本帖最後由 paul 於 2009-7-13 17:39 編輯
Alloy/Steel wheels
In general, alloy wheels differ from normal steel wheels because of their lighter weight, which improves the steering (gyro effect) and the speed (acceleration and braking) of the car. Alloy wheels are also better heat conductors than steel wheels, improving heat dissipation from the brakes, which reduces the chance of brake failure in more demanding driving conditions.
Alloy wheels are prone to galvanic corrosion if appropriate preventive measures are not taken, which can in turn cause the tires to leak air. Also, alloy wheels are more difficult to repair than steel wheels when bent,
For passenger vehicles, alloy wheels are not only for improved driving performance, they are also for cosmetic purposes. The alloy wheel itself is shiny and/or has an intricate design, so there is no need for paint or wheel covers. By contrast, steel wheels either have to be painted steel rims with a chromed wheel nut, or be hidden with plastic wheel covers.
Alloy wheels are more expensive to produce than standard steel wheels, and thus are not included as standard equipment on base models of many non-luxury vehicles, instead being marketed as optional add-ons or as part of a more expensive trim. However, alloy wheels have become considerably more common since the 2000s, now being offered on economy and subcompact cars, compared to a decade ago where alloy wheels were often not factory options on inexpensive vehicles. Alloy wheels have long been included as standard equipment on higher-priced luxury or sports cars, with larger-sized or "exclusive" alloy wheels being options.
A big advantage of alloy wheels is that balancing them is easy. The balancing weights are attached in the centre unlike steel wheels where they are attached at the edge of the rim. Thus wheel balance is not disturbed by tyre removal, etc.
There are different types of alloy wheels. Some are cast, which are the most commonly seen on the road, while others are forged. Forged wheels are lighter and stronger, yet much more expensive than cast alloy wheels. Forged wheels are typically purchased by enthusiasts, luxury/sport vehicle owners.
Most aftermarket wheels are cast, while only a few above are forged, such as DONZ forged, Vellano, and Weld. Many companies have been formed over the years (some recently) due to the increasing demand from street racing enthusiasts and the rising demand for larger diameter wheels.
Cast aftermarket wheels have also been oversaturated due to the vast influx of inexpensive chrome wheels from China and India.
Magnesium alloy wheels, or "mag wheels", are sometimes used on racing cars, in place of heavier steel or aluminum wheels, for better performance. The wheels are produced by one-step hot forging from a magnesium alloy known as ZK60, AZ31 or AZ91 (MA14 in Russia).
The mass of a typical magnesium automotive wheel is about 5–9 kg (depending on size), Magnesium wheels are flammable and have been banned in some forms of motorsport in the UK following fires which are very difficult to extinguish. Mag wheels have been known to catch fire in competition use after a punctured tire has allowed prolonged scraping of the wheel on the road surface. Some variants of Magnesium alloy wheels may have low corrosion resistance.
They have the disadvantages of being rather expensive and not practical for most street vehicles. Aluminium wheels are often mistakenly called "mag wheels". |
