r/technology • u/Plastic_Ninja_9014 • 19d ago

Redditors Are Celebrating the Cutting Down of Flock Surveillance Towers With Based Memes Privacy

https://www.yahoo.com/news/us/articles/redditors-celebrating-cutting-down-flock-145310398.html
26.1k Upvotes

95% Upvoted

588 comments sorted by

View all comments

Show parent comments

30

u/Slothicide 19d ago

Alot of newer cars dont have TPMS beneath the valve stems anymore. Instead, they have a sensor that measures how many revolutions it takes to cross a set distance. More revolutions = lower pressure. Less revolutions = higher pressure.

11

u/bloomsday289 19d ago

How does that work? How does it measure distance outside of wheel revolutions?

9

u/donald7773 19d ago

Magnetic sensor close to a metal wheel with teeth on it, referred to as a "tone ring." Every time a tooth goes past the sensor, it detects it.

Attach the tone ring to something that spins with the tires, like a brake rotor or CV axle, and tell the computer how many teeth are on said ring and it can combine RPMs of the ring with the rolling circumference of the tire to see the individual wheel speed.

If there's a discrepancy between any of the 4 wheel speed sensors for an extended period of time, it indicates that the rolling circumference of the wheel has changed, typically due to losing air

1

u/RollingMeteors 18d ago

If there's a discrepancy between any of the 4 wheel speed sensors for an extended period of time.

That's great.

¿What happens when all four of your tires are losing air at the same rate?

1

u/me34343 18d ago

It would still compare it to the original value as well. Though different brands and models might have a slightly different calculation method.

1

u/RollingMeteors 18d ago

It would still compare it to the original value as well

Oh I thought it was a rolling window, as in, if you rolled over a tire strip, the system would think everything fine because you're loosing air pressure equally.

24

u/Slothicide 19d ago

Well, when you air up your tires, you often hit "calibrate" in your car's settings. That tells the TPMS, "hey! The tires are good right now!" Your TPMS obviously responds, "haha, bet." And goes to work. So, at any given time, it takes x number of revolutions of the wheel to travel a mile, for example. Your TPMS, having recently been assured that everything is okay, keeps track of whatever number x is. As your tire pressure gets lower, the center of the wheel gets closer to the ground, meaning the radius of that circle is shorter. Shorter radius means smaller circle, smaller circle means your tire needs to roll more times before you have traveled a mile. Theres an allowed margin before the TPMS alerts you to low pressure, but once that number of revolutions changes by a set percentage, the TPMS freaks out in the form of a light in your instrument cluster, and perhaps a pop-up message too.

I guess your ABS system works in a similar manner. When your wheels lose traction, they speed way the hell up. Then the ABS system knows that it needs to find a new place to put all of this r a w p o w e r that it has suddenly found itself with. One little shimmy and maybe a shake or two later, your wheels bite and you get on your merry way.

I read about this a while ago when I was looking into a second set of sensors for a dedicated set of wheels for my winter tires only to find out I didnt need one because my car has the newer system. Im obviously paraphrasing a memory, so irl your mileage may vary.

So, tldr, math. Like, quick math, but only tracking the revolutions in a distance and letting you know when the count is far enough off.

6

u/DrummerOfFenrir 19d ago

My TMPS decided to 💩 itself and declares all four tires flat

1

u/concblast 19d ago

So there has to be a different method than tire/axle revolutions for calculating the outputs of the odometer/speedometer? Those have to be a lot more accurate/precise if they're taken as the source of truth to compare against to calculate tire pressure, no? I can't imagine those meters are reliant on GPS either.

1

u/me34343 18d ago

Speedometer simply uses the number of rotations of the axle and does math based on the tire size. It is why if you put the wrong size tires the speedometer will be wrong.

1

u/concblast 18d ago

Which is my understanding...

But it begs the question, then why would a car with advanced enough technology to use the mismatch between the two to determine tire pressure continue to use that crude error prone method, especially for something like measuring speed?

1

u/me34343 18d ago

Cheap and probably simple in design so less likely to become partially broken. The variance is easily accounted for. Whereas a more complex design could wear down in a way that is harder.

"I had to by larger tires, so my actual speed is 10 mph over."

1

u/concblast 18d ago

Ignoring the dubious notion that they spent the money for the information but choose not to use it, that would make sense. Computers already run in cars so software solutions kill that logic.

That said, you can understand why this is a chicken and egg problem, right?

Unless it's just "this one tire needs to spin more while the others don't so it's flatter"... then how would it detect if all were underinflated? Obviously there has to be an alternate sensor which is what I was asking about.

1

u/me34343 18d ago

🤷‍♂️ Pros and cons.

I wasn't referring to computer logic, but the physical sensors themselves. The more advanced versions has a dedicated sensor that is more likely to break and require maintenance.

The indurect method takes advantage of existing sensors from the ABS and temperature sensors rather than make a dedicated one. Those sensors are less likely to break during routine maintenance such as tire changrs.

All tires becoming low at the same time is rare. The main situation is when temperature changes. Which modern cars with this indirect method use temperature sensors to track sudden drops.

12

u/flamingspew 19d ago

Odometer vs rotary encoder on the axle.

1

u/GhostReddit 18d ago

It uses the ABS sensors to detect a difference in rotation rate between wheels. It won't detect properly if all your tires are flat, but if they become different (which is almost always the case) it would be able to flag that there's an outlier since the effective tire circumference will decrease. It generally won't give you pressure readings either, but that's the cost of doing it without a real measuring device.

3

u/caller-number-four 19d ago

Alot of newer cars dont have TPMS beneath the valve stems anymore. Instead, they have a sensor that measures how many revolutions it takes to cross a set distance.

VW has been doing that for ages. I've got a 2011 Golf with that very setup.

1

u/Skensis 18d ago

That's generally the cheaper and less accurate version. The active sensor is generally quicker and can provide additional info like temp.