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Many think that driving in the rain is simply about bravery or an added sensitivity with the inputs. While those two aspects will benefit a driver dealing with a wet track, it’s just as important to adjust the suspension and, if possible, the engine, to get a car that is more predictable and less edgy towards the limit. Since the limit is so much lower, one must transfer weight less dramatically, and the car is generally softened in the suspension department.
The first things one must consider are the tires and the spring rates. Intermediate tires work well for semi-wet or damp conditions, whereas the fully-grooved tires must be brought in for monsoon races. Generally speaking, fresher tires with a harder shoulder allow the tires to cut through the water and give a more incisive steering feel. Springs and swaybars should be softened as much as necessary, since the limit is lower and the window between sliding and spinning is narrowed somewhat. The softer swaybars will allow for body roll, but since cornering speeds are slower, there isn’t too much of a hindrance here. In fact, if a chassis is stiff enough, the swaybars can be disconnected completely.
Softer springs are extremely effective since the added bump and rebound will make a more compliant platform. As the springs are softer, the rear and front are allowed to squat more, and place more weight, theoretically, on the chosen axle. It’s important to remember that for cars dependent on aerodynamics, like formula cars and prototypes, their springs cannot be too soft since the aero platform must remain stable to benefit from that downforce. On that note, wings should be turned up all the way - to hell with drag. Downforce, grip, and tire temperature generation from this are much more important than reduced top speed, though it does depend on which circuit the cars are running.
Additionally, the roll laterally from softened swaybars will help give the driver a sense of an impending slide since there’s a “buildup,” a moment at which the car’s lean transitions into either understeer or oversteer. This gives a driver a little more time to react, and with highly-strung racing cars, this is a must. With big power, an engine in the middle (which is often, but not necessarily, the case), and a responsive engine, it’s quite easily to turn a minor slide into a spin. However, too soft a setup can result in roll-oversteer, where the inside wheel loses contact with the surface of the road.
The brake bias can be shifted more to the rear. Since grip levels are reduced, the ability of the front brakes is diminished; they won’t accept the same braking forces as they would in the dry. This means the rear brakes will take more of the braking burden, but too much rear-bias is a real mistake, since locking the rears in the rain almost inevitably results in a spin. As always, finding the happy medium is the goal.
For engine mapping, a more progressive power delivery is ideal, even at the expense of some top-end power at times. It’s always tough putting the power from a powerful engine down cleanly in the dry, let alone in the wet, so sometimes limiting torque at low revs is a good way to keep forward momentum without much wheelspin.
The final alteration to make is in regards to camber. Because the grip is reduced, the car won’t force itself onto the outside tires as hard as it rounds a corner. Negative camber is designed to counteract this leaning by having the tires cantered out slightly while the car is in a static state. Then, when cornering, the tire leans over, so that when fully leaned over, the tire will be sitting upright and offering the largest contact patch.
However, since the grip levels are lower, the tire won’t lean as much, and therefore the negative camber has to be reduced so that the tires are almost upright in a static state. This means better turn-in ability as well, and a larger contact patch more of the time.
These tweaks will offer a car that is faster, more predictable and less tiring in the rain. Since racing in the best of conditions is stressful enough, hopefully these suggestions will prevent a few gray hairs and a bent racing car.
