FROM SUN TO RAIN
What if the weather suddenly turns from sunny to wet? We asked Energy Corse specialists Marco Sigalini and Simone Sorio, who had to deal with this at the Le Mans KZ World Championship
The main objective of all adjustments made for a wet track is to gain as much grip as possible – the rest comes later, or as a consequence.
Yet, exactly what you need to do to “get in gear” for the rain depends on whether your kart is gearbox or not.
If you drive a shifter, what you want is more wheel drive in order to use all the horsepower you can, so you’ll work mainly on the rear end; if you drive a non-shifter, you’ll be looking to get more overall grip, so set-up changes will be evenly divided between front and rear.
Of course, some drivers prefer to keep their set-up unaltered from dry to wet, if they feel it is well-balanced.
In dry conditions, the chassis is usually set as low as the rules allow. When the track gets wet, you need to increase ride height, to shift the overall weight of teh kart higher up off teh ground. In fact, the higher up the center of mass, the more the load tire digs into the ground and so the better corner-through grip. We could state the basic rule as: “when wet, go as high as possible”. You also want to shift the spacers that separate the stub axles from the Cs past the stubs.
The other element to work on is body position when driving. Besides, trying to gain bite by shifting his body weight towards the load tire, the driver can add a pillow to his seat to raise his own center of mass and thus contribute to raising the kart’s overall center of mass. Of course, it all depends on personal preference. Some people feel uneasy driving with a pillow.
CAMBER & CASTER
The camber is the angle of incidence of the tire tread relative to the pavement. On a dry track, you normally set camber on the negative end, going for extreme settings if there is excessive grip. In fact, the tighter the camber, the less tread on the pavement and so the “freer” the chassis.
When the track gets wet, the opposite applies: set the camber close to 0 or even at real positive settings. By “real” we mean adjusted to account for driver weight, which entails a 1 or 2 degree variation on the baseline setting of kart alone. So, to get a real 0 camber angle, start from an “under by 4 or 5 mm” setting.
Caster can be defined as the wheel alignment angle that conditions the tilt and height of your front tires through corners. In wet conditions, it needs to be positive to determines an increase in front tire load and so enhanced corner entry. Normally, the difference between dry and wet is of 1 or 2 degrees. Yet, this guideline should be adjusted to the specific track you’re on. On many tracks, there is a 10 second variation in average lap time from dry to wet conditions: in this case, you’ll need a smaller caster increase.
According to CIK-FIA regulations, rear-end track width can’t exceed the width of the bumper. So, considering that rain tires and rims are narrower, in the rain you need to widen out (140 cm).
There are no limitations for front-end width and the average rule is giving it an extra 5 or 6 centimeters overall to give the kart more stability and enhance corner-entry.
Another thing to consider is that tracks with more rubber get more slippery.
When it comes to brake force distribution, we usually privilege the front end of the kart, because it’s with the front brakes that you can pull brake-off sprints “at the limit”. Percentage-wise, this means 70% up front and 30% rear.
Wet conditions call for greater balance between front and rear: you should aim for 50/50 or, if it’s really slippery, invert the ratio and give more force to the rear end. This helps keep the tires straighter when letting off the brakes and gives the kart more overall grip.
When it rains, setting the air box facing backwards and/or covering it helps keep the engine dry. Just remember, since this makes carburetion richer, you’ll have to compensate by prepping your carb with leaner settings, as we explain in the engine tips that follow.
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