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Centrifugal Force!

Discussion in 'The Pub' started by trd2000, Oct 27, 2013.

  1. #1 trd2000, Oct 27, 2013
    Last edited by a moderator: Oct 30, 2013
    I once hit 72 on my mountain bike.... The centrifugal force on the valve stem opened it and the tyre instantly deflated and came off the rim..... I was going down a steep hill into oncoming traffic on an ally rim.... I know it was 72 cause it was the top speed recorded in my speedo... Still is

    <mod> split from Top speed you have ever reached thread.
    • Winner Winner x 1
  2. Gave it a hug, then walked passed it, jumped into my cage and drove to work(n)
  3. Um wrong thread????

  4. How did you come to that conclusion...
  5. yeah yeah yeah wrong thread.....glad you noticed....
  6. Well... There was no damage to the tube. The air came out the valve. I had those screw up valves. Presta valves? Schrader? That you use with deep V rims. I hadn't screwed them closed a month or so prior so they still had the little weight on the valve centre pin loose....

    anyway I put the tube and tire back on, pumped it up and screwed it closed and never had another issue.
  7. Wow. Not only is your mountain bike awesome but it exists outside the laws of physics that govern the universe. :)

    Centrifugal force doesn't exist...you mean centripetal force or more accurately, the absence of it. Unless your mountain bike exists in some parallel universe, which I suspect it might.

    And yes, I'm a physics Nazi :)
  8. Oh boy. You could be in for a rude shock. I'll kick it off.
    The absence of centripetal force? That's a new one.
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  9. centrifugal force is the direct opposing force to centripetal force, but without centripetal, centrifugal could not exist.
    centrifugal is basically just inertia.
    so in a corner the road is pushing on your tyres, the force of your tyres on the road is inertia.
    or something like that, i only did grade 12 physics.

    anyway, your bike is a piece of shit if the tyre fell off.
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  11. Lol .... Sorry I did and do know that. I just couldn't remember the correct word so resorted to common vernacular. I was wrong to think nobody would be so impressed by their own awesomeness that they would have to point out something which is so close to common knowledge while adding precisely nothing to the convo... But thanks for reminding me of the word I was after.

    The tyre stayed on for a little while... Maybe 100 meters.... But I was going down about a 45 degree hill with another 2-300m to go.... Try no front tyre pressure in your POS motorbike and let me know how it goes ;-)
  12. #12 iClint, Oct 29, 2013
    Last edited: Oct 29, 2013

    Don't apologise as you were right in the first place the correct terms centrifugal.

    centrifugal force is moving or tending to move away from a centre

    Centripetal force is moving or tending to move towards a centre

    Whether it is true or not, centrifugal force is the reason they say to use valve stem caps or right angle valve stems.

    for monkeyboy to argue the existence of centrifugal/Centripetal force is akin to saying their is no such thing as gravity.
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  13. Think of a biking riding in a circle. Centrifugal force is pushing the bike out of the circle, centripetal is the force pushing it in towards the centre (e.g. grip of the tyres). But... Centrifugal force is what you perceive, it's actually inertia trying to make the bike continue in a straight line. Looking at it from another way: While you are turning, the centripetal force of the tyres is pushing you towards the centre of the circle and the inertia of the bike trying to continue in a straight line feels like a force pushing you away from the centre of the circle - that felt outwards force is centrifugal.

    The mountain bike valves? Centrifugal force would have pushed the valves in to the rim, away from the hub. I'm cornering hard or a hard bump increased the tyre pressure and forced the valves out.

  14. Simply put centrifugal force pushes the valve in... the spring in the valve pushes the valve out... if the centrifugal force over powers the stored energy of the spring in the valve, the valve opens and lets air out.

    Whether a valve core has enough mass for centrifugal force to over power the spring is debatable, but if you spin the wheel fast enough it is certainly possible.
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  15. O.K. I get it now. A presta, if the cap/nut is loose, it can let air out.

    Does a presta have a spring? Or is it just air pressure pushing the inner stem out and being held shut by the cap.

    And this should be about bike speed.:(
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  16. There's your problem, you were going over 68....
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  17. Not sure, but it is the same principle anyway, if centrifugal force over powers the stored energy of the pressure in tube holding the valve shut, the valve opens.
  18. O.K. Got it.

  19. spring and tyre pressure.... ive never actually looked at the design ov a tyre valve but as the valve core is kind of loose when theres no pressure in the tyre i assume the tyre pressure helps seat it... with whatever pressure i was running on the day, 72kph was the magic number...

    like i say id ridden it round without tightening it for a while and had done some off road downhill sections with no worries... re: centrifugal/centripetal it's a really common mistake for people to confuse them, ones reactionary to the other... it takes a special kind of no life to get hung up on it.
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