What a way to start the day. Yesterday morning I was greeted by a low tire warning a minute or so after I left my driveway in the 2009 Audi S5. But that's not to say the tire went low somewhere in those first couple hundred yards--it doubtlessly dipped below the trigger point while the car sat overnight.
The delay comes from the way most TPMS systems operate. The in-wheel pressure sensors and their transmitters are battery powered, but the need for long battery life means they don't broadcast continuously. Update intervals range from once per minute to once every three minutes, and reports are not necessarily issued at engine start.
And that's why I got a half-mile or so down the road before the warning came on.
I drove directly to my neighborhood gas station, where the normal-looking left front proved to be at 28 psi instead of the 39 psi that's specified for an S5 front tire. I topped if off and drove on to the office without further incident.
The reason for this pre-dawn delay was a leaking plug/patch installed last month after Brent picked up a large hunk of debris.
According to our trusty local tire store, the guy who installed this plug went a little overboard and bored too large a hole, causing our slow leak and making it impossible to re-repair. So we've had to install a new matching Dunlop 255/35ZR19 tire at a cost of $330. Total damage with tax, tire disposal fee, mounting and balancing came to $396.18.
The good news is this: TPMS saved the day again. We've had more than a half-dozen experiences like this, in which leaking tires that never actually looked low never had a chance to develop into roadside flats.
My gripes? The S5's TPMS minimal system does not have position intelligence or a direct pressure readout, so I had to check all four tires with my own gauge to find the low tire. On top of that, the system requires a manual system reset through the MMI screen after you reset your pressure (and the trigger threshold) to whatever accuracy your handheld gauge possesses. Most cars do this automatically.
Dan Edmunds, Director of Vehicle Testing @ 10,985 miles
texases says:
10:15 AM, 10/29/09
Does the AWD need equal-sized, equally-worn tires? I know Subarus are picky about that.
texases says:
10:15 AM, 10/29/09
Does the AWD need equal-sized, equally-worn tires? I know Subarus are picky about that.
cr_driver says:
10:18 AM, 10/29/09
I concur with your gripes, so much for an overenginereed vehicle. Brilliant audi....
azggjones says:
10:19 AM, 10/29/09
So if Stokes went "a little overboard" why would they not pay for the tire?
thejohnp says:
10:31 AM, 10/29/09
^agreed. If they admit they messed up the patch, they should pay for a new tire.
azggjones says:
10:31 AM, 10/29/09
Correction.. If "Tire Pro" went "a little overboard" why would they not pay for the tire?
alex4515 says:
10:42 AM, 10/29/09
I definitely would have gone after the shop that put the plug in the tire, since I wouldn't have had to plop down $300+ (for ONE TIRE) had he bored the correct size hole. Also, is 39psi quite a bit higher than most standard tire pressures?
actualsize says:
10:44 AM, 10/29/09
Tire Pro is in Fresno, some 300 miles away from here. Stokes, our local, cleaned up the mess. We'd waste more than $300 in an attempt to recover $300.
audikrazy1 says:
10:50 AM, 10/29/09
TPMS is one of the biggest pains in cars now... i drive a 2009 Subaru legacy and i live in the North East and whenever there is a slight change in temperature the TPMS goes off. it is very sensitive. i know that it is supposed to be a helpful technology but it is more frustrating then anything. My mom's BMW is no better... she wound up having the local dealership put Nitrogen in her tires which has made it a little better but not much.
texases says:
11:00 AM, 10/29/09
^^Don't know why nitrogen would help.
actualsize says:
11:03 AM, 10/29/09
@audikrazy1: Do you set your tire pressures outdoors after the car has sat awhile? If not, you should. Setting them indoors in a heated garage is tempting, but the pressure out there in the cold is the one that matters.
crowb says:
11:07 AM, 10/29/09
+1 texases
Around 60% of the air in the atmosphere is already nitrogen. This "nitrogen only" tire inflation stuff is just a scam if you ask me.
actualsize says:
11:15 AM, 10/29/09
But you get to brag on your cool green valve stem caps.
mercedesfan says:
11:17 AM, 10/29/09
I thought it was ridiculous that the $33K C-Class only offered this kind of TPMS, it is inexcusable for a $60K car to not offer something more sophisticated. This is exactly the same setup that my sister's Subaru Impreza utilizes, which is fine for a $19K car, but come on Audi you've got to be able to do better than that for an additional 40 grand.
As an aside, I actually think TPMS is really helpful and have never had issues with mine (given I love in San Jose and temperature swings aren't really an issue).
joefrompa says:
11:20 AM, 10/29/09
Crowb - Not in this case. Nitrogen filled tires have much lower fluctuations in pressure due to temperature changes. They will reduce the incidence of a funky TPMS system.
My wife's 2008 Legacy GT notified us of a nail in the tire that resulted in a slow leak. Tire was at 27 PSI and went off...took about 4 days to lose 10 PSI. I keep all my tires set to around 36-38 PSI, and I don't have any TPMS sensitivity even on the coldest days.
That being said, I truly hate TPMS because of it's owner unfriendliness, the cost of replacement, and the way that most systems don't show the tire or pressure that is low (God Bless GM for doing that right on most of their cars). A low tire pressure warning doesn't tell me if I should:
A. Continue driving to the nearest air fill-up station
B. Pull over at the earliest convenience.
C. Put my flashers on and make damn sure I'm on the side of the road in the next 15 seconds.
Where as if I see my left front tire is at 27 PSI, or my right front tire is suddenly reporting 15 PSI, then I have important information that can help me make an appropriate decision.
Further, on my '08 LGT, why would I get winter tires/wheels? I either have to pay to get a spare set of TPMS sensors and then pay to have them properly calibrated, or I have to look at the TPMS sensor symbol all winter. Or put black tape over it.
To me, the current system of TPMS on most cars is worse than removing the dipstick from a car.
audikrazy1 says:
11:21 AM, 10/29/09
@ actualsize:
@ texases:
What i have been doing is brining all the tires up to pressure right before i go home at a gas station i do park in a heated garage but it does not seem to make a difference. The issue is when i park at school and the car sits all day and it goes from being 25 degrees in the morning to 45 when i leave during the winter the light comes right back on...
and as for the nitrogen in my mom's car it is said to be more stable then filling the tires with air... so far it has made a difference but not much of one....
hybris says:
11:25 AM, 10/29/09
I wonder when we are going to see other gases in car tires. Probably everything from Hydrogen and Helium to maybe even Xenon in your high end cars.
sealclubb3r says:
12:07 PM, 10/29/09
^^ Er, I don't think I would be too keen about filling my tires with a presurized, explosive gas (hydrogen).
crowb says:
12:12 PM, 10/29/09
@joefrompa -
I see your point, if it can really make a huge difference in reducing pressure fluctuations due to temperature changes. I just don't understand people paying so much more for air, especially when the air they are breathing is already mostly nitrogen. I just do what you do, put a few extra PSI in the tires with regular air and I never have to worry about the TPMS.
But I also drink tap water and do my own taxes, so what the hell do I know?
joefrompa says:
12:18 PM, 10/29/09
I don't know. What the hell do you know? :)
I've never used nitrogen, but I would IF my TPMS system kept going haywire on me.
Honestly, I actually consistently go back and forth between buying a newer BMW (or similar) vs. older BMW. And my criteria include:
1. No TPMS
2. Dipstick
3. Full size spare (on the 2003 BMW 540i)
I know that stuff is pretty minor, but I'm the type of guy who checks my dipstick at least once a week, wants a full size spare, and doesn't want to deal with the hassles of TPMS when swapping summer and winter rubber.
clicq says:
12:42 PM, 10/29/09
@joefrompa: if you don't want TPMS, you're stuck getting an older BMW, since TPMS been required on all model year 2008 cars and newer (http://www.nhtsa.dot.gov/cars/rules/rulings/tirepresfinal/index.html).
@audikrazy1: you know the pressure in your tires changes after you drive. You should check the pressure in your tires before you leave school, note how much air you need to add, then add that much at the gas station. If you're checking the pressure in your tires after you've been driving, the pressure will read higher than it should. Alternatively, just inflate a couple of PSI (2lbs or so) above the recommended, since TPMS only reports low pressure, not high...
yellowbal says:
12:58 PM, 10/29/09
I would take nitrogen if it was free, but personally would never pay for it.
Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%. (wikipedia)
hybris says:
03:19 PM, 10/29/09
@sealclubb3r
I wouldn't want hydrogen filled tires my self but it would be interesting if a tire at highway speed will get hot enough to hit the flash point of the hydrogen?
equ says:
04:49 AM, 10/30/09
In 2010, audis went to indirect TPMS. This finds flats through revolution sensors. While this system also has no way of giving you actual psi numbers and requires said resets, it has one huge advantage. When you're putting on other tire/wheel sets, there are no sensor thingies that you need to move around (or buy at great cost). Also, per an older post at edmunds, those thingies break sometimes. 2006 bmw's had this indirect system as well, and as I always switch to winter tires, I prefer it. If I have to break out the pressure gauge and press a reset button on the odd day of failure, so be it.
The best direct pressure gauge was on 2007+ porsches, you get a pretty readout of all of your psi's. Not sure if it's as accurate as a trusty gauge, but it's a whole lot more convenient.