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One of the first things you learn when racing in the rain is that the dry line is likely not the fastest/grippiest line in the wet. That's because the dry line tends to have a lot of rubber laid down on it and this rubber layer can be slick when wet. The dry line can also be polished smooth over time, whereas the less used part of the pavement tends to be more abrasive and porous, making for better grip in the wet. It's also important to be aware of the fact that paint and concrete tend to have a lot less grip when wet (because these surfaces are less porous), so it's best to avoid concrete patches or painted lines or curbs.
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| As you can see from the recommended wet line (right), the best approach is often to make the straights as long as possible and the corners as short as possible by going in extra deep and using a very late apex (source: speedsecrets.com). |
Every track is a little bit different in the rain because the age and condition of its asphalt varies and drainage tends to differ too. So it always takes some experimentation to find the grippiest/fastest line around a circuit in the wet, but as a general rule its best to “shorten” the turns and “lengthen” the straights by going in deeper, making a sharper but slower turn and then using a very late apex. And since water runs downhill, if a corner is banked you'll probably find more grip (less water) up high in the turn. Point being, use your eyes and your head and you'll find the driest and grippiest parts of the track to use when racing in the rain.
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| Given how quickly available grip decreases as the depth of the water increases (source: Michelin), seeking out those parts of the track with the least amount of water seems like common sense, but a lot of drivers fall in love with the dry racing line and have a hard time deviating from it. Don't be that guy (or gal). |
Now that you have an idea of how your tires will behave in the wet and how to find the best wet line, it's time to consider how your car behaves in the wet and how you as a driver can best control it. Traction changes in the wet, but not necessarily in a predictable way. Braking is not nearly as compromised as acceleration. This means the driver will find himself struggling more with controlling wheel spin coming out of corners than fighting brake lockup. It's also important to be conscious of the fact that lateral grip (cornering) is reduced more in the rain than longitudinal grip (braking and acceleration). The reasons for this include the shape of the contact patch and the direction of siping/grooving in the tire's tread as well as its compound, but other variables including tire temperature (which is harder to build in the wet, depending on the compound) and pavement that's been worn smooth in the corners also contribute. So even though you may feel like there's great grip under braking, don't be fooled into thinking the same amount of grip will be available in the turns or when jumping on the gas pedal.
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| As the above charts illustrate (source: Michelin), both road surface and and tire compound play important roles in determining how much traction you'll be able to find on a damp race track. Being conscious of these variables means you'll be less likely to be caught out if the rain starts to fall while you're on track. |
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| Banked ovals can have surprisingly good grip even in heavy rain due to good drainage! |
