Went out to eat yesterday and while at the resturant a cold front came through dropping the temperature 20+ degrees.
When leaving the resturant the "low tire pressure" light came on showing all four tires were low.
I checked each tire and they were all eight pounds low from the 36lb they were supposed to be.
To be accurate I must say the the temperatures have been getting cooler over the last month before this cold front hit so the actual drop in temperature would be more like 30+ degrees over that full period.
Now I know that tire pressure will drop somewhat(usualy 2psi) with the drop in ambient temperature but I've never had this big a drop in pressure berfore, is this something peculiar to run flats?
This is a new Mini Cooper and the tires all have green valve caps and I had allways assumed that indicated they were nitrogen filled, apparently not the case.
If I were to fill the tires back to the 36lb called for, what will happen when the ambient temperatures go back up?
Will they then be overinflated?(especialy when warmed up on the highway)
Is it normal for run flats to make such large pressure changes with ambient pressure changes?

 

I have no comment, but your post did make me think of this one from another forum that I am copying in its entirety:

 

Yea, OK got it.
Need to change out the summer air for the winter air..

Honestly though, I've never experienced that many psi with a climate change before and was just wondering if run flats were more sensitive to teperature fluctuations and if so should I expect to re-adjust the pressure again after this cold snap is through?

 

I had the same thing happen a week ago with my Clubman (new in May). On a cold morning, the tire pressure warning went on for all four tires. They were all at about 28 psi. I filled them all up to 36 and everything seems fine.

 

I have been thinking about tire pressure lately myself. I have never checked or felt the need to add air. They look fine. I know you cant tell all from looking but I am not new to low profile tires. I guess I got lucky buying in winter. I apparently started with correct pressure. Hit summer and they were likely over inflated. Now the temps are a dropping and I am likely back in spec. I wil l be checking them tomorrow. all sacrcasm (but all true). I have nothing to add here.

 

As an aside, Putting more air in my continental run flats actually improved ride quality quite opposite from what I expected. 36 psi -> 45 psi. Max on sidewall 51.

 

Correct me if I'm wrong, but I thought the TPMS light indicates one or more tires is low, not necessarily all four? I have noticed that whatever the time of year, after about a month I need to add air. Also, I run my continentals at 38, which is what the owners manual specs for a MCS driven under 100mph.

 

Does the TPMS use difference in rotation to determine pressure via ABS sensors, or is there an actual pressure sensor at each wheel?

And following the owners manual means changing oil at 15K intervals and auto tranny fluid never. :O

 

What a coincidence! New topic...just got off work and received the low tire pressure warning for the first time ever. I drove in a bit of dirt today so I was worried I possibly caught a nail.

Weather is reporting 55º here, which is cooler than it's been. No tire appeared flat so I just drove home. About a month ago the pressure was 35 all around. After driving about 2 miles home it showed 31 all around. I guess I will just re-adjust tomorrow morning.

 

I just read a long thread on this subject. Seems the consensus was the first gen mini had the rotational difference TPMS, while the second gen mini had the TPMS sensors, IF it has metal valve stems..

 

Same issue here. Its getting colder in Boston & when the temp dips down to 30-35 Degrees the Low Tire sensor comes on for all 4 tires(Run Flats) & sometimes just for one. Tire pressure is Always Fine when i check them. I just keep resetting it. Little bit of a pain in the ****. I'll have it checked by the dealer. 2013 Countrymen S All4

 

Don't you remember high school chemistry? PV = nRT.

 

Update- I checked pressure today. They were all four 34lbs. I took them back to 38, as recommended in the driver door sticker, and reset the monitoring system. Oddly, I too think the car felt better in that the bumps didnt seem quite as jarring after the increase in pressure. That's converse to what I may have thought going in.

According to my 2013 owners manual, it says the system is still sensing rotational differences.

We bought the car in January and I have never checked the pressure as the tires "looked" fine. Realizing now that the runflats combined with the low profile probably don't give away much to a visual inspection. I'm all good now. And I learned a little

 

Same thing happened to me , it's been unusually cold her in NoCal mid 20's in the AM and on Sunday warning light said Front Passenger tire was low. The this morning it was 31 and got all four tires low , took it to a local shop, they said the tires were at 26psi , except the one I filled on Sunday, very weird, I also have RFT's but my inside door sticker recommends 32psi, so that's what we filled them to.

 

Ditto, the first cold day this fall the run flats threw the error. I usually have mine a little low anyway, 32psi, so it took a couple of days and resets to get the system to go along with the wide swings in temperature we went through during the change of seasons in my area.