Tyre temperature difference

ZZZZ

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Ignorance truly is a bliss: never before had I given a thought to the difference in tyres' temperature, between front and rear - that is, until I got myself a new gadget, in the shape of TPMS bluetooth (BLE) valves and an iPhone app.

39506866405_3ed0ee7038_o.png


Apparently (after a 15-mile trip) the driving axle is almost 10ºC hotter, which is logical, however I have no idea, whether that should only be, say a couple of degrees, or a couple of hundred :shock:

OK, so a tad exaggeration here, but still?
 

LostKiwi

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On an FWD car your front wheels:
Drive the car forward
Perform the bulk of the braking
Do the bulk of the cornering
Have more weight on them

The rear wheels on the other hand just have to tag along behind preventing the body scraping the tarmac.
 

rf065

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Once when on the m/way I'd left the tyre pressures showing on the dash, I was surprised how quickly they dropped by 2 or 3 psi as soon as we hit a rain shower and the wet roads obviously cooled the tyres in only a few seconds.

Russ
 

M80

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I'll be interested to learn from your new gadget how much temperature difference and with it pressure difference when the sun is beating down onto one side of the car.

I noticed difference when checking pressures one summer. That might mean we make adjustments when we shouldn't as correct pressures might be restored when driving.
 
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ZZZZ

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I'll keep an eye on it - interesting point Martin.
I only ever adjust, or check for that matter, the pressure when the tyres are cold, of course.
Although winter 'cold' and summer 'cold' are two different things.
Here's how it looked in the morning:

40359206242_25fa321ed9_o.png


Same temp, and correct pressure difference between the front and the back.
 
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ZZZZ

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The rear wheels on the other hand just have to tag along behind preventing the body scraping the tarmac.

There are alternatives you know o_O :

26618969749_c5b6251b2d_o.jpg



.

.

On a serious note - thanks Alastair, I sort of know that - if only due to the fact that, I had to replace the front tyres already, and the rears are still about 6mm. The old car didn't have the S mode :) And the GLK was 4Matic :rolleyes:
 

Craiglxviii

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On an FWD car your front wheels:
Drive the car forward
Perform the bulk of the braking
Do the bulk of the cornering
Have more weight on them

The rear wheels on the other hand just have to tag along behind preventing the body scraping the tarmac.

I’m stealing that for tomorrow’s design review!!!
 

LostKiwi

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There are alternatives you know o_O :

26618969749_c5b6251b2d_o.jpg



.

.

On a serious note - thanks Alastair, I sort of know that - if only due to the fact that, I had to replace the front tyres already, and the rears are still about 6mm. The old car didn't have the S mode :) And the GLK was 4Matic :rolleyes:

That's overkill.... Could have used a much skinnier one for better unsprung weight! ;)
 

LostKiwi

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Are you sure those cold pressures are right David? Looking at the pressure and temperature variations it suggests fronts may be underinflated.

I'd typically expect not more than 10% change cold to running.
 
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ZZZZ

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Are you sure those cold pressures are right David? Looking at the pressure and temperature variations it suggests fronts may be underinflated.

I'd typically expect not more than 10% change cold to running.

Well, it was really cold. I normally do 35/38 - but I'm sure you're right - I'll double check tomorrow.

Would seem to me you could use less pressure in the rear tyres and improve the ride somewhat.
I actually quite like the ride quality - it's a sports suspension, on 18" wheels (both factory) and 10mm extra width tyres (225/40).
It's not an S class by any means, but then it never meant to be.
 

oigle

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Are you sure those cold pressures are right David? Looking at the pressure and temperature variations it suggests fronts may be underinflated.

I'd typically expect not more than 10% change cold to running.

Particularly in English winter. Bit more pressure rise in our summers here.
 

M80

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I don't want to be cynical, and I can appreciate the convenience of the system,
but I would prefer to compare the display readings with results from your previous and trusted method.

Please tell, is this an Android readout on the 9" head?
 
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ZZZZ

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I'll do a direct comparison next time I use my Air Compressor.

The app didn't work fast enough on the 9" Android head unit, so I removed it.
Even on my iPhone it takes at least 2-3 minutes to update. The screenshots are (resized down) from iPhone.

I'd classify this TPMS as another amusement value gadget, just like the GPS/GPRS tracker, or a left mirror camera :)
 
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C350Carl

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That's pretty cool. Where did you get the valves from as I like that?
 
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ZZZZ

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That's pretty cool. Where did you get the valves from as I like that?
I bought them from AliExpress - just search for BLE (bluetooth low energy) TPMS VC601:

28135491219_483a76c0bf_o.jpg


Other than silly tyre icon stickers, on top of valve caps (which I removed), the finish and build quality seem very good.
 


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