I'd concur with this too.
In addition to not being a Physicist, nor am I a Kinesiologist, but I wonder if, as bipedal creatures, we have a better-developed sense of balance on our feet than on our asses? Too much whisky of course challenges this assumption, but under sober conditions, this may be yet another advantage of standing(?).

 

As someone still recovering from a cracked rib I received from an endo on my mtn bike a couple weeks ago, TELL ME ABOUT IT!

 

Or tequila....

But yes, this is what I was referring to when I suggested the benefit to handling we bring to a motorcycle in a 360 degree ability to shift our weight to influence COG. And then there's that thing...and it may be called COG also...where you consider how our body position affects that centerline deal...you know...where you see those drawings of a motorcycle leaning over in various positions, and the rider's position has a line drawn through his center mass to the contact patch of the motorcycle's tires. Fascinating stuff, but I think we generally understand how our standing, sitting, hanging off, and scooting fore and aft all can have a positive effect on handling in the appropriate situation...even if we're unable to succinctly describe all the scientific ramifications. If a rider stands up in technical terrain and doesn't feel the improvement...if a rider scoots forward or aft and doesn't feel the effect...if a rider purposely loads the right or left footpeg and doesn't feel/realize the difference...then that rider don't need to be on no motorcycle.

 

Just thinking about my comments about the CRF250X guys using excessive power - it's not an opportunity that's open to me a bog standard KLX

 

It's one of the great paradoxes of single-track vehicles: a 5 year old can intuit how to ride one, but even a learned adult struggles to explain how!

 

Indeed:
http://www.dailymail.co.uk/sciencete...ing-maths.html
And that does not even mention bumps or standing up!

Interesting that they include the gyroscopic effect of the wheels in the equation. The safety expert website mentioned earlier could be wrong.

I like the video of the lego bike. One of my mates rides his MTB like that

 

Not that I can explain it (but now that my internet is back up and running at home, I'll try)...
I don't think standing lowers the CofG but it lowers unsprung weight. Now that the knees come into play standing, you have lowered that weight, by taking it off the seat and putting it onto the pegs.
For example, when Camelbaks became popular MTBing, riders soon realized that taking weight off the bike(water bottles, tools, etc) made the bike handle better. So we went from seeing bikes outfitted with multiple water bottles, pumps and tool bags to bikes that were just naked bikes with a rider carrying all that on their back (making it sprung weight, thanks to the knees).
I know when I put the Baker tank on my bike it changed handling in a negative way (at least when full). If I were to carry that fuel on my back, the bike would still handle as it did before, my back may just be a little more sore.
Before I dig the hole any deeper...
Hope all is well with all you KLX freaks. It's been a good summer of riding for me! A new riding buddy has shown me tons of old "roads", which are now more like rocky stream beds, and how to connect them all together. I've been in KLX heaven. Standing the whole time to lower my unsprung weight.

 

First off, James Davis is a self appointed expert, who's done enough plowing around to get that "expert" title. He has little high performance experience much less off road. I don't have a huge amount of respect for his "authority". People see me as some authority on motorcycle mechanics because I understand the cam drive system. I am not an authority on mechanics in general because I make a part. I do know a fair amount and I give information and some advice, but that does not make me an authority. Talking a lot with a closed point of view does not make an expert except in the eyes of the legal profession where Mr. Davis is considered an "expert". Just don't see it.

He failed to give the actual facts that make the myth.

First off, let's clarify the use of terms, mass is constant force is gravity based. You have the same mass on the moon, but your force due to gravity will be far less (I'm thinking it's like 61% less). But everything we are talking about is on earth and is thus affected by the earth's gravity. So that pretty much makes the two terms "center of gravity" and "center of mass"(... well, four terms - "center of gravity", "center of mass", "centre of gravity" and "centre of mass" for those in Europe) are the same. The mass will have force accorded by earth's gravity.

When the motorcycle is considered alone there is a center of gravity based on mass.

When a load is placed on the seat the location of that force raises location of the center of gravity relative to the motorcycle.

When a load is placed on the foot pegs force actually lowers the center of gravity of the motorcycle.

Remember, we are talking physical forces and where they are placed on the motorcycle, not the combination of two masses (rider/motorcycle).

If you only talk about combined masses viewed as one, there is a serious problem with it, because the one mass can easily move where it is placing the forces. A simple lean to the front and the mass of the motorcycle relating to forces will shift forward and vice versa. That dynamic loading is what is confusing to all.

It is about the effect of forces applied to a motorcycle chassis.

As a rider and being dynamic in placing forces on a motorcycle, we can shift the center of gravity of the motorcycle bearing the forces by simply moving where the forces are applied to the motorcycle independent of the combined mass since part of the mass is infinitely able to vary position in an instant. Standing up places all the forces of the rider on the foot pegs, thus making the center of gravity or mass of the motorcycle alone lower. The combined mass is actually higher, but the dynamic nature changes the way the motorcycle chassis perceives the load applied to it. That is what is affected when a rider stands up. They can more easily shift around over the bike, while applying the load lower on the chassis, making it easier to maneuver the motorcycle itself.

If you want to see this in action watch a trials rider in a tough section shifting weight right/left, fore/aft all the while keeping the motorcycle relatively stable and upright underneath them as the forces of their weight is on the pegs. Totally different dynamics than the same shifting around would apply if they could perform the same shifts with the forces of their weight on the seat (well, pretend the trials bike has a seat). The combined center of gravity is higher, but the motorcycle chassis center of gravity is far lower than that of one where the rider is parked on the seat. It is all about the application of forces, not just a single fixed mass.

By the way, going up hill or down hill affects the center of gravity of the masses pending a variety of measures and where loads are placed. Same is true when leaning side to side. The center of gravity changes with every move even if nothing else in the mass moves. Think CRF450R "hill climber" that weighs the same and sits at the same height as a standard CRF450. Sitting horizontal on flat ground the center of gravity is the same. put them on a hill and the long rear swing arm places the center of gravity far forward of the center line and higher due to the angle at which the motorcycle is at relative to horizontal. Big differences, same mass. Now have the rider stand on the pegs being flexible in position and figure where the center of gravity of the motorcycle as loaded, but independent of the rider position, is located.

It is pure physics, mechanical nature, and knowing what one is really investigating. Standing on the pegs versus sitting in the seat per the motorcycle argument is purely relating to the motorcycle chassis loading, not including the rider center of mass. It is only about where the rider is placing the forces of their mass on the chassis - the seat or the pegs. 200 lb on the seat makes a higher center of gravity than 200 lb on the pegs. Always has and always will be.

 

One side note that might emphasize my point...

What happens to that combined load when a rider unweights the pegs?

Both masses are still present, the combined center of mass is still nearly the same location, but the motorcycle chassis perceives there is less load and it will go over a bump or log easier. Again, the trials rider who can bounce around by unweighting and even clamping their feet against a bike pulling it upward due to application of the rider's mass upward, maybe backward or forward depending on if they're bouncing the rear or front tire or both.

In a moment in time the two as one still have the same center of mass by calculation, but the motorcycle chassis is perceiving something totally different in loading. The rider has radically altered the effects of gravity of the motorcycle chassis using a jumping action to unweight the bike while still on the bike! - his mass going up off of the chassis and with boots clamped against the frame, adding an upward force it in the process.

Same bike, same rider, same masses, same stationary center of mass by calculation, but hey, it's all about the dynamic nature of the rider, how they apply forces and how they can affect the motorcycle itself. It never is just "that simple" now, is it?

Tell that to James Davis!

 

Hmmm, if what you're saying is that standing on the pegs lowers the point at which the rider is applying his/her mass to the bike, I totally agree. But if by extension you're saying that it somehow also lowers the centre of mass, I continue to think that's incorrect because CoM is independent of where or how objects are connected.