Motorcycles and physics

Referring to wheelie from a stop, with a heavy bike (Harley)....pretty easy to get my 150 hp ZX9R up.....not as easy with a Road King.....I'm not big enough and it isn't powerful enough to do it by leaning back....
as to experience, I've been riding since 8....42 years, so I must be out of my mind!!!!!!!

 

Actually, you balance the bike on take-off by blipping the throttle.
If you *uck up, and the front end is too high, you hit the rear brake (and clutch in to avoid stalling).
A contrario, if the front end is too low, give it gas and it will go back up a bit.

Those are band-aid techniques, that you should only use when you *uck up on take-off (unless you're really good and brake during take-off and keep the bike balanced with a throttle blip in the air ... pretty advanced technique).

Last time I hit the front brake while in the air, the front wheel went straight for the ground and I ate some dirt.

 

Yep, I left out a force in my inital diagram. Oops! Sorry not to get back and corect my mistake earlier.....

 

haha we don't even want to discuss the theories and practices involved with grabing a ton of brake on the face of a jump and how to deal with it.

I will say it does work very well to drastically lower the trajectory off the jump and allows you to go MUCH faster. But quite scarry the first few times you try it.

 

Faster, as in keeping a lower trajectory at a higher speed, thus effectively traveling less distance (lower arc) and there for getting from point A (takeoff) to point B (landing) in a shorter period of time.

Simple explination: Watch Bubba ride, and pass guys in the air while flying below them. He hammers that bike so hard on the face of the jump he can hit it going faster while staying quite a bit lower to the ground.

 

does the girl have big tits?

 

I wouldn't know, I still can't get rid of the throttle blip on take off!

I'm not sure about #3. But yeah, he hammers it, hits the face of the jump on the brakes, minimizes the suspension kicking up via body movement/kicking the bike sideways, and stays in the air a bit less than those who just clear the jump (like I do).

It is smart and Bubba is really good with scraping split-seconds on each jump, and it's become "normal" for the top pros, but I still remember when McGrath started doing it ... it looked like witchcraft! I'll try to dig up a nice time-saving jump picture of Bubba (or Carmichael) ... it's impressive.

 

don't think so pal....

 

no not at all, untill you get very good at bike control you are ALWAYS on the gas hard leaving a jump. It keeps the bike much more stable in the air and front end up. Rookie mistake is to let off the gas coming up to a jump, which sends it into a nose down, plant your face in the dirt type crash.

And yeah watch pros take off on big jumps, they can hit the face going 20mph faster than is required to make the distance. Heck bubba yanks his bike over so hard trying to keep it low, there are pics of one footpeg digging into the jump, now that takes some balls and a lot of skill.

 

That's the pic I'm looking for.

 

http://www.personal.psu.edu/users/j/a/jal440/072103stewart680.jpg

This one is SWEET!
http://www.peterfoleyusa.com/shoug7-27/bubbacomposite.jpg


http://adrenalintrip.extreme.com/uploads/809246503-0.jpg

Note: nobody crashed during these photos, all done and executed as was planned.



You guys watch the first 2 SX rounds this year in Canada? Bubba is layin wood to RC, 2-0 so far. Round 1 bubba washed out in a corner, was in something like 12th place, and came back to win it by a good margin. 1st time anyone has crashed in a race with RC and come back to beat him. Round 2 wasn't even funny, led it from lap one and lapped up to 4th. It was actually funny to watch, he had something like a 10sec lead and was playing games with RC. If Ricky would throw out a fast lap, and it seemed like he was working really hard to catch up, Bubba would toss out a couple that were tenths quicker, then just chill for a bit. First time I have ever seen RC flat out say he couldn't hang, going to be an interesting year in SX and MX.

 

Perhaps my explanation wasn't clear.. but I am NOT wrong.. You just stated the same thing I did. I said, the wheelie will "decrease" and the bike will dip (aka the front wheel will come down).. I'd suggest you read more carefully next time.

 

woah way to dig up a 6 month old thread. Oh and just for reference you are correct on how the bike will react, but completely wrong in stating that caliper placement has any effect on it.

No matter where on the rotor the caliper is mounted it is still going to put the same force on the fork/chassis. The calipers are mounted on the rear of the fork purely because it's the most logical place to mount them. This is due to a number of things, bracket/dropout strength, line length, fender mount (on sport bikes) etc. On a linear compression (aka slider fork) setup like that rotational load has no mechanical effect on the action. This is not true for most all other types though. Any swingarm or linkage type can change dramatically due to braking and/or acceleraton forces.




On this very topic (and it makes a very dramatic realization of the effects) did anyone catch the MX race where Bubba's motor siezed up mid-air? He was haulin the mail (judging by the placement of the track I would say 4th gear, probably mid 50ish mph. At this most inopprotue time he went of a small drop and the motor locked up. It threw the front of the bike down and tossed him over the bars, into the ground like a rag doll. That boy has taken some SERIOUS hits this year.




So I heard this riddle about an airplane on a treadmill.......

 

What on earth did you do to that 9R to get 30 more HP????


Wheelies are easy. Just stand up, give her a little bounce and time the throttle with the bottom-out. Whaa laa.

 

Doing wheelies on the open road is just plain reckless and stupid. Flame away, but we see more 'expert riders' in our trauma center that either leave dead or with scrambled eggs for brains than walk out on their own power. Ride safe, guys - sorry to be such a downer.