If you inflate your caravan tyre to its recommended pressure, then add 250kg of personal and habitation items to it, do you believe the pressure inside the tyre increase ?
Here's a topic to debate.....
- Thread starter ProfJohnL
- Start date
Oh Prof! What have you started? No, the pressure on the tyre increases but not the pressure inside the tyre.
Seems to me the answer is 'no'
Only way pressure would increase is if either the volume of the inside of the tyre changed or the temperature changed. Unless the extra load caused very significant deformation of the tyre - which it doen't- then the pressure should remain the same at least to the accuracy you are able to measure it with conventional tyre pressure gauges.
On the road, the pressure might change a bit, but this would probably be due to a temperature rise due to greater contact pressue caused by the increased load.
'Significant deformation' would have to be such as to reduce the contained volume not just re-arrange it into a different shape, so a slight bulge in the sidewall at the bottom of the wheel wouldn't count.
There, A nice big target to shoot at !
Only way pressure would increase is if either the volume of the inside of the tyre changed or the temperature changed. Unless the extra load caused very significant deformation of the tyre - which it doen't- then the pressure should remain the same at least to the accuracy you are able to measure it with conventional tyre pressure gauges.
On the road, the pressure might change a bit, but this would probably be due to a temperature rise due to greater contact pressue caused by the increased load.
'Significant deformation' would have to be such as to reduce the contained volume not just re-arrange it into a different shape, so a slight bulge in the sidewall at the bottom of the wheel wouldn't count.
There, A nice big target to shoot at !
Well the volume of air in the tyre is fixed, and the surface area on which it acts is also fixed. As the payload increases, the tyre, being elastic, simply changes shape, thus maintaining the surface area and the same pressure, assuming temperature remains constant. That is of course up to its elastic limit, after which the pressure will increase followed by a big bang... :woohoo:
Seems to me the increased weight will not increase the pressure of air, assuming the temperature remains the same before and after the weight addition.
For a fixed mass of gas at constant temperature, the volume is inversely proportional to the pressure. According to Boyle a distant relative I think of The Prof
And
For a fixed mass of gas at constant pressure, the volume is directly proportional to the kelvin temperature. Courtesy of an even more distant relative of The Prof I believe a Mr Charles ( Not Ray) :kiss:
For a fixed mass of gas at constant temperature, the volume is inversely proportional to the pressure. According to Boyle a distant relative I think of The Prof
And
For a fixed mass of gas at constant pressure, the volume is directly proportional to the kelvin temperature. Courtesy of an even more distant relative of The Prof I believe a Mr Charles ( Not Ray)
:kiss:
Martin24 said:
Hello Martin,
Yes this was a deliberate fishing trip to see how savay readers are. I'm glad to see that so far all respondents have correctly understood the pressure in the tyre remains the same, its the contact area the tyre has with the ground that increases as the load increases until the area x pressure = load.
This was prompted by reading some replies on another car forum, where some wildly inaccurate comments were made, and it made me wonder if the same misconception was rampant here on the PC forum.
But, why have tyre fitting companys gone over to using Nitrogen, for filling tyres rather than air. ?
Your answers please.
Your answers please.
Damian
Moderator
EH52ARH said:
Simply as a marketing tool to fool some of the public into thinking they are getting something "special".
Unless you intend towing, or driving, at the same speeds as F1 cars, the whole Nitrogen "thing" is a waste of time.(and a good money spinner)
It certainly is a money spinner ...... especially at £2 a tyre!! It would be nice of the company to tell you this before they inflate the new tyres too!
Allegedly then Nitrogen is less susceptible to pressure changes with temperature rise.
BUT I thought the tyre manufacturer factored that in when calculating the cold pressure reading using ordinary air?
Seems a bit of a gimmick to me. And maybe using nitrogen could actually be detrimental to the tyre in the long term due to running at too low a pressure :silly:
BUT I thought the tyre manufacturer factored that in when calculating the cold pressure reading using ordinary air?
Seems a bit of a gimmick to me. And maybe using nitrogen could actually be detrimental to the tyre in the long term due to running at too low a pressure :silly:
I had nitrogen (for free) in the tyres on my last car. The local tyre centre would adjust the pressure up or down as required free of charge so I don't see how it is a money spinner for them. Indeed, it's a cost. As the tyre pressure on that tug was the same loaded or empty I never used the service. I was led to believe that the nitrogen is less likely to leech out and therefor the pressure would remain constant. It's certainly the case that on that car I never had to adjust the pressure.
To get back to the Prof's question. I had a physics teacher at school who would blow one balloon up inside another then ask us what would happen to the pressure and size of the outer balloon if the inner one slowly deflated. :S
To get back to the Prof's question. I had a physics teacher at school who would blow one balloon up inside another then ask us what would happen to the pressure and size of the outer balloon if the inner one slowly deflated. :S
To get back to the Prof's question. I had a physics teacher at school who would blow one balloon up inside another then ask us what would happen to the pressure and size of the outer balloon if the inner one slowly deflated.
image: http://www.practicalcaravan.com/media/kunena/emoticons/dizzy.png
:S
One long faaaaaarrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrt :evil:
image: http://www.practicalcaravan.com/media/kunena/emoticons/dizzy.png
:S
One long faaaaaarrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrt :evil:
This is one of thoughs "if you had a trailer full of birds and they all took off at once, is the trailer lighter* Questions. B) B) B) B)
No difference at all.
No difference at all.
Some interesting answers. In short you can not state that the volume of the tyre will not change because, by their very nature, tyres are elastic and therefore the volume is bound to change even if it is imperceptible. As you load the wheel up more the tyre will deform and therefore the volume and pressure will change. Importantly this will be imperceptible. There are so many variables to consider, even the centrifugal/ centripetal forces acting on the tyres when rotating will make a difference as will temperature and moisture content of the gas contained within the tyre. Which brings me onto nitrogen. Seventy odd percent of the air we breath is nitrogen,the rest being oxygen, hydrogen, carbon dioxide, water and sundry other gasses. As far as I am aware the stuff they put in tyres is white spot nitrogen which is moisture free (or as dry as it is reasonably practicable). I'm not sure that it makes any difference to be honest.
saint-spoon said:
Are you talking about gross weight (trailer and load) or nett weight (trailer without load)?
I compromise and use about 80% N ! :lol:
http://www.popularmechanics.com/cars/how-to/a3894/4302788/
http://www.popularmechanics.com/cars/how-to/a3894/4302788/
Which then leads us to which is heavier?WoodlandsCamper said:
A ton of feathers or a ton of lead?
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