Porshe 911 (997). Manual - part 266

If the rims (wheels without tyres) 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 tyre.

• 

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 tyre pressure is an important prerequisite.

• 

Place the balancing weights at the prescribed position.

• 

Explanation of terms

Geometry error (radial and lateral runout)
Radial and lateral runout of the rim and/or rim/tyre assembly.
Flat spots
Flat spots can occur on the tyres if the vehicle is idle for extended periods.
Radial force variations

The radial force is a force that compresses a tyre. Based on its size, a tyre has softer ( -item A- ) and more
rigid areas ( -item B- ) due to design and production-related factors. Given this, the tyre compresses to various
extents at a constant wheel load ( -arrows 1- ) and a constant tyre pressure ( -arrows 2- ). This varying spring
action ( -X- ) in the tyre 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
tyre on a wheel balancer that measures radial force variation while applying a constant load to the tyre. This
simulates the rolling of the tyre on a driving surface. Variations in radial force occur independently of the
direction of rotation of the tyre 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 tyre 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 tyre 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

Diagnostic system: reading out fault memory and activating systems

General

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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.
Tyre seating pressure
This is the filling pressure after the tyre has been fitted on the rim at which the tyre bead, coming out of the
deep bed, must pop over the hump of the rim bead.

Balancing/optimising wheels

The entire process is divided into three operations.

1. Fitting the tyre 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.

Further to 1: Fitting the tyre on the rim

–  Remove rubber residues and dried-on tyre paste from the rim, especially from the rim bead and the hump.

–  Examine rim for damage; remove old balancing

weights.

–  Use the prescribed tyre mounting paste (only TIP TOP Universal, order no. 593 0601, 3.5 kg

bucket, or Contifix) so that the tyre does not turn on the rim the first time the car is driven, thereby
counteracting all your careful work. If the tyre turns by as little as 20 mm with respect to the rim,
this can worsen an optimum balancing result.

–  Fit tyre on the rim. When doing so, it is a good idea - and even necessary in individual cases - to fit

the tyre in a favourable position with respect to the wheel (matching). Compare Controlled and
Uncontrolled matching below.

Tyre filling cage

WARNING

If the tyre seating pressure is too high (max. 4.0 bar permissible), personal injuries are possible in the
event of tyre or wheel destruction.

Diagnostic system: reading out fault memory and activating systems

Explanation of terms

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→ Maximum tyre seating pressure 4 bar! This value must not be exceeded.

→ For tyre seating pressure over 3.3 bar (possible in the event that several unfavourable factors

should occur simultaneously / max. 4.0 bar permissible) use a tyre filling cage.

–  Fill tyre. Important: At the latest when the pressure reaches 3.3 bar (max. 4.0 bar in tyre filling cage), the

tyre beads (coming out of the deep bed) must pop 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 recommended lubricant (tyre mounting paste). Then repeat the process.

Important: Damage to the bead core resulting from incorrect tyre assembly/disassembly will cause an
increase in fluctuations in power (radial/lateral fluctuation in power). This is apparent when you roll
the tyre on the driving surface.

• 

–  Uncontrolled matching: Turn the tyre 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 tyre on the rim using the bead centring

line.

–  Set the prescribed tyre pressure.

Further to 2A: Measuring radial force variations

–  Tension wheel on balancing machine with radial force variation measurement (vibration monitoring

system).

–  Observe the operating instructions of the balancing machine (adjust the machine from time to time).

–  The contact surfaces of the wheel on the balancing flange (levelling surface) and the centring surface must

be clean.

–  The display disabling function must be switched off.

–  Adjust tyre air pressure to 2.6 bar (best test pressure) when balancing and measuring radial force

variations.

–  Particular attention must be paid to the wheel mounting when measuring radial force variations and when

balancing. Using the special pressure pieces provided by the manufacturer of the balancing machine will
ensure that wheels are balanced accurately and there is the highest possible repeat accuracy. Observe the
operating instructions.

Maximum deviations permitted in radial force variation results:

Front wheels

Rear wheels

Radial force variation (peak to peak vibrations)

max. 170 N

max. 170 N

1st Harmonic (variation)

max. 125 N

max. 150 N

If these values are exceeded, the tyre must be matched on the rim.
If these values are not reached, the wheel must be balanced.

Diagnostic system: reading out fault memory and activating systems

Further to 1: Fitting the tyre on the rim

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Note

A new tyre must be fitted if the radial force variation cannot be reduced to the values listed in the table.

Further to 2B: Stationary balancing with optimisation of rolling smoothness

–  Clamp wheel on stationary balancing machine.

–  Observe the operating instructions for the balancing machine. Adjust the machine according to the

manufacturer's instructions (if necessary).

–  The contact surfaces of the wheel on the balancing flange (levelling surface) and the centring surface must

be clean.

–  Centre (clamp) the wheel from the inside with centring clamping device - see Workshop Equipment

Manual, Chapter 3. This centring 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. 25/35 g) means that the tyre was fitted correctly and the quality
of the tyre and rim is good.
A value of 80g/80g (90g/90g using the tyre pressure monitoring system) should not be exceeded with interior
balancing behind wheel centre. A considerably different distribution, e.g. 35/90 g is very unfavourable; 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
optimisation program (controlled matching).
Tyre 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) → 440519 Removing and installing wheel.

• 

–  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 130 Nm (96 ftlb.).

–  Tyre pressure according to the specifications.

Diagnostic system: reading out fault memory and activating systems

Further to 2A: Measuring radial force variations

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