Altitude and tire pressure?
 

I was wondering what effect large changes in altitude can have, if any, on my tire pressure? I just wonder as had some weird tire pressure readings lately, but have also been going from sea-level to over 4,000m. If I inflate (using hand pump) my tires at 4,000m, I assume the air is thinner - when I decrease altitude will the tire then have less air in it - or do you just have to pump more times to achieve the desired PSI? :confused

Cheers,
RTW

Tyre pressure is measured as an ambient pressure, so if the tyre is inflated at sea level to 2 bar, when you are at 4,000m the gauge will tell you that it's more than 2 bar.

If you inflate to what you think is 2 bar at 4,000m and descend to sea level the pressure will measure less.

And then you need to factor in temperature... :innocent:

Just ride your bike... :thumbup1:

In 4.000 metres attitude the difference of the pressure will be just 0.600 Bars, or in PSI +/-0.8 so means that a tire at an average of 28 PSI could be 1 PSI more or less, up or down….
As my friend Ted says: JUST RIDE IT!!! :scooter:

I believe you've misunderstood what the 0.6 bar represents. It's a comparison against 1.0 bar at sea level, so it's a 40% loss and hence the difference for a tyre at 28 psi would be 11.2 psi.

Please correct me if I'm wrong.

http://www.morocco-knowledgebase.net/tim/pringles.jpg

This is the effect on a tube of Pringles at just 2,500m. I think at 4,000m it would have burst but I was hungry so I ate them and never found out :innocent:

I've ridden from 0-4500 metres in one day. My tyres didn't look or act any differently. Never seen or heard of anyone adjusting them.

I'm sure the science is accurate but in the real world... Just ride.

The question was about unusual tyre pressure readings, not how the tyres acted on the road.

I thought this forum was about riding... :o

Seems right, altitude from sea level to 4K meters won't have a huge affect on cold PSI reading.

The other thing mentioned was HEAT, which can have an affect. And another factor NO ONE mentioned that also affects PSI is ... MOISTURE.
Moisture combined with heat can give a boost to PSI, not always desirable ... especially on a race track. Traveling? Just ride! bier

Typically, you set tire pressures when tires are cool. Once super hot, pressures can go up maybe 3 to 5 PSI on a tire that measured 30 PSI cold. The other thing that can cause eve more rise is moisture. Moist air is bad for an accurate,
consistent pressure.

Many Petrol station air hoses will emit A Lot of moisture with the air. (true here in USA, where you can often SEE the moisture in the air!) Racers use Nitrogen in their tires to mitigate this variable and maintain more stable pressures.

For a traveler, most times its a MOOT point. Just ride.
A 3 to 5 PSI rise is not likely to have great affect.
If it does ... stop and let out a few PSI ... but air back up later if required.
bier

Hey Tim, News Flash! These two points are LINKED. You can't talk about one without mentioning the other. Pressures affect the ride and the ride (and bike) may need pressure adjustment depending on what the pilot "feels". The Pilots perceptions are KEY to it all.

If my bike "feels" weird (what ever the hell that means!) I might get off and put a gauge on the tires ... or maybe use my EYES and notice I've got a flat. doh

Seat of the pants "feel" is our last best hope for survival on a bike! bier

I understood that moisture in air causes no significant departure from the ideal gas law under normal practical driving conditions. When that is pointed out, all sorts of other reasons surface like causing rust on the rims or the tyres rot out on the inside which in itself is a load of rot or it rusts the steel cords or... or... .
The bit about using nitrogen in normal car and truck tyres gets shot down every time it is raised so I don't know why it can't stay dead.

As for the actual pressure inside a tyre. Couldn't you make an argument that if you go up in altitude, the air pressure is pushing less on the outside of the tyre so the tyre becomes effectively over inflated - but high altitudes are usually associated with lower ambient temperatures which reduce the running pressure, thus mitigating any altitude effects.

Then again ....

or maybe even .....

Just ride.

Excellent point....

We need a official science boffin to solve this for us :)

They are too busy with the global/climate warming/change/cooling conumdrum.

Boyle's law applies though.

"the law is accurate enough to be useful in a number of practical applications. It is used, for example, in calculating the volume and pressure of internal-combustion engines and steam engines".
From Boyle's Law - HowStuffWorks

I had the three main gas laws—Boyle's, Charles' and Henry's—drilled into me from my days in BSAC (scuba).

Gases heat up as they are being compressed, one of the two reasons for immersing scuba tanks in water whilst being filled (the other being to mitigate the effect should a bottle fail). Gases rapidly cool when being deflated which is why those tiny CO2 canisters used to inflate a tyre have a mesh cover—the canister drops to subzero temperature.

Charles' law states the pressure varies directly in proportion to the temperature (°K) which is why you are told to measure tyre pressures when the tyre is cold, but many people don't realise this. When the hot tyre cools the pressure drops and the tyre is under inflated.

On another thread here or maybe another forum, someone was asking me how I was getting on with mousses in my KTM 690R (supposedly the equivalent of 0.9 bar or 13 psi). I had to say that I couldn't actually notice any difference between my 690 in Spain with mousses and my 690 in the UK with standard inner tubes which are probably at 2 bar.

So as Ted says, just keep riding.

There is one situation where tyres need to be inflated to a non-resting value and that is when the vehicle is stored in a heated garage but will be operated in a very cold environment. I guess if it was stored in airconditioned garage but operated in summer desert conditions a similar allowance would need to be made.

I stored (laid-up) my bike in Poland for 6 months last year. On my return I naturally wanted to check the tyre pressures before the ‘off’ .. in a westerly direction.

When I was digging-out my little electric pump from under the seat, an old-timer at the storage depot gestured to me, as much as to say "No Problem .. no problem", and with that he reeled out the hose from his firm's compressor .. pointed quizzically at the inflator's nozzle gauge with a enquiring look on his face. He couldn’t speak a word of English btw, let alone count numbers in English.

I needed 35 psi in the rear - and 30 psi in the front - and therefore flashed all my fingers+thumbs three time (30) plus again with one hand (5), thinking that this was clearly indicating to him the number 35 [psi].

Trouble is, my Polish friend interpreted this signal to mean 3.5 Bars!

So off I went, not with 35 psi in the rear but with 3.5 Bars, or over 50 psi.
[And 43 psi in the front.]

I know .. I know, should have checked with my own pressure gauge afterwards just to be sure. But I didn’t. doh

Do you know what? I travelled for more than 2,000 km before checking my tyre pressures again .. and then realised the earlier misunderstanding and mistake. And yet, to me, there was no discernible difference between 35 and 50 psi in the rear – and, in the case of the front: 30 psi (2 Bars) and 43 psi (3 Bars).

--------------------------

On the other hand, of course, I have clearly noticed – as have we all, no doubt - that there is definitely a different feel to a bike's handling when your tyre inflations are significantly lower than the recommended pressures.

--------------------------

Moral of the Story: Do what Ted et al said, as it doesn't matter hugely if your apparent tyre pressures go up or down a little bit with altitude. Ultimately, providing you have enough pressure at the bottom of the tyre .. then it won’t look flat! :thumbup1:

You must have been gliding over the tarmac. :rofl:


When new bikes were delivered to dealerships, they're inflated to this pressure. They don't set them before posting them off from the factory.

If I'd forget to adjust them, I'd test ride at 60 PSI.

And usually I'd not notice. Even when giving it some beans.

doh

:thumbup1:
I've noticed on some bikes it can be more difficult to "feel" tire pressure differences, especially if just plodding down a straight, dry road on an unfamiliar bike.

But on MOST of my bikes ... I can feel even a 3 to 5 PSI change. My DR650 (Ohlins shock, Race tech forks) is quite sensitive to tire pressure changes. Ride and bump absorption can be harsh if over inflated, and unstable/squirmy if under inflated.

An over inflated front tire can be QUITE dangerous, especially if pushing a bit hard on a twisty WET road on a fully loaded bike. Beware. Also, under hard braking you're more likely to lock up and slide if tires are over inflated and cold. :nono::rain::oops2:

Under inflation is more obvious .... IF you're well tuned into your bike via "Seat of the Pants" method. :mchappy: Trust your gut, if something does not feel right, check it out!

Just a thought, would it be fair to say that a great percentage of riding at altitude is done on less than perfect roads. If so would one not have lowered pressure anyway?

Ideally, yes. But plenty of room for variation depending on BIKE weight, luggage weight, pace ... and of course the road itself. How bad is bad? Off road I really prefer to run lower pressures ... but if you go to fast and hit something ... bad news. My last Baja Trip ... riding at night on a remote off road track I hit something ... doh No flat, not problem, never even knew it happened until next day.
https://lh3.googleusercontent.com/-T...6_MJ2V4-XL.jpg
This pic from earlier trip on same road. At night it was a bit crazy but not all that bad. My problem was I was going too fast.
https://lh3.googleusercontent.com/-W...2/P1000442.JPG
:oops2:
So running low pressures can come with risks in terms of keeping your wheels safe. Go too low ... you risk bungered up wheels .. or worse, broken wheel.

Go too high and you get a horrible, harsh ride and poor traction and even worse control. I go with LOW pressures and just try to be careful.
:D:D:D

With all 3 you can have some fun in the global warming debate. :D

As the graph shows, atmospheric pressure at 4,000m is roughly 0.6 of the sea level pressure of 14.7 psi, so if you filled your tires to 30 psi at sea level, the gauge reading at 4,000m would be 30psi + (0.4 x 14.7 psi) = 35.8 psi. Not enough to burst a tire, but plenty to see on a tire gauge.


Think of it this way, if you took your bike to outer space, zero atm, your gauge reading would be one atm (14.7 psi) higher than the sea level reading. That is the most that an altitude change can affect your tires. The change is not a percentage of the initial pressure, but a percentage of the loss of atmospheric pressure. if you started with 100 psi sea level, at 4,000m, you would have 100 + (.4 x 14.7) or 105.8 psi.






http://hildaandtrojanasteroids.net/atmexpfalloff.jpg

That's really interesting - thanks all the for responses.

"In 4.000 metres attitude the difference of the pressure will be just 0.600 Bars, or in PSI +/-0.8 so means that a tire at an average of 28 PSI could be 1 PSI more or less, up or down….

Javier...
Dakar Motos


“El mejor remedio para la Boludez, es la Inteligencia…”"


Seems Boludezes ruledoh

In my younger days I did the tyre pressure thing when I was racing, how on different tracks at different altitudes how heat in tyre rise to extreme temperatures so scrubbing rubber, cooking your tyres,,,,,,I can tell you that every thing you read is true it is about all those thing mentioned,
but really come on in the would of touring don't worry it's really not that important, you will know what your bike is doing on Tarmac and on soft ground, in any case you will not be going fast enough to make any serious changes,,,,
As ted said ride your bike and don't get involved in a load of bull.
There is guys much more experienced on here than me that will tell you what tyres and inner tubes to use but I think the same answer will be by most its up to you what you are happy with, as regards pressure guide lines are road 30-40,,,,, off road 15-25,,,,, but it's like every thing m8 it's a guide.

Unlike me I just keep my pressures the same road or off road as its not a race

Altitude and tire pressure?
 

Totally, I'm riding a 250 around Latin America, I couldn't care less about minor performance quirks. It was just that after coming down in altitude my rear was flat the next day, so it got me thinking how much air pressure can affect tires. That was it really.

I've never suffered from pressure loss,,,,well I don't think I have,,, I don't know if northern Italy qualifies as the same sort of altitude you have done,
It would be interesting to know what your tyre pressure was before you went up and what your pressure was when you come down, did you have a cap on the valve

Could be several things, as discussed in this thread. Could even be someone let air out of your tire? :innocent: (kids?)
Twice, while traveling in France, had folk flatten my tires because they did not like where I'd parked the bike. (parked it for security). So they let air out. This happened to some of our guys in Mexico as well (vandalism in that case).

But could also be temperature and moisture in air. All affect PSI readings more so than Altitude. Riding hard with loaded bike for hours will raise pressures. Once things cool, PSI drops right off. Learn to do COLD and HOT checks to determine the differential between the two. In my experience moist air in tube has a BAD affect on pressure readings. bier

Altitude and tire pressure?
 

Molly thought the same, could have been kids or something. I think the tire was probably low already at altitude but it was dead flat, so maybe it was something else. Valve was definitely capped.