Rain racing

Wet racing events are a unique experience, particularly for the unskilled and inexperienced. As such, it can be surprising, fun or, frightening. What's the difference? Obviously, water decrease grip levels. The tires must be treaded so that they could drain the water. This reduces the amount of rubber on the ground, and gives the tire an extra toll. At 60mph, the average road tire drains one gallon of water per second, all in the area of the contact patch alone! 

However, with the right tire, grip levels on a wet track or road are not drastically reduced. The serious problem begins when water mixes with other chemical agents. Soaked dirt turns into highly slippery mud, oil, diesel and rubber marks from tires -- all contributes to a further reduction in grip levels. Depth of water also changes the equasion. Banked pieces of tarmac can turn into little pools of water and foliage that are very slippery.

The way around this problem is based on driving style rather than mechanical car setup. The idea is to look for the grippiest parts of pavement. Those pieces are normally treated as where no one has driven before the rain, but it is in fact much more complex: Slopes tend to drain water away from certain positions on the track, while making other sides of it flooded. Also, the most common place for dust and even oil is the sides of the track, to where cars are skidding and on which "marbles" of dirt from the shoulders lay.

The rain line is normally sharper and tighter. First, we brake slightly earlier and deeper into the turn, and wait for a relativelly late stage to turn the wheel. Not the average late APEX, but a still-later one. At the right moment, we turn the wheel decisivelly into the turn and than let the car turn by it's own, while trailing off of the brakes. Also, as we turn-in, APEX and Track-out, we would not be using the whole width of the track, because the built-in banking of the track surface will cause water drainage to the sides of the track.

Things to beware of:

1. Glimmering surfaces: As you look up, scan the road surface ahead for anything shiny. This would indicate oil or diesel, which decreases grip levels. Beware of them and adjust your line to avoid them where possible and/or beneficial. If you must drive over a relativelly slippery part of road, try to adjust your line so that you drive over it with a minimum of steering input, at a reasonable speed and as close as possible to a constant speed.

2. New pavement or concrete are normaly more slippery, though not quite as the former. They often requires changes in line and pace.

3. Standing water and streams should be avoided where possible. They can result in hydroplaning, which creates the most dramatic reduction of grip, only comparable to glare ice or skidpad enthol. 

4. First rain: The more dry and hot the road surface is, the more slippery it turns when soaked in water. Even on a dry track, dew can absorb oil and dust and create little points that are almost as slick as first rain. Whenever it rains after 4 days of dry weather, it is a first rain. First rains are also a psychological hazards because drivers take time to readjust themselves to the conditions.

The second problem: Visibility

Visibility in the rain is reduced. Check the glass of the windscreen, side windows, rear window and helmet, and even use special materials that can be scraped over the glasses from the inside (and some from the outside) to avoid the fogging of the visor. Most airconditioned cars have the ability to defume the front windscreen, and sometimes the side windows and the mirrors. Use these options. Combine them with cold air intake from external circulation and a partially open window.  For fog on your helmet-visor, breath downwards.

The greatest hazard: Hydroplaning

Hydroplaning is when a car exceeds it's ability to drain the water on the surface. The result is for the car to skim somewhat over the water, reducing grip levels to about 0.1 as slippery as glare ice, on normal tires! The feeling is that the car's progress and acceleration are somewhat hindered and engine RPM increases. The wheel feels very light.

During hydroplaning, any sudden movement will jerk the car into a nearly irrecoverable skid. The normal course of action is thus to gently-gently reduce throttle input to a minimum, without lifting-off. If ineffecient, ease off of the pedal completly. If this is inefficient, reapply slightly. If this is inefficient, or if the car skids, declutch. In the latter case a steering correction will also be required.

If you get oversteer and you try to use the throttle to renew rear grip, you are bound to either overpower the rear wheels of a rear-wheel drive car (making the situation worst) or spin the front wheels of a FWD to a level where no forward acceleration or weight transfer takes place. The line between too little and too much is more thin as grip levels are reduced, so we simply bang down on the clutch. This gives us natural tire rolling action that helps reduce the slip angles (no tractive forces working on the tire), a bit of acceleration during oversteer or a bit of deceleration during power understeer or even power oversteer.

A note on setup

Besides changing tire type, other changes can also make a car more fit for rain racing. A car on the rain tends to slip less and roll less. Hence, making the car generally softer, and maybe readjusting it's camber are helpful.

Coefficients of Friction

I have compiled the grip levels on various road surfaces:

• Dry Pavement: 0.89-0.75. Ranges between high quality tarmac and racetracks and main roads, to bumpy, cracked tarmac, concrete, or white/scrubbed tarmac.
• Wet Pavement: 0.60-0.50. Depending on water depth and the type and smoothness of the soaked road surface.
• Dirt, Grass; Gravel, Mold, Rocks: 0.58-0.42. Gravel, mold and rocks are less grippy, but a wheel sliding over gravel or loose dirt, tends to dig into them, hence slowing down and regaining grip. With gravel, it also finds a grippier layer beneath.
• "First Rain:" 0.38-0.32. A small rain shower after at least three days of dry weather and some traffic. This causes dirt, oils, rubber left-overs and acrilic colors, to float over the water, making it seriously slick. Even when the water dries out, the foliage can remain.
• Diesel, Petrol, oil, brake fluid, fresh tar: 0.30-0.20. These are all defined as oils, but these are rather sticky, giving better grip that most people think. They tend to become quite more slick when they absorb moist.
• Mud: 0.30-0.25. Mud and animal feaces are to be aware of when driving on rural roads.
• Partial frost/Hail: 0.60
• Advanced frost: 0.53
• Full frost: 0.39
• Fresh Snow: 0.36. Grippy tarmac beneath can help make slides more recoverable, like with loose dirt.
• Packed snow: 0.35. Chance of frost or ice beneath the snow.
• Snow and ice: 0.32
• "Black ice": 0.30. Small, thin layers of frost that are penetrated by sun rays.
• Bright/wet ice: 0.24
• Motor/gearbox/differential oils: 0.19
• Glare ice: 0.19. Ice at the temperature range that offers minimal water buildup untop of the ice.
• Skidpad surface: 0.12. A surface made of a chemical agent (enthol) resembling icy condtions or hydroplaning.
• Hydroplaning: 0.15-0.9.