As others have alluded to, the coax tends to limit the maximum travel of a magnetic base should it break loose, so any actual damage is likely to be limited to your own vehicle unless there is a lot of free and unsecured coax that would allow the antenna and base to travel a significant distance. In practice they do not typically come loose if properly installed and an adequate magnetic base is chosen for a given sized antenna and vehicle mount location. And if they do come loose, the coax nearly always keeps the antenna closely associated with your vehicle (up to and including the opportunity to reattach elsewhere) so long as there are no long lengths of unsecured coax (so try to limit your unsecured coax lengths). If one were to totally separate (if somehow even the coax detached) the real danger would not so much be to the driver behind you (aside from their possible loss of control due to unexpected surprise) as the antenna and following driver are likely moving at similar velocities along the same vector (its time on your vehicle imparted the forward momentum), so any impact is much more likely to be frightening to the other driver than it is to inflict major damage. What would be genuinely terrifying in this unlikely case (with coax detaching entirely) is if the antenna struck an oncoming vehicle as then the forward momentum your vehicle imparted on the antenna/base will be added to the forward velocity of the oncoming driver! However, even if such penetrates the windshield it will not impart its full force onto the other driver/passenger as considerable energy would have been consumed in the act of penetrating the windshield (windshields are rather tough), but that does not mean that there is not a chance of serious injury -- and that is excluding the chance of serious injury if the shock and surprise causes the other driver to lose control of their vehicle.
Years ago, I had a CB antenna with a magnetic base. I was driving in a rain storm that turned to sleet. Ice built up on the roof, and the antenna slid off. The cable saved the antenna. 73 Mitchell W3XE
I had a antenna one time that came loose when I was going 55 on a two lane and a semi going the other direction blew it off, scared the heck out of me she it hit the window... most antennas have better magnets than that one though.
I had one come off on the highway many years ago. That was the last mag mount I ever owned. I've drilled holes w/nmo mounts ever since.
I applied carbon fiber sheet on the roof of my car as the 1st layer for protect the car paint, and attached adhesive to the bottom of my Mag mount then.
I had a mag mount , a large base big magnet mag mount come loose swung down and busted out the back window in my van at 60 miles an hour, scared the hell out of me and the window was 60 bucks as well to buy, be careful.
Yep, I had one come off the back of my Z-28 whilst zipping down the freeway one night. Nice shower of sparks from the antenna being dragged behind the car by it's coax.
I would worry less about that little antenna than a high gain one that's 7 ft tall on a triple magmount, blowing off.
+1 on the Radio Shack CB antennas getting bumped by tree limbs. Now I use a Wilson, but it sometimes gets a slow speed hit by tree limbs. Never comes off at highway speeds on the roof of a full size SUV though. I have used many types of magnet mount antennas and all of them I buy, have had strong enough magnets to make me worry more about scratching paint or getting them off, than them falling off at speed.
I've dumped a half dozen magmount antennas over the years. It is almost always due to wind. At our interstate speed limit of 80mph, into a 60-70 mph head wind, most magnets just give up. From large CB style down to little cell booster whips. The most I've lost on one day was three. And on 10-31-03, I got in a nasty wreck. One of those triple magnet units with a hamstick came shooting off. The magnets stayed on the truck but everything else flew off. The coax broke as well. I was walking around after getting released from the hospital a few days later and found the contraption in a ditch. I kept what was left as a conversation piece. Ever since then I drill everything that isn't a rental vehicle.
