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Unread 27th June 2011   #1
The other Dave
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TyrePal

Iíve recently bought a TyrePal in order to monitor tyre pressures & temperatures on the car & van.
Last weekend was the first time that Iíve used it whilst towing. It worked very well giving a constant reading of both pressure & temperature for all tyres, but has raised a question that Iíve been unable to find an answer to. Car tyre pressures of 34 & 40 psi all increased by about 4psi whilst towing at a constant 60mph on the motorway, but the pressure of the tyres on the van increased by 12psi, from 54 to 66. This is more than I would have expected, but could be normal as both increased by the same amount. Temperature of all tyres increased by about 40C. Retuning home on Sunday when it was very hot gave similar results.
Does anyone know how much pressures should be expected to increase, or has anyone else fitted TyrePal? If so what is your experience?
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Unread 27th June 2011   #2
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No particular experience but your results do not surprise me. The caravan tyres are more heavily loaded that the car's are. For instance our approximate 1500kg sits on two wheels ie 750kg a tyre. The 1800kg car sits on four ie 450kg a tyre.
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Unread 27th June 2011   #3
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Sounds about right to me and nothing unusual

They do tell you to check the tyre pressures cold before setting off and that is why










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Unread 27th June 2011   #4
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Practical caravan recently tested these ,surely if they are designed for caravans they give you an idea of what to expect ? or what is the point of having them, you would see one tyre change pressure so you would then stop to investigate to avoid a puncture i suppose which would be a good thing
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Unread 28th June 2011   #5
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Quote:
Originally Posted by The other Dave View Post
Iíve recently bought a TyrePal in order to monitor tyre pressures & temperatures on the car & van.
Last weekend was the first time that Iíve used it whilst towing. It worked very well giving a constant reading of both pressure & temperature for all tyres, but has raised a question that Iíve been unable to find an answer to. Car tyre pressures of 34 & 40 psi all increased by about 4psi whilst towing at a constant 60mph on the motorway, but the pressure of the tyres on the van increased by 12psi, from 54 to 66. This is more than I would have expected, but could be normal as both increased by the same amount. Temperature of all tyres increased by about 40C. Retuning home on Sunday when it was very hot gave similar results.
Does anyone know how much pressures should be expected to increase, or has anyone else fitted TyrePal? If so what is your experience?

With an increase in temperature there will be an increase in pressure for a fixed volume of air (as in a tyre).
About 4 psi increase from the cold pressure is about right for a car driven normally.
The 12 psi increase for the caravan tyres suggests they are under inflated and running hot.
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Unread 29th June 2011   #6
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If you are unsure as to the accuracy for the unit do a tyre pressure check when the unit confirms the hot pressure.
The side walls of tyres on a single axle are doing a lot of work with side wall flexing etc and the load as suggested. What was the tyre pressure when cold and what size tyres caravan load weight etc ?
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Unread 6th July 2011   #7
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Why do they set the pressure so high in caravans?
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Unread 6th July 2011   #8
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This is because they tend to carry greater loads.

For example my car weighs 1700kg but has 4 tyres each carrying appox. 425kg. The van weighs only 1200kg but has two tyres each carrying 600Kg so have to support a quarter of a ton more weight despite the van being lighter full than the car is empty.

Hope that clarified things.
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Unread 6th July 2011   #9
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Quote:
Originally Posted by oldtugger View Post
Why do they set the pressure so high in caravans?
It is the pressure which carries the load. The tyre construction is designed to hold the pressure.
Single axle caravan tyres carry nearly as much load as the four tyres on the average car therefore the tyre is "stronger" and the pressure higher.
A twin axle caravan spreads the load over four "lighter" tyres with correspondingly lower pressures. Fine until a puncture overloads the remaining tyre on that side!
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