cobalt

I just replaced the old MXX3's with PS2's. Major improvement.

Today the TIREPRESSURE LOW signal came on pointing to the front right tire. I checked the tire it read 38PSI the other 3 at 40 PSI. I reset all 4 tires to 36 PSI now all 4 signals came on instead of the one. Bumped them back up to 40 and all is OK.

The manual says something about testing and reseting the system but does not explain how. Can the pressure setting be adjusted? Is running the low high pressure test a form of setting pressure for the system? The previous tires were set at 36 and the system worked fine.

Thanks

MikeN

The manual for my GT has the reset procedure in it........more like a test rather than a reset. It basically states to lower tire pressure about 10lbs below recommended pressure, drive the car and make sure all corners issue a low pressure warning. Then it states to put in 10lbs over the recommeded pressure, drive again, and make sure all warnings go off. Mind you there are different warnings......solid and flashing arrows mean different things......one is low pressure, the other is a bad sensor(s). I believe for the GTS you need 36 psi all around. So try about 37 in all and see if that puts the warning to sleep.

The system is not adjustable.......the sensors are either on or off depending on pressure. While the system can be defeated (search for "RDK" for the method), I find that once you just get past it being really sensitve and figure it out a bit it works just fine, the problem being is that on a 75 degree morning tire pressure is lower than when sitting in 95 degree sun. So in the morning the system may give you a warning, but in the afternoon it may not. Start out with 37 PSI in the morning and you should be fine all day.

Alan

The system (well actually the sensors) are supposed to be temperature compensated (and they are to a degree) but the temperature compensation doesn't seem to be perfect- as you noted.

I've often wondered if a modern system that is programmable for pressure could be interfaced to the console warning system. SmartTire systems seem to be pretty good but I don't want more displays to mount in the car....

Another thing on the long list of possible future projects...

Alan

Schocki

How accurate is your pressure gauge?

I drive mine @ 40 PSI too and it works great.
The german owner's manual actually tells you to increase the pressure by 0.3 Bar when you get the warning. The warning is usually triggerd slightly below 2.5 Bar or 36 PSI. If you increase the pressure by 0.3 Bar or 4.3 PSI you are right @ 40 PSI and everything is fine! If I run below 40 PSI and I drive above 100 MPH the RDK warning is also triggered. The light stays off if the pressure is @ 40 PSI. From what you posted everyhting is working as advertised!

bigs

Mine did the same thing. And they were EXTREMELY sensitive to tiny incremental changes in tire pressure. If I tried to run my tires at 38 psi, I'd get a warning for all four tires. If I bumped the pressure up to 38.5 (as close as I could tell on my gauge) the warnings would all go away. And this seemed to be the situation no matter how many different gauges I tried.

I always thought that was strange, since recommended pressure in my owner's manual is 36 psi.

I would just cancel the nanny warning message, but there was still that mildly annoying small warning light that wouldn't go away.

My mechanics also told me there was no way to adjust the trigger pressure on the RDK system.

So, I solved my problem by purchasing new wheels and getting rid of the whole system. It bugged me.

For those who have never seen the pressure sensors - which I hadn't until the rims were removed - they look like a small, round disc - roughly the size of an old 50 cent piece - embedded in the wheel, containing a small, thin, internal diaphragm which responds to air pressure.

I have wondered if their accuracy might change with age if the thin diaphragm becomes more brittle, but I don't know for sure.

Alan

Mine also seem to alarm at about 38 psi. On hot 115 degree days I get more warnings some in the morning that don't repeat later in the day... compensation issue I think.

My tires are OK @ 40 psi but its not like you have much choice unless you can live with frequent warning (or no warning if you disable). It would be nice to have programmable limits for the new various modern tire options.

Alan

bigs

I can't figure out why the factory didn't engineer the system so that it wasn't triggered unless the pressure hit, say, 32 psi or so.

I mean, the whole point is to warn you if you've got an air leak and you're heading toward a flat, right? Or at least heading toward dangerously low pressures.

Seems like a psi of 32-34 would be a safe trigger pressure, and you'd have a little more leeway to work with - you know, just in case you're an old fart who likes a somewhat comfortable ride.

Alan

Bigs,
Some of the new ones let you set various warnings. Low pressure warning at one value and serious low pressure alert at another lower value. Some will even warn you immediately if the pressure is reducing quickly. Great way to sort the routine maintenance issues from the real emergency.

The Smart-Tire can even readout actual pressure per wheel while under-way

Alan

ColinB

I disabled my RDK system after weeks of frustration and concluded that Herr Ing Dr Porsche was having a laugh at my expense. However on my 89 car the front tyres run at 2.5 bars and rears at 3.5. I have 225/245 tyres. Are the GTS pressures all the same?

Colin 89GT

Vilhuer

When RDK was new high performance tires needed higher pressure than todays modern rubber. Porsche wanting to give as much warning as possible did set limit as high as possible. Way the sensors are build do not allow adjustment in them. Modern systems use different type which were not available at the time.

IIRR there are two types of sensors and GTS use lower on all fours while S4 and GT have low on front and high at rear.

ColinB

Thanks Erkka
As ever you are a mine of information.
Colin 89GT

cobalt

The GTS manual recommends 36 PSI all around for the 225/255 summer tires and 36/44 for winter tires. I don't plan on doing much winter driving so 36 was fine. I was reading about the heat compensation, yesterday it was close to 100 degrees so that may have something to do with it. I was rather surprised that i never had a warning at 36 PSI using the same gage with the MXX3's yet with the PS2's it will not accept anything below 40 PSI. I had heard these things were a PITA but this is the first I experienced it.

I also noticed that the manual states not to inflate the tire to more than 88 PSI. I will talk to the tire guy and see. I know they pump the pressure up really high to get the tire to seat. It may be possible that they exceeded 88PSI and have thrown the sensors out. This may explain why I was able to read 36PSI before and now I am locked into 40 PSI.

Today it is much cooler. I will play with the pressures and see if it makes a difference.

You have to admit for the limited computer technology of the time it was quite an advanced system.

Thanks, I will paly with the pressures and let you know.

MikeN

Actually if they inflated to 88 psi or over they probably destroyed the sensors and they are not cheap......in fact I think they are some of the most expensive doo-dads for a 928......like $350 each, two per wheel.

Porsche factory wheels with RDK came with a nice metallic gold sticker mounted on the inside with red writing to warn tire changers about the system. Most are covered with brake dust or long gone by now.

The system was really very nice for the time and still has use today. Porsche was really **** about tire pressure with the 928 capable of running at 170 MPH
so hence the "strict" system. S4 and GT models had 3.0 Bar (44psi) rear sensors and 2.5 Bar (36psi) front sensors. GTS models had the 2.5 Bar sensors all around for the upgraded 17" rubber.

Again, once you get the know the system it's really pretty nice......kinda like the 928 in general!

cobalt

Yes, the system appears to be functioning. The arrows are flashing so the sensors should be OK. I know solid arrow means one or more sensors are bad. That makes me very happy now that I hear they are $350 a pop. Just surprised that they appeared to require higher pressure with the new tires vs the old MXX3's. The ride is great at 40 PSI these tires feel soft compared to the old Michelins even at the higher pressure. Boy do they grip like glue.

I wish I had some of this info yesterday. With the cooler weather today it makes it hard to compare. I will start at 37 PSI and go from there.

ROG100

As per the manual I increase the pressure as the ambient temperature increases.
Here in TX average is about 98F. Like Schocki mine are currently at 40PSI.
I find the RDK very usefull at helping me maintain the correct pressures.
I don't know why so many people have a problem.

The only time it gives a warning is when the pressure drops in one or more tires.
When it does I pump them back up to the correct pressure.
There is a very good graph in the manual that gives you pressure versus ambient temperature.

Long live RDK.