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Comment by phkahler | Hacker News Reader

TPMS sensors are almost completely redundant if you have an ABS/TC module they can passively infer low tire pressure.

TPMS is mandated now, in part thanks to urging by their makers.

My 2 year old car doesn't have TPMS sensors, it just uses the ABS system to give a vague "low tire pressure" warning, with no indication of which tire or how low it is.

I prefer the real TPMS sensors despite the higher cost since then when the light comes on, I know which wheel it is, and what the actual pressure is -- if it dropped from 35psi to 25psi, I can make it a few miles to the next exit, but if it's 10psi, I probably need to stop now.

How does a TPMS mandate existence or inexistence prevent you from getting that option when buying the car or installing the aftermarket version?

I didn't advocate for or against a TPMS mandate, but I don't want a third party system because a factory TPMS display will be built-into the car's instrument paenl, I don't need to velcro a separate TPMS display to my dashboard and either hardwire it or keep it charged. Plus I know that the OEM system is engineered for that car, I don't have to worry about installing repeaters because there's too much metal between the sensors and the receiver.

But that said, I do believe that the TPMS mandate is worthwhile, I've been alerted a couple times already to a nearly flat tire. (both times due to damage while driving, so I wouldn't have noticed it even if I checked my tire pressure every time I drive the car, which I doubt many people do)

OK, so you're saying that aftermarket TPMS might not be convenient, however, like I said in the original comment, you still have the option to buy the option when buying the car.

Would a pressure reading TPMS system be offered by manufacturers if they already implemented the cheaper passive ABS based system?

As you said previously, TPMS gives a more verbose output than ABS based system. That's a pretty obvious selling point

Is it? My car doesn't offer it as an option, it only offers the ABS based system. Does any car offer the more granular TPMS system if they already offer the ABS based system to fulfill the legal requirement?

Would you be willing to share the make and model of your car?

2021 Honda Accord.

From the owner's manual:

Instead of directly measuring the pressure in each tire, the TPMS on this vehicle monitors and compares the rolling radius and rotational characteristics of each wheel and tire while you are driving to determine if one or more tires are significantly under-inflated.

There's no other TPMS option available for that generation (10th Generation) car at any trim level, not sure about the new 11th Gen coming out this year.

I was kinda in the wrong, that appears to be correct. Honda is advertising the ABS based system as TPMS and is not offering any "upgrades".

What does "ABS" stand for in this context?

Anti-lock braking system

https://en.wikipedia.org/wiki/Anti-lock_braking_system

It doesn't actually require the ABS (anti-lock braking system), but uses the ABS wheel speed sensors to count wheel rotations, so it's essentially a free way to add TPMS, no additional hardware required since ABS is already required, just need software to track wheel rotations.

https://en.wikipedia.org/wiki/Tire-pressure_monitoring_syste...

Hah, my car does have real TPMS sensors but the dashboard display is such that the only thing it can say is a vague "low tire pressure" warning, with no indication of which tire or how low it is. I should get an OBD adapter one of these days.

Speaking from experience, OBD will not necessarily help you here. Something has to put the TPMS data out on the CAN bus. The rudimentary system in my old Corolla does not do this, so the only way to debug a malfunctioning TPMS system is via sdr (or an expensive tool, or a trip to the tire store).

Not just "the" CAN bus, but the one you're sniffing. Many cars have multiple busses that carry different traffic.

Yeah that’s really frustrating. Different manufacturers have different offerings here. My Toyota has nothing more than the lame “low pressure” warning, but my wife’s company Chevrolet actually shows numeric values for all 4 tires.

Give us the data!!!

A basic mechanical pressure sensor is the much cheaper and more reliable system.

How does a mechanical pressure sensor work? I've only seen electronic ones, how does the mechanical system warn the driver about low tire pressure while driving?

> I prefer the real TPMS sensors despite the higher cost since then when the light comes on, I know which wheel it is, and what the actual pressure is

What car do you have that reports this level of detail? It's much more common for cars to pop a generic "low pressure" icon with zero other details.

My Ford Transit van shows the numerical pressure of all 6 tires. Haven't had a low pressure warning yet so I'm not sure what level of detail it gives, but with a few clicks I can pull up the pressures on the instrument panel display.

It also sends the data to Ford so I can see the last read tire pressure on the FordPass app.

That’s really cool.

Kia Niro also has numerical pressure for four tires. It really helped when I noticed one tire dropped a couple of pounds before the actual TPMS warning on the dash. Took it in and they patched the slow leak. I am now inclined not to buy a car without a numeric display of the pressure in individual tires. It is way too useful a feature.

Lots of higher end cars will show a diagram with the pressure of each tire labeled.

2012 Jeep Grand Cherokee and 2015 Jeep Cherokee show tire pressure in each tire.

My Toyota Camry reports the pressure reported on each TPMS sensor. Only drawback is I don't know when one matches which tire so when refilling the air, I have to guess a bit.

I my Nissan Leaf (2012) has a screen showing the current reading on each tire.

My 2016 F-150 reports each tire’s pressure.

Generally the cars that have direct TPMS with sensors in each wheel report pressures (and also throw a warning when one is low) whereas the indirect systems that infer it from rotational speed only throw the warning and give you no more information (eg, which tire is low).

My wife's 2008 Subaru Impreza had the worst of both worlds -- the cost of direct TPMS and no more information than the idiot light.

The 2017 Chyrsler Pacifica shows numeric tire pressure at each tire in one of the info screens in the gauge cluster. Also has engine and transmission temperatures. No indicator about which gear the automatic transmission is in though (it does show PRNDL, but not 1-9). I forget what it showed when a tire was low; it might have said which tire it was, or I mighr have flipped to the info page quickly, anyway it notified me promptly when I got a wheel weight embedded in my tire.

Also, when the brake lights go out, it tells you in the info screen, and it says which one. Which is pretty neat.

Might vary by trim, I've got the 'Limited'

One thing a family member has that I'd like is seat belt indicators for every seat in a recent Toyota Highlander. Otoh, I don't like the lane departure warning (it does audible first, the Pacifica is more subtle, it only beeps if you don't respond to the nudges on the wheel)

My Audi RS 5 on the MMI has a screen that shows real time all four pressures, and all four tire temperatures.

That sounds like a preference, which I can respect. It does not IMHO warrant a government mandate for the equipment.

Eh, I prefer real sensors. My car tells me which tire is low. And I can see current pressures for any wheel if I want. Plus I have sensors on my trailer (which definitely does not have ABS) so I can monitor the pressure in those wheels as well.

Using ABS to passively guess if a tire is low is a big downgrade in functionality.

But a decent upgrade in vehicular privacy!

Things that make you go hmmm...

Triple redundant if you have a $0.99 gauge (presumably all drivers have functional eyeballs).

TPMS sensors are much more precise than ABS/radial speed sensing.

And completely unnecessary. Its absurd to mandate them IMHO.

It was mandated in response to the Firestone scandal/disaster. Over 200 people died because Ford intentionally under-inflated Firestone tires on the Explorer. Also, the tires weren’t very good in the first place.

I guess it got everyone thinking about how dangerous under-inflated tires are on the highway. My guess (and it is a guess) is that radial-velocity pressure estimation wouldn’t have been precise enough and would have either tolerated dangerous under inflation or annoyed with false-positives.

If all your tires are equally low, would ABS-based systems even notice?

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