The size and width of these tyres will determine how the car handles in different conditions and typically provides the optimum overall performance. A wide tyre, by comparison, is a tyre that exceeds the original tyre.
Reasons for switching from narrow tyres to wide tyres – if the car's specifications allow for it – can range from performance enhancements to aesthetic appearance. Because the contact area is more substantial, for example, wide tyres can grip and accelerate on dry surfaces much better than narrow ones. They're also great for specific applications like winter driving conditions.
These modifications are road-legal so long as the driver is aware of the changes in handling to their car, for example, when it comes to cornering and braking, and they don't exceed the safety guidelines recommended by either the vehicle or tyre manufacturer. The documentation that comes with your vehicle will further specify the widest tyres you can fit to the rim without impairing safety or performance.
For comparison, you can identify your car's stock size on the tyre sidewall, under the fuel cap, or on the pillar of the driver's door. In a sequence of markings like 225/50 R 17 98 H, for example, the first three numbers "225" represent the section width, in millimetres, of the tyre from one sidewall to the other.