Michelin Agilis Camping Tyres maximum running pressure

[Matrix Meanderer]

Having finally traded in my 7 year old Snooper for the new Cobra C8500 with Tyre Pilot sensor system (great price at the NEC show), I set up the Tyre Pilot sensors on all four road wheels of my Adria MH.

 

Running the system on its first trip 500 mile round trip I found that I had to set the "Low" and "High" pressure levels as follows to avoid the alarm going off:

 

Front Axle LOW 4.8 Bar Cold Pressure 5 Bar HIGH 5.7 Bar

Rear Axle LOW 5.3 Bar Cold Pressure 5.5 Bar HIGH 6.5 Bar

 

The HIGH pressure under full load and long trip conditions was a revelation to me !

 

I have tried without success to find advice on the operational pressure and sadly the Snooper (Performance Products) written and technical support advice also did not provide any answers

 

So my question is - is this much higher pressure with a hot tyre a common change in pressure experienced by others?

 

Also I have had to set the tyre temperature at 70 degrees C to avoid the alarm going off.

 

By the way - the sensors were easy to fit and the software good once you understood the order in which things need to be done.

 

Any observations on similar experiences would be helpful.

 

[StuartO]

Tyres always have the maximum inflation pressure as part of the labelling on the tyre itself, so all you need to do is look at the tyre wall.

 

This refers to the inflated pressure when cold, so of course it rises as the tyre warms up but I'm not aware that Michelin publish what that increase would normally be expected to be.

 

[nimod]

http://www.tyresafe.org/wp-content/uploads/2015/12/motorhome-leaflet.pdf

[Robbo]

Thanks for the link Nimod.

 

I've recently been trying to navigate to it on the Tyresafe website but with no success. I thought they'd taken it down for some reason. They have a section for Caravans but nothing for Motorhomes (as they used to), unless you use your archive link. Many thanks :-D

[Brian Kirby]

Matrix Meanderer - 2017-03-19 10:09 AM.....................So my question is -

 

1 is this much higher pressure with a hot tyre a common change in pressure experienced by others?

 

2 Also I have had to set the tyre temperature at 70 degrees C to avoid the alarm going off. ...............

1 Yes, when the vehicle is driven friction between tyre and road, and within the tyre itself, causes it to heat up, so heating the air inside the tyre, which consequently expands, resulting in an increase in tyre pressure.

 

2 Not 70C surely? Perhaps 7C, or maybe 70F (which still seems to me unrealistic)?

[Derek Uzzell]

The rule of thumb is that a 5°C increase in ambient temperature will result in a 1psi increase in tyre-pressure. So (purely as an example) if you inflate a tyre in the UK to 60psi on a cold day in February when the ambient temperature is 10°C, then drive to sunny Spain where the ambient temperature is 25°C, if you check the pressure in Spain you should find it is around 63psi.

 

If I remember correctly, tyre manufacturers quote inflation-pressures at an ambient temperature of 20°C. I once asked a Continental technician about this, who said “Just ignore the ambient temperature and inflate to the quoted pressure.”

 

As it says on the Tyresafe document

 

"Note: The loads and pressures moulded on the sidewalls of many tyres are a North American requirement and do not apply in the UK and Europe.”

 

Nevertheless, unless it’s known otherwise, it’s sensible to consider such a pressure to be a maximum.

 

TPMS systems that involve sensors being screwed on to the end of the tyre-valve stems (eg. Tyre Pilot or Tyrepal) operate similarly and often share components.

 

Guidance for Tyrepal’s Solar system is as follows:

 

"Tyre Pressures and alert levels

 

The following alert levels are suggested, based on the vehicle manufacturer’s recommended tyre pressures:

 

High pressure alert level - 20% above recommended pressure

Low pressure alert level - 15% below recommended pressure

High temperature alert level - 70°C (factory default)"

 

On that basis the pressure figures given in the original posting would read

 

Front Axle LOW 4.2 Bar Cold Pressure 5 Bar HIGH 5.9 Bar

Rear Axle LOW 4.7 Bar Cold Pressure 5.5 Bar HIGH 6.6 Bar

 

If the LOW-pressure alert is set too close to the COLD pressure figure (4.8bar is just 3psi below 5 bar) the system is going to ‘warn’ whenever the ambient temperature falls significantly.

 

Tyres get hot when a vehicle is being driven and, although 70°C sounds a lot, if the ambient termperature is well up and the tyre has been exposed to sun, the temperature of the air within the tyre will already be high. There’s also the scenario where somebody screws up the TPMS installation procedure so that the system fails to recognise a tyre is being stressed and is overheating. This may be why the Tyrepal temperature-alert level is set to 70°C as a factory default (I think that’s also the case with Tyre Pilot) and, although it might be possible to set the level higher, it may not be possible to set it lower. (Just a guess...)

[Matrix Meanderer]

Derek Uzzell - 2017-03-19 6:26 PM

 

The rule of thumb is that a 5°C increase in ambient temperature will result in a 1psi increase in tyre-pressure. So (purely as an example) if you inflate a tyre in the UK to 60psi on a cold day in February when the ambient temperature is 10°C, then drive to sunny Spain where the ambient temperature is 25°C, if you check the pressure in Spain you should find it is around 63psi.

 

If I remember correctly, tyre manufacturers quote inflation-pressures at an ambient temperature of 20°C. I once asked a Continental technician about this, who said “Just ignore the ambient temperature and inflate to the quoted pressure.”

 

As it says on the Tyresafe document

 

"Note: The loads and pressures moulded on the sidewalls of many tyres are a North American requirement and do not apply in the UK and Europe.”

 

Nevertheless, unless it’s known otherwise, it’s sensible to consider such a pressure to be a maximum.

 

TPMS systems that involve sensors being screwed on to the end of the tyre-valve stems (eg. Tyre Pilot or Tyrepal) operate similarly and often share components.

 

Guidance for Tyrepal’s Solar system is as follows:

 

"Tyre Pressures and alert levels

 

The following alert levels are suggested, based on the vehicle manufacturer’s recommended tyre pressures:

 

High pressure alert level - 20% above recommended pressure

Low pressure alert level - 15% below recommended pressure

High temperature alert level - 70°C (factory default)"

 

On that basis the pressure figures given in the original posting would read

 

Front Axle LOW 4.2 Bar Cold Pressure 5 Bar HIGH 5.9 Bar

Rear Axle LOW 4.7 Bar Cold Pressure 5.5 Bar HIGH 6.6 Bar

 

If the LOW-pressure alert is set too close to the COLD pressure figure (4.8bar is just 3psi below 5 bar) the system is going to ‘warn’ whenever the ambient temperature falls significantly.

 

Tyres get hot when a vehicle is being driven and, although 70°C sounds a lot, if the ambient termperature is well up and the tyre has been exposed to sun, the temperature of the air within the tyre will already be high. There’s also the scenario where somebody screws up the TPMS installation procedure so that the system fails to recognise a tyre is being stressed and is overheating. This may be why the Tyrepal temperature-alert level is set to 70°C as a factory default (I think that’s also the case with Tyre Pilot) and, although it might be possible to set the level higher, it may not be possible to set it lower. (Just a guess...)

 

Thanks Derek for locating the information that I was looking for.

Actually (confession time) using my best pair of glasses, I have now found the information in the Tyre Pilot documentation tucked away in section 10.5 of their manual. Must be a man thing not to fully read the instructions!

 

At least my hot running settings are about right, maybe I'll change the cold settings.

Despite the experience of my previous occupation as a science teacher (a very long time ago) I remain surprised just how much the hot tyre pressure rises and indeed the 70 degrees C operational temperature.

 

Anyway, I do recommend the monitoring system but one word on installation, I had to remove the plastic wheel trims on the Ducato wheels to install them and then carefully position the trim when replacing so as not to foul the sensor. There is just enough room on the cut out to avoid any need for cutting off more plastic.

Will be interesting to see the temperature rise this summer when driving in Europe.

[Gerry McG]

Brian Kirby - 2017-03-19 4:47 PM

 

Matrix Meanderer - 2017-03-19 10:09 AM.....................So my question is -

 

1 is this much higher pressure with a hot tyre a common change in pressure experienced by others?

 

2 Also I have had to set the tyre temperature at 70 degrees C to avoid the alarm going off. ...............

1 Yes, when the vehicle is driven friction between tyre and road, and within the tyre itself, causes it to heat up, so heating the air inside the tyre, which consequently expands, resulting in an increase in tyre pressure.

 

2 Not 70C surely? Perhaps 7C, or maybe 70F (which still seems to me unrealistic)?

I've seen tyre temperature around 55c in my BMW whilst driving across France on the autorotate in mid summer when the ambient air temperature was 35c