Wheels and Tires: Service and Repair
WM 44 Balancing/optimizing wheelsGeneral
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. accumulations of material at one point of the tire structure (spring action of tire changes as the tire rolls), can cause rolling and steering imbalance.
Information
^ 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/prerequisites
Wheel suspension elements must be in good technical order.
The wheels must be clean and without foreign objects in the tire.
Use a tire measuring gauge, e.g. V.A.G 1435, to check axial and lateral runout values on wheels without flat spots. Values less than 1.0 mm - better around 0.5 mm - are desirable.
In order to achieve low radial runout errors or to optimize smoothness of rolling, it is expedient - and necessary in individual cases - to match the tire (i.e. to mount it in a favorable position with respect to the wheel).
If the rims (wheels without tires) are true but the complete wheels have large axial and radial runout values (due to ply breakage or other damage), tire replacement may be necessary.
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. Refer to information about putting on the balancing weights.
Balancing/optimizing wheels
The entire process is subdivided into four operations.
1. Mounting the tire on the rim.
2. Stationary balancing of the wheel (eliminating the static and dynamic imbalance) with optimization of the rolling smoothness.
3. Mounting the wheel on the vehicle.
4. Electronic fine balancing (static balancing) of the wheel on the vehicle after stationary balancing. Required only in exceptional cases.
Further to 1: Mounting 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 destroying all of the careful work. If the tire turns by as little as 20 mm with respect to the rim, this can worsen an optimum balancing result.
- Mount tire on the rim. When doing so, it is expedient - and necessary in individual cases - to mount the tire in a favorable position with respect to the wheel (matching). Controlled or uncontrolled matching.
- Uncontrolled matching: Turning 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.
- Fill tires to a pressure of approx 3.0 bar. At the latest when the pressure reaches 3.0 bar, 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 generously coat all necessary surfaces with lubricant (tire mounting paste) again. Then repeat the process.
- Check the fit of the tire on the rim by means of the bead centering line.
- Set the prescribed tire pressure.
Further to 2: Stationary balancing with optimization of the rolling smoothness
- Clamp wheel on stationary balancing machine.
- Observe the operating instructions of the balancing machine; occasionally adjust the machine if necessary.
- The support surfaces of the wheel on the balancing flange (levelling surface) and the centering surface must be clean.
- Center (clamp) the wheel from the inside with centering clamping device. This centering clamping device fits on all wheel balancing machines approved by Porsche.
Check radial and axial runout during the 1st measuring run. Values less than 1.0 mm - better around 0.5 mm - are desirable.
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. 25/30 g) means that the tire was mounted correctly and the quality of the tire and rim is good.
A value of 80/80 g should not be exceeded. A greatly different distribution, e.g. 30/70 g is very unfavorable; this usually indicates incorrect mounting. Problem wheels of this kind often have pronounced radial and axial runout values.
This can be remedied by matching (use correct mounting paste). Improvement is possible with uncontrolled matching (manual); significant improvement is possible in almost all cases with rolling smoothness optimization program (controlled matching).
The tire pressure must not be less than 1.5 bar overpressure during balancing.
Permissible residual imbalance less than 3 g, or max. 3 g per plane.
Further to 3: Mounting the wheel on the vehicle
Information
^ Never use an impact bolter!
^ Observe grease specification and information on the two-piece wheel bolt!
- Mount wheel with suitable commercially available tools.
- If necessary, mark the position of the wheel on the wheel hub before removing the wheel. Use a piece of adhesive tape to mark the wheel and the wheel hub. This will preserve any optimum balancing result previously achieved by means of fine balancing (finish balancers), even after the wheel is re-mounted.
- Screw in wheel bolts by hand and then tighten evenly. Start at the top when tightening. Always observe the specified tightening torque of 130 Nm (96 ftlb.).
- Tire pressure according to the specifications!
Further to 4: Electronic fine balancing
For electronic fine balancing of the wheels on the vehicle, refer to the operating instructions from the equipment manufacturer for information about handling the equipment.
When performing fine balancing on all wheels, start with the front axle (4a).
On vehicles with all-wheel drive, all four wheels must be raised and must be able to turn freely!
Fine balancing of the front wheels to correct torsional vibrations of the steering wheel at approx. 120 km/h.
Fine balancing of the rear wheels to correct vibration at 180 km/h and speeds greater than 230 km/h.
The following applies to both the front axle and rear axle:
the measured-value pickups must always stand on a firm surface,
the measuring stand support must be located as close to the wheel as possible,
doors and lids must be closed and the vehicle must not be touched during the measuring operation,
ensure that the lifting equipment used (jack, platform lift) does not touch the vehicle.
Affix balancing weights on the outer plane (uniform procedure/could also be distributed or affixed on the inner plane). Under no circumstance remove the weights affixed during stationary balancing. Mark the balancing weight required by electronic fine balancing using a prick punch in order to distinguish it.
Read out and delete the ABS/PSM fault memory after fine balancing in the case of vehicles with TC or PSM.
Further to 4a: Fine balancing of the front wheels
Information
^ On vehicles with all-wheel drive, all four wheels must be raised and must be able to turn freely!
^ Ensure that the take-up fork of the measuring support does not damage any parts!
- Position measuring support at the front axle on the right and left. Before the first measuring run, re-check to ensure that slipping from the measuring support is not possible!
- Center the sensitivity control. Carry out a measuring run.
- Affix balancing weight if necessary. Then perform a check run. If the result is unacceptable (precondition: the work was performed properly), calibrate the finish balancer. This means that the sensitivity control must be adapted to the actual situation.
- If the balancing result is still not quite right even after calibration (for example, 5 g), change the balancing weight according to the balance correction table (balance correction schematic) and thereby eliminate the residual imbalance.
Further to 4b: Fine balancing of the rear wheels
Information
^ On vehicles with all-wheel drive, all four wheels must be raised and must be able to turn freely!
^ Do not damage any parts with the take-up fork of the measuring support!
- Position measuring support at the rear axle on the right and left. Before the first measuring run, re-check to ensure that slipping from the measuring support is not possible!
- Set the sensitivity control to 3...3.5 (depending on the equipment version). This corresponds to approx. 1/3 of the max. sensitivity.
- Perform measuring run at a speed of 130 km/h or 1,150 to 1,200 rpm (wheel revolutions) in the highest gear. Affix the corresponding balancing weight.
- Perform a check run. Calibrate the finish balancer if the balancing result is unsatisfactory. This means that the sensitivity control must be adapted to the actual conditions.
- Then (in the case of a good balancing result) slowly increase the speed to 190 km/h and carefully observe at what speed vibration can be felt at the steering wheel and/or seat again (mainly at 175 ± 5 km/h).
- Maintain this speed and re-balance the wheels in the same way as at 130 km/h. Do not affix any new weights; instead, improve the wheel running smoothess by changing the existing weights according to the balance correction schematic.
The imbalance values shown here in this speed range are not real values. They are actually max. 1/4 to 1/3 of the indicated values.
The subjective impression in the vehicle is the decisive criterion here. The balancing process is complete only when no more vibrations caused by imbalance are perceptible!
Balancing weights
Balancing weights: Adhesive weights as used previously (no special version necessary).
Affix both weights on the inner side.
Information
^ Observe program selection and operating instructions of the balancing machine.
Affixing the adhesive weights
Information
^ Remove the protective film only immediately prior to 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, provisionally 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 adhesive weight must be in contact uniformly over the entire surface.
- Check to ensure that the balancing weight is seated firmly. It must not be possible to detach the weight that was just stuck onto the rim by the application of a shear load at right angles to the longitudinal axis of the weight.