VW Touran manuals

Volkswagen Touran Service Manual: Taper

Taper is caused by slightly offsetting the tread and/or the belt by a few tenths of a millimeter from the geometric center of the tire. Taper cannot be recognized visually nor can it be measured with workshop equipment.
   
Components of a Tire
1 -  Bead
2 -  Shoulder
3 -  Tread
4 -  Steel belt
A -  Geometric center of tire
B -  Actual position of belt. It can be offset to inside or outside.
  Taper
Shown out of proportion to provide a better illustration.
1 -  Belt/tread offset
F1 -  Unequal forces on contact patch
F2 -  Unequal forces on contact patch
Fk -  Force of taper
The offset produces differences in rigidity of the inner and outer shoulders of the tire, which lead to differing forces on the contact patch. Due to this, the belt and tread will not be pressed against the road surface with the same force (F1, F2). A taper forms. The resulting force (force of taper Fk) can become so large depending on speed, that the vehicle pulls to one side.
If the force (Fk) on one wheel of the axle is, for example, 50 Newton and on the other wheel also 50 Newton, and both forces are exerted in the same direction, the forces are additive. Reversing a tire on the rim can compensate for the pulling because the forces then act against each other.
Because the direction in which the force of taper is exerted is not visible at the tire, only road tests and targeted rotation of wheels and tires can establish which tires cause the pulling.
The tire consists of numerous components and materials which are vulcanized to a single part at the end of a complicated manufacturing procedure. This leads to differing construction tolerances which can make themselves noticeable through more or less strong lateral forces (lateral forces of taper). These forces can also develop in new tires.
One-Sided Pulling on Front Axle
Pulling to one side can be caused by the suspension. However, experience shows that in 90% of all complaints, the tires cause pulling to one side.
One-Sided Pulling During Normal Driving Style
On a straight, level road surface, the vehicle wants to pull to one side at a constant speed or with moderate acceleration. A force can be felt at the steering wheel.
One-Sided Pulling During Strong Accelerating
Pulling to one side during fast acceleration is, in part, due to the design of vehicles with front wheel drive. Various frictional conditions of left and right wheels, for example, possible irregularities in the road surface (pot holes) and consequently varying adhesion to ground have a substantial influence on the handling characteristics. This does not constitute a complaint in the sense of warranty coverage.
  Taper
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