short version.. it depends a lot on the car/chassis/suspension but as a rule if you go to a wider track on the rear of a fwd car it will promote understeer ,if you make the track wider on the front while leaving the rear as standard it can make the steering very pointy ie initial turn in will be sharper but again this is relevant to castor/camber angles .most of the above is relative to how severe a change you make to the track and how wide the wheels are above standard , also the profile of the tyres can make a large difference to the handling of a vehicle ,tyres are an integral component of the suspension ,too low a profile =harsher ride, and less sidewall deflection can induce oversteer or understeer depending on the chassis setup and tyre pressures..