The Dark Side lies: it does not have cookies.
Here at RideApart we like to try to keep you abreast of all the latest trends, for good or for ill, and friends, I am here to tell you that this one is not that new, but it is, in my opinion, an ill one. Do or do not, but in this case, I'm going to tell you: do not.
A few years ago when a friend of mine got wind that I had access to a pneumatic tire machine, he asked if I would help him out by spooning a new tire onto the rear wheel of his Honda VTX. Sure, I said. I am nice like that.
So he brings the disembodied wheel to my old shop with its smoothed-out rubber and in the other hand he has a … a car tire. Friends, I can tell you this through my shame: I did it. I put a car tire on a motorcycle. Worse, someone else’s motorcycle.
This is what’s referred to as “Dark Siding”: that is, mounting a car tire on the rear wheel of a motorcycle.
The good news is, the swap (once I got that used-up stiff-as-hell heavy-bike cruiser tire off there) went really easy. Do you know why it’s so easy to mount car tires? That’s the bad news.
Car tire sidewalls have zero integrity. None. And that means they’re super easy to mount—you can toss them on the rim and get the first bead on by hand, almost just by looking at it funny. But when I ran the machine around the second bead and pulled it out of the clamps and put it on the floor before inflating it and seating the beads, that tire was flat. When a car tire goes flat (most of you drive cars, and you’ve gotten a flat tire in said car, and you’ve seen it), the rim is on the ground in seconds. When that happens while you’re driving your car's thumpa-thumpa-thumpa noise is bothersome, and if you keep driving you will ruin your car’s rim.
When a tubeless-applicable street-biased motorcycle tire loses all its air, you can sometimes limp that squishy, sickeningly ill-handling thing to the next safe pullout. Because you’re not completely out of rubber, and while there’s no air helping that tire stay inflated, it’s still stiff. It’s not safe, and it’s not predictable, but it’s THERE.
I am here to tell you that you get to make your own life choices. I will say that I’m not going to go on about how when I have followed a Dark Sided motorcycle through the twisties and saw daylight underneath the flat part of the tread when the bike leaned over, it gave me the wibblies and made me back way, way off. I am not going to expound upon the absolute calamity that would be a flat car tire on a motorcycle. Neither will I say that you’re not only taking your and your erstwhile passenger’s life in your hands, but that of everyone behind you. You’ve mounted a run-flat on your bike, you say? Magnificent. I will still tell you that I don’t want to ride near you. Don't "at" me.