How a kart’s setup be changed by replacing an old tyre with a new one

INTRODUCTION

All types of motorsport have this dilemma, including karting, of course: what should be done with the setup when you switch from having four used tyres to fit four new tyres? Can the setup remain the same or do you need to make changes?
Having doubts is founded, because it is not always said that a kart with used tyres will be well-balanced once it has been fitted with new tyres, thus risking not being able to fully exploit the extra grip ensured by the latter.

1 PERFORMANCE

You do not need to be a professional driver to notice the difference in performance when you switch from used tyres to new ones: even amateur drivers with little experience feel the greater grip around bends, the fact of being able to accelerate before leaving bends without slippage of the rear tyres and, more generally, the perception that the vehicle is easier to drive.
In support of these "sensations", if you have an accelerometer mounted on the kart, just make an XY chart called a G-G diagram to easily compare the level of longitudinal and lateral accelerations obtained on one lap.

Every single point of the graph represents an instant of the lap: it is clear that with new tyres (green dots) you can achieve greater lateral acceleration, on both bend directions

2 BALANCING

Changing from used tyres to new tyres can change the balance of the kart and, consequently, it may be necessary to change the setup. By "balancing" we mean the relationship between how much grip is generated on the front axle compared to the rear: if the front prevails it means that the kart has a lot of grip at the front and will tend to suffer from oversteering; on the contrary, understeering will instead be the problem.
The particular construction of tyres, their mix and the way in which they are used can lead to a change in this balance as the wear increases: foreseeing and anticipating this change allows obtaining a setup that is always able to exploit the vehicle to its limit.

With balance excessively displaced towards the rear, the kart can find it difficult to follow the desired trajectory.

With excessive balance at the front, the kart has too much grip at the front, the rear cannot keep up with it and this results in oversteering.

3 WHEN MODIFICATIONS SHOULD BE MADE

“Foresee and anticipate", we said. Without doubt, however, the question is not simple and only a a high level of experience can result in knowing what changes you need to make to the kart in advance. The answers change according to the manufacturer and the type of tyres, as well as the condition of the track. Precisely for these reasons, our initial advice is to not change anything for the first few times after new tyres have been fitted. In fact, this is the only way to understand whether or not, in addition to the highest level of grip, the vehicle is behaving differently. Once this is understood, the next time you will be able to know the problems and anticipate them by making the necessary changes to the setup.

HOW A KART’S SETUP BE CHANGED BY REPLACING AN OLD TYRE WITH A NEW ONE