Are you playing on realistic car performance? If so, different teams have different performing cars.
If not, try to brake later into the corners, and remember F1 cars don't lose grip if you brake hard and start to turn at the same time. My personal habits when I started playing F1 were from other racing games where the tires can't take as much force and you basically have to slow down to speed before the corner. After a while I realized you could brake late and be 100% on the brakes as you start in on the corner without it slipping. Apparently F1 tires can hold something like 7 lateral Gs.