Porsche 996 TT, Repair Manual

Page: 341 / 2099

Customers should be informed that the full performance of new or newly mounted tyres is achieved
only after a distance of 100 to 200 km (60 to 120 miles) has been driven. Extreme driving manoeuvres
(acceleration, braking) should be avoided. •
The absolute limit on how far the tyre can turn on the wheel must be regarded as 20 mm. An optimum
balancing result will be worsened in this case.
•
Mark the relative positions of the tyre and wheel for reference. •
In order to optimise smoothness of rolling, it is expedient − and necessary in individual cases − to mount the
tyre in a favourable position with respect to the wheel (matching).
Uncontrolled matching
Turning 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.
Fitting
Maximum permissible radial runout and lateral runout of the light alloy wheels = 0.7 mm. Maximum
permissible radial runout and lateral runout of the wheel with tyre = 1.25 mm. Values less than 1.0 mm
better around 0.5 mm are desirable.
After mounting the tubeless tyres, inflate them without valve insert to approximately 4.0 bar gauge
pressure in order to ensure that they are seated properly on the wheel. At the latest when the
pressure reaches 4.0 bar, the tyre beads must pop out of the deep bed and over the hump of the
wheel shoulder in order to avoid fractures of the bead core. If necessary, interrupt the process and
coat all necessary surfaces with lubricant (tyre mounting paste) again. Then repeat the process.
Screw in the valve insert and set the prescribed tyre pressure.
If new tyres are to be mounted or the tyres of one axle are to be replaced, tyres of the same make and with the
same specification code must always be used on each of the two axles. If tyres are replaced on one axle only,
the different tread depth than on the other axle can cause a noticeable change in the familiar handling. This is
especially the case if new tyres are mounted on the rear axle. This effect decreases with increasing tyre
mileage.
Note
If a tyre is damaged and it cannot be determined with absolute certainty that there is no ply damage
with all of its consequences or if the tyre was thermally or mechanically overloaded due to a loss of
pressure or other prior damage, we recommend replacement of the tyre in question for safety reasons! •
einordnung
General 278