I saw a few questions about this in other threads (on rc groups) and wrote the below as an answer.

High CG and driving on the crashbars :-| hmmmmm.... my english is crap so I bet things will be misunderstood, but I will try to list a few things I tought about when I designed my bike. You will have to draw the right conclusions yourself. I will try to keep this as simple as possible:

You always have to consider the following factors:
Overall weight.
Speed you are going at.
Curve radius.
CG position in relationship to the Wheelbase center.
CG Position off ground
Contact points of the tires to the surface
Contact point of the crashbars in relationship to the tire contact points.
Rules how a bike is supposed to look like.

You always have to know that there are two different driving situations in a curve: Only the tires have contact, the tires AND the crashbars have contact with the surface. These are two completely different driving dynamic situations! The fastest way to drive is when only the tires have contact.

The bike will always center the (dynamic) CG over the line you can draw between the contact spots the tires have to the suface. It will also always try to balance itself against the centrifugal forces in a turn. Or the other way round it will only drive if this is in balance ;-)

The higher the CG the more leverage the overall weight has under acceleration. This means the bike will wheelie easier.
High CG means that it is harder to flip the bike from one side to the other. The CG has a bigger lever and therefore its harder to move the bike over.
High CG makes a bike more unstable, needing heavier wheels to keep it stable, this lowers the CG again ;-) *LOL* I think you know what this is going to end in......

The contact spots of the tires go off center the further you lean the bike into a curve. This is one point where a higher CG could be better than a lower CG. The further you lean a bike into a turn the more the contact points go off center of the bikes geometrical middle. The lever for the CG inreases so you need more leaning angle to keep the bike balanced when you have a low CG. But a lower CG has less leverage in relationship to the ground ..... again there IS a sweet spot ;-)

Lay the bike on the side on its crashbars. Look at it from the top. The tirecontact points and the crashbar contact point draw a tringle. Now look where the CG is. It will be somewhere in this triangle. Whatever edge of this triangle the CG comes close to will cause more or less problems. And I can assure you when the CG comes close to any of the triangles corners... the crap hits the fan ;-) But once again, having the bike on its bars is only one driving state, it is faster to drive only on the tires.

Putting the bike on the bars always causes the bike to unbalance to the better but usually to the worse! The transition from having the bars on the ground or not has to be smooth. So you have to find a sweet spot where these two driving states fit together without making the bike unstable.

So what did I do? I looked to find the best way a bike:
Accelerates on the straight (no bars)
Accelerates out of a turn (no bars)
Brakes into a turn (no bars)
Flips from one side to the other (no bars)
Drives straight and stable at all speeds (no bars)
Doesnt wheely (no bars)
Keeps grip on the front or rear tire at high leaninig angles (no bars)
Doesnt loose grip on the front under braking at high leaning angles (no bars)
Stays stable when on power at high leaning angles (no bars)
Minimum "highsider" problem when coming out of a drift (no bars)

Then there actually is a simple place where to put the crashbars, because all Crashbars have to do is:
Start the bike up when on its side.
Be a limiter that you dont go over the maximum leaning angle.
To lead the bike back to stability when one of the tires loose grip.

So DONT mix up CG and crashbar position! They do completly different jobs on a bike.

Maybe one simple way to find out if you have got it right is the following:
Lay the bike on its side onto th crashbars. Fully steer to the side its laying on. You then should be able to slowly accelarate and the bike should drive in a straight line!! This shows if the crashbars are positioned properly in relationship to the CG.

Center of gravity and crashbars

by Edi Winter