when if you're on the brakes, your geometry would be steeper and you would turn quicker? It would make sense for your bike to want to turn more with steeper geometry right? Just something I've been pondering http://www.gixxer.com/forums/images/graemlins/dunno.gif

its a physics thing. While there is logic to your statement, you aren't looking at the dynamics.

I would have to find and dig out my dynamics book to give you a proper answer, so instead you get one from the hip. ..and I quote from the all knowing web,

"Answer: Nitro MacMad - 21/11/2003 00:31:10
Dear Rahul

The simplest questions are sometimes the most difficult to answer, but here goes...

A fast rotating mass will transfer a force acting to change its axial angle into an axial change 90 degrees round from the applied force (assuming you have enough speed and mass for a given force, of course). The scientific reason for this is that "it is conserving its angular momemtum".

If, like this nutter in a shed, (read that as inventive genius) you have trouble understanding what scientists mean by that try, as I did, to visually reduce the gyro wheel into a smaller, easier to understand, thin slice like a pendulum.

If you release a rod pendulum and half way through its swing turn its loosely held pivot through, say, 90 degrees - the pendulums path of swing doesn't change but its pivot angle does. Stick back all the missing slices to make a solid wheel again and -voila- you have a gyro. This mathematically predictable precessional ability that gyros possess can be used for the devices that you can read about on this site

The gyros propensity to turn an "action" acting to change its axial angle into a ninety degree displaced "reaction" on its axial angle does, I am assured by the scientific community, conform to Newtons third law.

However....

While it does seem to conform to the conservation of energy "laws" (darn - no perpetual motion there then!) I personally see its motions containing shed loads (engineering term) of EQUAL but less than a nats (engineering term) of OPPOSITE and therefore its motions have nothing whatsoever to do with Newton.

NM



Answer: Jeff Harris - 29/12/2003 01:54:35
Understanding the gyro's working isn't really all that difficult. Based upon conservation of angular momentum and the fact that a spinning object will continue to spin about its axis unless acted upon by an outside force (torque)...it's pretty easy to see we're speaking about Newtonian mechanics being able to provide all the answers. Most of that is covered elsewhere in this web, but not in a very user friendly way.

Using your right hand...stick your thumb, index, and middle fingers out so that they are at right angles to each other....orthogonal, with your index pointed ahead of you and middle pointed to the floor, then your thumb should be pointed to your left. (It's even easier to do this if you have tinker toys or something that will let you build the 3 axes....I've been known to use toothpicks stuck in olives).

Your thumb represents the spin axis of the gyro, your index the torque axis, and your middle the precession axis. Or spin, input, and output.

Now either imagine yourself with a 2nd right hand or borrow someone else's (that's why the tinker toys make this easier). Aligning the 2nd thumb with each of the axes note that the direction that the fingers are curling and refer to it as the positive rotation about that axis.

With that mental model (or real one) in mind...consider 2 facts about gyros. 1. A positive torque results in a positive precession. 2. A gyro precesses in a way to align the spin axis with the torque axis.

A simple bicycle demonstration helps. When you lean a bike to the right, the torque is about the forward axis, and the spin access will precess to meet the torque axis, causing the handlebars to rotate clockwise.

However, if you turn the handlebars clockwise, then the spin axis wants to line up with that, and if the turn is sharp enough the bike lays you down to the left, because the spin axis is trying to orient itself to point down. A strong, but effective lesson.

When observiing a gyro with it's spin axis parallel to the earth's spin access, its mount will appear to tumble in an almost 24 hour period. However the angular rate will depend upon your latitude....at the equator 15.041 degrees per hour, at 45 N or S at 10.6 degrees per hour, at 60...7.5 degrees per hour and so on...in other words earth rate = earth rate X cos Lat. (Do I foresee a pretty good classroom project?)

Earth rate is considered apparent drift, the gyro is really remaining fixed in space. Another apparent drift comes from when you move the gyro about on the surface of the earth, and yet another is the apparent drift of coriolis acceleration. Additional drift can be caused by gravity and elipticity effects.

A free gyro can be disturbed in it's balance and begin to oscillate, on the earth's surface that oscillation will settle down to one with a period of 84.4 minutes as the gyro is acting as though it were a pendulum with a length equal to the earth's radius.

With correct balancing a gyro can also be used as an accelerometer....by being allowed to pivot a linear displacement will be sensed as a torque that is proportional to the acceleration. This can make for a pretty basic spring return acceleromter, though magnetic bounding would be more effective.

The precision of a gyro is dependent solely on its rigidity. Rigidity is proportional to moment arm and thus the greater the mass, spin, and mass distance from the spin axis, the more rigid the gyro. Defects in manufacture, balancing, and environmental factors will cause drift...in this case inherent drift...that can be measured and corrected for when the gyro is used in rate calculations such as inertial navigation. Environmental factors cannot be measured on the test stand, so they must be maintained during application; the effects of flaws in manufacture and balancing can be calculated ahead of time.

Not all gyros use spinning masses...some use dither frequencies of light such as ring laser gyros, however the mechanizations work out the same for typical applications.

I hope this helps."

Basically, when you input the torque conter to rotation, the conservation of angular momentum is going cause the bike to stand up. Lighter wheels will dramatically reduce this effect.

thanks! I actually understood that http://www.gixxer.com/forums/images/graemlins/smile.gif

i found with certain tires, it helps too.

Here is a simplified version .
If you brake in a straight line the weight transfer occurs in line with forks (straight).
If you brake with the bars turned the weight of the bike tries to pivot around the steering head(to the outside of the turn)
This is for the front brake.

Further to post.
This effect is more prunounced at low speed, try full lock,front brake 10k, fall over OUCH.
At higher speed is counteracted by gyro effects but still destabilises bike to use front brake in a turn.