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Can someone explain why individual TPMS reporting would've been so much more work?

I'm not a car tech guy but figure by logic that the Model S has to have individual tire pressure sensors in order to trigger the TPMS warning. So why not simply step it up a notch and tell you which tire is low? I'd love to know what the massive undertaking would've been, or if this is just one of those things they didn't get to...

What makes you think that your car will not be getting that in the future? They are prioritizing their roll out.

I never mentioned that, would be great to get in a roll out. Just looking to understand the "technology time" difference, if you will, between installing a TPMS system and installing it with individual reporting...for my own education. :)

My guess is the car doesn't keep track of which tire is mounted on which wheel, as that would require updating when you rotate the tires.

For example, when I had the TPMS switched over to my track tires at the service center, it was reading the TPMS on the tires that were inside the car just fine, and never complained about them not being mounted. If it can't tell tires mounted from tires inside the car, it can't tell which tire is mounted where.

So, just giving you 4 tire pressure numbers and not being able to tell you where they were is only marginally more useful than just saying a tire is low. However, even that would be useful in deciding whether it is just slightly low due to cold or if there is a real problem before driving a couple of miles or getting out and looking at them, so maybe they could make the message give the lowest read pressure and not say what tire it is on.

Each TPMS sensor transmits a unique ID over RF. Therefore, it only requires a software update where you can indicate which sensor is installed for each wheel. (Currently you can only specify a "set of four" sensors for all wheels at once.) Once each sensor and the wheel it belongs to are identified, the car can then show individual tire pressure for each wheel.

I expect Tesla to implement this is in the future. In the meantime, you can vote for this feature on Teslatap or in the prioritized software list on this forum.

Couldn't they do something more automatic? I would guess that the pressure in a tire varies as you drive. I'm not sure how sensitive the measurement is, but if it's accurate enough, this could be used to tell which reporting tire is which as you drive. A right turn, for example would tend to put additional pressure on the left tires. A stop would tend to put additional pressure on the front tires. Since the car knows when it is turning and stopping, it could use the tire pressure fluctuations over a few minutes of driving to calibrate which tire sensor is which.

@chrisdl - yes, but I suspect the center console computers have very limited access to the CAN bus for the car, so you are talking about firmware changes to safety-critical portions of the car to allow access to writing to the TPMS controller. Those changes are going to be more conservative and take longer, and there are lots of things I suspect are considered higher priority, particularly considering they just added the Reset TPMS button which addressed the #1 TPMS-related need (and saved them money of having owners bring their cars by the shop to swap tires).

Also, the UI for such a feature is awkward -- assuming that owners didn't write down the TPMS sensor ID while the tire was unmounted, how do they tell which tire is mounted where if the radio receiver can't distinguish the mounting locations? The way you do this now is to have a reader which triggers the sensor and reads the ID (and the range is great enough when the service center switched to my track tires, we had to take them out of the car so only one would trigger at a time), and then you feed those IDs to the TPMS controller via the ODB2-like connector behind the cubby.

I do suspect that it will happen, I just wouldn't expect it to happen anytime soon.

FWIW, I asked this question at my local service center a month ago and was told the car does have the ability to read pressure on all wheels separately and a future software update will provide the info. They are just prioritizing and working on the graphics for it, etc is less important than other updates (like nave).

@jat: You bring up valid points.
Adding a wheel by wheel TPMS configuration and view would mainly comprise building a nice UI and some control logic to support a manual procedure to identify each wheel (deflate tire or use a magnet to identify sensor). We know that Tesla can make nice UIs, so I'm not too worried about the software complexity. I'm not sure if they want to add such a procedure to an otherwise minimalistic car, but I personally would like to have it.

@elguapo - each sensor reports its own ID, pressure, and temperature, so that isn't the problem -- the problem is telling which sensor goes with which location on the car.

My Lexus LS460 would show the tire pressures, including the spare tire, but did not tell you which tire was in what position. You just got 5 numbers. Better than nothing, but also somewhat annoying.

GM came up with a clever system (if I remember correctly) to identify a sensor with a specific tire. You went around the vehicle letting some air out of each tire in sequence, and it beeped when it recognized the pressure change and identified that sensor. Of course you had to add back in air to complete the process, but it wasn't too bad. You had to redo the process when you rotated the tires or changed them. I suspect the dealers hated the extra time/effort required (or they just passed the cost onto the consumer at a nice markup).

Some manufacturers have a sensor pickup by each tire, so they know which tire is associated with the sensor, but this is more expensive, and is rarely done. Not something that could be retrofitted.

My Porsche reports individual tire pressures. It has a reset function to identify the tires when tire positions got messed up. It takes a few minutes to finish the resetting. I don't know how that's done though.

@carlk | NOVEMBER 19, 2013: My Porsche reports individual tire pressures. It has a reset function to identify the tires when tire positions got messed up. It takes a few minutes to finish the resetting. I don't know how that's done though.

Porsches have TPMS receivers near each wheel well and can tell which tire's pressure they are reading. It's a real handy feature:

What happens when you rotate the tires? How does that work?

I got a screw in my tire on Sunday. The car warned me that my tire pressure was very low and it told me to pull over. (I was already parked at a Supercharger when the alarm went off.) I used a $2 tire guage and found that one of my tires did have low pressure and then I noticed the screw in between the tread.

I used the Tesla inflator with the goop option turned off and it got the pressure up over 40 pounds. It wasn't losing pressure rapidly and so I went to a tire shop that was half a mile away.

The tire shop was impressed with the Tesla air pump because it was strong enough to take the tire over 40 pounds. I got the tire fixed and I was on my way.

I'm sure that Tesla will have this feature soon. Still, it's surprising that they launched without it. My 7 year old car displays individual pressures. And yes, you have to deflate in sequence if you want to re-learn the tire position.

Funny. A guy at the service center told me they haven't yet because in the system it's recorded in millibars instead of PSI. I didn't push, but I think that change is just a simple multiplication factor.

Personally, I would rather not have individual tire pressures than to have to let air out and pump it back up - I can check the pressures myself with a gauge if it isn't noticeable visually.

When my tire was "very low" I couldn't tell by looking at it.
I have the 21" wheels on it now so I wouldn't have suspected anything without the alarm. Honestly, I thought that the alarm was a bug because it was my first drive after the update. I had a false TPMS warning after an update a long time ago.

Yes, it would have been nice if I knew right away with an indicator. It would have meant a few less minutes in the rain trying to find out which tire was low. I'm happy that the car gave me a message to pull off the road safely before I had a bigger problem.

Wow I didn't realize how much stuff goes into a simple TPMS display in the Porsche. I did get annoyed that when the TPMS went off in my model S I had to check all the tires. Well I hope the fix does come along eventually.

There may also be some issues around the multiple vs. single antennas. I believe the service center said that I had one central antenna but when I had major TPMS issues the final fix was to put an antenna by each wheel, which implies that at least by VIN 83XX they were still using one antenna, not four.

Yes you don't know how nice it is until you got used to the individual pressure display.

@jat@jaet.org No you don't need to let out the pressure to reset TPM in the Porsche system. For other systems it's probably only when you do tire rotation which shouldn't be a big deal.

You don't actually need to let air out of each tire to match the sensors. It's sufficient to hold magnet next to the valve. (If you have a magnet handy.) That'll also trigger the sensor.

Are you guys sure that the Mod S even has individual sensors on each wheel?

I've seen three different TPMS systems:

1. Rather large, individual sensors strapped around the wheel. The sensors are about the size of a deck of cards and held in place by metal straps that go around the entire circumference of the wheel.

2. Smaller, individual sensors built into the valve stems.

These sensors can report tire pressures rather accurately-- I think within 1 PSI or so-- for each wheel. Then there's the last system, which these days is the most common:

3. Using the anti-lock breaking sensors to measure the RPM of each wheel, and sound an alert when one differs significantly from the others.

System #3 is much less expensive than the others (incremental cost zero in most cases), but is also much less accurate, since you have to lose a fair amount of pressure for the system to notice. My Audi A6 uses this system. If your car has a feature whereby you can "tell" it somehow that all the tires are at the correct pressure (since it can't tell there's a problem if all tires are equally low), then this is what you have for sure.

So, how sure are we that the Mod S uses individual sensors in each wheel?

Dramsey:
AFAIK the Model S uses system 2 with a single receiver.

In believe system 3 is currently forbidden in the USA (correct me if I'm wrong).

I have been ignoring the "Tire Pressure is Low" warning when it is below freezing outside. It would be great (and too much to ask for I'm sure) if the TPMS could account for the contraction of air when it is cold!

CarlE, So you want your Tesla to ignore the fact that your tires are actually low on pressure just because it is cold out? The system is reporting a low pressure because -wait for it- ta da- It really is low on pressure.

@CarlE_P439 That's why individual tire pressure display is useful. You could never be able to tell if the "dummy waring" is because of a few psi loss due to temperature or from real air leak.

Any Roadster owners here? I seem to remember people mention Roadsters have the real pressure display. I wonder what's the reason Tesla decided to go backwards.

A Prius can tell you which tire is low. My F-150 pickup and BMW motorcycles can tell me the specific pressure in each tire on a real time basis. This should be doable on a hi-tech car like the S.

@Dramsey - the Model S uses Bao Long 433mhz sensors built into the valve stem. To switch TPMS (before 5.8), you had to scan all the sensors (activating them individual with the reader) and then upload the sensor IDs to the TPMS processor via the OBD2 connector behind the cubby.

@carlk - I was talking about other systems, for cars that can't tell which sensor is mounted where, not Porsche which includes individual sensors.

@Theresa - it could calculate what the pressure would be once it is up to temperature (the TPMS sensors report the temperature inside the tire as well), and if the adjusted pressure is within the expected range then don't alert for it.

Thank you jat@jaet.org. At least one person understood what I was trying to say!!

Air needs to be added in winter, released in hot weather. Measure after parking a few hours.


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