The internet is awash with people using a spritz or two of brake cleaner or starter fluid to bang set a bead on a tire. As you can see above, there’s a right way and a wrong way.
Getting a tire to mount right on a rim can be a challenge. Hell, I spent a week trying to mount my first tubeless mountain bike tires a few months back and found a lot of the same tips and tricks being used there as you find in the four-wheeled off road and stance car scenes.
The central problem is you want a tire to press right on up to the inside lip of the rim and kind of lock in place. Tires have a kind of raised edge right at the inside lip, and rims have a raised edge, too, on the inside of their outer edge. As you inflate the tire, its bead pushes out to the edge of the rim and forms its airtight seal. This is called “setting the bead,” and usually it’s a pretty easy job both on a bike or a car tire. Pumping up the tire with air is usually enough to set the bead on anything ordinary, and if it’s tough, slightly overfilling the tire with air will get you the pop ... pop ... ping! of the bead seating. Amazingly, I dug up some fantastically low-res images on government websites that I am free to use to illustrate my point.
Here you can see a fueleconomy.gov diagram of a car tire, with its lipped bead:
And here is how that bead seats into a rim, as seen in a NHTSA cutaway:
Sometimes, though, a tough tire on a wide rim will not quite want to work its way to the bead. This is why you see people lubricating the bead with soapy water when mounting a tire.
It’s also why you see some people (particularly those in the off-roading world) use a ratchet strap to help set a bead. The idea in this case is to press the tire down and out towards the lip of the rim, doing some of the work for you before you start trying to blast air into the tire. Here’s an example:
And here’s a more low-tech example on a small tractor tire using a rope:
Both of these methods help you out if you don’t have a giant air compressor to get a huge blast of air in to really pop in a tricky bead. But what else gives you a big blast of air pressure? An explosion! This is the fundamental theory of using fire to set a bead. There really isn’t that much fuel needed to get even a pretty big tire to set its bead, as seen here on a Jeep:
You see the same technique in the world of stance cars fairly often, as people try and mount tires on wider and wider wheels. Even a pretty normal tire will need some help to stretch out and meet the lip of the rim. Here’s Hoonigan doing it with a strong “don’t try this at home” warning a few years back:
Car And Driver also has its own step-by-step guide to using fire to set a bead while out in the field, with similar intonations not to do this. As someone who grew up in California and had to live through many a smoke-filled summer from wildfires, I, too, would not encourage anyone to do this while in a dry field or pine forest they happen to be Jeep’ing through.
As you can see in the videos, not a ton of combustable fluid is at hand. Too much of an explosion and you risk not just inflating the tire enough to set the bead, but enough to blow out the tire altogether.
That’s exactly what happens in this video uploaded to Reddit’s terrifying What Could Go Wrong subreddit. The video itself is overflowing with wonderful Brazilian energy, and every word in Portuguese uttered is dripping with confidence, even as the guy dumps basically a full Mountain Dew’s worth of gas into this tractor tire:
I apologize that I can’t embed the video, as our CMS isn’t quite as friendly to my old hacks that would get anything in here. I do encourage you to click the link above and watch the video.
The best I can do otherwise is give you a frame-by-frame.
Let us first enjoy the optimism presented here. What could go wrong, indeed!
A key element of this process is to slap the tire first, patting it as you would a horse.
Here we can see a truly large volume of combustable liquid going into the tire. How much liquid? Too much.
The guys hook up air to the tire — fire might set the bead, but this air is meant to keep it set and filled with air. Our hero in the blue jeans is making a safety trail of fluid that could have been longer, honestly. A few hundred feet would have been comfortable for me.
Our second and only other safety measure is to use a lit rag on a stick to set things off. Ear protection? Nah. Eye protection? Nah. Rag on a stick! You’re good, bud.
Here, for just a moment, we see that this actually worked! The bead, as you can see in this frame, is set. Look at how snug that giant tire is to the bead. Perfection.
And just one frame later, our failure is more than present. The explosion of the tire blowing out is enough to distort reality. Our protagonist has turned wiggly. I would not want to be an ear drum anywhere near this.
Here, also, is a good view of the tire itself blowing out. You can have too much of a good thing.
And here is our aftermath. The bead is not set, the tire is on fire, and the windows on the tractor are trash. We have now entered into a new calculus of wondering — would it have taken less time to set this bead using a non-explosive method than it will take now to fix the broken glass on this John Deere? We may never know.