Snip...

Youse guys- arguing about standing up on a motorcycle.... but the short answer is you are both right.

The physics part is where Conrad et al. are correct. Standing up moves the COG of the entire vehicle up. It also increases the moment, which would seem to make the bike harder to move but really doesn't because this is where Chet is right-

The word he used is great- uncoupled. Standing or even lifting up enough so the only thing touching the bike are your hands and feet really do uncouple the rider from the bike so the bike can 'dance' under the rider and make faster and smaller corrections when riding over rough ground. It even works on a pig as heavy as a C-14 when going over a gravel road. The observation is correct but the application of the 'it lowers the COG' or 'it lowers the effective COG' is not; it works but not because the COG moves but rather because the bike and rider are much more free to move independently and each can move faster, again allowing the bike to bump and bounce along without having to rock the rider back and forth also. It also gives the rider a better ride just because he / she does not have to jostle back and forth with each small movement of the bike.

I have seen the 'lowering the COG' idea before, even printed in a magazine with line drawings to show how it works. Some even show that when riding on an angled or banked surface, one should stand and then put all of his / her weight on the outside (where the ground is lower) peg to 'drive the tires into the bank'. Somewhere in merry old England, Newton is spinning in his grave and thinking 'buy them books, they eat the pages.' Standing up on a motorcycle moves the overall COG up.... always (it IS a rule after all). Putting all your weight on one peg, without changing the angle of the bike, does nothing. Not to worry though, such terribly mistaken ideas and even worse, much worse, have actually been patented. Sometimes it is really hard to spot the rule (read: physical laws of the universe we live in) violation right away. At least it is not 'as wrong' as thinking KiPass is not wonderful and the answer to all the world's problems....

Brian

The short answer is that G and I are right and the retired guy is wrong. 

I said that the CG moves upward when the rider stands on the pegs and it was I who used the word 'uncoupled'.

What do I win? 

Dignity and self- respect.... priceless.

:-)

Brian

The short answer is that G and I are right and the retired guy is wrong. 

I said that the CG moves upward when the rider stands on the pegs and it was I who used the word 'uncoupled'.

What do I win?

Dignity and self- respect.... priceless.

:-)

Brian

 

I brought the rear bag protector bars with my Canyon Cages. I didn't install them, because i didn't like the look without the bags on (I rarely have the bags on).

So Of course by bike tipped over with the bags on one day. There was a Oh @#$$ moment. But when I righted the bike and inspected. The bags never touched the ground. The fromt cages kept enough clearance. I may have just got lucky, but just saying the rears (In my case) can be left off.

Either the Canyon fronts or Top Blocks *will* prevent smashing the bags *if* the pavement is perfectly flat and it doesn't go down hard, and etc.   But having the rears adds additional protection in many more situations AND helps prevent the bike from cantilevering over, which will also smash the mirrors and possibly other top stuff when only the fronts are present.

In my case (and in many peoples' cases), the bags never come off except for deep cleaning or maybe at a motel.... certainly always on when riding.  In that situation, they look fine (the rear McE bars blend very well... the front Canyons are quite visible).  But you are both right that the rear McE bars  look very odd when no bags are on.

I'm not sure why I'm foolish enough to join in on the CofG discussion but here goes anyway.  I agree with Brian and just want to add that the word everyone is looking for is inertia.  The inertia of the bike is reduced when you stand up thereby decoupling your mass from mass of the bike.  It makes it much easier to move the bike around and change direction or attitude. 

The center of gravity of a system is simply the addition of the CofG of all the components of the system by using a weighted average.  Let's say the CofG of the bike is 25 inches off the ground and it weighs 650 pounds.  Let's say the CofG of the rider, when seated is 40 inches and they weigh 200 pounds.  The CofG of the two of them will be:  (650*25 + 200*40)/850 = 28.53  When the rider stands up his CofG will increase to about 60 inches.  Substituting that for 40 in the above example yields a system CofG of 33.23 inches.

You can plug in whatever numbers you want but the CofG of the system will always be higher when standing than sitting. 

The short answer is that G and I are right and the retired guy is wrong. 

I said that the CG moves upward when the rider stands on the pegs and it was I who used the word 'uncoupled'.

What do I win?

As a way of saving face-you said "decoupled"   And I'm still retired
Would it be safe to say that the COG is dynamic when standing?

Only if it's moving.

Only if it's moving.

As in riding?  So it would be safe to say the overall COG is "shifting" as we ride, sometimes lower, sometimes higher.  What counts is what works, physics be damned   I sure do wish I was better at words, speaking, understanding, and written as I know for a simple fact that the carried weight is lower when yer on the pegs as my ass is some 32 inches higher than my feet

No, the center of gravity is static unless something is moving up / down (easy boys!) rather than forward.

Now when the bike leans, the C.O.G. definitely moves and it gets lower because both the rider and the bike get lower. The way to achieve the lowest possible C.O.G. is to lay the bike down which is what I think some people are doing on the road occasionally- not 'crashing' but 'lowering the C.O.G.' in an effort to.... yeah, this just ain't gonna' work.

How about this: The teacher calls on Little Johnny to use the word definitely in a sentence. He appears a bit surprised and then asks her if farts have lumps in them. She responds 'Goodness, no!'. He says: "Then I definitely just XXXX my pants."

There ya' go Chet, the best out for you that I can provide.... If physics don't work for ya', confuse and misdirect them....   

Brian

As a way of saving face-you said "decoupled"   And I'm still retired
Would it be safe to say that the COG is dynamic when standing?

With all the Fu---- rain we are having this summer my back road area,  2.5 ac. has turned into a mush , wiggle,  OMG will I make it type ride   
Cold front comming hopefully will STOP this rain 1, 2, 3, 4 inches per day been hear 28 years never have seen rain like this   
Will try standing on pegs , If  I crash, I will FIND YOU   

As a way of saving face-you said "decoupled"   And I'm still retired
Would it be safe to say that the COG is dynamic when standing?

uh huh.   

I'm not sure why I'm foolish enough to join in on the CofG discussion but here goes anyway.  I agree with Brian and just want to add that the word everyone is looking for is inertia.  The inertia of the bike is reduced when you stand up thereby decoupling your mass from mass of the bike.  It makes it much easier to move the bike around and change direction or attitude. 

The center of gravity of a system is simply the addition of the CofG of all the components of the system by using a weighted average.  Let's say the CofG of the bike is 25 inches off the ground and it weighs 650 pounds.  Let's say the CofG of the rider, when seated is 40 inches and they weigh 200 pounds.  The CofG of the two of them will be:  (650*25 + 200*40)/850 = 28.53  When the rider stands up his CofG will increase to about 60 inches.  Substituting that for 40 in the above example yields a system CofG of 33.23 inches.

You can plug in whatever numbers you want but the CofG of the system will always be higher when standing than sitting.

Are you sure that you mean to say inertia and not momentum?   

Look guys, I'm going to have to lock this thread if you keep mucking it up with facts on physics.  It's making my brane hurt and I don't like that when it happens.

Maybe we should post some 'top heavy' pics instead?

You first.

Let me sharpen up the sword a bit...

New thread?

Let me sharpen up the sword a bit...

I guess that answers my question.   

Are you sure that you mean to say inertia and not momentum?

Yes I meant inertia.  Inertia is the property of a body which resists change in velocity, acceleration or direction.  A large inertia makes it hard to change the state of a body, whether that body is in motion or stationary. 

Momentum is mass times velocity.  You can increase your momemtun by either increasing weight or velocity or both.  And momentum is conserved so if you run into another biker of the same weight and stop, they should take off at the same speed you were going when you hit them.  Of course frictional effects make it all not work exactly like that, but pool players know how it works on the pool table.

Yes I meant inertia.  Inertia is the property of a body which resists change in velocity, acceleration or direction.  A large inertia makes it hard to change the state of a body, whether that body is in motion or stationary. 

Momentum is mass times velocity.  You can increase your momemtun by either increasing weight or velocity or both.  And momentum is conserved so if you run into another biker of the same weight and stop, they should take off at the same speed you were going when you hit them.  Of course frictional effects make it all not work exactly like that, but pool players know how it works on the pool table.

Unless the collision is inelastic...