Wheels: Service and Repair

Balancing/optimizing wheels
Tools

Balancing/optimizing wheels:

Balancing/optimizing wheels
General

Excessive wheel imbalance not only produces vibrations and causes the steering wheel to shake, but also results in increased wear on various parts of the running gear.

Even if the wheels are correctly balanced, excessive geometry errors (radial and axial runout) and misshapen tires, e.g. accumulation of material at one point in the tire structure (spring action of tire changes as the tire rolls), can cause rolling and steering imbalance.

Note: Achieving a good result requires utmost care, observance of the instructions and procedure, and attempting to eliminate even the very last gram of imbalance.

Recommendations/requirements
Wheel suspension elements must be in good technical order.
The wheels must be clean with no foreign objects in the tire.

Use a tire measuring gauge, e.g. measuring gauge NR.136 to check radial and lateral runout values on wheels without flat spots. Values of less than 1.0 mm are desirable - around 0.5 mm would be better.

To limit the number of radial runout errors and to optimize smoothness of rolling, it is a good idea - and even necessary in individual cases - to match the tire (i.e. to fit it in a favorable position with respect to the wheel). Follow tips and fitting instructions as well as information on tire mounting paste for tires.

If the disc wheels (wheels without tires) are perfect but the complete wheels have large axial and radial runout values (due to ply breakage or other damage), it may be necessary to replace the tire.

Balance used wheels only after they have been warmed up by driving, otherwise flat spots will simulate imbalance. Never perform matching in the case of flat spots.

Correct tire pressure is an important prerequisite.
Place the balancing weights at the prescribed position .

Balancing/optimizing wheels
The entire process is divided into three operations.
1. Fitting the tire on the rim.
2. Stationary balancing of the wheel (eliminating static and dynamic imbalance) with optimization of rolling smoothness.
3. Fitting the wheel on the vehicle. Electronic fine-balancing (static balancing) of wheel on vehicle (after stationary balancing) is not required (status July 2002).

Further to 1: Fitting the tire on the rim
- Remove rubber residues and dried-on tire paste from the rim, especially from the rim bead and the hump.
- Examine rim for damage; remove old balancing weights.
- Use the prescribed tire mounting paste (only TIP TOP Universal, order no. 593 0601, 3.5 kg bucket, or Contifix) so that the tire does not turn on the rim the first time the car is driven, thereby counteracting all your careful work. If the tire turns by as little as 20 mm with respect to the rim, this can worsen an optimum balancing result.
- Fit tire on the rim. When doing so, it is a good idea - and even necessary in individual cases - to fit the tire in a favorable position with respect to the wheel (matching). Compare Controlled and Uncontrolled matching below.

WARNING: Danger of accident due to high tire seating pressure.
^ Personal injury may occur in the event of tire or wheel damage (due to the coincidence of several unfavorable factors).
-> Maximum tire seating pressure 4 bar! This value must not be exceeded.
-> Tires must be filled in the filling cage. Tire filling cage





- Fill tires to a maximum pressure of 4.0 bar. By the time the pressure reaches 4.0 bar, at the latest, the tire beads must pop out of the deep bed and over the hump of the rim bead in order to avoid fractures of the bead core. If necessary, interrupt the process and coat all necessary surfaces generously with sliding compound (tire mounting paste). Then repeat the process.
- Uncontrolled matching: Turn the tire on the wheel 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: With 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.
- Check the fit of the tire on the rim using the bead centering line.
- Set the prescribed tire pressure.

Further to 2: Stationary balancing with optimization of rolling smoothness
- Clamp wheel on stationary balancing machine.
- Observe the operating instructions of the balancing machine; adjust the machine from time to time, if necessary.
- The contact surfaces of the wheel on the balancing flange (leveling surface) and the centering surface must be clean.
- Centre (clamp) the wheel from the inside with centering clamping device - see Workshop Equipment Manual, Chapter 3. This centering clamping device fits all wheel-balancing machines approved by Porsche.

Check radial and lateral runout during the first measuring run. Values of less than 1.0 mm are desirable - around 0.5 mm would be better.

Consider the size of the measured balancing weights and their distribution on the inner and outer planes (inner and outer rim flanges) critically.

A uniform distribution with low values (e.g. 35/40 g) means that the tire was fitted correctly and the quality of the tire and rim is good.

A value of 110 g/110 g (120 g/120 g using the tire pressure monitoring system) should not be exceeded with interior balancing behind the wheel centre. A considerably different distribution, e.g. 40/90 g is very unfavorable; this usually indicates incorrect fitting. Problem wheels of this kind often have pronounced radial and axial runout values.

This can be remedied by matching (use correct mounting paste). This can be improved with uncontrolled matching (manual); significant improvement is possible in almost all cases using the rolling smoothness optimization program (controlled matching).

Tire pressure during balancing at required pressure.
Permissible residual imbalance of less than 3 g, or max. 3 g per plane.

Further to 3: Fitting the wheel on the vehicle

Note:
^ Never use an impact bolter.
^ Observe information on the two-piece wheel bolt. This is described in the chapter on wheel removal and installation (fitting wheel on vehicle).

- Fit wheel using a suitable commercially available tool.
- Screw in wheel bolts by hand and then tighten evenly. Start at the top when tightening. Always observe the specified tightening torque of 118 ft. lbs.
- Tire pressure according to the specifications.

Balancing weights





Balancing weights: Adhesive weights as used previously (no special version necessary). See also Spare Parts Catalogue.
Attach both weights to the inner side.

Note: Observe program selection and operating instructions of the balancing machine.

Attaching the balance stick-on weights

Note:
^ Remove the protective film just before sticking on the weight, as prolonged exposure to the air will reduce the bonding strength.
^ Pay attention to cleanliness.

- Determine exact position of the balancing weights (if necessary, temporarily stick on the balancing weights with a strip of adhesive tape until the correct position is determined).
- Prepare bonding surface on the rim. The bonding surface must be perfectly clean and free of grease.
- Remove protective paper from the bonding surface of the weight and press the weight firmly into place.
- The balance stick-on weight must be in uniform contact over the entire surface.
- Check the balancing weight is seated firmly. A weight freshly affixed weight must not detach itself from the rim under application of a shear load at right angles to its longitudinal axis.