Archive of BMW Motorrad Club Cape (2006 - 2019)

Nice report.  Just one little issue that continues to propagate a misconception (read total lie, complete cr@p, misinformation, ... you get the picture).  You wrote "Rony also covered the stand-up riding technique in detail, confirming how the point of gravity actually moves down when one stands up, changing the weight from your seat to your foot pegs."

How many time must I re-iterate:  standing up RAISES your centre of gravity.  There is no debate, no 'but', no nothing.  It is a scientific fact - indisputable.  The only people who get this wrong are the ones failing Physics 101.

So, why should you listen to me and not an experienced motorbike trainer like Leon, Rony, Lourens, Jan or whomever?  Because I am a space physicist who rides a motorbike.  If you want more explanation or even demonstration, I can provide it.

Yes, the bike does handle better in sand when you stand up - and that is because you decouple the bike from your body (i.e. allow it to move freely), and because you increase the angular moment about its longitudinal axis.  It is NOT because you are 'lowering the centre of gravity'.

All you need to know is that you must stand up.  Forget the lie about centre of gravity.

Manie, thanks also for your honesty about facing your fears.  There is no magic sauce that lets some people do it easily and others battle - everybody battles in the beginning, and for some the journey is a bit longer than for others :).

The real losers are the ones who give up after one go thinking that they can never learn to ride sand.  And as you have found, proper training makes a big difference.  Well done.

Well done Surfer!!!!!!!!

Hmmmm... I think it lowers your point of gravity as the contact points with the bike are not the seat but the pegs.

The pegs are lower than the seat Logics 101.

The centre of gravity has abolutely nothing to do with the contact point.

Yes, the contact point has everything to do with how well you can control the bike etc etc, but nothing at all to do with the centre of gravity.

A quick thought experiment:

• Having a heavy top-box when riding in sand makes it harder, so then
• why not have the top-box at the back where it is currently, but support it there with a frame that connects to the bottom of the engine instead of the back of the seat?
• That way the top box would (according to you) actually be connected below the centre of gravity of the bike and make it more stable the heavier you pack it.
• If what you say were true, then all (or at least some) pannier racks would be bolted onto the bottom of the bike, not hang from the top of the rear subframe.

If I stand on my pegs and my legs were completely ridged then you would be right, but they are not and therefore neither is your theory.

Stop looking at life scientifically, rather be more flexible like my legs

Some things just work, no explanation needed.

Yes, some things just work - like standing up in sand.  BUT it is not because of a lowering of the centre of gravity, because when you stand you raise the centre of gravity. 

I am not disputing that standing up works - I am just annoyed that people continue to use the wrong explanation for why it works.   Surely if you used the right explanation it would help people understand it better and apply it better.  Because the gravity thing is something people clearly don't understand or they would be agreeing with me not continuing with fallacious reason.

Hi Tony

Well put.  When you stand you are able to easily shift the CoG left or right to counterbalance the bike.  This is made even easier because the CoG of your body is now higher when you stand and has a greater moment of inertia (i.e. moving it has more effect on the bike).

Another factor that is often neglected, is that when the bike lurches with you sitting on it, you get flung to the side and end up turning the handle-bar in the exact direction that will make the bike lean even more in the direction it has flung you.  This is called 'positive feedback' and makes the whole system unstable.

When you are standing, when the bike leans left you tend to stay upright, and the handlebar turns towards the lean (negative feedback).  This makes the system more stable.

The gist of it is that although standing raises the CoG, the improved body control and negative feedback on the steering outweighs the effect of a raised CoG.

Hihi, just as I always mention during the training, guys will write books about the combined (Rider and bike) centre of gravity but none of them or all of them make sense as they all contradict each other or agree/say the same thing in different words. No harm or damage is done to bike or rider on my courses so get up on your pegs and ride, it works

Whew, Surferdude you have got the scientists going.  I don't understand any of it except the "stand up because it works" bit.

It is an excellent course which I can highly recommend to anyone new to riding off the tar. 

My confidence levels have increased dramatically.  I hope not too dramatically though, because that is when I usually come short.

You guys don't know what you are talking about......when one stands on one's footpegs, one is further away from the ground, and the fear of one falling is increased accordingly.......thus, one makes a little (or a lot) more effort to keep one's ass away from the dirty road.

Hi Rony

I agree that nobody is harmed on your courses and from all reports people are gaining great skills and confidence while having tremendous fun.

I also agree that standing up is essential for better and proper control of your bike in technical riding (take trials bikes as an example, they do not even have a seat).

But the scientific fact is that when you stand up you raise the centre of gravity of rider and bike (and you cannot consider them seperately unless the rider has fallen off or left his bike at home :).  It is an indisputable, provable, measurable fact.  I cannot believe that I even need to have this discussion - it feels like Joshua Slocum sailing solo around-the-world meeting President Kruger of the Transvaal (who believed the world was flat and told Joshua he was "sailing on the world because it is a flat disc").

Yes, you must stand up, yes, it makes it easier, no, it does not lower the centre of gravity, because it actually raises it.

And don't use weasel words like the Country Trax guys do, saying it "lowers the effective centre of gravity".  There is no such thing - by definition the "effective centre of gravity" is the "centre of gravity".  And it gets raised when you stand up.

Maybe a good topic for Mythbusters to investigate...!

Sorry guys, I did not want to start a rumble in the jungle. Being a scientist myself (unfortunately in chemistry and not physics), I have learned that perceptions, logic and science don't always result in the same conclusions. So unless someone scientifically proves to me what really happens to the cog, and that it IS in fact the cog and not some other mass related phenomenon or only the flexibility to move your body around that's involved in making the bike (feel) more stable, I won't take any sides just yet. Maybe the answer is much deeper than science. Maybe by standing up our brains convince ourselves that the bike is more stable even though it might not even be true. You know the power of the mind theories? Hahaha, look where I am going with this....

Anyway, thanks for reading my reports guys. I will never use it to play guys off against each other. If that was the impression...my apology. While you guys sweat it out to find the answers, all I want to do is just ride my bike and have fun in the safest way...

(PS. So what if you lift your arse from the seat, put all your weight on the pegs, but make sure you head and body stays more or less at the same height....will the cog stay the same, will the stability of the bike stay the same? Just wondering.....)

"Maybe the answer is much deeper than science." = FAITH

Faith in that Rony says it will work, and when you believe it and it does it changes everything.

Then the fear of the sand is overcome.  

Ok, if it is faith you need to convince you:  take it on faith from me - when you stand up you raise the CoG.

And both Manie and Charl have admitted that no experiment or proof will work for them (Charl: rigid legs etc, Manie: that it IS in fact the cog and not some other mass related phenomenon ) - their minds are made up based on what a biker told them, and no Space Physicist is going to convince them otherwise.

All I am saying is that the CoG goes up when you stand.  That is a measurable, calculable and provable scientific fact.  You both seem to be assuming that if what I am saying is true the bike should be more unstable, and only a lowering of the CoG could make it more stable.

The stability of the bike depends on far more than the CoG, and in any case, given that the bike weighs 3 times more than you, and your standing raises your CoG by about 15cm, and thus the combined CoG moves up about 4cm - you are not talking about a lot here!

And Charl, whether your legs are rigid or not, the CoG goes up when you stand.  But, if your legs are rigid the bike is more likely to be unstable - because you will not be able to actively balance the bike.  This does not mean the CoG only goes up when your legs are rigid - it means the bike is more unstable when your legs are rigid.  The CoG goes up anyway.

In summary again, when you stand on the bike:

1. the CoG goes up
2. the bike becomes more manageable due to (1) your decoupling from the bike, and (2) your contact point moving from a single point high up (your bum on the seat) to two contact points on either side of the longitudinal axis of the bike (your feet on the pegs) lower down.

Ahhhhhhhhhhhhh...!!!!

Now I get it, don't stand up just decouple yourself from the bikes seat.

Charles, I'm sure you know that I've just used this opportunity to up my forum points and that I could never scientifically prove anything you say to be wrong.

So, stand up, look up and ride that bike to a new destination every chance you get.

In the old days when Rony and Charles were small and years before I was born, the expert would say "I am a Bishop" (or even better, a POPE - although there was only one of them so they had to make him infallible in order for him to be really convincing), and he would say "I am telling you the earth is flat, therefor it IS!". 

Unfortunately the admirable qualification of BISHOP or POPE didn't go far enough to explain scientifically with sums and things, so quite a lot of discussion occurred, involving loud voices, red hot pokers and thumbscrews to conclusively PROVE that the earth is flat.

Personally I can understand both arguments because the earth really is flat where I live, but it obviously isn't in France and Italy, which is where the bloke came from that eventually invented a globe which proved his point, so now the discussion is over and we've moved on to Center of Gravity; strangely the Pope isn't interested in that so now we've got to work it out for ourselves.

Although I'm not THAT concerned, probably because the only time that CoG is of relevance to me is when I'm wishing I was on top of the thing and not under it, and then I really don't have any interest in where it is, I just want it OFF me!  But it would be nice to understand it just so I can sound intelligent at the bar or on the Wilddogs Forum.

I've been meaning for ages to get someone who actually works with this type of stuff (like a university prof who works with formulas and not topboxes), to explain it in scientific terms and to show the actual proof for once and for all using pictures and sums and things, but I never seem to get round to it, so if anyone does have a good contact for a Physics 101 lecturer, please ask him to write an essay for us, preferably using scientific terms that we would understand like bum, boots, pegs, saddle, open up etc.  He can even stretch it a bit to include things like Kilograms (spelt Kg?) and other units of height so that it's kind of conclusive.

I must say discussions like this really spoil one's simple enjoyment of the good things in life.  Now it's bugging me whether the CoG of a beer bottle gets lower as you drink the beer???!!!  Damn - things are never going to be the same again!

Now it's bugging me whether the CoG of a beer bottle gets lower as you drink the beer???!!!

Sadly, it does.  And in accordance with the Law of Conservation of CoG,  as the CoG of the bottle gets lower, the CoG of you gets higher, until eventually you are so unstable you can no longer stand, not even on your bike.

Fortunately this deleterious condition is somewhat mitigated by your legs becoming much less rigid, which, as per "Red Adventure's 3rd Law" means that CoG no longer applies and you may lie down.

Clear now?

Aah the cogs are turning. Clear!  Thanks so much!  Now I can drink  beer safely without worrying about a headache BEFORE I drink any.

I am really enjoying this thread - especially because I am too dof to have an opinion on the subject.

Charles, perhaps a stupid question - do objects have a centre of gravity in space? Do things have to balance out there?

Hi Geoff

Yes, objects in space have a 'Centre of Mass', which is the point that you can use as where all their mass is concentrated for purposes of calculation.  (It would be the middle of a spherical object).

Now, the moon and earth are bound (connected) by their gravitational pull on each other, and although we like to think that the moon goes around the earth, actually, the earth and the moon rotate about the centre of mass of the two objects.  Since the earth is bigger and heavier, the centre of mass is closer to the earth (it might even lie under the earth's crust).  So the earth wobbles as it rotates about this CoG of the two.

On the bike, when you go flying, technically you and the bike have a combined centre of gravity, but since you are already falling it is of little interest other than academically :).

Thanks Charles.  

I won't pretend to fully understand, but I find it very interesting.

I watch science and scientists with bemused amazement.  On the one hand they know so much and on the other hand they know so little.  I often wonder where the search for knowledge will end - if it will ever end.

When my thinking goes down that path my mind eventually boggles so I go and make a peanut butter sandwich. That I can cope with.

LOL @ this debate resurfacing again! Kudos to Charles for sticking with it... I would've given up trying to explain it long ago

Thanks to Charles and the other scientists - and non-scientists! I found the explanations extremely interesting. We all know what works in practice after a course or two, but the science behind it adds understanding to some.   On the same lines, has anybody got any idea of the quantums involved when moving your weight opposite to the lean angle? And when you shift your weight forward while doing this, how much the grip of the front tyre effectively increases?