Tires With Run-Flat Capability (Pax)
Tires with run-flat capability (PAX)
Construction of tires with run-flat capability (PAX)
Run-flat tires (PAX) are specially developed tires that differ from conventional tires as follows:
^ The inner and outer bead diameters differ in size. This makes it possible to add a support ring inside the tire.
^ The tire is secured differently to the rim.
^ This allows the tire height to be greatly reduced. This was made possible by the reduced bead area due to the special connection between the tire and rim.
^ The tire beads are formed such that they engage in the rim seat. Therefore, the tire remains firmly secured to the wheel/rim even when there has been a loss of inflation pressure.
Construction of the bead area for a standard tire
1. Wheel flange
2. Inner plies
3. Bead core
Construction of bead zone on tires with run-flat capability (PAX)
1. Loop
2. Inner plies
3. Bead core
4. Wheel flange
Seating of tires with run-flat capability (PAX)
Due to the construction of the tire, it remains firmly attached to the wheel in all driving situations.
A wedged-shaped component of the tire is thereby pressed between the bead core and rim by the load. This occurs regardless of the tire pressure.
Dimensions of tires with run-flat capability (PAX)
As compared to standard tires, run-flat tires (PAX) have different dimensions and designations.
Run-flat tires (PAX) can only be installed to special wheels designed for the PAX system.
1. Width in millimeters: tire width from sidewall to sidewall on the standard rim (corresponds to the width dimension on standard tires)
2. Outer diameter in millimeters: maximum diameter of the new tire
3. Nominal diameter in millimeters on standardized rim seat
4. Small bead diameter in millimeters: outer rim seat
5. Larger bead diameter in millimeters: inner rim seat
Codes and designations on tires with run-flat capability (PAX)
As compared to standard tires, run-flat tires (PAX) have different codes and designations on the sidewall. This makes it easy to identify run-flat tires.
Codes and designations on tires with run-flat capability (PAX)
245 - tire width in millimeters
690 - tire diameter (outer) in millimeters
R - Radial construction
500 - Nominal diameter of standardized rim seat
A - Construction type index for the wheels with run-flat capability (PAX); "A" stands for asymmetric, since the two rim seats have different diameters.
99 - Maximum permissible load of tire (99 = 1550 kg)
Y - Speed code ("Y" stands for a permissible top speed of 300 km/h).
Support ring
Dimensions
Overview of important dimensions:
Codes/designations
Example: 90-500(35) CLI A 1 876107
90 - Nominal width in millimeters
500 - Nominal diameter in millimeters
35 - Height in millimeters
CLI - Support ring versions: CLI = clip support ring / FL = standard support ring
A - Construction type index, asymmetrical. Indication of tire with run-flat capability (PAX)
1 - Support ring version
876107 - CAI, international article code
Wheels for tires with run-flat capability (PAX)
Dimensions and codes/designations
Example: 235 x 500 A - 5 - 41
235 - Nominal width in millimeters
x - Single-unit
500 - Nominal diameter of standardized rim seat in millimeters
A - Asymmetrical
5 - Number of wheel bolt holes
41 - Rim offset in millimeters
Tire pressure sensor
Construction
Run-flat-tires (PAX) are always installed in conjunction with a tire pressure monitoring system.
The wheel electronics consist of a pressure sensor incorporated within the valve.
The pressure sensor transfers the registered signals to the aerial of the tire pressure monitoring system.
The pressure sensor is secured to the wheel via a bolt connection.
Tire pressure monitoring system
This system informs the driver of the current tire pressures by sending the registered pressure values to the instrument cluster display via a control module.
There, differing displays appear depending on the type of vehicle and loss of pressure.
For more information about this system, please refer to SSP 219 "Electronic Tire Pressure Monitoring".
Inflating
Observe the following important points when inflating the tire:
- Only inflate after mounting the tire with valve core installed. Check whether the beads have properly seated at 1 bar.
- If one of the beads is not seated properly, do not let air out of the tire, but apply the mounting roller to the appropriate bead and press on lightly while turning. The bead will then seat itself properly.
- Then fill up with air until the specified inflation pressure for the vehicle is reached. Tire gas for standard tires can also be used.
Note:
^ Do NOT overfill tire (e.g. up to 3.5 bar), even briefly, as is permissible with standard tires.
Wheel alignment
The procedure for adjusting the wheel alignment on vehicles with run-flat tires (PAX) is the same as for vehicles with standard tires.
Generally, the same measuring heads and fasteners for standard tires with rim protector can be used on PAX wheels. (Install to the inner side, secure to tire tread).
Repairing tires with run-flat capability (PAX)
General information
It is not always necessary to replace a tire after it has lost pressure and then been run in an uninflated condition.
Note:
^ The affected tire should be removed and checked for damage by qualified personnel. Mounting of tires and checking tires for damage must only be carried out by qualified personnel.
After a run-flat tire (PAX) has lost inflation pressure, check the tire as follows:
- First remove as much gel residue from the tire as possible. Use the flat side of the putty knife to do so.
- Then clean away any remaining gel residue from the tire and support ring using water and a cloth.
- After separating the tire and support ring, check both components (PAX) according to the following criteria.
Note:
^ When re-installing, make sure the support ring is the correct size for the tire and wheel dimensions.
^ As with standard tire/wheel systems, the PAX wheel must also be checked before installing.
^ Damaged wheels must be replaced.
Checking tires
When checking a tire, look out especially for the following:
^ Surface erosion or ripples on the inner side (inflation pressure was too low or not sufficient for the load)
^ Loose rubber or loose radial threads
^ Separated or deformed bead core
^ Damage to tire bead with cord ply visible
Checking support ring
As with tires, the support ring does not always need to be replaced after driving with a flat tire.
Replace the support ring if the following damage is discovered:
^ Broken parts or missing sections
^ Tears in the running surface/separating walls
^ Punctures and holes
^ Blistering and discoloration due to overheating
Repairs on tires
Note:
^ Run-flat tires (PAX) must not be repaired using a tire patch or similar.
^ Flat tire sprays/foams must not be used with PAX tires, as these products are not compatible with the gel in the tire.
General information
In all cases, work on PAX tires can only be performed by designated specialist shops.
These shops must have the correspondingly trained personnel and the required special tools. A list of all shops that are qualified to repair PAX tires can be found on the Internet under:
www.paxsystem.com
Dealers who have become qualified shops for repairing PAX tires have the necessary shop equipment.
They also have the qualified personnel who have been trained for working on PAX wheels/tires by the tire manufacturer or other qualified trainers.
The PAX logo can be used to distinguish the shop as a PAX service center.
The tire manufacturer offers training and technical support.
The manufacturer also passes on the necessary know-how for mounting and removing the tires/wheels.
The shop will be listed in the database of authorized PAX system service centers.