News

Motorcycles and physics

Discussion in 'Other Off Topic Forum' started by 2000YELLOW360, Dec 21, 2005.

?

Bike's wheelie

  1. Increases

  2. Decreases

  3. Doesn't change

Multiple votes are allowed.
Results are only viewable after voting.
  1. 2000YELLOW360

    2000YELLOW360 F1 World Champ

    Jun 5, 2001
    19,800
    Full Name:
    Art
    OK, you're riding along on a straight stretch of highway. The sun is shining and life is good. A Ferrari comes alongside. There's a pretty blonde driving it, so you decide to show off. You pop a wheelie and, being an expert rider, pace the Ferrari.

    Assuming the bike's front wheel is still spinning, if you feather the front brake (engage it lightly), does the bike rise higher or come down a bit? Why?
     
  2. To remove this ad click here.

  3. jungathart

    jungathart Guest

    Jun 11, 2004
    3,350
    NoVA, AmeriKa
    Full Name:
    Komrade Jung
    bike would rise. law of conservation of angular momentum.

    (saw it on a recent Trek rerun. forgot the name of the episode, but in it Kirks gets the girl)

    :D
     
  4. Z0RR0

    Z0RR0 F1 Rookie

    Apr 11, 2004
    3,445
    Montreal, Canada
    Full Name:
    Julien
    Actually, the front end would drop (momentum blah blah blah)
    Braking in the air is a trick we always use in motocross.
     
  5. Dubai Vol

    Dubai Vol Formula 3

    Aug 12, 2005
    1,418
    back in Dubai
    Full Name:
    Scot Danner
    Depends on where the front brake caliper is positioned, if my force diagram is right....
     
  6. Z0RR0

    Z0RR0 F1 Rookie

    Apr 11, 2004
    3,445
    Montreal, Canada
    Full Name:
    Julien
    It depends of nothing, the front end drops. I still have the scar to prove it! ;)

    The front wheels turns in such a way that when you brake, the momentum is transfered to the whole bike ...
     
  7. To remove this ad click here.

  8. shiggins

    shiggins Formula 3

    Nov 20, 2004
    1,280
    A rotating wheel has an angular momentum. If you apply the brakes, regardless of it you 'feather' them, a transfer of angular momentum must occur. The answer most certainly is not "doesn't change", Art :p. The bikes wheel will pitch downwards. I did an experiement too, and it confirms this.

    Now, I wait to be told I am wrong, and all about the assumptions I made. :)
     
  9. We did it too ridding dirt
     
  10. SrfCity

    SrfCity F1 Veteran

    Nov 1, 2003
    9,842
    Orange County, CA
    Drops. You lose the gyro scope effect ;)
     
  11. Meister

    Meister F1 Veteran
    Silver Subscribed

    Apr 27, 2001
    5,383
    Duluth, MN
    Full Name:
    The Meister
    Don't guys who jumb bikes, (like Robbie Kneivel) hold the front brake while in the air to keep the front of the bike "down?"
     
  12. To remove this ad click here.

  13. PeterS

    PeterS Three Time F1 World Champ
    Silver Subscribed

    Jan 24, 2003
    39,616
    95370
    Full Name:
    PeterS
    That was YOU on the bike and your wife was in the 360...Correct?
     
  14. Ducman491

    Ducman491 Formula 3

    Apr 9, 2004
    1,361
    Mentor OH
    Full Name:
    Jason
    I'm no help I can't do wheelies.
     
  15. 2000YELLOW360

    2000YELLOW360 F1 World Champ

    Jun 5, 2001
    19,800
    Full Name:
    Art
    Yup, got my new leathers today!

    shiggins, I put my answer like that because I didn't wnat to give people hints. I should have just waited to vote. I know what the correct answer is...too bad they don't have a separate motor for the front wheel or you could make it drop or rise as you like!
     
  16. bst1

    bst1 Formula 3

    Aug 13, 2005
    1,034
    MARYLAND
    Full Name:
    BARRY T
    braking a spinning front wheels will pull down the front end....did it on dirt bikes as a kid, same on my Ninja.....never could get the Harley's off the ground!!!!!!!
     
  17. big41

    big41 Rookie

    Sep 29, 2005
    2
    The front end would drop. On dirtbikes when jumping you never grab the front brake because the motorcycle would dive and there is no way to bring it back up because once the wheel stops spinning in the air it doesn't start spinning again. That is why motocrossers hit the rear brake to bring the front end down, they can get that wheel spinning again.
     
  18. Meister

    Meister F1 Veteran
    Silver Subscribed

    Apr 27, 2001
    5,383
    Duluth, MN
    Full Name:
    The Meister
    I guess I had the front and rear mixed up...knew they hit one of the brakes though.
     
  19. KingPayam

    KingPayam Formula Junior

    Jun 14, 2004
    440
    Full Name:
    Payam
    definately drops. Now try hitting your back brakes hard during a wheelie and report back.
     
  20. SRT Mike

    SRT Mike Two Time F1 World Champ

    Oct 31, 2003
    23,199
    Taxachusetts
    Full Name:
    Raymond Luxury Yacht
    Art,

    I just took my bike out to try it out to get an answer, and due to it being 14 degrees out and ice on the roads, i crashed.

    I was just wondering where to send the repair bill, or would you prefer just to send me your duc as payment? Your choice

    :)
     
  21. 2000YELLOW360

    2000YELLOW360 F1 World Champ

    Jun 5, 2001
    19,800
    Full Name:
    Art
    Put the repair bill in a plane on a conveyor that matches the wheel speed in the opposite direction. When it gets to me I will take care of it! :)
     
  22. Baasha

    Baasha Formula 3

    Jun 20, 2004
    1,172
    NorCal
    Bingo! According to most modern sportbikes, the caliper is placed along the side of the wheel. So by applying the brake, the linear force would change making the bike "dip" first but then compensate and rise forcing the wheelie to "increase". So when applying the brake, the bike will "dip" causing the wheelie to decrease.

    However there are several factors to this problem. Also, isn't it easier to figure out by doing the linear force diagram instead of using angular momentum? (the latter requiring the ang. momentum of the whole system etc.)
     
  23. 2000YELLOW360

    2000YELLOW360 F1 World Champ

    Jun 5, 2001
    19,800
    Full Name:
    Art
    No idea what you are getting at, but you are wrong. Bike's front end goes down. It does not matter where the caliper is on the rim. Simple conservation of momentum. If you try to force the wheel to stop spinning, the bike tries to spin about the wheel. It will always be in the same direction. Try it sometime.
     
  24. DMOORE

    DMOORE Formula 3

    Aug 23, 2005
    1,712
    San Diego
    Full Name:
    Darrell
    I agree with Art, Front end dips regardless of where the brake is located. (front of forks, behind forks ) or inside(drum) all the same effect.
     
  25. bst1

    bst1 Formula 3

    Aug 13, 2005
    1,034
    MARYLAND
    Full Name:
    BARRY T
    Not much different than hitting the front brake when on the ground...the bike will dive front end down due to the momentum of the bike continuing in the forward rotational direction.
     
  26. bst1

    bst1 Formula 3

    Aug 13, 2005
    1,034
    MARYLAND
    Full Name:
    BARRY T
    Now the hard part is getting the bike up in a wheelie in the first place!!!!!!!!!!
    Best technique is to hit front brake to compress the front fork shocks then gun the throttle, weight of rider backward, lift handle bars and WHEELIE!!!!!!!!
     
  27. ROGUE GTS

    ROGUE GTS Formula Junior

    May 24, 2004
    827
    Kalifornia
    Your out of your mind if you stab the brake in order to lift the front wheel, and makes me think you have no business being on a bike at all. All you need is throttle and maybe a little clutch. Even on drastically underpowered bikes you can lift the front end by just leaning back.

    And yes stoping either wheel from spinning while in the air will most definitely make the bike rotate forward. Now generally you don't grab the front cause 1, it's sketchy when you land, and 2nd there is no way to make it start spinning should you need to.

    You would really be amazed how much effect it has on the bike when you have a 15+lb wheel spinning at 40mph and stop it instantly.

    MX is an excellent teacher of physics, when you get it wrong, it hurts and usually a lot.
     
  28. DesmoDog

    DesmoDog Karting

    Jan 2, 2005
    102
    Dexter, MI USA
    Full Name:
    Craig Kenfield
    ???

    Hard part? The vast majority of the wheelies I've done have been unintentional. If the bike won't wheelie under it's own power, than it's too dang small. :)

    And yes, under braking the front end will drop, makes no difference at all where the caliper is located, etc etc...
     

Share This Page