wheel and the wheel's centreline.
Offset is usually stamped or engraved into the wheel and is measured in millimetres of 'ET' [ET is the short form of the German word 'Einpresstiefe' which literally translates as 'insertion depth']
Positive Offset wheels have their mounting face toward the front face of the wheel. Most front wheel drive vehicles have positive ET wheels. Eighties and Nineties Volkswagen wheels are usually ET38.
Zero Offset wheels have their mounting face even with the centerline of the wheel and are by definition "ET 0".
Negative Offset wheels have their mounting face toward the rear of the wheel - powerful rear-wheel drive cars often have wheels with negative offset. What does PCD mean?
PCD stands for 'pitch circle diametre' and is the diametre of a circle drawn through the centre of your wheel's bolt holes. P.C.D. is measured in millimeters and also indicates the number of studs or bolts the wheel will have. Volkswagen Alloy Wheels are usually either 4x100 [i.e. 4 bolt holes drilled through the centre of an imaginary 100mm circle] or 5x100 [VR6s, GTis and MK4s] What does Centrebore mean?
The 'centerbore' of an alloy wheel is the size of the hole at the back of the wheel which the 'hub' fits into. To help the wheels to seat properly this hole needs to be an exact match to the size of the hub.
Most modern wheels are what's called 'hub-centric' - this means that the hub which protrudes from your car [and mates with the equivalent sized hole at the back of your wheel] is 'load bearing'. All the studs or bolts do therefore is hold the wheel onto the hub!
If you have' lug-centric' wheels, the state of your studs or bolts is obviously more critical - be sure to replace these from time to time and always 3/4 tighten the wheels off the car to ensure they're centred. What does Plus-Sizing or Up-Stepping mean?
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 tyres to keep the overall rolling radius the same. Benefits
- Plus-Sizing will improve the handling of your car! - each step will reduce the proportion of flexible tyre 'sidewall' to rigid alloy. This will improve response, will help keep the tyre tread square to the road and will improve your car's 'feedback'. If done properly speedo and odometer accuracy will be retained and the car's sure to look better.. Disadvantages
- In the majority of situations, tyre inches are lighter than wheel inches. Plus-sizing can make your overall wheel/tyre package heavier. Reducing the profile of your tyres will also reduce your car's damping deflection under compression [the ride quality will get worse] Other disadvantages can include you needing more expensive tyres, your brakes looking puny and people's grannies laughing and calling your car a pram. Alloy Wheel Care
As anybody who's stepped into a motor factors in the last 10 years will tell you, there's a huge variety of specialist wheel cleaners on the market, all designed to help make the job of cleaning your new rims that little bit easier, unfortunately the real key to a great finish is hard work.
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.
Source - matey-matey