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Reprogramming TPMS for new wheel size

15K views 41 replies 13 participants last post by  MeteorGray 
#1 ·
Hey all,

I currently have the OEM iTouring size wheels/tires on my car (16"). In the near future I am planning on upgrading to 18" Enkei wheels and Tirerack has warned me that I would need to reprogram the TPMS to account for a different wheel size.

My question is, will resetting it like you would for a low tire also act as a "reprogram" for a new size wheel, or will I need to take it in and have the system programmed?
 
#4 ·
Xmsteel...would suggest you do a bit more research as to whether you will trigger the TPMS by changing tire/wheel size and not necessarily trust the responses here. Many people here have changed their tire/wheel sizes.

Firstly, the Mazda system is an indirect system vs. a direct system. The indirect system is based on tire revolution where the direct system is based on an actual sensor inside the tire/wheel which measures pressure and temp. Secondly, each car is designed with a specific tire/wheel size as it relates to the speedo....makes sense so far? Some have 16" and others have 18" wheels. Changing the tire/wheel size from original specs will be affected. Therefore, the TPMS system is also designed around the tire/wheel size.

All I'm saying is maybe switching rims/tires won't affect anything based specifically on the Mazda 3 system, but there is enough literature out there which supports what the tire dealer is suggesting. You would need to get further confirmation on people who have made the exact same switch you have in mind...exact same wheel and tire size.
 
#5 ·
Its important to inflate all the tires to the same PSI and properly reset the system using the button on the dash to tell the system what is considered "normal". Once that is established, the system looks for individual wheel speed differences that deviate from that "normal" baseline by a preset percentage. The system cannot discern which tire is low however, and it will not trigger an event if all 4 tires are low.
Just FYI, the indirect TPMS system in your 2014 model does not care what size the wheels are. It works by sensing wheel speed using the ABS sensors. A soft tire has a slightly smaller diameter, so it turns at a different speed. When wheel speed difference drops below the preset system tolerance level, the light comes on. So, it does not matter if the wheel is 16", 18" or any other size what so ever.
 
#9 ·
Non sequitur....Since the system relies on relative wheel speed rather than overall wheel diameter to function, tire size only counts if the tire sizes are mismatched. Even then as long as the system is properly reset after installation it won't make a difference....:dunno:
 
#14 ·
If 17maz3's description is correct, there would be no need for the reset button. With known tire size from the factory (on the door), simple calcs would reveal revs expected and be burned in.

The reset capability seemingly tells us the system is likely entirely independent of fixed size.

Is there any indication in docs to the contrary?

Sent from my SM-N950U using Tapatalk
 
#16 ·
I agree if you live in a city with a one way system and turn right on leaving home, drive around the block and return from the left, your outside wheels wile have traveled further than the inside ones. So you can't have a fixed calculation, you need a fudge factor. Lets say you always run your car with the tyre pressures at the maximum and you live where there is little temperature variation whereas I run mine softer or live in a climate that has large fluctuations day to night. Perhaps you park with the drivers side in hot sunlight so your tires are warmer than the passengers when you start the journey, so the pressures are up. the diameter larger, less rotations for the first mile or two.
What I am saying is that each ABS sensor passes the wheel rotation info to the computer that says "why is that single wheel going faster that the other three"? and "is it a little over a long time"?
Resetting simple clears the memory so the count starts from zero and removes any flag from the system.
 
#17 ·
So from what I'm reading it really shouldn't matter as long as all four are matching and properly inflated?

Next question and one I didn't even think of, difference in speedometer accuracy. What would the impact be going from a 16x7.5 wheel on a 205/60R16 tire to a 18x7.5 wheel on a 215/45R18 tire?
 
#25 · (Edited)
Correct. Xmsteel isn't changing anything now that he has clarified tire size. However, back to my earlier digression....ANYONE, considering a change in wheel dimension on any car should consider how that will affect gear ratio...the simple physics of it all is fairly simple 8th grade math, but as it relates to cars and what components it affects is something you should have a greater understanding. This is basic car knowledge for anyone who services their own car. Example, upsizing will generally drag a car (create more stress on the drive components and affect economy) if you don't adjust the final gear drive...both off the line and at speed. If one is asking the question about changing original wheel/tire equipment and what is affected, then it's best to just stick to rotating your stock Mazda wheels/tires.

So you can't be "rocking" out between changing from 13" inch to 19" inch as long as you keep the tires inflated...there is a big deviation on gear ratio. You are affecting everything connected to the drivetrain including ABS, which back to the topic is connected to Mazda's indirect TPMS which in itself is an imperfect system.

In regards to warranty, as an example BMW and Porsche dealers have signs in their service centers in the US stating they do not service any cars still under warranty, with after market wheels if the service they are doing has anything "connected to wheels". I hear in Europe it can even be more restrictive. I wouldn't be surprised if other European car dealers have similar polices in the US. In the fine print at the tire shops, read. The tire shop is not responsible for any damages if any equipment being installed (including tires and rims) do not meet original factory spec...this includes upsizing just 1" which is a popular option.

I wasn't inferring that changing wheel diameter completely voids a car's complete warranty as protected by US warranty laws, but if a manufacture can connect a problem to a significant change in wheel diameter, and say the car is being serviced for transmission issues, brakes, etc, then the owner maybe SOL for repairs.
 
#26 ·
So you can't be "rocking" out between changing from 13" inch to 19" inch as long as you keep the tires inflated...there is a big deviation on gear ratio.
Twas a joke. A simple exaggeration pointing to the basic functionality of the system. I probably shouldn't joke when people take things so literally. If you know basics of car function and physics, one would probably see all the reasons you shouldn't run 13" wheels... let alone these:
 

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#31 ·
Temperature is not an issue. The system compares tires to each other, not to themselves. Besides, when driving, all the tires will change the same as they heat up so there should not be any difference between tires. Thats the one big downfall of the system though - if all 4 tires loose pressure at a similar rate, the system won't work.
 
#32 · (Edited)
arathol said:
If one sensor detects a 26% loss, the light goes on. The reset procedure initializes the system and whatever the current pressures are when the reset is done is what the system uses as a baseline. So, it doesn't really matter if one wheel is turning faster than another. If you reset the system with uneven pressures and / or different diameters, that is what the system will read as "normal" so the light won't illuminate. Once the system detects a change from that "normal" condition that exceeds the preset threshold, the light comes on.
arathol said:
The system compares tires to each other, not to themselves. Besides, when driving, all the tires will change the same as they heat up so there should not be any difference between tires. Thats the one big downfall of the system though - if all 4 tires loose pressure at a similar rate, the system won't work.
This describes two different methods of operation that are similar but sufficiently different to be important.

The use of a reset button implies operation in the first quoted manner. Googling around is not showing information specific to Mazda, but rather generic principles of differential TPMS, including this link to the initial NHTSA proposal in the early 2000's: https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/tirepressure-fmvss-138.pdf. To wit:

"Alternative 1 would require that the driver be given a warning when tire pressure is 20
percent or more below the placard pressure for one to four tires.

Alternative 2 would require that the driver be given a warning when tire pressure is 25
percent or more below the placard pressure for one to three tires."
[/code]

In their analysis, Alternative 1 is direct TPMS and Alt 2 is indirect. Their critique of Alt 2 centers on the inability to detect when all 4 tires are low, which is your quote 2 method of operation. Though at this point in history, there is no reason Alt 2 cannot detect all 4 tires being low if operation is as like your quote 1, or by using the on board GPS for independent speed if needed for confirmation. Adoption of the final FMVSS standard was for alternative 1. So your quote 2 method of operation would not cut it.

A 2008 article on Audi's system, https://www.adandp.media/articles/audi-rolls-with-indirect-tpms, describes algorithms able to detect independently:

"Consequently, indirect TPMS generation one didn't cut it since FMVSS 138 also requires pressure loss detection on all four tires."

"Audi is opting for the indirect route. That's right: indirect TPMS. Although the generation 1 approach didn't work, NIRA Dynamics, which didn't participate in that technology, has developed a software-based system that, explains Forssell, has sufficiently robust algorithms such that it can handle the NHTSA requirement of detecting 25% of tire pressure loss within 20 minutes while driving at a speed of 31 to 62 mph; the detection time is generally much faster than NHTSA's 20-minute requirement. There are no wheel-mounted battery-powered sensors. No radio frequency transmitters or receivers. Rather, the NIRA Dynamics system, designated TPI (for "Tire Pressure Indicator"), makes use of the wheel speed sensors that are part of the antilock braking system (ABS) and electronic stability control system (ESC). A processor is needed as well.

"Wheel speed sensors have been around since the introduction of ABS, and have proven to be mature, stable and reliable," Forssell says. They are used as input to the NIRA Dynamics software. At first, the processor that will make the calculations is a stand-alone system. For example for the '09 Audi A6, there will be what Roscher describes as a "little gray box." That's the processor. "Eventually," he says, "it will be integrated into the ESC processor." It is simply a matter, going forward, of making accommodations for the indirect TPMS system in the controller.

Essentially, the NIRA Dynamics TPI system "learns" the radii and frequency characteristics of properly inflated tires. Then, it is able to detect whether there are deviations from normal, which would be a result of the loss of tire pressure (e.g., when a tire loses pressure, there is a change in the radius as the tire rotates, which has a consequent effect on the measured parameters). The system can detect a change in any or all of the tires (remember that the previous indirect systems measured pairs of tires unlike this one, which has inputs from each of the tires)."


Given that 2008 Audi method of operation and our reset button, operation is likely linked to a history of each individual tire compared to itself, with additional information comparing tires to each other.
 
#33 ·
Everything you have linked to was published before the Mazda system was introduced, probably even before it was designed. The article is not even about the Mazda system, its a system used by Audi some 10 years ago....
You are reading way too much into this. When you push the reset button, this clears all previous data and tells the system that all four tires are considered within normal operating range (that is why the reset procedure requires you to set the pressures in all four tires before initiating the reset). So, if one tire has 20 psi and the other three have 50 psi when you initiate the reset, the system does not care because those values are what you have entered as normal by initiating the reset procedure. What sets the system off is deviation from those "normal" values. The system compares the data from each sensor and when it detects an increase in the speed of one tire relative to the other three due to a significant loss of pressure in one tire (deviation from the values set by initiating the reset procedure, in this case 20, 50, 50, and 50 psi) the light comes on. As before, the down side is its probably not going to register a problem if all four tires lose pressure, and sometimes it won't register if both tires on one axle lose similar amounts of pressure.
 
#34 ·
As before, the down side is its probably not going to register a problem if all four tires lose pressure, and sometimes it won't register if both tires on one axle lose similar amounts of pressure.
The FMVSS requires independent ability to measure all 4 wheels, including if all 4 lose pressure in sync. The system has to be more sophisticated, in line with the Audi setup. We're on an enthusiasts' site, details are interesting and why we're all here.
 
#37 ·
When my car was delivered, the dealer hadn't done a very good job of prepping. The tire pressures were all over the place, one up near 60 psi. No lights or warnings ever. I have used four different set of tires in different sizes, used 16" and 17" rims, not a single alarm or warning, and never had to reset anything. Is that a good thing? Probably not. I suspect the system is just as described, a low cost system that "works" in order for Mazda to say the car has a TPMS of some sort. Its no better really than any of the other idiot lights on the dash that only warn you when its probably too late to do anything but pull over and call a wrecker..... Any way around, I don't really care as I don't pay any attention to it anyhow. I don't need a flashing light to tell me there is a problem. Any competent operator should be able to tell that a tire is soft long before that 26% threshold is reached.
 
#38 ·
Here's another data point for us to consider. I've had my 2015 hatchback for about 8 months now. I bought it at auction, after the previous owner rear-ended someone. In addition to being a voracious roll-your-own smoker (seriously, there was loose tobacco behind the door cards), they also didn't give a damn about tires. The car had three different brands of tire on it, and while all inflated properly, the front pair were worn almost to the wear bars. In order to fix the car, I bought a 2014 M3 sedan that had the rear end obliterated as a parts car. It had all the front end parts I wanted and was even the same color, so win-win.

The worn-out front tires on my car were fine for summer here in Oregon (where it doesn't rain at all), but since it started raining, there have been a few scary moments. Then I got the bright idea to swap the front wheels/tires from the parts car. I noticed while swapping them that they were a bit bigger in diameter than the old ones. I had jacked up the car just enough to get the old ones off, but had to crank the jack a couple extra turns to get the new ones on. Old and new tires are both the same stock tire size (205/60r16) and on the same factory steel rims. I chalked the difference up to being ~95% tread vs ~10% tread. I also noticed that the newer tires (Bridgestone Ecopias) looked like they squished less than the old no-name tires, which might be the difference in the quality of construction.

BTW, the rears on the car (which I didn't change) have about 60-70% tread on them. Also, the tire pressures on all of the tires are the same, though they are a bit low (down 5-6psi) as I haven't compensated for winter temps yet. But the new and old tires all have the same pressure in them.

The kicker here is that after putting the newer tires on the car, it threw the TPMS warning light after about 10 miles of driving. I never saw that light come on while on the old tires, and I had added a bit of air to them from time to time. So, given that the newer front tires are clearly larger in circumference than the old ones, it seems like the TPMS has tripped because it has seen an rpm difference between the fronts and rears.

As soon as I get a chance, I'll correct the pressure in all the tires and take it for a drive and see if the TPMS goes out. Then I'll reset the TPMS and take it for another drive.

More to come...
 
#40 ·
Your tire light will come on anytime the pressure is adjusted, tires rotated or replaced/swapped. Your system responded properly because you didn't do a reset of the TPMS per the owner's manual after swapping the tires.

I didn't know that Mazda went to a indirect TPMS system. My '04 had sensors. I did a oil change and rotate at the shop on a 2017 Mazda 3 hatch without giving notice to the sensors or lack thereof. What happened? Owner came back in about 30 minutes and said her tire light was on. Checked pressures, OK. Didn't notice sensors but wondered if it had the old Ford sensor stuck to the rim thing. Researched and realized that it was indeed a indirect system and needed to be reset due to the rotate. I assumed that nobody was doing indirect anymore. I was a Toyota Tech for years and saw all of their indirect systems convert to direct. I was surprised that Mazda went backwards from direct to indirect.

Still curious about the system. I hear the experiences people have. I would think that there would be a standard in the TPMS module that would still be able to detect a low tire outside of the recommended pressure based on the speed sensor reading and what should be seen based on the factory tire size and pressure. The plus side is that if it doesn't as it appears, then different tire sizes and pressures can be freely run and the TPMS system will still work based on the baseline reset reading. Personally, I like that.
 
#41 ·
Okay, I forgot to post the results. Sry.

After correcting the tire pressure in all four tires, I took it for a drive and the TPMS light stayed on. I think this is because the light stays on till you reset the system. Has anyone had a low tire, gotten the TPMS light, added air and had the light go out by itself?

So I reset the TPMS system and all has been well since then, despite the difference in tread depth between front and rear tires. I think this also means that the system can tolerate slight differences in tire diameter.

Karl
 
#42 ·
Last year on a highway trip I began hearing a very subtle thump-thump-thump, but it wasn't loud enough to cause me to immediately stop.

A half-hour later the TPMS alarm activated, so I stopped at the first safe spot to check the tires. My pencil-type air pressure gauge told me that all of my tires had the same, proper pressure. Suspecting another problem from the thumping sound, I then ran my hand around each of the tires' treads and sidewalls and found that one tire had a longitudinal bulge in a portion of the middle of the tread. I then knew that the tire was beginning to suffer belt separation and so was expanding to the point that the TPMS noted it was revolving too slowly compared to the other three tires (which would logically imply to the TPMS that the tire was actually gaining pressure, and it decided this was as dangerous as losing pressure which, in this case, certainly was true even though no pressure actually was gained :=).

Since I was not far from home, I didn't bother putting the donut on and proceeded at a slower pace down the road. Before I pulled out, I reset the TPMS to see if the alarm would go off for the duration of the trip. Within a few feet of rolling forward, the alarm activated again and remained "on" until I got home. So, my TPMS refused to accept the tire as "normal" and so it immediately alarmed again after the reset.

Obviously, the TPMS did not allow the faulty tire into the normal category when it was out of rotational-speed harmony with the other three. I'm glad it thinks that way. It served me better than the newer type of pressure-monitoring TPMS, which would not have alarmed since my faulty tire had perfect air pressure because it had not lost a pound.
 
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