Don't ever want to lock a front wheel. You will flip the bike. Eack bike handles differently. On my old Raleigh Grand Prix the rear would just start to lift as got close to lockup. My Trek is far different. The rear wheel will lift with only moderate braking on the front. On my recumbent I've never had to go to wheel lock but my guess is that locking the front will result in loss of stering, a skid and wreck. A rear wheel skid could be just as bad although possibly recoverable if you got off the brakes quick enough.

'bent Brian