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    What could cause a tyre to be hotter than the others on a straight highway?

    Yesterday I aligned all the tyre pressures exactly the same (to 0.1 PSI) when the car was cold (first thing in the morning).  After about an hour on a pretty straight motorway I noticed that the front drivers trye was 10degC hotter than the other 3 tyres (the computer can display pressures and temps as you travel along).

    Today I had my alignment checked and there was nothing out of the ordinary, all within specs.  So I rang my local Audi dealer and spoke to a technician.  All he could think of was maybe the calliper was sticking slightly or something was rattling about in the tyre (although then I would feel steering vibrations - which I don't).  Shocks were also mentioned but if I am driving along a straight flat motorway then I can't see that being the reason either.

    Just driving about town and the tyre gets 5degC hotter than the others  So I have booked the car in for an investigation on Friday.  I was wondering if anyone here had any other ideas what it could be though?


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    Re: What could cause a tyre to be hotter than the others on a straight highway?

    I can think of

    a) Alignment (did you also check toe setting?)
    b) The rubber is not used similar to the other tires (e.g. a flat spot from braking)
    c) Something sticks in the tire (stone or something)
    d) Suspension adjustment, (spring/damper/ride height)
     

    You could swap tires to see if it's the tire.


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    Thanks!

    Yeh, if they cant find anythng on Friday then I think a tyre swap would be the best option.


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    Click for bigger picture!


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    I think this normal in that the road friction is not the same at all times.

    For example my TPM starts with the required pressures when cold but afterwards they often vary in their increase. Often all 4 tyres rise by say, 0.2 bar each, but in most cases there are variations. My car doesn't read temps but pressure is a function of temperature anyway.

    I think that the curves, the camber and the road surface all contribute to some variation. That's my theory at least.


    --
    It's not where you're going, it's how you get there that counts

    Re: What could cause a tyre to be hotter than the others on a straight highway?

    reginos:

    My car doesn't read temps but pressure is a function of temperature anyway.

    I don´t want to spread any wrong information, but I do believe that Porsche´s TPM reads both pressure and temperature and adjust the nominal and target pressure values according to the later.

    Back to Alex´ question, I suppose you haven´t read the tire temperatures on the outside? I´d be curious to see whether the tire itself is heated up, if it´d be exposed to a misalignment it should show higher temperatures at either the inner or outer side wall.

    Other than tire related temperature increase, I could only think of a mildly grinding front brake (readable with an infrared thermometer as well), a clogged brake airduct or thermal exposure coming from the engine.


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    You forgot the most likely explaination, bad sensor...


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    Ferdie:
    reginos:

    My car doesn't read temps but pressure is a function of temperature anyway.

    I don´t want to spread any wrong information, but I do believe that Porsche´s TPM reads both pressure and temperature and adjust the nominal and target pressure values according to the later.


     

    Not exactly. It sets the target pressure according to the ambient temp. (on an assumption which I don't remember now) and compares with actual pressure. Tyre temp. is not measured by TPM.


    --
    It's not where you're going, it's how you get there that counts

    Re: What could cause a tyre to be hotter than the others on a straight highway?

    SciFrog:

    You forgot the most likely explaination, bad sensor...

     Yes! Smiley


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    reginos:
    Ferdie:
    reginos:

    My car doesn't read temps but pressure is a function of temperature anyway.

    I don´t want to spread any wrong information, but I do believe that Porsche´s TPM reads both pressure and temperature and adjust the nominal and target pressure values according to the later.

    Not exactly. It sets the target pressure according to the ambient temp. (on an assumption which I don't remember now) and compares with actual pressure. Tyre temp. is not measured by TPM.

    My understanding is that the TPMS sensor units do measure actual in-tire air temperature along with actual air pressure, and uses this temperature to "correct" the actual pressure to the equivalent pressure you would see if the air in the tire were to be at 20°C. The resulting "corrected" pressures are those you can call up from the background only when the car is stationary.

    However, Porsche's TPMS does not allow you to display these air temperatures.


    --

    fritz


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    fritz:
    reginos:
    Ferdie:
    reginos:

    My car doesn't read temps but pressure is a function of temperature anyway.

    I don´t want to spread any wrong information, but I do believe that Porsche´s TPM reads both pressure and temperature and adjust the nominal and target pressure values according to the later.

    Not exactly. It sets the target pressure according to the ambient temp. (on an assumption which I don't remember now) and compares with actual pressure. Tyre temp. is not measured by TPM.

    My understanding is that the TPMS sensor units do measure actual in-tire air temperature along with actual air pressure, and uses this temperature to "correct" the actual pressure to the equivalent pressure you would see if the air in the tire were to be at 20°C. The resulting "corrected" pressures are those you can call up from the background only when the car is stationary.

    However, Porsche's TPMS does not allow you to display these air temperatures.

    I am not sure.

    The handbook when explaining the screen with the deviations,  says" in accordance with physical principles, the air pressure changes as the temperature changes. For every 10 C change in air temp ,the tyre pressure increases or decreases by around 0.1 bar"

    Not clear if it takes the temp of the air inside the tyre into account of the ambient temp.Smiley


    --
    It's not where you're going, it's how you get there that counts


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    reginos:
    fritz:
    reginos:
    Ferdie:
    reginos:

    My car doesn't read temps but pressure is a function of temperature anyway.

    I don´t want to spread any wrong information, but I do believe that Porsche´s TPM reads both pressure and temperature and adjust the nominal and target pressure values according to the later.

    Not exactly. It sets the target pressure according to the ambient temp. (on an assumption which I don't remember now) and compares with actual pressure. Tyre temp. is not measured by TPM.

    My understanding is that the TPMS sensor units do measure actual in-tire air temperature along with actual air pressure, and uses this temperature to "correct" the actual pressure to the equivalent pressure you would see if the air in the tire were to be at 20°C. The resulting "corrected" pressures are those you can call up from the background only when the car is stationary.

    However, Porsche's TPMS does not allow you to display these air temperatures.

    I am not sure.

    The handbook when explaining the screen with the deviations,  says" in accordance with physical principles, the air pressure changes as the temperature changes. For every 10 C change in air temp ,the tyre pressure increases or decreases by around 0.1 bar"

    Not clear if it takes the temp of the air inside the tyre into account of the ambient temp.Smiley

     

    If you think about it, it has to be the air temp inside the tire as it has a material influence on the air pressure inside the tire. Ambient air temperature does not have a real influence.

     


    --

    fritz


    Re: What could cause a tyre to be hotter than the others on a straight highway?

    fritz:

    If you think about it, it has to be the air temp inside the tire as it has a material influence on the air pressure inside the tire. Ambient air temperature does not have a real influence.

     

     There is no such thing as a sensor for pressure alone, they always measure temperature too. They need it to calculate their output in bar, although some sensors have a mode that only communicates pressure to the outside world (i.e. pulse width).

    So chances are very high, the temperature display comes from the very same sensor. In that case I'm pretty sure that the temperature is not very accurate.


     
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