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Discussion Starter #1
Noticed that the rear tire pressure had dropped 6 pounds in one tire, and about 3 in the other rear tire

my front tires have lost about 1-2 pounds also

this has happened over about a 1 month period. While the temperature has dropped to freezing level recently, I used nitrogen inflation so did not anticipate temperature to be a factor in this equation.

This is on my winter tires ( pirelli 275/40/20 snows )

when I had the tire shop install the snowies on my stock 20s the tire guy did mention that one of the seals on one of the sensors was gone and replaced it - cost about 3 bucks to replace the seal

I'm wondering...

1) shouldn't my tpms dash light have come on when 6 pounds are lost on a rear tire?

2) are tpms sensors covered under the factory warranty even if you didn't buy / install your snowies at the dealer?

3) what - (other than the obvious running over nails etc- which there is no evidence of in the tires) could be causing this drop at weird rates in each of the 4 corners of the vehicle?

4) could it have something to do with the tpms sensors?
 

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The First temp drop of the season drove me nut's, It will not tell you which is the low tire and it is recommended that you add 6 lbs. to all of them drive around awhile and the light will go off. Ever since the Feds required TPMS in all vehicles this is a problem with all cars. I got a loner Enterprise one morning and every car in their fleet had the TPMS light because it got cold the night before. We will have to wait until they get the kinks out and it will be at least a valuable off road feature as time goes on.

The Porsche TMPS will tell you the air pressure in each tire. That would be the one I like. Most Porsches don't have spares anymore so they call that light the one the signifies that your day is now ruined.
 

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Using nitrogen in the tires will have no effect on the pressure reduction when it gets cold. PV = NrT except for supercritical gases. So as T goes down so does P. Buy a small compressor and re inflate the tires after the first low temp in the winter.
Ever wonder why they tell you that under inflated tires makes them heat up, (which should increase the pressure in the tire) but the low pressure light doesn't go off even after 200 miles of 80+ driving?
 

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2006-2009 Range Rover Sport
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What are you measuring pressure with?

If you don't have one, invest in a good dial gauge like thishttp://www.autometer.com/cat_gaugedetail.aspx?gid=2460&sid=1. In addition to lasting forever, I find them more consistent than the fancy looking $20 digital gauges that read in 0.1 psi increments, or the $5.99 pencil gauges.

Once you get a good gauge these questions might answer themselves.

That said, if you really did lose 6 psi over a month, you have a slow leak somewhere. 1-2 psi/mo is within reason.

TPMS only comes on if you are underinflated--not if you are overinflated and lose pressure.

Don't waste your money on nitrogen. Plain old air is good enough. The problem with most air from the gas station is that it has too much water vapor in it which really can screw up the pressure reading as it cools or heats. The only advantage to nitrogen is that it's dry. When you use a gas station air compressor, let it blow off air for about 5-10 seconds before putting it on the valve, since that is when most of the water in the compressor tank comes out.
 

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the sensor should come on... because they are set to have 45lbs in the back and 38lbs in the front...remember to measure it when its cold
 

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2006-2009 Range Rover Sport
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Up to MY2010, North America specs for cold inflation pressure s/b 38psi front and 42psi rear. Lone Rangerover, what is the pressure on yours? I am thinking perhaps your snow tires were overinflated to begin with... Many tires shops usually don't know / don't check the inflation pressure recommended by a certain car manufacturer, so they tend to rely on max PSI pressure indicated on the sidewall of the tire, which is often too high.
 

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2006-2009 Range Rover Sport
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x2 on that the sensors should have come on for a 6 lb. drop. i'm not sure if factory warranty will cover it unless it's not working per spec, but you never know who those dealers will argue that it's not covered.
 

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Discussion Starter #8
umbertob said:
Up to MY2010, North America specs for cold inflation pressure s/b 38psi front and 42psi rear. Lone Rangerover, what is the pressure on yours? I am thinking perhaps your snow tires were overinflated to begin with... Many tires shops usually don't know / don't check the inflation pressure recommended by a certain car manufacturer, so they tend to rely on max PSI pressure indicated on the sidewall of the tire, which is often too high.
I was running the factory 38 front and 42 rear- with nitrogen.

I have found it less prone to psi loss/ gain in temperature changes in the past

that's why this strikes me as a bit odd.

I told the shop to put in 38/42 and made them write it on the work order - but I didn't Check it other than visuallyafter they were done until about a month later

Maybe I'll go back there - have them add nitro back to the factory specs, and check it this time when they're done Hopefully that works.
 

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2006-2009 Range Rover Sport
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j/c how much are you being charged to fill up your tires w nitrogen?
 

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Good, because its a complete bunch of gobbledygook for anything less than a Formula 1 car.
 

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Discussion Starter #12
I don't have an f1 car, but I've noticed a significant difference in colder temps, as well as the convenience of far more consistant temperature readings on a second set of wheels that are largely sitting until the track day

also, I have set of 19" snowies on my 911, filled with nitogen - and last year, driving in 6 inches of snow & ice in subzero temperatures did not net a single psi lost, and very consistant driveability and fun.

P.s. The fun stops and the shovels come out at about 8 inches of snow & frozen ice with a 911...but a he'll of a lot of fun to drive until then

This what surprised me with the reading fluctuation on my rrss.
 

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If you think it makes a difference, fine. I know some places that charge $10 a tire to do it and the LR dealer wants $75 for the whole truck. Since I like to mess with the SA, I asked if that includes the donut spare as well. Just don't want to see anyone waste $$.
 
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