Unreliable results measuring MPG / overinflation valve stem failure - Fuel Economy, Hypermiling, EcoModding News and Forum

Cd · 03-30-2008, 11:35 AM

Yesterday, I aired my tires up to what I thought was 50 PSI. It turns out it was closer to 65-70 PSI - but this measurement was taken after the blowout *on a ( very ) hot tire. ( Maximum inflation listed on the tire is 44 PSI )
I was in a hurry and did not check the PSI using more than one guage. I have found ( and especially yesterday ) that tire guages are horribly inaccurate sometimes.
I guess I have found my limit, because I had the blowout. Thankfully, what occured was that my valve stem developed a large leak around its' base - so there was no dramatic explosion like I always feared.
( I'm not saying that an explosion could never happen, but thankfully this time around it didn't )
The tire is fine, but needs the valve stem replaced.

* On the tires that weren't blown of coarse .

Daox · 03-30-2008, 11:57 AM

I use an accutire digital pressure gauge. Its quite accurate. Those slide types I hear can be pretty inaccurate.

extragoode · 03-30-2008, 12:05 PM

My personal favorite is the little dial types. No batteries, instant read, and I don't have reset it like a stick gauge. The one I have been using for 3-4 years now I wouldn't trust to be exactly accurate, but it's always within 1 or 2 psi of the Jeep's internal senser. Would you double check with another of the same type, or use two different types to be extra sure?

extragoode · 03-30-2008, 12:08 PM

Another thing is my air compressor is a little baby 1 gallon 90 psi thing. I can tell within what my pressure is within ~10 psi just by listening to how hard the compressor is working. That probably wouldn't work at all on a compressor that was even just a little bigger.

trebuchet03 · 03-30-2008, 12:20 PM

How old was the stem?

johnpr · 03-31-2008, 01:06 AM

just an fyi, they do make high pressure stems, you might get an odd look or a speech if you as for them to be installed when its being replaced but we always used them at the tire shop on applications over 45~ psi,

just a thought, and stay safe

bhazard · 03-31-2008, 01:17 AM

Yeah, when I worked at the tire shop I worked at we had three stems. A regular short stem for most applications, a long version of it for wheels with the stem hole in a deep spot or a lot of steel wheels with covers, and then the high pressure stem for, well, high pressure applications, mainly big LT tires, the ones that are rated at like 80 psi and such.

Cd · 03-31-2008, 01:21 AM

Quote:

Originally Posted by trebuchet03

How old was the stem?

I purchased the tires around a year and a half ago.

They only have a couple of thousand miles on them ( perhaps less )

I have had them aired up to 50 + PSI since I bought them.

Since I changed jobs around two months ago, I walk to work and take a bus around town. Before that, I was putting 74 miles a week on the car.

I drive the car maybe once every two or three weeks ( around a mile ) just to keep it from falling apart.

I'm guessing this is one of the contributing factors that led to the failure. ( The car just sitting. )

trebuchet03 · 03-31-2008, 01:33 AM

Gotcha - it's interesting to know the weakest link here is the stem... Which personally, I have no problem with that. If I had to choose my weakest link - it'd be the stem

Were this particularly long stems? What region do you live in (hot/cold)? Where is the car stored (UV exposure)? Humidity? Which wheel was it on (front/rear - left/right)? Did that side of the car face south (again, UV exposure)? Frequent rotation? Any distinguishing characteristics on the failed stem (discoloration in rubber or steel, steel fracture, etc. - compare to other good stems)? Point of failure (stem base, stem valve, inner seal ridge, vertical or horizontal crack)?

Sorry for the question bombardment - this is failure analysis treb

cfg83 · 03-31-2008, 03:26 AM

bhazard -

Quote:

Originally Posted by bhazard

Yeah, when I worked at the tire shop I worked at we had three stems. A regular short stem for most applications, a long version of it for wheels with the stem hole in a deep spot or a lot of steel wheels with covers, and then the high pressure stem for, well, high pressure applications, mainly big LT tires, the ones that are rated at like 80 psi and such.

Thanks! If I had known this then I would have requested high-pressure stems when I got my new tires. I think this needs to be part our FAQ.

CarloSW2