Right, time for an essay.
'Handling' is a bit of a loose term, but in the case of tyre selection it could embrace a number of things: the ultimate longitudinal and lateral force generating capacity along with slip characteristics which will determine your tractive abilities, how the tyres transmit ride characteristics to the vehicle, it could also imply the type and quality of feedback at the steering wheel.
Smaller rim, larger profile vs larger rim, smaller profile:
In maintaining the overall size of the wheel/tyre combo, you could choose a smaller rim with a larger profile tyre, or a larger rim with a smaller profile tyre.
The larger rim selection would mean that the contact patch would be shorter than a wheel with a larger profile
(but they would be of the same width).
This has several implications, not least minimised tractive capabilities through the reduced contact patch, but also, the pneumatic trail that is generated when the tyre is rolling will act with a smaller lever arm on the steering system, therefore degrading steering feedback.
Smaller rim, larger profile vs larger rim, smaller profile, wider:
Allowing the larger rim to have the same contact area as the larger profile tyres would mean having wider tyres.
Now there is no tractive advantage/disadvantage, but the steering feel is still degraded compared to the longer thiner contact patch of the small rim/large profile combo.
In terms of the suspension options and handling, there is a fundamental issue involved in our obsession with aftermarket sus systems
- firstly, with cars that are possibly 20 odd years old, there is the issue of wear, so the sus may well need renewing anyway, but the other point is that if you make the sus stiffer, then you will prevent or reduce weight transfer.
Weight transfer effectively limits how much lateral force the tyre will be able to take.
The more weight there is on one tyre, the less lateral force it will be able to generate.
Even if the weight is transfered off the inner wheel during cornering, the benefit found there will not compensate for that lost by the more laden outer wheel.
The more load transfered, the more the total lateral force generation at an axle will suffer.
The less load transfer there is, the better grip there will be available to corner.
In terms of camber, you can automatically generate some lateral force by tilting the tyre on it side.
In general, cars in static positions are set up with some amount of negative camber
(ie top of the tyres
= a shorter distance than bottom of tyres across an axle pair).
This generates a lateral force acting towards the centreline of the vehicle.
When cornering, the outside wheel will provide more force given the extra load on the wheel, which will point towards the centre of the vehicle.
In cornering the centrifugal force needs to balanced, and it will act from the centreline towards the outer tyre.
Having negative camber automatically helps to balance this force.
(The inner tyre will obviously produce a force in the
'wrong' direction here, but given the reduced weight over that tyre, the advantage of the negative camber remains).
i will have a good read through it later when its not 7am.