Crash Course in ABS

[bonox]

I thought that they could detect the onset of lock up through the rate of deceleration of the wheel, so did not let them lock. Is this nit the case?

that is the case, depending on the system. Newer 4th and 5th gen systems (mostly on cars) sense the onset of a lock by looking at rates of change of wheel speed - i've mentioned this before, but the computer is built around the capabilities of the vehicle - move a long way outside those boundaries (eg much better tyres) and you won't get a better stopping distance because the computer hasn't been updated to reflect the new capability.

Early versions only looked for a locked wheel - newer ones don't. Don't confuse that however with a new system locking a wheel - if you get a huge rate of change of wheel speed, the wheel may still lock for a fraction of a second - eg coming off smooth asphalt onto a wet steel manhole cover under hard brakes for example.