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Travelling Overseas
Can anyone help me with an answer. I plan on travelling overseas with my mtn bike, i've been told to let the air out of my forks & shock, is this true and why?
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Only partly true.
AFAIK all cargo holds are pressurised, mitigating the need to do anything.
Any decrease in atmosphere pressure will cause a pressurised item (tires, shocks etc) to gain pressure, the amount in this case is all irrelevant.
Simply by sitting on your bike you will increase the pressure more than any commercial flight can. When you land a massive jump the pressure will spike... and shocks usually survive just fine being bottomed out many times a ride.
Letting ~1/3 out of everything would be more than enough. I certainly wouldn't let ALL the air out of anything.
For me personally, I'd leave everything except the rear shock, as i run that pretty high, and the chance of it sitting at over 300psi for hours may not be great, so id drop it to 150.
Tires and forks run much lower pressure, so the % increase doesn't affect them as much.
Yep cargo holds are pressurised but planes do run at lower pressures than sea level (notice your ears pop when descending)
I dont let any air out of anything when flying and have had no probs (i run tubeless)
But if you had a road bike with 120psi in your tyres im not sure how that would go.
I just got back from Rotorua and let the air out of everything, only because Qantas told me to and they do X-ray to check. Tried to bring back a couple of C02 cartridges and they let me fly from NZ to Melbourne with them but wouldn't let me take them Melbourne to Perth. Go figure.
How do they x-ray your shocks and fork?
As I advised on his blog, the most the pressure is going to jump by is 15 psi, and that's if you go to 0 psi hard vacuum outer space. 15psi = sea level air pressure. So dropping your knobblies to 20 psi at sea level should be more than adequate to keep them within max pressure limits and I wouldn't bother touching forks or shock. They handle 10-20x or more the static inflated pressure when you get near the end of the stroke on compression anyway - zero risk of an incident.
For road bikes, yeah I'd drop the pressures but then most have tubes so reinflating from zero is much less hassle.
But if it stops airline management from stressing, no harm in complying.
Hawkeye is correct - you can go pressurised - especially if you are riding a Cannondale Lefty. They are self deflating over time, so they should be OK.
But seriously - I've done a couple of trips with the bike - lowered the pressure to about half (tyres and shocks) and all was OK. The lower temps in the cargo hold will be more than likely lower your overall pressure: http://en.wikipedia.org/wiki/Boyle%27s_law
As always - you can always ask your local bike mechanic for advice. Have a great trip!