Proper Repair Unit Selection & Placement for Shoulder Punctures
PURPOSE: This service bulletin will explain TECH’s recommended practices for installing and positioning repair units in radial truck tyres with shoulder or upper sidewall injuries. Today’s radial truck tyres have been engineered to provide better fuel economy, less rolling resistance and longer life. In turn, TECH has developed new repair units and has adopted new installation procedures in order to repair these tyres, thus achieving the best results.
Due to the high flex characteristics and increased heat buildup in the upper sidewall and shoulder areas of today’s radial truck tyres, additional precautions should be taken in order to properly repair punctures in the shoulder area. The use of a standard puncture repair unit in the shoulder (S-T) area will result in the repair unit being exposed to more stress in the upper sidewall, due to the characteristics of the tyre. This could potentially result in a premature repair failure.
The repair unit selected for these injuries may need to be longer and/or offset over the injury to get the ends of the fabric reinforcement plies out of the high flex area of the upper sidewall. The S-T area measures 1.5” (40mm) in from the tread edge on truck tyres. (See fig. 1)
When selecting a repair unit for use in the S-T area, the repair must end outside of the flex area. To achieve this placement, the repair unit oftentimes will be required to shift toward the bead to get the fabric plies beyond the midpoint of the sidewall. Due to the shorter length of a standard Centech Radial Nailhole Repair Unit, these repairs will not extend beyond this high flex area. In order to get the repair unit beyond the high flex area, a longer Centech Reinforced Shoulder Repair (RSR) Unit should be used. The CT-24 should be used to repair injuries in medium truck tyres up to 5/16” (8mm) after preparation. In heavy truck tyres, 12.00R, 315/80, 445/50, etc., an RSR-26 should be used because of the larger flex area.
When using an RSR in the shoulder, the end of the repair unit may still be positioned in the high flex area when centered over the injury. To avoid this, the repair unit may be shifted up to 25% of its length in the bead-to-bead direction. This will ensure the fabric ends of the repair unit extend beyond the high flex area and still offer sufficient reinforcement over the injury.
In order to allow for proper placement of the repair unit, it is recommended to use the appropriate TECH repair template for the repair unit being used. TECH’s redesigned templates have a window on them that will allow the technician to see the injury and properly place the repair unit over the injury. The window in the template also shows the distance in which the repair unit may be shifted in order to position the ends of the repair unit outside of the high flex area of the sidewall. When shifted in either direction, the injury must fall completely within the window for the repair unit to properly reinforce the injury while still ending outside of the high flex area. (See fig. 2)
For step-by-step procedures on performing a proper repair in a radial truck tyre, refer to TECH Repair Manual RM-5, “Two-Piece Repair Method for Passenger, Light Truck and Truck Tyres.”
Repair Template Incorrect Placement Before Offset
Repair Template Correct Placement After Offset
(Repair Unit Reinforcement End Completely Out of Flex Area)