In the automobile jargon, the transfer of load represents the variation of the exerted forces enter the tires and the coating (not to confuse with the Transfert of mass which is a displacement of the center of gravity of the vehicle). The transfer of load is carried out during various accelerations (acceleration with the familiar direction, braking, turn) is with forces applied to the surface of the tire parallel to the coating (see Pneumatique).

Reason of the transfer of load

For example when the vehicle takes a turn, there is exerted on the tires of the horizontal forces, perpendicular to the direction of the car (see Centrifugal force), these forces create a couple on the car which would tend to make him make a rotation, however as the car remains quasi-horizontal, it is no rotation, the couple describes previously is compensated by another exactly opposite couple whose forces are exerted by the road on the tire of direction perpendicular to the road. It is noticed that it is the tire opposed to the direction of the acceleration which subbit the most pressure, example: tires of left in a turn on the right. These forces vary the pressure that the tire exerted on the road, and thus make change the capacities of adhérance of a wheel. There exists the same phenomenon with acceleration and braking, along a different axis of rotation. One sees on the image that the higher the center of gravity is, the more the couple created by the accelerative forces is high, the more the transfer of load will be important.

Adherence of the tire to the road

to include/understand the consequences of a transfer of load, it should initially be included/understood how a tire " colle" with the road: Up to which point the tire does adhere to the road? In fact it would rather be necessary to say, which is the maximum force exerted on the tire perpendicular to the road before this one does not skid:

In fact the side maximum force is quasi-proportional to the force which sticks the tire to the road (p on the diagram), however last a certain threshold, the side maximum force does not increase as much compared to the force p that previously.

Effect of the transfer of load

We will take the most frequent effects: It should be known that as considering previously if one then increases too the force perpendicular on the ground to the tire, the side maximum force does not increase proportionally any more.

Simple situation of turn

A car with a center of gravity raised, which undergoes strong transfers of load in turn, will less better hold the road in turn than an identical car with a lower center of gravity.

Turn and braking

If a car brakes, the transfer of load goes on the front axle, thus the tires postpones are less " collés" with the road. At the time of a strong turn with a braking, the side forces exerted on the back tires will not be sufficient to draw the rear wheel-axle unit towards the interior of the turn as much as the fact the front axle on the nose gear: the car oversteers.

Acceleration

If a car accelerates, the transfer of load goes on the rear axle, the back tires are thus more " collés" with the road, it is thus interesting, for the sporting cars to put the driving wheels at the back, to avoid ice-skating.

Braking

If a car brakes, the transfer of load goes on the front axle, if the majority of the mass is then located at the back during braking it y' aurat a good distribution of the masses on the tires. Thus the sporting cars with engine postpones have the reputation to better brake that with front engine.

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