7 tricks for... reducing understeer

1 INTRO

First of all we need to define what understeer is. This term (often abbreviated “US”) is used to refer, substantially, to the loss of cohesion of the front of the kart with respect to the rear, with the kart’s consequent inability to maintain its trajectory. From the driver’s point of view, it’s easy to see you’re suffering from understeer when you’re forced to turn the wheel excessively. Fundamentally, understeer (just like oversteer) can have different causes: driving style and kart set-up. Let’s see how to resolve this problem which, when manifestly present, compromises performance, tyre wear, but above all, the enjoyment of driving.

Understeer implies the loss of cohesion of the front of the kart, with the consequent difficulty of maintaining the kart’s trajectory.

2 SET-UP

As previously mentioned, a first cause of understeer can be linked to vehicle mechanics, whether because of the kart’s set-up, or because of the state of wear of the front tyres. In these cases the kart changes trajectory and the driver has to turn the wheel significantly when entering a turn or, after a precise entrance, has to do so to maintain the desired trajectory. To better analyse the phenomenon, it’s necessary to determine at what stage in the turn understeer occurs, because the “cure” to apply can vary depending on exactly this parameter.

The stages into which a turn can be subdivided

3 SET-UP - ENTERING THE TURN

The “symptom” of understeer that appears at this point is a difficulty bringing the kart into the turn. The remedies can be: increasing front-track width; opening the toe out; reducing rear-track width by a few mm. If you increase front-track width, what you actually obtain is greater grip potential for the front axle throughout this stage of the turn, thanks to the reduction of vertical load transfer on that same axle. Opening the toe out, on the other hand, is a typical modification done to improve directional control and, therefore, the entrance stage of the turn. But you have to be careful not to exaggerate, to avoid excessive tyre wear in the straightaway and also a slight speed loss. The entity of the modifications needs to be on the order of one mm each time. Reducing rear-track width, finally, has the purpose of reducing rear axle potential, particularly between entering the turn and the middle of the turn. Conceptually, it’s as if you were working more on the idea of worsening grip in the rear rather than improving it in the front. By contrast, you need to consider that a narrower track width in the rear could generate more understeer when exiting the turn, given that the rear is more solid and tends to give the kart greater “push.”

Increase front-track width

Open the toe out

Reduce rear-track width, one mm at a time

4 SET-UP - MIDDLE OF THE TURN/EXITING THE TURN

Symptom: the kart enters the turn but struggles to maintain the clipping point. Remedies: increasing front-track width, increasing caster, attaching the front torsion bar. The first two operations have the effect of generating a better rotation of the kart, with the rear inside wheel lifting up more easily. The bar, on the other hand, particularly if placed near the chassis’ “C” attachment, helps increase front precision, so, in these cases, it’s opportune to attach it. Even moving your seat back slightly helps avoid oversaturating the front axle, because the front tyres have to generate less force given the reduced mass pressing down on the axle. Our suggestion, at any rate, is always to try one modification at a time, in order to better evaluate the effect of each individual intervention.

Increase front-track width

Increase caster

Attach front torsion bar

Move seat back slightly

7 TRICKS FOR... REDUCING UNDERSTEER