Hello guys. I am modeling a car in simulink. I got into problems with weight transfer. The models I found all calculate weight transfer just from CG high and wheels base. I think that in weight transfer there should be also added aerodynamic drag weight transfer and maybe a weight transfer due to torque? Torque opposite to torque that is at the driven axle. Problem is that if I add the torque weight transfer Iam getting negative normal force at front so car would actually flip. Not sure if the torque calculation is right.

My equanation for it: Fnormal_T = Torque/wheel_base

That value Iam substracting from front axle and adding to rear axle.

Based on the way you ask the question and the fact that you're using Simulink, my guess is you're doing a pseudo-stable linear approximation. If that's true, just put CGh, F/R_axle_distance and grip_level/acceleration into your equation and you're good to go.

Wheel-base along won't do you much good. You need the horizontal distance between the axle/wheel and the CG. You can calculate this using static weight distribution, which is usually easier to get from spec tables of real cars. Aerodynamic weight is just dynamic weight, treated the same way as static weight in each frame. For aerodynamic drag, you need, in its simplest form, height of aerodynamic pivot/center.

Real cars do flip under heavy acceleration, so it's fine if your model does. I don't know how it handles the near-flip situation though. When the car rotates a lot those simple formulas no longer work. If you have to simulate wheelie/flip, make sure the weight-transfer formula gets cut-off when front load reaches zero.

Kelling may have answered more usefully above, but to provide the correct equation, should it be needed:

Quote from L@gger :

My equanation for it: Fnormal_T = Torque/wheel_base

That value Iam substracting from front axle and adding to rear axle.

You want to divide the axle torque by the wheel radius, to get you force (neglecting inertial effects from the wheels, though it sounds like you're not worrying about slip). Multiply this force by the height of the center of gravity and you're back at a torque. Then divide this by your wheelbase and you're back at a force. This force is the longitudinal weight transfer. The longitudinal position of the center of gravity does not affect the weight transfer (though naturally, it does effect your static loads, and thus how easy it would be to get the vehicle to wheelie).

I think that is correct from memory; if anybody spots anything wrong, please point it out!

Thank you guys.

Yes I am calculating with slip and made some simple Pacejka tire.

Quote from Bob Smith :

You want to divide the axle torque by the wheel radius, to get you force (neglecting inertial effects from the wheels, though it sounds like you're not worrying about slip). Multiply this force by the height of the center of gravity and you're back at a torque. Then divide this by your wheelbase and you're back at a force.

Didnt saw this equation yet. I am going to try that.