If you drive in modern traffic, I guarantee no one will give you enough space to stop with a 4 wheel drum set up. And even if you leave that much room to the next car, someone will put 2 cars in it before you can back off more.
this. and it can't be emphasized enough, is the truth.
unless you live out in BFE or only tootle to get ice cream on sunday mornings drums aren't going to cut it in the city with normal modern traffic.
i drive my D300 pretty regularly in traffic and despite it being a ginormous orange truck with a flat bed people still look at me, make eye contact and then proceed to pull out directly in front of me without the slightest comprehension or thought that i need room to stop.
and it's even worse with an old car because there's no "intimidation factor" of a big *** truck bearing down on them.