"Could anyone explain the reason as to why kart tyres work differently?? Am i missing something obvious? My initial suspicion is that it is something to do with kart tyres being significantly smaller than most others"
As a karter who designed tyre/suspension sytems for Lotus told me:
The difference is to do with the relative thickness of tread and sidewall between road and race tyres. In a racing tyre, the dry tread and sidewall is much thinner than in an equivalent road car and the amount on energy retained by them or produced by hysteresis is much less than its road going equivalent.
The racing tyre is held in position and shape by the pressure inside it and the shape of the rim, in a road tyre the shape is determined by the shape of the tyre.
When a car has very flexible, low hystereis sidewalls the tyre is generally 'low profile', just to keep the tyre located above the rim and the tread is far thicker; kart (and F1) tyres are not low profile because their parameters for use are entirely different.
This also explains why the pressure strategy for wet and dry tyres is entirely different. In a wet racing tyre you have thicker tread and stiffer sidewalls to create the heat that cannot be put into the tyre by driving and have to strike a different balance between the mechanical grip of a stiff tyre and the chemical grip of heat'
HTH
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