What is an aero disc?

An aero disc is a rigid cover that fits over the face of a wheel you already own. It turns an open spoked wheel into a smooth or partly closed face. It is an accessory fitted to a wheel, not a wheel itself, and that single sentence clears up most of the confusion around them.

Two things the search results get wrong

They are not bicycle disc wheels. Search for an aero disc and half the results are triathlon and time trial wheels. On a bicycle, a disc wheel is a complete wheel built as a solid disc, and it exists for measurable aerodynamic reasons at racing speeds. On a car, an aero disc is a cover over a wheel you already have. Same words, unrelated products.

They are not all the same thing. The name covers a ninety dollar universal plastic cover that clips to the rim, and a made-to-fit composite disc that fastens through the wheel, and everything between. The price range in this category is more than twenty to one, and what separates them is not the idea, it is how they mount and how well they fit.

What they actually do

A wheel is a hole in the side of a moving car with a fan in it. Covering the face reduces the turbulence coming off the spokes. That is a real effect, and it is why land speed cars, endurance cars and a lot of electric cars run smooth wheel faces from the factory.

On a road car at everyday speeds the fuel saving is small enough that you will not notice it at the pump, and anyone promising otherwise is selling. We wrote the honest version of that answer separately. Buy aero discs because you want the car to look like that. The aerodynamics is a true footnote, not a reason.

How they mount, which is the part that matters

There are three approaches, and the difference is the whole product.

• Clipped to the rim. Cheapest, and the one most likely to move. A thin panel spinning at speed with air pressure changing across its face works at whatever is holding it.
• Trapped under the lug nuts. Common on universal sets. It puts a part between the wheel and the hardware that holds the wheel on, which is worth thinking about carefully.
• Fastened through the wheel on a spacer. More parts and more cost, and the disc is mechanically held rather than gripped. This is what we do, and it is the safety argument more than the aesthetic one.

Do you need new wheels?

This is the question most people are actually asking, and the answer depends entirely on the maker.

Some aero discs are designed around one manufacturer's wheel and are sold with it or for it. If you like the look and you own something else, that route means buying wheels first. Others mount through a bolt-pattern spacer and fit what is already on the car. Ours are the second kind, which is the reason we exist. There is alonger comparison if you are weighing one against the other.

Are they universal?

Not honestly, no. Anything that covers a wheel has to match a diameter and a bolt pattern, and a part you have to modify to fit a rotating wheel is a part to think twice about. What is achievable is a disc made per diameter that mounts through a spacer covering the common patterns.

For reference, ours are made in 18, 19, 20, 21, 22 inch and the spacer covers 5x112, 5x114.3, 5x120, which is most of what is on the road. We publish every car we have checked, 44 models across 13 makes, including the one we tested and refused.

What they are called

Aero disc, aerodisc, aero disk, aero wheel cover, wheel disc. Same object. If you go back far enough it is a moon disc, the spun aluminium cover run on dry lake cars in the 1950s, and the idea has barely changed since. The rally cars of the 1980s ran a vented version called a turbofan for brake cooling, which is a different job done by a similar looking part. We wrote aboutwhere the shape came from if you want the long version.

What they cost

A universal plastic set is around ninety dollars and it will give you the silhouette. Made-to-fit composite discs run from a few hundred dollars to well over a thousand a set. Ours start at $499 a pair, and what the money buys over the cheap set isrigidity, mounting and fitment rather than an exotic material. Ours are a carbon composite with a carbon fibre look, and we say so plainly rather than letting you assume the weave is structural.

Is one right for your car?

If it is a daily you are not attached to and you want the look cheaply, buy the plastic set. If it is a car you have already spent money on, or you want it finished to match something specific, that is what a made-to-fit disc is for. Either way, check the diameter and the bolt pattern before you spend anything. You can check yours against ours in about thirty seconds, or send us the car and we will confirm it by hand.