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Comment by lqet | Hacker News Reader

Pneumatic tires are one of these things for which "reality has a surprising amount of detail" holds. Anyone who ever changed a standard tire on a bike can attest to that. There is so much going on: wires inside the tire for stability, cloth to withstand the air pressure (which the tube cannot), beads to interlock with the rim flanges to keep the tire in place (but only when pressurized), etc.

I have witnessed bike tires where the bead/flange interlock wasn't perfect, and the inner tube was quickly swelling out between a small gap between rim and and bead until it burst with a bang that was louder than a gunshot. I once had a tire where the inner cloth was slightly damaged, and the tube was slowly creating a bulge in the tire over several days until it also burst. I found it amazing that all these counteracting forces still create something you can safely drive on, often for years, without problems.

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Modern bike wheels and tires are also moving in an interesting direction: carbon rims are increasingly made 'hookless' (straight flange without the 'hook' which locks the tire bead) because it's easier to manufacture, lighter and more aerodynamic, while tires are tubeless, which is also lighter and less prone to punctures, but then the tires are harder to manufacture and more expensive. And lower pressures must be used so the tire does not pop off the hookless rim, so the rims and tires are also getting wider to hold more air, where once 17mm inner rim width was common for road bikes, we are now getting up to 25mm.

Lower pressure is required with wider tires (stress in the tire casing is proportional to P*r). Which is good, because it turns out that lower pressure, when coupled with flexible tires, is actually lower resistance than high pressure.

Tubeless "just" allows for lower pressures without pinch flatting. The lower limit on pressure is to have enough to keep the bead seated, and not burping air. If you run lower than that, you've got to go tublar.

> Which is good, because it turns out that lower pressure, when coupled with flexible tires, is actually lower resistance than high pressure.

Yes, on rough (real world) road surfaces, rolling resistance is lower. (Ignoring aerodynamic drag of a larger tire profile.) On smooth surfaces like velodromes, skinny tires at stupid high pressures are faster. (I only bring this up because I race at a velodrome.)

The seal between wheel and tire in a tubeless tire is good enough to hold air for months to years. That's incredible, when you think about it.

For bicycle tires (at least), this is true I guess, but the sealant is going to degrade to the point where one may not be able to ride that bike that's been set up tubeless for a few years, without changing out the sealant.

Maybe in cars at 30 PSI. In bicycles at road pressures (60+ PSI), even with sealant you lose a few PSI every day.

Hookless rims are actually a pretty old technology. I had a beater 10-speed from the '70s with hookless ISO 630 aluminum rims. Then as now, they tend to run a lot tighter tires than hooked rims, and that bike, as are many newer ones with TLR rims, was kind of a bastard to change a tire on.

Source: Among other things, I work at a bike shop part-time and have volunteered as a bike mechanic in the past.

But these were with tubulars, yes?

On my beater? No. Hookless rims for clincher tires. No idea why, but common enough that the bike coop I got it at had a standard down charge for them.

Hookless for road bikes is a dead end manufacturing fad that only exists to increase manufacturers' margins. It does not provide any aerodynamic benefit. The weights are not substantially different. The low tire pressure maximums are not suited for road tires. The manufacturing cost savings are not passed on to consumers. Hookless might improve strength in a way that matters when tires are flat or otherwise bottom out (i.e., maybe useful for MTB, where the pressure maximums are not a concern). Hooked wheels are moving wider, too, of course. 21mm internal is now relatively common and you also see 22-24mm internal road wheels.

28mm is actually common. That's what I have on my brand-new Giant TCR (which is to say: an aggressive, go-fast road bike).

You are right 28mm is currently a common road tire width, but that's the total external tire width. What I mentioned rising from about 17 to (not yet common, but getting there) 25mm is the inner rim with - the narrowest measure between opposing rim flanges.

As a recovering bike mechanic of 20 years (my retirement goal is to be able to afford doing that job again, it’s joyful but hard to make a living) the writing has been on the wall for several years about the many benefits of wider tires (and rims too I suppose). From fewer puncture flats, to greater comfort and traction, to actually lower rolling resistance, I dknt see a move back to narrower tires being something that ever happens and I couldn’t be happier about that fact! I’m too slow and old to reap any performance benefits, but my comfort and enjoyment of wider tires makes me ride my bike more. https://www.renehersecycles.com/bq-tire-test-results/

Completely argee - I use 35mm tires on my 'road' (repurposed gravel) bike since ages because I just like it that way and never felt the need to go narrower.

C17 rims are considered very narrow in road cycling these days. It's been a few years since 17mm were new and upcoming. Campagnolo widened their Zonda wheelset to C17 in, easy to remember, 2017 and they were late.

The goal of performance oriented riders (for many, fixated might be the more accurate description) these days is to run the widest possible rim that will still hold their tire width of choice reasonably well. This has several reasons. One is that wind tunnel treats have repeatedly shown that there's an aerodynamic sweet spot where the rim is slightly wider than the tire, despite the increase in total frontal area for a given tire width (google "105 rule"), another is that riders want the suspension benefits of lower pressure but as little as possible of the downsides of the extra drag of wider tires, the extra mass of wider tires, increased danger of pinch flats and decreased lateral stability. Wider rims help with all those compromises.

The amount of energy in an inflated tire is surprising...

https://www.youtube.com/watch?v=1VLhLcJJefo

To be fair, truck tires are an entirely different level than most car tires. More air at much higher pressure. I did some research on what actually happens if you try to slash a tire. A car tire is only slightly risky, but a truck tire can flay your hand.

Please tell us more about your research.

What is the safest method to vandalize car tires?

Unscrew the inner valve stem and it's an annoyance that doesn't create permanent damage.

I suppose a more committed vandal could go on to do permanent damage after deflating the tires at reduced personal risk.

One of the more evil variations I've heard of involves pinning a bb or pebble between the cap and valve pin, creating a slow leak that's invisible until you think to take off the cap.

NASA has actually looked into this & found the ideal method for safely vandalizing tires https://www.thedrive.com/news/nasa-built-a-tire-assault-vehi... (it's an RC robot w/ a drill, for testing how space shuttle tires perform when damaged)

That's neat, but... at that point they must have considered just getting someone to shoot the tires with a gun at a safe distance?

maybe a small drill bit in the sidewall

And on the next level are tires of mining trucks, like that caterpillar 797 which can carry 300+ metric tons of rocks.

This is true for any compressible fluid. Work = -pressure * delta_volume. That amount of energy is why there are different standards for stress-testing something like a pipe, depending on the medium it's carrying. Occasionally you'll see an engineer or technician stress test a pipe carrying a compressible gas similar to one carrying a liquid. I can't remember the exact ASTM standards, but I think a compressed fluid should be tested to around 110% rated pressure and an incompressible fluid at 150%. If they use the wrong one on a compressible fluid, it's putting a lot more energy in the system. If it fails, it can be a bad day.

this is why people shouldn't pipe compressed air in PVC. PVC is rated for 300psi (iirc). However, it derates pretty quickly in cold temperature. If 150psi of air is pressurizing PVC pipe and it ruptures, its going to be a terrible day. Where if water pressurizes PVC pipe and it ruptures, its just a little messy.

there's a whole subreddit for that (and other misadventures): /r/tiresaretheenemy

Apparently z-nails are inexpensive but excellent caltrops against cars and boy-racers.

Ever seen Rubber?

Yup, pretty amazing. I had a bike that I rode a fair bit - same tires for 20 years. Back in the day, cars used to have flat tires pretty regularly - no longer - now some cars don't even come with the little donut wheels.

It is genuinely amazing how reliable tires have become.

> now some cars don't even come with the little donut wheels

Those cars come with “run flat” tires, which supposedly allow you to drive a few miles without damaging the wheel when the tire is flat. After which, instead of patching the tire, it must be discarded. Quite the advancement.

That was the case on some nicer cars when automakers stopped providing spares. But many cars today come with neither a spare nor run-flats. Many now are shipping with a normal tires, an inflator, sealant, and a roadside assistance telephone number.

Doesn’t seem like a bad trade off for not having to replace your rim, if the tire blows out and you’re unable to stop.

No they don't.

> I had a bike that I rode a fair bit - same tires for 20 years.

Impossible. A fair bit is 20km+ a day which is ~4000km/yr. That's in the order what an average tire is rated for (5-10Mm). Let's say you had tires 4 times as good, you still needed to change 5 times.

That's a lot of precision, considering "a fair bit" has approximately zero significant digits.

Removing the spare tire is not an advance.

Spare tires under normal operation are dead weight which is the costliest possible engineering compromise to make on a vehicle, as it decreases every performance characteristic: acceleration, deceleration, cornering, fuel economy, etc.

Their only reason for existing is to compensate for the historically poor observed reliability of tires. This has recently improved with TPMS mandates and better engineered tires.

AAA estimates 220 million flat tires annually in the US.[0]

The existence of spare tires has nothing to do with poor observed reliability. It is because of lack of 100% reliability. It's because when people get a flat, they don't want to be stuck and have to be towed. They want to be able to do something about it and get back on the road. All my flats have happened not because I lacked TPMS sensors but because something poked right through. Low tire pressure only accounts for 15% of flats. [1]

If you work for AAA, then sure, trying to convince people to get rid of their spares makes sense. But waiting around for AAA doesn't sound like a fun plan for me, especially when they won't be able to put a spare on for me, but will have to tow me somewhere.

[0]: https://cluballiance.aaa.com/public-affairs/press-release [1]: https://tiregrades.com/buying-guides/how-many-flat-tires-per...

> The existence of spare tires has nothing to do with poor observed reliability. It is because of lack of 100% reliability.

Do you carry a spare battery, or spare keys? Because AAA says those are also among their highest reasons for service calls.

> All my flats have happened not because I lacked TPMS sensors but because something poked right through.

Simple punctures in tread can usually be fixed with an inflator kit, or a plug kit.

Not having a spare is definitely a problem when you need it. But a spare is needed so rarely today. And that is a major, major advance.

One hundred years ago, a car with two spare tires were not that unusual--tires were sufficiently unreliable that you might not manage a trip without _two_ flats, but tires improved, and now the only long-overland back-country adventurers carry two.

A hundred years ago, spare tires were also carried in a somewhat more visible and easy to access location. I'm sure "symmetry" was a consideration in having two as well.

The movie clip of the Taiwan tire fabrication facility is very nice! We take so much of technology for granted.

If you found a bike tire this amazing, I can't wait for you to discover _anything even slightly more complicated than an inflated tube inside a rubber/cloth shell_.

This reads like someone just came back from outer space and was stunned by the complexity of all of the systems that got them there. I'm all for appreciating the little things, but we have to draw the line with overdramatization somewhere.

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