I’d say that 100% of the 10 or so tire punctures that I’ve suffered in my life as a driver were all the result of a nail or screw. I can’t figure out how a nail lying on the ground can somehow be at the correct angle to get through a tire. Can anyone help me visualize how?
Also, when most of us see broken glass on the road we avoid it. But I can’t recall ever experiencing a puncture from broken glass. Am I just lucky? With glass, I would think that the car’s weight would crush it before it could go deep enough to cause a puncture. Has anyone gotten a flat from just glass?
Ever step on a rake? Probably the same principle. The head of the nail/screw is usually pretty wide, so it probably gets levered somewhat vertical by the tire and then penetrates.
It may also just be a physical manifestation of the sheer perversity of inanimate objects, although that’s venturing more into metaphysics than actual physics.
I didn’t read PastTense’s link and it probably says the same thing, but the short answer is that that your front wheel tire it up and it sticks in your back tire.
How many of the “10 or so” have been in your front tire, probably very few or none.
This. I’ve had several flats on car and motorcycle, and most of them have been on the rear tire(s). The one front flat I can recall, it was a tack that was just barely long enough to penetrate to the inside of the tire, and had a head wide enough to ensure that was probably sitting pointy-end-up in the road when I ran over it.
One rear-tire flat was from a nut pick (at right in photo). Clearly there was no way this was going to stand up on its own; it must have been set to tumbling by my front wheel running over it.
I’m gonna go with that perversity of inanimate objects thing. Way back when I used to work at a shop that did tires, we’d see all sorts of weird stuff stuck in tires. Even stuff that you really wouldn’t think could cause a flat like twigs or plastic pens. It’s just a matter of hitting at the right angle.
I suspect that while nails and screws are definitely the #1 threat to tires, they’re somewhat over-represented because they almost always stay in the tire. My recollection is that you’d have a screw or nail still in the tire maybe 50-60% of the time, but the rest of the time you’d just have an unexplained hole or cut. I think a shard of glass hitting your tire at just the right angle could probably cause a flat, but the shard definitely wouldn’t still be in the tire when you got to the shop. I suspect that’s the case with a whole range of road debris.
One thing with the “front wheel kicks it up” school of thought is that on tires with more aggressive tread designs, it’s very possible for the tire to grab a piece of debris and fling it in front of the tire to get run over on the next go around. Or just get stuck in the tread and move around until it gets enough purchase to make a hole. FWIW, with flats I’ve personally had I’ve never noticed any front vs. rear bias. I don’t doubt that rear flats are somewhat more common, though.
And don’t forget, all bets are off if you roll over a spot where a car accident happened. Then you have A)lots of strange things and B)things propped up on other things.
A few years ago one of our work trucks got a flat and the tire guys pulled a door handle out of the tire.
A couple of months after that, my dad pulled a rusty chunk of leaf spring out of his tire. Though I don’t think that was related to an accident. I’m sure it just fell off an old truck and he rolled over it.
My last flat was caused by a fairly large tube like a piece of a bike rack that was jammed through the outer sidewall of the the front, driver’s side tire like a spear. I still can’t figure that one out. I was going about 80 mph on an interstate highway in the far left lane when it happened so there had to be some weird physics involved.
All my punctures were caused by large headed nails that look like tacks. I’m assuming the nails without heads that punctured my tires were those placed there by jealousy.
I had a fork go through my tire, tines end first. The handle was sticking out, but I couldn’t pull it out because the tines somehow get bent at 45 degree angles inside the tire. I still cannot imagine how that happened!
I also had a nail go through a bicycle tire, in one sidewall and out the other, straight across.
Broken glass is a common cause of punctures for city cyclists. It doesn’t usually give you a puncture immediately, though. What happens is that you run over the glass, and a little shard gets embedded in the rubber. Then it gradually works its way deeper and deeper into the tyre, until it pokes right through and hits the tube. (In fact even if you don’t have a puncture, if you ride a lot on the street and check your tyres you will probably find little bits of glass in there - it pays to pull them out with tweezers if you spot them, before they dig right in.)
Often by the time it causes a flat the glass is totally invisible from the outside of the tyre, so it pays to check before putting the new tube in, otherwise the same thing happens.
For obvious reasons, checking by running your finger round the inside of the tyre, while effective, is not without its problems. So it’s wise to always mount the tyre with some identifiable mark (eg the manufacturer’s logo, or the start of the writing) lined up with the valve hole of the tube. That way, when you find the hole, you can line it up with the tyre and easily find the little piece of glass. Trying to dig it out is another matter, of course…
I worked in a shop that did tires as well, and sometimes I saw rusty nails. I suspect sometimes people drive over old, mostly rotten boards with nails sticking up, and the board gets crushed, but the nail sticks, and then gets driven further and further in as the person drives.
I once saw a Champion spark plug that had punctured a motorcycle tire and caused a wreck that totalled the bike. The insulator was still stuck in the tire; the electrode end was long gone. Champion’s motorcycle plugs used to be pretty bad, so we kidded that we finally found a good use for one.
The impact happens pretty quick. It seems that there has to be some mechanism where the tire pushes down on the head end of the nail and flips the nail up where it is driven into the tire.