Vehicle brakes...

[Externet]

Hi.

If a vehicle centre of mass is below the blue line that joins shafts; applying brakes makes the rear axle heavier and increases  rear tire friction with pavement resulting in shorter stopping distance.  Is that right ?

If a vehicle centre of mass is above the blue line that joins shafts; applying brakes makes the rear axle lighter and decreases rear tire friction with pavement resulting in longer stopping distance.  Is that right ?

 

 

[MigL]

Brakes have proportioning valves that apply dissimilar hydraulic pressure front to rear, and take the vehicle's weight distribution into consideration.
Front heavy vehicles ( usually front engine/transmission/drivetrain ) will go through several disc brake pads on the front axel before the rear ones halfway worn.

[Ken Fabian]

Externet - I don't think it it works like that - the overall braking force aligns with the road surface, where the tires contact the road - not through the centre of gravity. Applying the brakes applies a torque between those tire/road contact points, which are lower than the centre of gravity, and the rest of the vehicle. All of the vehicle mass is above the line of braking force. That torque from the brakes will try and rotate the vehicle around the axles - but because of the rigidity of the body the combined result is a single torque lifting the load from the rear wheels and transferring it to the front - effectively the front tire/road contact points become the pivot point. As that happens the braking ability of the front brakes is increased and the rear brakes is reduced. (As MigL points out, they have the means to balance the difference between front and rear brakes - less braking to the rear, so the rear wheels don't lock up).

Having the centre of gravity lower than the axles does reduce that tendency of the torque from braking to force the vehicle nose down, by placing it closer to the road surface and the line of braking force, but does not eliminate it.

Edited June 10, 2019 by Ken Fabian