Why Add Custom Wheels to a Car
A set of custom wheels can add to a car’s appearance and improve handling and performance. They may be necessary in order to fit wider tires as well. This may be a positive addition if the owner chooses wisely, but it could also be a mistake if the choice is based on appearance alone.
Realizing that the original automotive designers were balancing cost, appearance and performance, it can be understood that the final result was a compromise. That can be improved upon by focusing on performance, for example, but there will be an increase in cost. There is an old “hot rodding” saying, “Speed costs money, how fast do you want to go?”
The appearance of a car with new custom wheels is a matter of taste. There are wheels available in countless designs and each design is available in various diameters and widths. The “Old School” wheels of fifty years ago were an attempt to mimic cast or forged magnesium wheels found on racing cars. Magnesium wheels were impractical for street use due to their great expense and propensity to corrosion. They were also brittle and prone to cracking when impacting a pot hole. The term “mag wheel” was applied to the cast aluminum wheels of the day, some of which were full aluminum castings while others had cast aluminum centers with steel rims riveted to them. They were offered with the exposed surfaces “as cast” or chrome plated.
In the case of both the magnesium racing wheel or the street aluminum wheel, the wheels were lighter and offered better heat dissipation, improving handling and brake heat reduction. Although the aluminum wheel was a better choice for street applications it still required more care than the standard steel wheel from Detroit.
Castings, aluminum or magnesium, have an issue withporosity. The nature of a casting is such that, after the molten metal is injected into the die and it begins to cool it “out-gases”. That part of the molten metal that contacts the die surface cools first and forms a surface “skin”, but below the skin exist voids caused by the trapped gases. There are various methods of casting aluminum intended to limit these voids but some voids are simply unavoidable. When the casting is machined some of the voids may be exposed. Some smaller, almost microscopic voids almost certainly will exist, and these will result in a slow air leak when assembled with a tire and pressurized. Most manufacturers “vacuum impregnate” cast wheels with an epoxy or other material to fill the voids and prevent leaks. Forged wheels, while more expensive, are stronger and not prone to porosity causing leaks.
With the vast number of custom wheel designs on the market the customer should consider the vehicle’s use. If the car will be a “daily driver” he may want to consider a less intricate design. Brake dust is a common detractor from a custom wheel. Disc brakes will generate brake dust and it will collect in the pours of a rough cast surface finish and be very difficult to remove. A smooth or chromed surface is much easier to keep brake dust free and a less intricate design makes cleaning easier.
The relationship of the wheel mounting surface, the surface that contacts the brake disc or brake drum, has an important relationship with the wheel centerline. This determines where the tire will be located relative to the vehicle suspension and inner fender panels and is referred to as the “offset”.Many custom wheels can be ordered with a non-standard offset. This can accommodate a wider wheel, preventing it from interfering with suspension or body panels. The owner would be well advised to ensure there is sufficient clearance at the maximum suspension travel. Some manufacturers offer wheel spacers rather than various wheel offsets.
Suspension design is a subject for another time but the suspension is affected by the tire/wheel combination. Suffice it to say that the suspension was designed so the weight of the vehicle was on the approximate center of the tire contact patch and the load evenly spread over the wheel bearings. Front end alignment, caster and camber, adjusts the load point on the front tires to improve handling and cornering control. If the owner is attempting to increase tire width and uses increased offset to accommodate the tire he can negatively impact handling. He may also overload one of the wheel bearings and will certainly suffer unusual tire wear. Prudence is the key when adding tire width.
With the addition of extremely wide tires, such as in “drag racing cars”, the suspension and body panels are modified to accommodate the tire. Consider that this is a very specific application and not something to live with on a daily basis.
There are companies that have performed test mounting of custom wheels and tires on various cars. They can be found with a simple internet search and can recommend a tested custom combination for most cars. A good looking set of wheels and a car that handles as good, or even better than the original, will be well worth the expense. So, how fast do you want to go?
