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TKART magazine Track Test Tech | The caster: how to work on it
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test The caster: how to work on it

25 January 2016
This is a major parameter of front-end geometry and overall weight distribution on a kart. The caster is the tilt angle (front/back) of the kingpins (the bolts that the stub-axles pivot around). It regulates tire behavior through bends by raising the outside front wheel and lowering the inside front wheel. In turn, this causes more or less of a weight transfer to the front end and more or less of a load reduction on the rear inside wheel, sometimes great enough for it to lift off the ground.
test in points

Verify how the kart reacts on track depending on weather caster is positive or negative

Test 1: fully discharged (negative) caster, meaning: top eccentric shifted forward
Test 2: fully charged (positive) caster, meaning: top eccentric shifted backward

At the Adria Karting Raceway in Adria (RO), Italy alt

Well-kept even surface with good, but not excessive grip after a full race weekend. The test was performed using high-performance tires (specifically, Vega Whites)

26°C / 79°F
Getting down to details: as you steer to enter a corner, if caster is set high, the front outside wheel “unloads” (lifts) more and the front inside tire goes down lower, generating a braking effect (keep in mind that with Ackermann angles, steering has greater effect on the front inside than the front outside tire). So, the higher the caster, the greater the weight transfer to the front-end of the kart and thus the greater the vertical force that pushes down on the front inside tire, loading it to the ground. The result of all this is an increase in front-end grip.
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