Wheels/Tires - Steering Wheel Shaking at 50-75 MPH
Cayenne1/05 4405
Binder - 4, Running Gear
This bulletin replaces bulletin Group 4, # 1/05, dated 6-13-05
Shaking In The Steering Wheel
Vehicle Type:
Cayenne/Cayenne S/Cayenne Turbo/Cayenne Turbo w/Increased Performance (I no. E 81)
Model Year:
As of 2003
Concerns:
Shaking in the steering wheel in speed range from 50 - 75 mph (80 - 120 km/h).
Information:
Customer complaints about "shaking in the steering wheel" may arise on the above-mentioned vehicles in the speed range from 50 - 75 mph (80 - 120 km/h). The work procedures and measures listed in this technical information bulletin will address this issue.
This complaint may arise due to unbalanced wheels, radial force variation on the wheels or wheel attachment to the vehicle. If the vehicle is stationary for extended periods, flat spots may develop on the tires, which in turn can result in increased radial force variation. To prevent the formation of flat spots, the tire pressure should be set to max. 50 psi (3.4 bar) (storage and transport air pressure) before leaving the vehicle stationary for extended periods.
Danger!
Change in handling behavior as a result of increased tire pressure.
> Danger of accidents
> Before moving the vehicle after it has been stationary for extended periods, make sure that the tire pressure of the front and rear wheels is set to the values recommended for safe driving (See Owner's Manual "Tires and wheels" or the vehicle's tire pressure label).
If "shaking in the steering wheel" is experienced in the speed range from 50 - 75 mph (80 - 120 km/h), the wheels must be balanced using a Porsche-approved wheel balancer that can measure radial force variation (e.g. Hunter 9700/9712).
Explanation of Terms (Definitions Radial Force Variation
The radial force is a force that compresses a tire. Based on its size, a tire has softer (see Figure 1, Item A) and more rigid zones (Figure 1, Item B) due to construction and manufacturing related factors. Taking this into account, the tire compresses to various extents at a constant wheel load (Figure 1, Arrow 1) and a constant tire pressure (Figure 1, Arrows 2). This varying spring action (Figure 1, 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.
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.
Equipment
Work Procedure:
1. Verify the complaint.
1.1. Requirements
1.1.1. Set the tires on the front and rear axle to the prescribed cold air pressure (front: 38 psi/2.6 bar), rear: 42 psi/2.9 bar).
1.1.2. Take the vehicle for a drive on a 15-20 mile (25 to 30 km) stretch of highway or Interstate to check that the tires have heated up sufficiently and that there are no more flat spots. The tires must be heated up.
1.1.3. Immediately after you return, raise the vehicle to prevent flat spots from forming again on the vehicle's tires.
1.1.4. Take off one wheel.
1.2. Measuring the tire data with the wheel balancer
Note!
Before using the wheel balancer, check that:
> the mounting and centering surfaces of the wheel balancer are clean.
> the support surface of the wheel on the balancing flange (leveling surface) and the centering point are clean.
> the display disabling function is switched off.
If the specified standards are not observed, the determined values will incorrectly reflect observance of these standards, but problems will be detected in the vehicle.
1.2.1. Clamp one wheel on the wheel balancer and adjust the air pressure to (front: 38 psi/2.6 bar), rear: 42 psi/2.9 bar).
1.2.2 Measure the radial force variation. To do this, follow the operating instructions for the wheel balancer.
1.2.3. Measured values/subsequent procedure:
The following applies for Cayenne/Cayenne S/Cayenne Turbo:
> If the radial force variation (maximum deviation/peak to peak) exceeds 38 lbs (170 N) or the 1st Harmonic 25 lbs (110 N), the tire must be matched to the wheel. If the measured values for radial force variation 38 lbs (170 N) and for theist. Harmonic 25 lbs (110 N) are not reached, the wheel must be balanced, (Step 2).
The following applies for Cayenne Turbo w/ Increased Performance Kit (I no. E 81):
> If the radial force variation (maximum deviation/peak to peak) exceeds 32.5 lbs (145 N) or the 1st Harmonic 21 lbs (95 N), the tire must be matched to the wheel. If the measured values for radial force variation 32.5 lbs (145 N) and for the 1st. Harmonic 21 lbs (95 N) are not reached, the wheel must be balanced, (Step 2).
Note!
If the matching procedure cannot reduce the radial force variation to the values of 38 lbs/25 lbs (170 N/110 N) or 32.5 lbs/21 lbs (145 N/95 N) (Cayenne Turbo Performance Kit) as specified under Step 1.2.3, a new tire must be mounted.
2. Balancing/finish-balancing
2.1. Balance wheel, see Workshop Manual '44 Balancing/optimizing wheels'. To achieve optimal results during balancing, the wheel must be mounted with the rear Direct Fit cone (Hunter tool no. 192-147-2) and pressure piece (Hunter tool no. 175-379-2) when using the Hunter 9700/9712. This type of attachment enables precise balancing with high accuracy for repeat balancing. After balancing, the residual imbalance per level should be 3 g.
2.2. Carry out this procedure for the other three wheels starting from (Step 1.1.4. Then continue with Step 2.3)
2.3. Mount the wheels with the lowest residual imbalance values on the front axle. When doing so, observe the rotation direction of the tires.
2.4. Tighten the wheel nuts on each wheel with a tightening torque of 118 ft-lb. (160 Nm).
2.5. Set the tire pressure of the tires on the front and rear axle of the vehicle according to the specifications in the Owner's Manual or on the vehicle's tire pressure label.
2.6. Road test the vehicle. If there is still "shaking in the steering wheel" during the test drive, proceed as follows:
2.6.1. If the wheels were not matched and/or no new tires were installed in the previous work procedure, the wheels on the front axle must be balanced directly on the vehicle using an electronic finish balancer (e.g. Hofmann SD 20), (Step 2.8).
2.6.2. If the wheels were already matched or if new tires were installed in the previous work procedure, the wheels must be balanced again while stationary on the wheel balancer.
2.7. Test drive the vehicle again.
Note!
Please read the operating instructions for the finish balancer before getting started. If the measured value determined with the finish balancer exceeds 5 g, additional balancing weights must be used.
Finish balancer: use longer mounting shafts for the Cayenne (measured-value pickups). (e.g. Hofmann 641 684 8 measured-value pickup for the Hofmann SD 20 finish balancer).
2.8. The following requirements must be met in order to check static imbalance with an electronic finish balancer:
2.8.1. On vehicles with air suspension, level control must be switched off as described in the Owner's Manual. (Owner's Manual 'Air springs with level control and vertical adjustment').
2.8.2. Tiptronic: the transmission must be in "P".
2.8.3. Manual transmission: the transmission must be in "neutral".
2.8.4. The transfer case must be in High Range position.
2.8.5. The foot-operated parking brake is released.
2.8.6. The vehicle must be jacked up using the four supports on the finish balancer in such a way that all four wheels can turn freely.
2.8.7. The engine is switched off. The wheels are driven by the finish balancer.
3. General information on mounting the tire on the wheel.
Note!
For vehicles with the tire pressure monitoring system, observe the special instructions under see Workshop Manual '44 Mounting tires for vehicles with and without tire pressure monitoring system (RDK)'.
Before mounting the tire on the vehicle, check the wheel for damage (cracks, dents etc.) as well as radial and lateral runout.
> Maximum permissible radial runout and lateral runout for light alloy wheels = 0.7 mm.
> Maximum permissible radial runout and lateral runout for wheel with tire = 1.25 mm.
> Values of less than 1.0 mm are desirable around 0.5 mm would be better.
When mounting tubeless tires, check that the sealing surfaces of the tire and wheel are clean and show no signs of damage. keep in mind that the bead base performs the sealing function on tubeless tires. When mounting the tire, use only the prescribed tire mounting pastes. Apply tire mounting paste sparingly. The following can occur if an unsuitable mounting paste is used:
> the tire becomes twisted on the wheel,
> the bead core is fractured during mounting if the seating pressure is too high,
> the tire bead is damaged,
> the wheel surface has been damaged by harsh cleaning products.
4. Balancing weights.
Note!
When using zinc weights (instead of lead weights) do not break off or clip off to reduce weight!
Attach both balancing weights on the inside (see Figure 2 - Balancing Weight Position).
Check radial and axial runout during the first measuring run. Values of less than 1.0 mm are desirable - around 0.5 mm would be better. Assess the determined weight of the balancing weights and their distribution on the inner and outer planes (inner and outer rim flanges) is very critical. A uniform distribution with low values (e.g 35/40 g) means that the tire was mounted correctly and the quality of the tire and wheel is good.
A value of 110 g/110 g (120 g/120 g on vehicles with tire pressure monitoring system) should not be exceeded with interior balancing behind the center of the wheel. A distribution, e.g. 40/90 g is not good; this usually indicates incorrect mounting or a wheel that has a pronounced radial and/or axial runout. This may be remedied by matching (use correct mounting paste).
Significant improvement is possible in almost all cases using the rolling smoothness optimization program (controlled matching). If wheels - whose rims are perfectly true-running - have large axial and radial runout values, the tire can be damaged due to ply breakage or other damage and must then be replaced.
References
Disclaimer