eddieo45

This might be one for my "Dumbest things..." thread but this is my first car with TPMS. My last CLK had "run flat indicator" which uses the ABS system to determine that a tire is low, and I assumed that the TPMS, with its more expensive and elaborate hardware would give me more info, like which tire. When I first bought the car the right front tire was losing air and I assumed the TPMS icon was telling so by lighting in the upper right section of my clock.

A few days after buying 4 new tires (from TireRack), I was surprised to see the TPMS light again, and I checked and rechecked that right front tire before deciding to check ALL the tires and finding the right rear a little low. Seems that the TPMS icon will always light in that spot and is not telling me anything about which tire.

This brings up another tire issue, which my tire installer says is somewhat common with Michelins. He says that getting a bead seal can be a challenge and that sometimes he has to grind and regrind the rim until absolutely smooth. He's been doing this for 40 years, and his father, who ran the business before him is still there and concurs. It's certainly as much aggravation for him as it is for me to mount and remount that tire (3 times so far). It can take 10 days to lose 3-10 lbs.

Now I've hit a pothole and destroyed the left front tire, bending the rim in the process. The wheel shop at the other end of town is truing the wheel and I'm driving on the space-saver spare. The TPMS icon flashes and I get an occasional "Tire monitoring not available" message so I assume TPMS requires all 4 sensors to be present and operational in order to work. Asked about the right rear tire issue, the wheel guy said he bets it's the sensor itself, which has a number of gaskets/washers and can be rebuilt with a $10 part. I plan to let him take a look at it after he mounts my new replacement tire when it arrives from Tirerack, hopefully Monday.

I think it goes without saying that the $19 for road hazard protection on each Michelin was the best money I've spent so far!

Yidney

Not sure what your question is exactly, but yeah, the system is fairly crude. It does not tell you which wheel is low, nor does it give you actual pressure info. In fact, as far as I can tell it is not actually measuring pressure per se, but just a differential in pressure. You can reset the system to have whatever is in your tires at the moment as "normal" or baseline. So if you have 30 lbs in all tires or 36 lbs, you can set the system to recognize that as normal, and it will warn you when any tire gets too far from that.

tw2

Sounds like more trouble than its worth. There is nothing like going around with a tire pressure gauge and being 100% happy they are all exactly where they should be.

Fatz

For me TPMS is not a replacement for checking the tire pressure manually, and adjusting it, every 2-3 months. TPMS is very useful however in assuring me that while running at highway speeds (and sometimes +) the tires are within some range of acceptability and I am not losing pressure (nail, rupture, seating, etc).

With low profile tires, it sure would be a bummer to exit your car and notice that your wheel rims are barely off the pavement and you've been driving on 5 or 10 pounds of air pressure.

Rudeney

TPMS is simply a govern mandated knee-jerk reaction to the Ford Explorer/Firestone Tire rollover incidents. It is there for no purpose other than to fulfill these requirements. Tire pressure should still be checked regularly with a quality tire gauge, and using the values indicated by the car - not "max pressure" stamped on the tire.

cal1

An all too common action of the government. i suspect once people start spending 100s of dollars per sensor, they will not be very happy with the TPMS government mandate.

Rudeney

It's not just the price of the sensors when they fail, but the price of needing a "seal kit" when you change tires. I had a heck of a time finding any tire store that could replace tires on my BMW X3 when I had it - apparently it uses some special kit or tool that no store could work with. I finally too it to my German indy shop and they did it, but it was $70 per tire just to mount and balance!

eddieo45

Thanks for having the discussion I'd hoped for, in spite of the fact that I didn't really ask a question. I've been told that other cars' TPMS will tell which tire and even PSI, so I assume MB just doesn't see the value in that (never the quickest to adopt some technologies).

cal1

I did a little research yesterday and it looks like the TPMS mandate took effect on 07 vehicles. MB has been using TPMS at least since 03 because my SL has it. When the TPMS batteries failed on my SL, the dealer quoted something like $150 per tire. I asked them if they could disable the system in Star. They said yes and did. They went on to say they could only do so on vehicles prior to 07.

Rudeney

In the USA, any vehicle built after September 2007 was required to have TPMS of some sort. This ranged from mechanically measure rotational speed differences through the traction/stability control systems, to electronic sensors in each wheel. The electronic sensors all do the same thing - they us RF to transmit the pressure in the tire to a receiver in the vehicle.

Most of the electronic sensors are powered by batteries that are charged by the centrifugal forces as the tire rotates. Unless those batteries go bad, there is no need to replace them. The extra challenge when dismounting the tire from the wheel is that the sensors are usually in the way and have to be removed. This requires a special tool and a seal rebuild kit for where the sensor mounts to the valve. On some implementation, the sensor sits very flat against the rim so it does not interfere with tire changing.

The alert to the driver can be a simple "idiot light", or it can also include the ability to display the individual tire pressures. The information is there, it's just up to the manufacturer to decide if they want to add the additional complexity to display the pressures. Due to the fact that there may be a range of acceptable tire pressures, the threshold for alert is set by the driver.

All of the electronic systems allow the driver to set the "proper" pressure. I see this as a huge defect, especially since this is a government-mandated safety feature. I know many people who get TPMS warning and simply press the "default pressure reset" button to make it go away. This simply tells the system that the current (and probably low!) pressure is "correct".

The mechanical ESP-bases systems like the W209 uses can really only tell when there ahs been a 30%-50% loss in pressure based on rotational speed differences. This is better than nothing, and also has the advantage of not allowing the driver to erroneously reset low pressures to be correct pressure. It appears that this can actually be enabled on the W209 instrument cluster via SDS. Looking at WIS, there are no additional parts - it just uses the ESP/BAS system and the MFD to alert the driver. I might go turn mine on to see what happens.

cal1

Thanks for the detailed info. Regarding the batteries, they apparently tend to fail after about 5 to 7 years or at least this is what one MB SA advised.

Rudeney

That's not surprising. I've not had a cell phone or laptop battery last much past two years, and they are in a much nicer environment than a hot road wheel.

Joey M

So what would happen if you put a set of wheels on without the TPMS? Could you just turn off the run flat indicator? Or would the car constantly yell at you?

Rudeney

It can be disabled via SDS.