Another TPMS query

[Hadrian]

I know we've talked about the TPMS on here a lot, but I have one  more question.

I haven't used the car for a few days, but when I went to move it earlier, the fault light was on. I checked the pressures, and they were all showing 30psi.

Down from about 35-36psi due to the cooler weather I expect. I cancelled the fault, but it kept coming back after a few seconds.

Question is: .........Is there a minimum pressure where the fault light won't reset. ?

 

Yes I know I could inflate the tyres and find out, but it's raining.

 

 

[Britprius]

I think at 30 PSI the system will give a low tyre warning. Is this the message you are getting? or is it giving a system error warning.

John.

[Hadrian]

It's the yellow tyre symbol showing.

[reeac]

The solution is to inflate them back to 36 psi which is the recommended pressure. I wouldn't be happy to run them at 30 psi. if the handbook says 36.

[Herbie]

43 minutes ago, reeac said:

I wouldn't be happy to run them at 30 psi. if the handbook says 36.

Nor would the OP's insurance company if he's involved in an accident.

[Hadrian]

As all 4 tyres are still reading the same pressure, I can only assume the pressure drop is down to the cooler weather.

It's happened before because of that.  The sensors are so sensitive.

[Bob99]

I was just about to set off on a motorway trip yesterday when the warning light came on. As I had recently been to wickes I was fearing the worst as I've had two punctures in new tyres recently after visiting there. I found all tyres were down close to 30psi. Probably due to the cooler weather but mostly to my lack of checking over the last month or so. Blew tyres back up to approx 36psi and everything ok. As I was a little pushed for time yesterday thought I'd check them all again today. They were all around 35psi so set them all to 36.5. The two front tyres are original bridgestones with 48000 miles on them and were down to 3-4mm and was looking to change them soon in time for the winter due to wear and age. When checking the pressure I found a crack in the sidewall of about an inch long in the front left, so two new tyres ordered to be fitted Wednesday. That will be Goodyear eagle assymetrics 3 all round then.

[Britprius]

2 hours ago, Hadrian said:

It's the yellow tyre symbol showing.

There should also be some guidance on the information screen apart from the warning light.

John

[Bob99]

I've mentioned it before on a post about tpms, we should have the individual tyre pressures displayed not just an indicator.

[reeac]

Stand by for some physics. Boyle' Law states that for a fixed volume of gas ie. in a rigid container, pressure is proportional to absolute temperature ie degrees Kelvin. 30 Celsius is 303 Kelvin and 20 Celcius is 293 Kelvin. A reduction of temperature from 30 C to 20 C will reduce pressure by a factor of 0.967 or from 36 to 34.8 psi. .An initial temperature of 40 C would give a reduction of 0.936  or from 36 to 33.7 psi. In practice the tyre will shrink in volume slightly as the pressure reduces but that won't be a big effect. It would seem that cooler weather can explain only some of the pressure reduction. If you inflate your tyres at a filling station then they will be slightly warm as a result of having driven there so need to be at least 1 psi higher to compensate.

[wharfhouse]

5 minutes ago, reeac said:

Stand by for some physics. Boyle' Law states that for a fixed volume of gas ie. in a rigid container, pressure is proportional to absolute temperature ie degrees Kelvin. 30 Celsius is 303 Kelvin and 20 Celcius is 293 Kelvin. A reduction of temperature from 30 C to 20 C will reduce pressure by a factor of 0.967 or from 36 to 34.8 psi. .An initial temperature of 40 C would give a reduction of 0.936  or from 36 to 33.7 psi. In practice the tyre will shrink in volume slightly as the pressure reduces but that won't be a big effect. It would seem that cooler weather can explain only some of the pressure reduction. If you inflate your tyres at a filling station then they will be slightly warm as a result of having driven there so need to be at least 1 psi higher to compensate.

That tallies with what I have always found - about 3psi between summer and winter - I alway use the same hand held pressure gauge and never ever rely on the garages... Even check after a service as they are often slightly out and different between tyres when I get the car back so I put them all right so I can monitor any change by comparing between tyres which then rules out any temperature difference. I also read that oxygen molecules actually leak through the rubber tyre whereas nitrogen molecules (being larger) do not. As air is approx 20% oxygen and 80% nitrogen over time (not sure how long) a tyre will naturally lose 20% of its air. That's why some tyre places fill with nitrogen as the pressure is more stable longer term. 

[ianhu]

My 2014 shows just the indicator light for tpms. But I'm sure the newer models show the individual tyre pressures for each on the dashboard clock. Pity we can't have that upgrade

Sent from my SM-G965F using Tapatalk

[Herbie]

My 2013 RX450h shows four individual pressures - but not which wheel they relate to!

[Hadrian]

Inflated all four tyres up to 35psi today, then once reset the warning light stayed off.

I take it  that apart from the cooler weather, tyres lose pressure over time ?

I also don't know if the newer IS300's have individual pressures displayed, mine doesn't.

[Herbie]

12 hours ago, Hadrian said:

I take it  that apart from the cooler weather, tyres lose pressure over time ?

Supposedly yes, but I swear that the only loss of air from my tyres over the last four months has been a tiny amount when attaching and removing my tyre pressure gauge!

[Britprius]

On 8/12/2019 at 10:57 PM, wharfhouse said:

That tallies with what I have always found - about 3psi between summer and winter - I alway use the same hand held pressure gauge and never ever rely on the garages... Even check after a service as they are often slightly out and different between tyres when I get the car back so I put them all right so I can monitor any change by comparing between tyres which then rules out any temperature difference. I also read that oxygen molecules actually leak through the rubber tyre whereas nitrogen molecules (being larger) do not. As air is approx 20% oxygen and 80% nitrogen over time (not sure how long) a tyre will naturally lose 20% of its air. That's why some tyre places fill with nitrogen as the pressure is more stable longer term. 

This is partly true, but also over time the percentage of nitrogen in the tyres will increase as the oxygen is lost and then replaced with 80% nitrogen from the compressor. For normal motoring use this is just a money making scheme.

John.

[Hadrian]

Using Nitrogen is a complete wast of time, unless you wear a back to front baseball cap. 🙂

They use it in aircraft tyres, but that for fire suppression.

[200h]

i know nitrogen is a more stable gas for filling your tyres as the nitrogen doesnt expand as much as air,

but surely your tyre pressure data should have fill pressures for both Air & Nitrogen as the tyre pressure

data is to allow the expansion of Air to increase so the tyre pressures are correct for the everyday use

of the car , if nitrogen doesn't expand as much then surely your tyres will be under inflated.

[rayaans]

Ours recently did this too just last week. All were showing 32psi. Inflated back to 36psi, drove around the block and it cancelled itself.

[Britprius]

On 8/15/2019 at 6:59 AM, 200h said:

i know nitrogen is a more stable gas for filling your tyres as the nitrogen doesnt expand as much as air,

but surely your tyre pressure data should have fill pressures for both Air & Nitrogen as the tyre pressure

data is to allow the expansion of Air to increase so the tyre pressures are correct for the everyday use

of the car , if nitrogen doesn't expand as much then surely your tyres will be under inflated.

All gasses expand at the same rate for a given temperature rise. See Boils Law.

John.