Why does the steering wheel get hard when i drive really fast?

What is your question?

Whenever i drive really fast or put the sports mode on while driving fast, the steering wheel gets realllyyyyyyy hard. i own a nissan tilda/latio from Singapore. It is a 2007 model. I live in St.Lucia. I love this car because it is really fun at high speeds but the steering wheel gets too hard and especially when i have to corner, i have to use both hands to turn the wheel in a little corner. It is really frustrating.