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low tire PSI on today

993 views 16 replies 2 participants last post by  jaye944 
#1 · (Edited)
OK, so I may be over reacting, but give us some... just in case scenario :yikes:

So haven't checked tires since beginning of dec, my usual maintenance is every month,

so driving on the highway, doing at least 120, get the warning, no shaking, no noise, get to work
all tires look good, as it's a 45 minute drive no point in doing a PSI test properly, I understand the warning comes on at 25% or worse. So for 36psi, that's about 9psi.

Should I see 9psi ? IF the tires are not low when I check any ideas, just reset the idrive?
I dont have TPMS sensors and not running RFT's, running go-flats for several years,
rear brakes were done about 3 months ago, fronts done about a month

ta !
 
#2 · (Edited)
Leakage rated vary. My cars leak air between one-half and one PSI every two or three weeks. Driving the cars seems to increase the leakage rates. Checking your tires only ever two months is not enough. It's particularly not enough when the outside temperatures are steadily decreasing, e.g. early-December to early-February in Canuckastan
.

From the Ideal Gas Law, tire pressures go up or down about one PSI for every ten degrees F.

You could also have an embedded nail or screw. It they're headless, they're hard to find visually.

Before FTM and TPMS's, my "flat tire detection system" was to adjust the pressures precisely with a dial pressure gauge, so that the pressures of the two tires on the same axle are identical. I'd do this early in the morning, when the car is completely cooled off, and before sunlight hits the tires (heating them up and changing the pressures). If the pressures on an axle are different in two or three weeks, I'd go looking for a nail or screw and always find one.

I even out tire wear by adjusting the pressures. I usually do it in two PSI and rotation stint (5k to 7k miles) increments. At these increments, there are measurable differences in wear patterns. So, running tires at nine PSI below where they should be will quickly have a significant, negative impact on the wear patterns.

I used to get paid every other Friday. My routine was to check all the cars' tire pressures the Saturday morning after pay day. It's also a good idea to check tire pressures before and after a day on the road. I only get paid once a month now, and I drive less. So, I now sometimes go three weeks in between checking pressures.

I'm taking it that that speed of 120 is 120 km/hr, which is 75 MPH is 'murican units.

The key to long tire life is "A.I.R.:" Alignment, Inflation, Rotation. Doing this, I'll get 45k miles out of my Conti' DW's (tread wear rating of 340) on my Cobalt, almost 40k miles out of my Michelin PSS's (tread war rating of 300) on my 535i, and between 55k and 60k miles out of the Bridgestone Dueler's (tread wear rating of 500) on Frau Putzer's X3.

My top five tire lifespans have been: 79k, 74, 70k, 70k, and 68k miles. I generally keep cars in integer increments (1, 2, 3) of sets of tires, leaving a few thousand miles on the last set of tires for the next owner.

I have to measure and top off my tires in the driveway, because my garage is too cramped. I do this in the early mornings, when all the old geezers in my 'hood are out getting in their "10,000 steps." My garage door is 31' from the public sidewalk (driveway is 1.9 cars long... WTF?). I top the tires off with a good bicycle hand pump. The geezers are always asking me "Do you have a flat tire?" This is one of the problems that will be solved with our next house, with a garage large enough that I can scoot in between the cars on my mechanic's stool inside my garage.
 
#3 ·
txs AP, yeah, 2 months is bad, in the cold, I sometimes get lazy,
I'm hoping it is just a little loss
I'll check it out later on
txs for the indepth

A
 
#4 ·
Yeah, cold makes the rubber less flexible too, increasing leakage. That's why things went all to **** on the space shuttle Challenger.

Making tire last has become a (so far) healthy obsession with me. In college, I worked in a bank's courier office where they put 1,000,000 miles/year on their fleet of about 15 vehicles. The only time they checked tire pressures was at oil changes. I offered to keep the tires up, but they didn't want to pay me any more hours. So, they bought a lot of tires. They also poo-poo-ed my idea to use synthetic oil, saving fuel (~2%) and extending drain intervals, with a net savings.
 
#5 ·
^ yup on the SS challenger, that was a major clusterFuq

amazing, an hour or 2 overtime costs them in the long run 1000's ! Pretty short sighted, like a lot of companies/managers, TBH, it's usually the bean counters
that don't understand that.... will blow 1000's on shareholders champagne. but stop free coffee for the workers
 
#6 · (Edited)
The project engineer for Morton Thiokol was so concerned about the booster O-rings failing that he didn't watch the launch.

Companies look to their biggest "cost centers" first for efficiency gains. Banks' biggest cost that they have control over is labor. So, they improve efficiency by scraping as much back from employees as they can, at least the lower-level employees. A transportation company would be more likely to look at vehicle maintenance for potential efficiency gains.

Senior managers at the bank I worked at had company cars, replaced every three years (when the IRS lets corporations fully depreciate passenger cars). They'd usually buy them for their spouse's car when they got a new company car. I'm sure they paid well below market value. Another scam was that those company cars would always get new tires right before being sold to the managers. This was in a relatively high density area, so the average mileage on those managers' company cars was almost always less than 36k miles after three years. They could have saved the bank and the managers money by just buying four tires and putting them in the trunk when they sold the cars.
 
#7 ·
Yeah I remember that from that TV movie for the challenger movie, really heartbreaking at the farce !

The project engineer for Morton Thiokol was so concerned about the booster O-rings failing that he didn't watch the launch..
 
#8 ·
anyway back on track LOL

when I finished work , I only had my digital airpump, though all tires looked ok, got on my knee in the carpark and started to check,

the driver front was down to 16psi, omg ! my heart nearly stopped, all the others were about 3 or 4 psi down.
that's not 25% lol, nearly 50%.

How the hell could I have been driving on 16psi, man, I learned my lesson !

So I pumped up to 32psi, drove home (45min on the highway) checked on the digital gauge I have, showed 35psi, I'll monitor it

Was wondering if hitting one of the numerous potholes on the 401, caused by winter may have knocked some air out ? strange for 1 tire, I thought it was a slow puncture maybe not
 
#9 ·
I'd look real hard at the tire that was way down. It might have an embedded nail that you haven't seen yet. That's the usual suspect.

Since I check my tires every two or three weeks, I'm only off one PSI or so unless I have a slow leak. I can handle that with a hand pump.

I was an engineer for the US Navy, and I worked on dangerous stuff. One of my continuing training classes presented case studies of projects that went particularly well and particularly poorly. The Challenger was one of the case studies, and the events described were so damning that that chapter was full of footnotes, unlike the other case studies.
 
#11 ·
so car had cooled down for 6 hours, tires went down to 31.5psi so normal, looked at as much tread as I could (it was dark) and a torch, all looked good,
will report back on Wednesday
 
#12 ·
checked this morning before driving (5am - so 8 hours after) PSI with my digi gauge is down to 30.5, so lost 1 psi, I'll keep checking over the next few days and make a decision on Friday as I have a half day
 
#13 ·
as an after thought ,I didn't check the others dammit, as AP stated, PSI can vary on temps
(4deg's this morning)
 
#14 ·
OH, I'm just wondering if checking tires so frequently is going to loose air ?
I use a digi gauge, you can't hear any pffft noise
txs !
 
#15 ·
I checked my tires again yesterday, all tires were fine, except one the drivers was 2 psi down,
took her in
and TADA a screw in the tread !
 
#16 ·
The plot thins...

Pressure goes up or down roughly one PSI for every 10 degrees F, per the Ideal Gas Law.

It's getting warmer here in Floriduh. I actually had to bleed a half-PSI out of my 535i's tires when I checked them today. My Michelin PSS's have 34k miles on them and have around 4/32" of tread left. I'll go another 4k miles or so and take them down to 3/32" of tread.
 

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#17 ·
txs for the stats dude !

LOL yeah,

all tires I double checked at same, i.e. backs 36 fronts 32, all where the same reading yesterday even after a run, backs 37 and fronts 33, except the drivers which was 30, no other thing could cause that
as I could not see a nail, I thought may be valve or reseal, but my tire guy showed me a nail !
 
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