To elaborate on my comment; obviously generated braking force is defined by how hard you push the braking pedal. The required force to lock the wheels (given that ABS is disabled) depends on how much traction the tyre has. Let's say our tyre has a constant friction coefficient of 1. That's a simplified situation where the tyre has as much traction force, as there is force on the tyre by the vehicle's weight.
This allows you to decelerate(or accelerate) with a maximum of 1G or 9.81m/s2, before your tyres start slipping. That means that you'd get to a stop in 2.83s when travelling 100km/h. You can see from this figure, that most supersports cars are limited in their 0-100 time by the tyres. They use as wide tyres as they can on the driven wheels, to maximise traction. Heating up the tyres and lowering their pressure, and a slick surface on dry hot asphalt further increases their traction. But it doesn't allow you to accelerate to 2G or something.(except for crazy top fuel dragsters) But that's why i'm rather sceptical about Tesla's promised 0-100 figures for the announced roadster.
In reality, a friction coefficient is not close to constant and way more complex. In reality, your tyres are always slipping, which is the main reason they wear out. It gets worse in corners, acceleration, braking etc. but it's always present in a certain amount.
Also, traction sharply decreases once the wheel starts slipping by a certain amount. I believe that was usually 20% or something. You only have kinetic friction at that point, which is always lower than static friction. That's the reason ABS works, it constantly regains static friction by releasing the brakes briefly. I hope this gives you an better understanding of how and why tyres work.