At what point does the Tire pressure sensor notice a difference? What is the tolerance of the system?
Does it go off if your tire pressure is simply low? If so, how many less PSI must it be?

I want to keep my tires properly inflated and didn't know if this system will alert the driver to low pressure (25psi when it should be 30psi or some such), or only when it is a major loss in pressure.

Thanks in advance for the information!

 

I was told by the MINI guy at the Continental Tire booth at MTTS Boston that the TPMS does not warn you until the tire is 25% below the set point. I asked this in a conversation about why MINI won't plug a run-flat.

 

I normally keep my tires at 33 psi cold. Last month I happened to check the tires and they were hovering at 30-31 psi cold. Intended to put air into the tires but didn't get to it that week. A week or so later the TPMS alert came on. WTH, I said to myself. Checked the tires and 2 of them were around 29 psi cold. Hmm...okay, decided to go ahead and drive to work. Alert went off after a bit of driving. Rechecked at work and all tires were around 30-31 hot. After work again the TPMS went off with 2 tires again at 29 psi. Put air in after that at 33 psi and never had the alert again. So...for me at least, the cut off seems to be 30 psi before it'll alert you.

 

My tire sensor went off when I had a slow leak in my right rear tire from a nail. Luckily, the dealer was able to patch the wheel and I didn't have to buy a new one.

From what I understand, the tire sensor will go off when the pressure in one or more of the tires is out of sync with the others, although I'm not sure what the psi change has to be to set it off.

CROC 411

 

Not so clear if it is 30 PSI or >10% difference.
But the good news from my point of view is that the sensor does seem to indicate when tire pressure is a little low and not just when there is a tire failure. The difference might be to forget a tire gauge and just wait for the sensor to tell you when tire pressure is low...

I look forward to further responses!
Thanks!!

 

The manual says the TPS measures wheel speed (RPM), and compares each wheel to the others. When one wheel is consistantly spinning faster than the others, it interpretes that as a flat tire and signals you. We'd have to figure what sort of difference in diameter that the loss of 3 psi makes with the tire to calculate the actual decision threshold.

Also, my MCS needed it's TPS calibrated when it was new and it took me several days to figure it out. Calibration was simple and consisted of telling the computer to start calibrating, then drive off. After about 2-3 minutes of driving, the computer signals it's done.

 

That's the old system, new MINIs have a pressure sensor in the tire which communicates with the computer. The change happened sometime in the last year, Tristan has the old system, Shawn has the new one. The new system has to be reset when you get the tires changed, even if the wheels never moved during the change. That confused the tire shop, and surprised me this time.

With the old system I had a tire down to 25psi, compared to 33psi before it warned me about it.

 

What BTWYX is describing seems to be direct and indirect monitoring systems. A 2008 MCS would have the former then. I'd still be curious what the tolerance levels are for the system though.

Explanation of the systems:
The direct TPMS includes a sensor located inside the tire that directly measures the temperature and pressure of each individual tire. It functions as soon as the vehicle begins to move, accurately measuring temperature and pressure, and issues timely warnings when deviations occur. It works on all road surfaces and full range of travel speeds.


Indirect systems, or ABS-based systems, measure the rotational speed differences between the left and right wheels to sense tire under-inflation. In general these systems have difficulty detecting more than one low tire and have performance constraints at high speeds and over varying road surfaces. Also, the time required to recognize a low tire pressure condition varies from one to ten minutes.

 

Interesting. I too had a nail in my left rear a few weeks ago. The sensor went off (you could also hear the air coming out). I drove to the dealer and they said they were not allowed to repair run-flats as Mini won't let them.

I then took the car to a Goodyear tire shop and they said they can normally repair them, but in my case the nail that had penetrated was too large (rule of thumb) so they couldn't do it (note: different argument from what Mini had said).

Long story short, I ended up getting the tire replaced at the Mini dealer, who were considerably cheaper than the Goodyear shop.

A couple of weeks after the replacement (and 300+ miles later) I was on the freeway and the damn sensor came on again. I pulled over at a Sheetz and checked the pressure in all four tires, the fronts were at 33, the rear passenger was at 35 and the rear driver side was at 32. I inflated it to 35 to match the other rear tire and it's been fine ever since. So given that it was a new tire and the dealership had balanced it, I don't know how it had lost pressure enough to set the sensor off.

 

My little tidbit....a couple weeks ago my TPMS warning light came on when I was leaving for work in the morning. Found the left rear at 29 psi, all the others at 33. Re-inflated it and it went a week before coming back on, same psi drop set it off. Took it to the local Discount Tire who found a small nail and patched it from the inside for free. Weirdly, according to the Owner's Manual, I should have had to reset the system since one of the tires/sensors had been worked on but I didn't. No more alerts since being repaired. On another note, my 2006 Cayman doesn't have TPMS but it became standard on 2007 models. On the Porsches, you can scroll to a schematic on the dash display that shows all four tires and their exact current pressure. I wonder if the MINI's sensors are "simpler" than that, or if not having the schematic ability is just a cost cutting measure.

 

I was thinking the same thing. On Nav-equipped MINIs there is a schematic of the car, including all four tires, with color coded pressure indicators (green = good, etc...). However, why stop short of displaying the actual pressure?

 

So do the 2008 Coopers (non-S) come with the indirect system? In other words if you purchase snow tires and wheels you would not require the TPMS sensors?

 

Its a lot more difficult to come up with a number which actually bares a reasonable resemblance to reality that saying "that looks good" or "that looks bad". A colour coded display is probably easier to read as well

 

That definitely makes sense, but I've also rented many recent cars (less costly than MINI) which do give you actual PSI numbers in the dashboard, so it can't be that the technology is that exotic...