One of the most obvious upgrades you can make to your car is to change the wheels. Larger, wider, lighter, or just a sportier design, the combination of upgraded alloys with lowered suspension can often do far more to make an otherwise standard car look muscular and athletic than anything else. We’re sometimes asked which “body kit” a car has, when in fact only the wheels and suspension have been changed – the visual effect of these changes can be that dramatic. Why is this? And what are the other advantages of upgrading your wheels?
We’re all familiar with wheels of different diameter – 18″, 19″ and so on. Larger diameter wheels can look more impressive, but they can also be heavier, which can affect the suspension and steering response, and they can be less comfortable – more on that later.
The width of the wheel is expressed as “J” – 8J means 8″ (measured just inside the rim where the bead of the tyre sits). BMW M series cars have wider wheel arches to accommodate wider wheels and tyres.
A measurement which sometimes causes confusion is wheel offset. Offset is the distance from the centre line of the wheel to the mounting face i.e. the wheel hub. This is often stamped on the wheel as ET, followed by this distance in mm e.g. ET45. A larger number like ET55 means that the wheel rim will be more tucked inside the bodywork and will run closer to the suspension components. A smaller number like ET25 means that the wheel rim will stick out further and run closer to the wheel arch. High offset wheels tend to look flat-faced. Low offset wheels look more concave or dished.
Of course, every car model has a unique body shape – we’ve already mentioned the wider arches on M cars. To give the optimum fitment on each wheel AC Schnitzer use either a centering ring or a hubcentric adaptor, also known as a “spacer”.
The effect of the adaptor is to move the wheel further out, so away from the suspension components and nearer to the wheel arch. This effectively reduces the offset of the wheel by moving the centre line of the wheel nearer to the mounting surface. So an ET43 wheel with a 10mm adaptor is effectively ET33, even though the shape of the wheel itself has not changed.
You’ll notice that the adaptor is not simply a flat disc, it has a “nose” in the centre for the wheel to locate on and ensure it is perfectly centred when mounted. To accommodate this nose and give the optimum offset, most AC Schnitzer wheels have a centre bore of 82mm.
The aim of adjusting the fitment this way is to give an attractive look, close to the wheel arch, but no so close that the tyres rub, and also to give the best handling characteristics from the slightly wider track. In some cases we’ll even recommend specific tyres to give the best result possible. This attention to detail, combined with lower suspension, is what gives cars the AC Schnitzer look or “stance”.
When you buy a wheel set or wheel/tyre set from AC Schnitzer we will supply the wheels with the correct adaptors for your car. The fitment has already been checked to make sure they will fit perfectly, without any issues, whether you have AC Schnitzer suspension or not.
The standard construction for light alloy wheels is by casting. Essentially this means pouring molten metal into a mould and letting it cool. The metal “blank” is then machined to finalise the shape before the cosmetic finish is applied. For most wheels we offer a choice of bi-colour (very dark gloss metallic grey with polished edges to the spokes and rim) or anthracite (dark metallic grey all over with a matt finish).
For some SUVs we offer split-rim wheels. Due to the large diameter of SUV wheels, it sometimes makes sense to use different materials for the rim and the spokes and then bolt the sections together. These wheels look very dynamic and come in sizes up to 23″.
For high performance cars we also offered forged wheels. The forging process uses high pressure as well as temperature to form the metal blank. This aligns the crystalline structure of the molten metal more closely while it cools, resulting in a stronger, denser alloy. This inherent strength means that more of the metal can be machined away, making the finished product lighter than a comparable cast wheel. A cast Type VIII wheel of 19″ x 8.5J is 13kg, the forged version is just 8.2kg, even though it looks similar.
Why does this matter? The wheel/tyre combination carries a lot of rotational inertia. The heaver it is, the more force is required to accelerate it, turn it and stop it. Lighter wheels accelerate faster and turn quicker. In addition, suspension and braking response is improved due to the reduced weight on the end of the suspension arm. Due to the extra processes involved in making forged wheels, they usually cost at least twice the price of an equivalent cast wheel.
Safety never takes a day off at AC Schnitzer! All genuine AC Schnitzer wheels are tested and TUV certificated, for your specific vehicle, for the safety of you and others. This means that not only are the production standards high, but also the size, offset and load rating is also correct for your specific vehicle. Cheap “replica” wheels are often not tested to any safety standard – don’t risk it! Buy genuine AC Schnitzer wheels from an authorised dealer.