What is the ‘wet line’, and how do we find it?

People often say that the reason there is less grip on the racing line in wet conditions is due to a build-up of rubber and oil. This is in fact a myth. In reality it’s the amount of physical wear the track has endured which makes the difference, with worn down, highly polished surfaces offering drivers less grip in the wet.

When asphalt is first laid down, there is a uniform roughness to the surface. Over the years, as many cars pass over the same piece of road, the sharp ridges and peaks in the road surface become worn down to a smooth surface.

If you look next time you are on track, you will see that the racing line has a noticeable shine caused by the constant abrasion of racing tyres. Off this line, it is the sharp ridges and peaks which yield greater grip in the wet.


This occurs because the two dominant forces affecting the performance of a tyre are adhesion and deformation. Adhesion is the chemical ‘stickiness’ between the tyre and the track, and deformation is the force which results from the rubber changing shape to fill in the gaps in the surface.

A wet surface prevents direct contact between the rubber and the surface, completely blocking the formation of the adhesive forces that work best on flat surfaces. Therefore, in the wet, a rough surface can generate far more grip by increasing the deformation of the tyre.

You can certainly feel the extra grip off line, but does the extra distance travelled negate the higher cornering force? The only way to tell is through trial and error, and this is where a predictive lap-timer becomes an essential part of the process. However, the lap comparison has to be based on GPS position rather than distance travelled, otherwise the results are meaningless.

A predictive lap timer displays the difference between your current lap-time and your previous best, in real time, at any point on the track. A positive number means you are going slower, and a negative number means you are going quicker.

OLED-Black with predictive laptiming

You get instant feedback on your technique, rather than having to wait until you complete a lap (or cross a split). As you approach a corner, simply glance at your current ‘delta’ and then check again once you have exited that corner. If the number has increased then you have gone slower, and if it has decreased, then you have gone faster.

Running with a predictive lap-timer for the first time is very enlightening, as you may make a small mistake in a corner and lose a couple of tenths, but due to a slightly slower exit speed, you can then watch the ‘delta’ climb upwards all along the following straight, eventually losing up to a whole second. It certainly makes you concentrate on your exit speeds!

This is an extract from our e-book on advanced circuit driving techniques. If you would like a copy of the full article, along with nine other chapters, please sign up here.

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