Why is new asphalt slippery?

Freshly laid asphalt has a film of bitumen coating the surface of the stones and often has oils that have not yet worn away. Until traffic and weather wear that film off and rubber starts to build up, the tyres cannot key into the stone texture properly, so grip is lower and less predictable.

How often are race tracks resurfaced?

It varies with the climate, the amount of use and the quality of the original surface, but many circuits resurface every decade or two. Tracks may also resurface sooner to fix bumps, drainage problems or grip issues, or as part of a wider redesign.

What Are Race Tracks Made Of? Asphalt, Concrete, Grip & Resurfacing Explained

Q: What are race tracks made of?

Most race tracks are made of asphalt, a mixture of crushed stone aggregate bound together with bitumen, laid in several layers on a prepared foundation. Racing asphalt uses harder, more carefully selected stone and tighter smoothness standards than ordinary roads. Some American ovals, such as Dover and Bristol, use concrete instead.

From the grandstand, a race track looks like a very wide, very clean road. It isn't. The surface of a modern circuit is engineered to a standard most public roads never approach, from the stones in the mix to the smoothness of the finished surface. And it is one of the few parts of a circuit that changes measurably over a single race weekend.

This guide explains what race tracks are made of, how the surface creates grip, why brand-new tarmac can be treacherous, how rubber transforms a track as cars lap it, and what happens when a circuit is resurfaced.

The short answer: asphalt, mostly

Almost every road circuit in the world is surfaced with asphalt — also called asphalt concrete, or simply tarmac. It is a mixture of crushed stone, sand and filler, called aggregate, held together with bitumen, the dark, sticky binder refined from crude oil. By weight, a typical mix is around 95% aggregate and 5% bitumen.

The ingredients are the same as on public roads. What differs is how carefully they are chosen. Racing asphalt uses hard, angular stone that resists polishing, so it keeps its grip for longer. The bitumen is often modified with polymers to make it more resistant to the heat and stress of racing. And the surface is laid to tolerances of smoothness far tighter than any road authority would require, because a bump that a road car wouldn't notice can unsettle a racing car at 300 km/h.

The layers under a circuit

A race track is not a single layer of asphalt sitting on the ground. Like a well-built road, it is a layered structure, and each layer has a job.

At the bottom is the subgrade: the natural soil, compacted to provide a stable base. On top of it go one or more layers of crushed stone, the sub-base and base, which spread the load and provide drainage. Then come the asphalt layers: a binder course, which provides strength, and finally the wearing course — the surface the tyres actually touch, typically around four centimetres thick.

The quality of the layers underneath matters as much as the surface. A track that is built on poor foundations will develop bumps and cracks as the ground settles, no matter how well the top layer was laid. That is one reason the groundwork is such a large part of the cost of building a race track, and why the asphalt itself is often described as the cheap part.

How a surface creates grip

Grip comes from two kinds of texture in the surface.

Microtexture is the fine roughness of the individual stones — the sandpaper-like surface of each piece of aggregate. It is what the tyre's rubber grips onto at the smallest scale, and it matters most in the dry.

Macrotexture is the larger-scale roughness created by the gaps between the stones. It gives water somewhere to go, so the tyre can stay in contact with the stone rather than riding on a film of water. It matters most in the wet.

Different circuits have very different surfaces. Some are smooth and kind to tyres; others are rough and abrasive, wearing tyres quickly. Bahrain, for example, is known for a surface that is hard on tyres. Teams study each circuit's surface carefully, because it affects tyre choice, strategy and car setup.

Concrete tracks and other surfaces

Not every track is asphalt. Several American ovals use concrete. Dover and Bristol are surfaced with concrete, and Martinsville uses concrete in its corners, where the cars' heavy braking would quickly damage asphalt. Concrete is extremely durable and stands up well to the stress of steep banking and heavy braking, but it offers different grip from asphalt and can be harder on tyres.

Some older circuits that were built on airfields still have sections of the original runway concrete. Sebring in Florida is the classic example, and its bumpy, patchwork surface is part of its reputation. And of course, many forms of racing don't use a hard surface at all: dirt ovals, rallycross, and the gravel and snow of rallying.

Why new tarmac is slippery

A freshly laid surface sounds like it should be the perfect racing surface: smooth, clean and free of bumps. In practice, it can be treacherous.

New asphalt has a film of bitumen coating the stones, and often oils on the surface that haven't yet worn away. Until traffic and weather wear that film off, the tyres can't key into the stone texture properly, and grip is lower and less predictable. The 2020 Turkish Grand Prix became the defining example: Istanbul Park was resurfaced shortly before the race, and with cool temperatures and rain added to the fresh, oily surface, drivers described it as feeling like driving on ice.

The opposite can also be true. Once the surface has been cleaned and worn in, a new track can offer very high grip and very low tyre wear, because the surface is smooth and even. The problem is the period between those two states, and circuits often hold extra running or use cleaning techniques to bring a new surface up to speed before a major event.

Rubber, marbles, and track evolution

A track changes over a race weekend even if nobody touches the asphalt. Every lap, tyres leave a thin layer of rubber on the surface along the racing line, and that rubber increases grip. A circuit that is "green" at the start of the first practice session — dusty, unrubbered and slippery — can be several seconds a lap faster by qualifying. Engineers call this track evolution, and it is why the best lap times are almost always set at the end of a session.

Off the racing line, the opposite happens. Worn rubber collects in small balls, called marbles, that act like ball bearings under the tyres. That is why drivers who move off the line to overtake or defend can lose grip so suddenly, and why the racing line becomes even more important as a race goes on.

Rain washes some of the rubber away, and wet rubber is itself slippery, so drivers often move off the usual line in wet conditions to find grip on the unrubbered surface. Painted lines and kerbs, which offer very little grip when wet, become hazards in the rain.

Drainage: the part nobody notices until it fails

A race track is built with a slight slope across its width, so water runs off rather than pooling. Drains at the edges carry it away. Get it wrong and standing water collects on the racing surface, creating aquaplaning risk and making the circuit unusable in heavy rain.

Silverstone learned this in 2018. The circuit had been resurfaced earlier that year, and in August the British MotoGP race was cancelled after heavy rain left standing water on the track and made it unsafe for the riders. The surface was relaid again the following year. It is one of the clearest examples of why drainage has to be designed into a surface from the beginning, not added later.

Resurfacing: when and why

Asphalt wears out. Heat, cold, rain and the constant stress of braking and cornering gradually degrade the surface, polishing the stones, opening cracks, and creating bumps. Most circuits resurface every decade or two, depending on the climate, how often the track is used and the quality of the original surface.

Resurfacing is a big decision. A new surface changes the character of a circuit: grip, tyre wear, bumps and even the racing line can all be different afterwards. Drivers often have strong opinions about old surfaces with character versus new surfaces with grip. Circuits usually resurface for safety, to fix drainage problems or bumps, or as part of a wider redesign of the layout.

How much asphalt does a race track need?

You can estimate this from just two numbers: the track's length and its width. Take a 5-kilometre circuit with a constant width of 12 metres, roughly a Grand Prix circuit at the FIA minimum width. Its racing surface covers 60,000 square metres. A wearing course four centimetres thick works out at about 2,400 cubic metres of asphalt, and at roughly 2.4 tonnes per cubic metre, that is nearly 6,000 tonnes — more than 250 truckloads, before you count the binder course underneath, the pit lane, the paddock or the run-off.

You can do the same calculation for any circuit, or for your own design. Open RaceTrackDesigner, trace a circuit or draw your own, and read its length from the analysis. Then use the measure tool to check its width, which is rarely constant — our guides to track length and track width explain the typical figures. Multiply the two and you have the area of asphalt the track needs, and a sense of just how much material sits under every lap.