Just bought one of those three magnet antenna mounts.....

[KB9BPF]

I strongly recommend that you add some sort of rope or strap as insurance that the antenna will not fly off.

Even if it doesn't injure or kill the people in the car following you, there will be a big cleaning job to be done after they soil themselves when the antenna comes off. 

[K1CJS]

At most, with the magnets moved inward a bit, you will lose a little of the stability and holding strength of the assembly.  All that means is that it will take less effort to make the magnet contact fail--but it shouldn't affect that too badly.  I would also use some sort of lanyard assembly on the thing to make sure that if magnetic contact were to be broken for any reason, the assembly wouldn't make someone following you ooze brown!   

[W8JX]

I strongly recommend that you add some sort of rope or strap as insurance that the antenna will not fly off.

I used a mag mount on the roof or a suburban for many years when traveling cross country a lot with ham stick and never lost one. The few time I upset it and laid it back on roof was when I forgot about it and drove under a low clearance object.

I have yet to see documentation and proof of the first "flying magnet mount" striking another car or person that some seem to worry about.

[KB9BPF]

'An ounce of prevention is worth a pound of cure', as the old saying goes.

Small VHF/UHF antennas on mag mounts? I'm OK with using them untethered. Big ones like hamsticks? I recommend a little cheap, foolproof insurance in the form a a piece of rope.

I've had VHF/UHF antennas on mag mounts come off due to birds flying into them while I was going 65 MPH. Fortunately the coax held it from coming completely away from the vehicle. A bigger antenna may 'part the line' as the Navy guys would say.

I have enough drama and stress in my life. If something as simple, cheap, and effective as a piece of rope can ensure one less window for Murphy to sneak in, I think it's worth the effort.

73
Brad KB9BPF

[KD5TXX]

I use a single 5" magnet and hamsticks and the only time I ever had one fall was when I go through a bank or drivethru that is to short.  I drive about 50k a year.  Easy answerer if you like the mount is...buy a new car;)

[KZ1X]

Interesting thread from another web site:

http://www.stormtrack.org/forum/archive/index.php/t-3664.html