Here you are talking about longitudinal dynamics so the explanation is different but still the physics and the points I raised before remain unchanged. Essentially, the longitudinal forces are an 'overdefined' set of forces acting on the CG. You have 2 forces but only 1 output (longitudinal acceleration) so the traction/braking forces are usually NOT dependent on the weight force that they carry. Or more correctly, the PEAK tractive force depends on the vertical force and the friction but unless you have AWD and 4 wheel ABS you generally can't have all wheels operating at their peak. What you can do at least is modify the which axle operates closest to its peak by moving the CG around with your body.Andres125sx wrote: I´ll take advantage of the occasion to see if you may solve a contradiction I´ve never managed to solve by myself, and the reason must be related with the discussion. It´s about the reason on MX bikes (not only on MX bikes, but that´s been my pasion for more than 10 years) you need to move your body forward or backward to improve traction on the wheel you need. Move forward to enter the corner and maximice turning perfomance, and move backward at the exit to improve traction and avoid too much sliding. This is a basic technic in motocross world.
My first though was since the total weight (bike + rider) is always the same, but you´re changing the vertical load on each tire, you´re changing the grip.
But then I think the total mass of the bike must be irrelevant for each wheel, because if you´re moving your weight forward/backward you´re also changing the mass each wheel must "hold", so the two effects should cancel each other as you´ve just explained...
For example, on a bike, 100% of the traction force comes from the rear tyre regardless of where you transfer the weight. And this traction force is responsible for 100% of the acceleration of the car. If you have a friction coefficient of 1.2 again and a baseline weight distribution of 50%, then the rear tyre has to accelerate the WHOLE mass of the car using only 50% of the vehicle weight as its vertical load. So its maximum tractive force is Mass x MassDistribution x Friction = Mass x 50% x 1.2 = Mass x 0.6 = 0.6g
If you move your weight back to give 60% rear distribution then you can get Mass x 60% x 1.2 = Mass x 0.72g. This is the physics behind why moving back helps traction.
On turn in - generally brake systems are designed to overbrake the front axle and underbrake the rear axle in order to leave some cornering stiffness available on the rear axle for stability. So if you are braking on the limit there might not be enough lateral force capability in the front tyres to give you a turn-in force from the front axle. However if you move forward it will increase the front axle vertical load which will decrease the front axle slip ratio and give you some margin to add some cornering force. The price you pay here is a loss of stability but perhaps this isn't such an issue at low speed offroad.
So basically - the DISTRIBUTION of the front/rear braking/traction forces is fixed by the braking system/driveline NOT by the CG location. However by moving around you can increase the vertical load and therefore grip on the axle which is closest to its peak (front axle in braking, rear axle in traction) to effectively increase the traction capability.
), and with that I can also corner much much faster than those cops. I also drag my footpegs with my pegy like I did with my mx bikes on bankings, as you can see on that picture, and that´s almost double the leaning angle those cops can achieve with a harley, so no, I´m not impressed at all with your videos...