Monday, Mar 21, 2016 at 07:40
Some people prefer the internal units and others like me, the external sensors.
There is no doubt that the internal ones will give a much more accurate reading of temperature. The pressure reading will be exactly the same however, To me this isn't a large problem because temp is a lagging indicator of a problem, and a slow one at that. An over temp alarm shows that something has been wrong for a long time, usually low pressure.
Internal units have other disadvantages that far outweigh the temperature IMHO of course.
1)They are not suitable for swapping out wheels, a big problem when touring with multiple spares.
2)Most ( but not all) won't accommodate 6 or more tyres.
3)The batteries are sealed, and despite the claim that they last 5 years plus, my experience has been that I had to buy all new sensors after 2 1/2 to 3 years. Bang $300 plus for new batteries
4)They can get damaged when changing tyres ( especially outback or DIY)
Externals of course have
-a less accurate temp display
-could be stolen in theory but it hasn't happened to me in 8 years.
-have to be taken off to adjust pressures. ( bu tso does a dust cap)
-can damage rims ( this has happened to me)
I now have the ABR sidewinder ??? 22 which are brilliant. The sensor batteries ran out about 5 months ago. I replaced them and they have been under water including salt water and they are fine. Their only downside it that the sensors could be a little smaller.
Each to their own, I have read bad reviews about the Tyre Dogs leaking after battery replacement ( and poor range) so agree with Allan about them.
Also regarding the original topic, I agree that a simple use of the PT law does not apply to tyres. Apart from the tyre changing shape as Allan points out ( which ignores one constraint in the
PT Law), Air is not a simple gas, and in most cases contains a large amount of moisture in the form of humidity. Anyone that owns an air tank will testify to the amount of water in what would be considered dry air.
I have no idea what the formula for that is, but I do know it ain't gunna be linear.
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