Page 25 - CTB n4 - 2013/4

REGROOVING
Regrooving: Making the Most out of your Tyre Assets
Retreading and Regrooving commercial truck and bus tyres makes sound economic sense. With most modern truck tyres having an extra layer of base rubber built into them, regrooving offers the easiest and cheapest way to extend the life of the tyre, without compromising on safety. However, depending on where you are in the world, regrooving is a practice that has not always been universally supported across the sector, particularly from certain parts of the retreading industry. This, however, has largely been due to inconsistent quality levels in the standard of regrooving, which, if carried out badly, can cause damage to casings and render them unsuitable for retreading.
It goes without saying, of course that precautions must be taken to ensure that the regrooving process leads to safe tyres but it is also undisputed that a correctly carried out regrooving policy can help you utilise your tyre assets to their full capacity, thereby saving you money.
The main benefits that can be accrued by carrying out a properly managed regrooving process are
An improvement in the life of the tyre by up to 25%
Improved grip and safety due to the increased tread depth reduced rolling resistance by up to 25% compared with a new tyre, which means lower fuel consumption. According to Michelin, for a tractor and semi- trailer combination used for long distance haulage, the fuel saved by regrooving the tyres instead of fitting new tyres can reach 2
litres per 100 km, depending on the number of axles equipped.
So how do you access these benefits? Let’s have a look at the facts;
The first point to make is that it is legally acceptable to re-groove tyres for most trucks, goods vehicles and PSVs over 2 1⁄2 tons unladen weight, all electrically propelled goods vehicles, all but the smallest trailers, so long as the original tyres were suitable for regrooving. A regrooved tyre can be fitted on every axle and correctly regrooved tyres can still be
retreaded. However, EC norms dictate that tyres designed and constructed so as to be suitable for regrooving must be marked on both sidewalls with the word REGROOVABLE. If they are not marked as such, then they are not regroovable.
Secondly, the regrooving operation must only be carried out by specifically trained personnel and according to manufacturer specifications. Manufacturers provide regroove tread patterns for their tyres and it is illegal to recut a tyre to any tread pattern other than that shown in the manufacturer's regrooving manual.
Re-grooving of tyres should be carried out when the depth of the original tread has worn down to between 3mm and 4mm. Tyres worn to the point where the original tread pattern is invisible (even in a restricted area) cannot be regrooved as it is impossible to evaluate the depth of the remaining rubber. When regrooving it is of fundamental importance to pay attention to avoid exposing the upper belts of the tyre and to ensure that an adequate layer of rubber is left to protect them.
As it is possible that the tyre may be worn unevenly it is important to check that the tread has a residual minimum depth of at least 2-3 mm.
Only tyres in good condition can be regrooved: When a tyre shows signs of irregular wear, perhaps through incorrect wheel balancing or steering geometry problems, it should not be re- grooved. Always check the tread
depth at several places around the tyres and make sure all regrooving is based on lowest depth found.
Before beginning the regrooving operation the tyre must be examined carefully to check that it is in good condition and that it has not already been regrooved. A previous regrooving is immediately recognisable to a specialist operator: the grooves lose their sharp corners, especially in areas with zig-zag grooves and there are characteristic signs (undulations) left by the blade within the grooves.
If the tyre has already been regrooved the tread wear indicators (TWI), that is rubber bridges at the base of the tread, will have been removed during the regrooving operation, and the groove bottoms will be smooth. Regrooving is inappropriate whenever the tread is scraped, cut or torn. Any tyre damage or repairs that have not been well executed must be rectified prior to regrooving.
Before starting the regrooving operation all foreign bodies (that could damage the cutting tool) must be removed from the tread and the condition of the groove bottoms must be checked.
The depth of the grooves must be measured at a number of points around the circumference of the tyre. The blade cutting depth must be adjusted in accordance with the minimum measured depth.
The regrooving must be executed with the specific cutting tool (gouge) equipped with an electrically heated blade, and preferably in a well ventilated place.
It is advisable to select a blade profile corresponding to the regrooving width and the profile prescribed for that particular tyre.
In order to adjust the regrooving blade correctly add the minimum remaining tread depth to the regrooving thickness specified by the manufacturer for that tyre size and tread pattern.
It is then necessary to fit the tyre onto a proper support, exert constant pressure and, following the prescribed pattern, cut the rubber at the bottom of the grooves following firstly the circumferential grooves and then the transverse slots where present After few centimetres measure the reegroving width and depth in order to check the correct choice and size of the blade. For tyres with “Zero Degree Belts” complete the regrooving in the direction of rotation indicated by the equilateral triangle placed on the tyre sidewall.
By carefully following the procedure described a thickness of rubber is left at the bottom of the groove that is sufficient to protect the upper belts of the tyre.
Under no circumstances should the regrooving blade be allowed to shave or notch the metal belts as this would render the tyre unsafe and could compromise subsequent retreading.
After the regrooving process is completed, tyres must be free of any defects, cracks, separations or exposed ply or cord.
Source: Continental, Michelin, Pirelli, Tructyre
Commercial Tyre Business 25