converted, I think that book you read is focussed heavily on open wheelers. The aero argument is all but irelevant for tin tops, especially those with 70's aerodynamics.

first thing to point out is that there are two types of grip and people get confused jumbling it all up into one thing. There is straight line traction, and then there is lateral cornering grip. And there are different physics at work in each. to explain that simply, putting more weight over a tyre that's trying to get straight line traction will increase its grip on the road, but adding weight to a tyre that's trying to produce lateral grip will reduce your cornering speed. A given tyre can generate only a certain amount of lateral force. The force acting against it is a combination of the mass and speed of the vehicle on it. increase the mass on it, and you reduce the speed that brings you to its maximum force. the small increase in lateral grip you get from pushing it harder against the road isn't enough to make up for that effect.

Weight transfer is king in straight line traction and the enemy to cornering grip.

when you go from a stock 155r12 (or whatever it is) say to a 205/60*13, the contact patch of the tyre changes shape, from a fairly long, narrow oval to a very short, wide oval shape - you've probably almost taken the first contact patch and turned it 90 degrees. The total size/area of the contact patch doesn't change significantly. The change in contact patch changes the way it interacts with the road and the amount of cornering force it can generate. Put simply, the tyre will generate its best grip in a direction iin line with its wide part of the contact patch.

The heavier the car, or the faster you want to go around corners, the wider the tyres should be. The only limitations to this rule in the real world are the restrictions of the available space in the gaurd, or the rules in the racing category - eg restricting rim width, rules govering flares etc. Open wheelers have the areo tradeoff to contend with, but the main limitation in most cases is the rules again.