26/08/2026
My friend Peter, from Barton Advanced Motorcycle Training, loves the science of motorcycle dynamics as much as me. He also loves to give great explanations by writing long posts, which saves me the bother.
Thanks Peter. 👌
SOME INTERESTING COMMENTS THAT WERE NOT DIRECTLY RELATED TO THE TOPIC
IN THE "WHY DOES A MOTORCYCLE GO AROUND A CORNER" SO HERE IS A REPOST FROM 2022 EXPLAINING SOME OF THE ISSUES RAISED IN THE PICTURE.
THIS IS A SHORT EXTRACT OF PART OF THE COURSE NOTES.
After having a chat with someone this afternoon thought it might possibly be useful to explain further what is meant by the phrase "the centre of gravity needs to pass through the centre of the contact patch" and how it affects so much.
There are basically two main forces acting on the motorcycle in a corner, one is trying to tip the bike over and outwards due to centrifugal forces, the other is the weight of the tilted bike trying to fall inwards. (mg = gravity) When these two forces are equal the angle of the tilt and arc will remain constant. This on the surface would seem a pretty obvious and simple thing to achieve. The big spanner in the works comes from two places, the big squidgy thing on top and the fact that the tyres have width. The two forces when combined create a new vector force (in the picture, the arrowed line) If you were to keep your weight directly in line with the centreline of the motorcycle this force line or vector force will pass through the centreline of the tyre, this means that the resultant force is passing to the outside of where the tyre is in contact with the road. Whenever this happens the bike is NOT in a stable state and still wants to stand up. In this state pressure on the inside bar will be required to keep the same arc, the bike is now in a state of induced instability. If you brake now the bike will want to stand up and try to run wide.
Do not confuse the fact that if you are braking in a corner (correctly balanced) your speed is reducing and by that fact alone the bike will require less lean to maintain the same arc (it is not standing up and running wide). This of course means that as the lean is reducing you can brake even harder, by about 10 degrees you can actually use pretty much full brakes.
This anomaly can be corrected by moving some of the movable weight (you) towards the inside of the turn, when sufficient mass has been shifted the vector force will now pass through the centre of the contact patch the bike will now be in a stable arc without the need for pressure on the inside bar. This also reduces the lean angle of the motorcycle by anything up to 10 degrees for the same radial velocity. The suspension will now perform better and be able to handle road imperfections far better. Neutrality of steering in the corner tells that you have this balance correct. Wave to your friends mid corner, it is now safe to do so. The wider the tyres and the lower the c of g the more this shifting of weight is necessary. The weight needs to be shifted inside by the correct amount and not "down", more on that another time.
Of course you could make it even worse by moving the body in the wrong direction, we have all seen it as someone pushes the bike down away from themselves, increasing the bike lean and creating additional instability and certainly holding those bars tight. DO NOT touch the brakes after entering a corner if you ride like that.
In the correct stable configuration it is now possible to apply the brakes during the corner without causing it to "stand up". If you bike stands up when you brake it is because the machine was in an unstable state to start with. Remember braking moves weight forward, shortens the wheelbase and reduces rake and trail, the opposite of standing up and running wide. If you are still counter steering whilst IN the turn you are doing something wrong.
Here is the bad bit for the boy racers, if done right you are highly unlikely to "knee down baby" on the road at least, and maybe even have "chicken strips". You will just be going faster instead without crashing.
P.S. Specially for the track guys, without getting this principles correct you are likely to find braking heavily right into the corner (trail braking) rather challenging.
Thanks for reading, hopefully I did a reasonable job of attempting summarising this in text form.
As a side note and to keep it interesting:
So where is this centre of gravity? Well the bike without rider has a natural one and its position varies greatly upon the style of bike. Sports bikes have a naturally low centre of gravity for high speed stability reasons and inherently are more affected by body position. Now we stick a rider on top and everything changes completely. To make it even more intriguing the centre of gravity will be different based upon the ratio of the bikes weight versus the rider. But all this is really the subject of another discussion.
Another visual way of looking at it in the video link.
https://youtu.be/bAkbqQpHzxk?si=bTZGD-kOXarMNjfj
