I got the tire pressure warning light on my 2003 MC on the way to work today. I've got the runflats, so I didn't feel the need to stop until I got to work, which went fine.

I did a visual inspection of the tires and didn't see the problem - is this something that I need to take to a tire shop to investigate?

 

You won't see a problem as the tires are designed to hold the car up even without air. Did you check the pressure in the tires?

 

No, I haven't checked the pressure - I'll see if I can dig up a tire gague and do that soon (pouring rain outside now).

How long do the runflats last?

 

I too get the warning every once in a while, and the tires have never appeared under-inflated. They always look fine, but actually are low!

 

So it could just be that I need to put some air in the tires, and not a flat?

 

It's stopped raining in Cary now.

Check your pressures. If it's just low, top it off, visually inspect for nails, screws, etc. Take it to the shop for a patch (or I plug mine myself) if it has anything in it.

You can drive up to 100 miles or so at 50 MPH with zero pressure - but that will destroy the tire and yield it unrepairable. In fact, driving for any significant distance on zero pressure makes a repair not a good idea - structural integrity of the tire casing may have been compromised. Hopefully you're just low and won't be buying a new runflat (which is pricey).

 

if you are some bar lower that you are suppose to be, your warning light will come out, even if it is not a flat... the flats will look fine even with no air in them, so you better check the pressure on all of them, and check the one that needs air to see if it as problem. good luck... oh and i think you can run 100 miles with a flat (not sure) some one else can confirm this.

 

I've had a couple of false alarms from the TPM. But with the runflats, a visual inspection is no good. ALWAYS have a tire pressure gauge in your car. This is especially important with runflats, as they don't sag like conventional tires to give a visual cue.

 

My tire warning indicator went off last week so i pulled off the freeway and checked the pressures (run flats). 29.5 to 30.5 so they weren't that far off from the 30 recommended. Reset the light and no problems since. Don't know why the light went on. Is this a problem off electrical glitches to start occuring on a 2003 model?

 

because they are an indirect system (they measure slight differences in rolling diameter, not actual tire pressure), its not uncommon for there to be false alarms every once in a while from the TPMS. My wifes goes off all the time, most likely b/c we replaced one damaged tire about 1500 miles in, so its ever so slightly larger in diameter than the other tires. For this reason, you MUST carry a tire guage with you, to know when your TPMS has a good point, or whether its a false alarm.

The system is overly touchy on purpose though, as false positives are ok (annoying, b/c you have to check the tire pressures) but false negatives would be far worse (the tire actually going flat, and the monitor not going off).

Its always a tradeoff, my mazda has direct measure TPMS (a small unit attatched to the valve stem measures air pressure), which is confidence inspiring, in that it never gives me a faulty reading, BUT, it means that my selection of aftermarket wheels was limited (the wheels must be able to accomodate the sensor), and twice so far there has been a leak in my tires that has turned out to be the TPMS itself leaking due to a pinched o-ring.

Each system has its benefits and disadvantages. Frankly, I prefer the indirect system on the mini, even with its occasional false positives. In the manual, it even states that "spirited driving" can cause a TPMS light to come on.

Visual inspection is NOT a suitable way to see if your tire is low, ESPECIALLY with runflats, but even with non runflats, tires have gotten such stronger sidewalls that this is simply no longer a valid way to check your air pressures. If you wanna do visual inspections, get some of these:

http://www.accu-pressure.com/cgi-bin...17.47693&pid=1

 

The light came on for me this past week. After looking at the tires I continued the trip as they looked fine. With it constantly pulling to the right the next 40 miles to work I thought I would stop at the tire shop to check the pressure. I was very surprized when the young man stated the rear tire had no pressure in it. As Deflake mentioned I could not visually see any difference.

I now carry a small tire guage with me.

Michael

 

I found the problem - a nail (or some other hunk of metal) in the area between the tread and sidewall. Pressure is still 20lbs in the tire, though, so I should hopefully be able to inflate it and get home without too much wear on the run-flat.

The next question is - if the tire's not patchable, do I get another expensive run-flat, or swap the back tires for normal ones?

 

Bummer - between the tread and sidewall isn't patchable - tire flexes too much in that area. You'll need a tire. You'll make it home, and can keep adding air, but your tire is toast. If you pay for shipping I'll send you a 2/3 used up runflat for free... LMK... but it may not be worth it.

ALWAYS carry a pressure gauge and check. Michael, no offense, but if your car is pulling to one side something's wrong, OK? Please pull over and check at your earliest opportunity - something serious may be going on and we want you safe, bud!

A visual check won't work well on runflats - or on most tires - unless you have a REALLY practiced eye, and the TPMS is MUCH more sensitive than that!

 

Not picking nits here... it's entirely possible you were thinking one thing & typed another. The TPMS doesn't measure the diameter of the tire, but the rotational speed of the wheel. It uses the same wheel speed sensors the car uses for traction control. If one wheel's speed drops below the other 3, it'll signal a flat tire.

Because flat tires drag, they roll slightly more slowly. This is also why spirited driving can trick the system, and why a patch of sand or gravel in the road can do the same. Again, one new tire among 3 older ones will do the same thing, as you mentioned, due to its larger diameter resulting in slightly slower wheel rotation.

In 4 years with 2 MCS's, I've probably had 12-15 TPMS alerts. Of those, 3-4 have been valid. But I value the peace of mind, and put up with the false positives. (I ditched the run flats early on & keep a plug kit, compressor, and Fix-a-Flat in the boot at all times)

 

Because flat tires are shorter, they spin faster. They're not slipping.

Yes, runflats look perfectly normal even when flat. But kicking the tires will reveal the flat one if you have no gauge handy...

 

To follow up, I found a nail in the rear drivers-side tire. Pressure in that tire was also around 20lbs, so it looks like a slow leak. I'm going to see if I can find somewhere to attempt to patch the tire today, and if that's a nonstarter, probably replace the two rear tires with non-runflats.

 

I had mine go off about 2 weeks after I gat the car. We were out for a day trip and it went off on a strech of highway. Got out, checked the pressure and they were al fie. Ended up being my wife setting something on top of the button and when we hit a bump the object pushed it. Still, I always have and always wil carry a tire pressure guage with me.

 

Thank you. Seriously, I can't imagine driving ANY car without carrying a tire pressure gauge. It takes seconds to check and can save you from being stranded on the side of the road.

The tire pressure warning light is there for a reason, pay attention to it. If it's nothing, so what... better safe than sorry. Mine comes on every once in a while and it's almost always a false alarm but oh well, it took me what... 2 minutes to find out?

Run flats are made to get you to a safe place even if you have something in your tire... they are not made for you to drive on and never maintain and pay no attention to.

 

hehe, not picking nits huh? sure. . .

its the same thing, but you are correct, the sensors responsible for the TPMS are the wheel SPEED sensors

the two quantities are entirely related though, which is why my wifes are super touchy since we replaced one tire only after about 2000 miles (its an ever so slightly larger diameter, which makes the TPMS think that 3 of the tires are flat sometimes. . .

 

I ended up replacing all four of my runflats with standard tires of slightly larger size as well (24.7" standard vs. 24.4" runflats). Should I get the MINI dealership to adjust anything (speedometer, etc)?

 

Nope. The sensors only look and the difference in the speed of the different wheels, not the absolute speed.
Glad to hear you replaced all four. Having different tires on different axles is not a good idea.