Question

The steering wheel of a vehicle is of large diameter

Answer 1

Hi-------
we know that torque is analogous of force
torque =radical part x force
now suppose we have constant force then if we increase radius then it give more torque.
i.e. for less force we can be produced more torque to increase distance or radius.
so we use steering wheel's diameter is large.
same phenomenon is also be use in open the door.
when we apply force (push) on door near the joints then we need more force to open it.
hope it help

Answer 2

It is easier to turn the steering wheel of a large diameter than that of a small diameter because less force is applied on the steering of large diameter which is at a large distance from the centre of the rim.