Rod
Registered user
What happens to your tyre pressures at the top of the mountain......do they go up or down .....?
Tyre pressure at altitude
- Thread starter Rod
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swissrob
Registered user
pressure in the tyre goes up as the atmospheric pressure is less.
dont even consider pissing about changing the pressures though otherwise you will have to do that during every single trip out no matter what altitude you are at.
dont even consider pissing about changing the pressures though otherwise you will have to do that during every single trip out no matter what altitude you are at.
Dr Feelgood
Guest
Up. As the ambient pressure decreases with altitude, the differential pressure across the tyre wall will get bigger, thus the pressure inside the tire will appear as increased.
They don't change the difference between the inside pressure and outside increases but not by much. Say you have 3 bar in your tyre and even in a vacuum the pressure is going to be 4 bar but for going up a mountain it's not worth changing because what goes up comes down also at a hight that would make a difference it's going to be colder. JJH
trainman
Registered user
i find in Norfolk they hardly change at all
Greger
Registered user
guage pressure in tyre is pressure above atmospheric, so as you go up the atmospheric pressure decreases so the guage pressure increases.
guage pressure will go up by about 1mb for every 25feet increase in altitude.
guage pressure will go up by about 1mb for every 25feet increase in altitude.
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Dr Feelgood
Guest
Nor people their socks.
WindyChuffer
Registered user
How high are you planning on going?
I know that the Globebusters crew on their London-Beijing trip top out at around 5,300 metres, and don't bother worrying about this. Much bigger fish to fry - such as the body coping with the altitude...
I know that the Globebusters crew on their London-Beijing trip top out at around 5,300 metres, and don't bother worrying about this. Much bigger fish to fry - such as the body coping with the altitude...
The tyre pressure won't undergo any significant change. It is dependent on the resistance to expansion of the tyre carcass, not atmospheric pressure.
Tyre carcasses are steel, kevlar, etc, and won't allow any meaningful expansion beyond their recommended inflation pressure.
If the container (tyre) size and the amount of air inside it don't change, then the internal pressure can't change either.
Tyre pressure gauges don't take ambient pressures into account. They are
calibrated to sea-level pressure (or whatever the industry standard allows.)
So no change there either.
At an insignificant level, the carcass will balloon a tiny amount as no material is totally inelastic.
Significant changes to pressure might be caused by extra heat generated as
the bike accellerates and brakes on those mountain slopes or if the air temp
is much lower than below.
So apart from the engine losing a little stomp, the bike would work fine.
Tyre carcasses are steel, kevlar, etc, and won't allow any meaningful expansion beyond their recommended inflation pressure.
If the container (tyre) size and the amount of air inside it don't change, then the internal pressure can't change either.
Tyre pressure gauges don't take ambient pressures into account. They are
calibrated to sea-level pressure (or whatever the industry standard allows.)
So no change there either.
At an insignificant level, the carcass will balloon a tiny amount as no material is totally inelastic.
Significant changes to pressure might be caused by extra heat generated as
the bike accellerates and brakes on those mountain slopes or if the air temp
is much lower than below.
So apart from the engine losing a little stomp, the bike would work fine.
Assuming the carcass of the tyre is a sealed vessel, the internal tyre pressure remains constant unless subjected to a change in temperature.
Piaf
Registered user
May I refer you to this for a definitive answer
http://www.sablesys.com/baro-altitude.html
Personally, I think you ought to change the air in your tyres as soon as you reach cruising altitude.
Let out all old sea level air and replace with some nice fresh high mountain air.
(I would never stop in Norfolk, with or without socks.)
http://www.sablesys.com/baro-altitude.html
Personally, I think you ought to change the air in your tyres as soon as you reach cruising altitude.
Let out all old sea level air and replace with some nice fresh high mountain air.
(I would never stop in Norfolk, with or without socks.)
Rod
Registered user
Well........thanks for all the replies.....I wasn't considering changing my pressures on my trip to the Alps & beyond next week, but it's a question that has always puzzled me.......
Thanks again.....
Thanks again.....
CuzGS
Registered user
Mate pressure decreases by 1millibar per 30 feet, there fore if you take a col of 3000m or 9000ft for cash, the px change would be 300mb or about 1/3 of a bar, however that is ambient.
In a pressurised system such as an aircraft or to a lesser extent a tyre where the air in forced into and "held" the actual change is far less, in an aircraft at about 35000 ft the pressure in the aircraft is around 5 to 6000 ft.
Bottom line is don't sweat it, unless riding at absolute extreme altitudes for protracted periods it's not a drama.
If we take temperature into account it gets v anal with things like temp dropping at 1.98deg per 1000ft , and things like density altitude v pressure altitude problems, it's still all horseshit for bikes though, just get on and ride over the hills, no drama
In a pressurised system such as an aircraft or to a lesser extent a tyre where the air in forced into and "held" the actual change is far less, in an aircraft at about 35000 ft the pressure in the aircraft is around 5 to 6000 ft.
Bottom line is don't sweat it, unless riding at absolute extreme altitudes for protracted periods it's not a drama.
If we take temperature into account it gets v anal with things like temp dropping at 1.98deg per 1000ft , and things like density altitude v pressure altitude problems, it's still all horseshit for bikes though, just get on and ride over the hills, no drama
trainman
Registered user
if anyone can find a sock that fits 6 toes i will gladly start wearing them
Dr Feelgood
Guest
Nowt ever chages in Norfolk
same shit different day
freeloader
Registered user
Fit your bike with the special tyres that aircraft use, it's a little known fact that the rubber used is semi-porous to allow some of the air to escape at altitude so that they don't explode. During the descent, they allow air back in - they're actually made of the same material used in self-inflating camping mattresses, so they reinflate themselves automatically.
trainman
Registered user
BMW have their own air at dealers but it comes in a nice box and is £10 a squirt
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