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Home >> Porsche >> 2011 >> Cayenne Turbo >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 47 (44 - Wheels, Tyres, Suspension Alignment (4.8L Non Turbo) -- 92A - Cayenne (92A)) >> WM, 440593 Balancing/Optimising Wheels >> Balancing/Optimising Wheels >> Explanation Of Terms

Explanation Of Terms

WARNING: This page is about a different variant/trim than selected.

Geometric error (radial and lateral runout) 

Radial and lateral runout of the rim and/or rim/tire assembly.

Flat spots 

Flat spots can occur on the tires if the vehicle is idle for extended periods.

Radial force variations 

G16330075Courtesy of PORSCHE CARS NORTH AMERICA, INC.

The radial force is a force that compresses a tire. Based on its size, a tire has softer (-item A-  ) and more rigid zones (-item B-  ) due to constructive and production-related factors. Given this, the tire compresses to various extents at a constant wheel load (-arrow 1-  ) and a constant tire pressure (-arrows 2-  ). This varying spring action (-X-  ) in the tire can cause vibrations in the chassis on even road surfaces and the driver may notice this as shaking in the steering wheel, for example. Measuring the radial force variation involves running the tire on a wheel balancer that measures radial force variation while applying a constant load to the tire. This simulates the rolling of the tire on a driving surface. Variations in radial force occur independently of the direction of rotation of the tire and are measured as the difference between the maximum and minimum radial force ("peak-to-peak" value).

1st Harmonic 

The changes in radial force variation can be broken down mathematically into individual variations. Porsche uses the value of the 1st Harmonic Variation (basic variation) to assess the tire from the point of view of rigidity. The 1st Harmonic Variation relates to the changes in radial force that cause the strongest vibrations. Other harmonic variations (2nd - 4th Harmonic) can also be seen in the changes in radial force. These relate to the changes in radial force that cause weaker vibrations.

Uncontrolled matching 

Turn the tire on the rim by 90° or 180° if necessary in order to achieve an acceptable value with regard to rolling smoothness (true running, imbalance and distribution of balance weights).

Controlled matching 

Using a balancing machine with matching program. In most cases, this produces an even better result with regard to the rolling smoothness (true running, imbalance and distribution of the balance weights) than can be achieved with uncontrolled matching.

Tire seating pressure 

This is the filling pressure after the tire has been fitted on the rim at which the tire bead, coming out of the deep bed, must pop over the hump of the rim bead. This seating pressure may not exceed 4 bar.

In certain cases, it may be necessary to measure radial force variations. This should be done before normal balancing is performed.

The entire process is subdivided into several operations:

  1. Fitting the tire on the rim.
  2. A - Measure radial force variations and optimise the wheels if necessary. Afterwards, balance the wheels.

    B - As an alternative to item 2 A, if there is no device available to measure radial force variations: Stationary balancing of the wheel (eliminating static and dynamic imbalance) with optimisation of rolling smoothness.

  3. Fitting the wheel on the vehicle.
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