Explain The Reason That Why Big Tyres Are Used In...

 wide rear wheels than the front is for the reasons of traction and the ‘look’. When a rear-wheel-drive car has a lot of power, it can cause wheelspin easily which is why wider rear tyres can give better traction.
However, wide tyres tend to follow grooves and ridges in the road more easily (‘tramlining’), they require more steering effort, create more rolling resistance (effort required to start them turning and to keep them turning) and make it more difficult to get good suspension performance through them being heavier. much extra grip when turning.

Simply , a kingpin offset is a part, basically called as pivot used in
 steering of the vehicles. This offset helps in rotating of the steering.