I just got my new 20" HRE P40's and had "the vendor"...install the TPMS Sensors and mount and balance the wheels before shipping.

My car had been in at the dealership when the rims arrived via UPS and took them to the dealership for the swap.

Little did I know my Porsche dealer charged me $129.00 to swap wheels....took them well over an hour and they had the car on the lift with the stock tires off when I got there....I was running late for an appointment and the tire "kid" pulls out and tells me he needs to do a test drive to ensure the TPMS is set correctly.....I am like....huh....sorry kid no joy ride today, I had looked it up in the manual and I can handle it....I gotta run.

Anyways I began by setting the tire pressures ....they were very close ....using my accutire digital pressure gauge.

I then followed the steps in the manual and I am reading 5 PSI low on every corner.

I checked the pressures with a new but mechanical gauge ....bang on to Accutire and 5 psi low than TPMS.

I went out and bought another digital gauge....confirmed Accutire was correct and returned it....sorry....

Anyways, "the vendor" has been of little help, I am just wondering if anyone can offer some advice.

Going to clean up the car tomorrow and post some pics!

Thanks in advance.

I tried posting this a few days ago in the Tech/Wheels and Tires and hoping the higher traffic here will help.

I have done the reset procedure several times and still came out with the same result.

If the sensors haven't been "coded" properly do the tires have to come off to reset....would this be a good thing to check....???? The vendor reassured me they were coded properly or my system would read anything.

 

never heard of that before. i know on the new 09's the tpms asks what size wheels in the system.. but they auto learn.. go back to dealer and say for 129 you want them to read properly.. all programming can be done without removing tire.. they just clip on to the stem on every other car ive seen to program.

 

Thanks, some good info...the procedure for the 08 is similar from the control menu.....maybe I should have been more patient....but geez over an hour to pop 4 wheels on...I was just in a hurry.

 

they are off by about 4psi. porsche should just rename them FTMS; flat tire monitor sensor. that's what those sensors are good for.

 

Tire pressure readings are so volatile in the hot summer . In my region even a cold tire is still facing a hot climate . Even worse I had one 997S which had one tire pressure recommendation on the door panel which was different from the owners manual . Throw a 20 inch wheel on the car and you just added another variable into the mix . Plus you have one guy shipping it, another installing it, a valet driving it, and you wonder why the confusion?

I would bring it back to the dealership and show them the problem . At least consolidate the accountability on the tire issue to one person . This way you don't face going on a wild goose chase if a tire issue surfaces.

 

Thanks for the comments guys.

Whenever I go to set the pressures I always start from when the tires are cold - the tires were N2 filled and I added only 2 psi to rears when i got them.

Looks like the sensors do work and do Pick up 3-4 psi when the tires get warmed up.

These are new TPMS Sensors - bought from the vendor.

I think I will pop by the stealership and have them check the coding :
- the TPMS sensors communicate fine
- they read differences in cold vs hot tire pressure.

Cheers.

 

Porsche shop owner I use all the time just got new Mercedes and he has same exact problems with his TPMS all summer long - so I guess you are not the only one who suffers with this.

 

Current gen.2 tpms used on Porsches the last year or two read from the abs sensors so diameter changes have the effect you are noting. Any P service manager knows this. FWIW - a lot of people find that the sensors' only value is if you develop a leak and you then get a warning; pressure readings are impacted too much by both ambient temperatures and how the car is being driven.

 

Thanks Tejoe - I am going to do some more homework on.

I stopped by the dealership today and talked to the tire kid - seemed very knowledgeable and he noted he as alot of difficulty matching TPMS readings to any gauge he is able to find. He did note that when he switches Cayenne wheels there is an option for the larger wheel ~ so that maybe the source. Not sure if I'm on the right track or not.
That being said I added 2 psi to the rears and got rid of the TPMS fault, I think I will just use it as an indicator of a "major" problem while driving.

Thanks all.

 

I have a fancy tire gauge and that's what I go by. Once a week on the way home, I overpump the tires a little at he station near my house, and adjust them with the mechanical gauge the following morning. I don't pat that mush attention to minor TMS fluctuations.

+1 to speedoflight, TMS should be FTMS

 

[quote=skay;2497833]I have a fancy tire gauge and that's what I go by. Once a week on the way home, I overpump the tires a little at he station near my house, and adjust them with the mechanical gauge the following morning.

+1 twice

 

A simple bathroom scale will let you fine tune the settings. Why now let the user tweak his/her tire pressure? Or design a better sensor... Maybe we'll see improvements to this system in the next 5 years, heh heh...

 

So can someone explain why the diameter of the wheel would make any difference in the tire pressure reading from the TPMS sensor?

I understand that for the system to tell you what the right pressure is - ie the display of the differential pressure form where it should be would need to know the size of the tire.

But the pressure inside the tire is unrelated to the size of the tire/wheel. Its an absolute number and its the same number on any make and model car or tire or wheel.

I would think the sensor gets a pressure reading and then transmits that reading value to the car. Now how that reading is transmitted could well be a problem, though I'd think an RFID sort of transmitter that spits out its analog reading to the car, and the car then converts that analog reading to a pressure is all it takes. The conversion from raw data to a pressure is fixed based on the sensor manufacturer.

 

+1 on that question. TPMS is a pressure monitoring system. Air pressure is not a function the of shape, or in this case the diameter, of the object in which the air is contained.
As for my experience with the system, early on I had a problem with the variance between dead cold tire reading with a gauge, various gauges actually, and a dead cold tire reading with TPMS and variances from side to side for identically pressurized tires. However, since my last check, tire gauge and TPMS have been dead on when cold and when warmed up both sides read the same IE.. both fronts read 36 and both rears read 43. But outside of making sure that my cold tire gauge readings for tires on opposite sides were identical, 33 front 40 back, I can't tell you why the problem went away. When filling I start high and bleed down to the desired reading.

 

This is a funny one. I had measured my pressures with a simple mechanical gauge and had them at 35/39 and they showed up uneven on the TPMS. I go to have my car in for the 20k service. Car comes out and the tires are EXACTLY 33/39 on the TPMS. Both sides exactly the same. I didn't try to check that against my gauge though. It seemed uncanny that they set the tires pressures to the exact factory spec and the TPMS read the exact pressure they needed to be. I wonder if they can set the pressure manually and then program the TPMS in the car to read the pressures as measured manually.