RUBBER RESPONSE • With reference to your article in Commercial
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Motor w/e January 31, 1987, headed "Getting in the Groove", the RMA wishes to comment: The Retread Manufacturers' Association has never stated that tyres should NOT be regrooved, but is clearly on record as stating that indiscriminate regrooving is often detrimental to road safety. Due to the "State of the Art" of regrooving it is recommended that where regrooving is carried out it is completed with care, attention and diligence — parameters which are not respected at the moment, as demonstrated by our survey on 10,000 tyres.
It is the first time, to our knowledge, that Michelin have indicated that regrooving can damage casings if it is not correctly carried out. This is exactly what the RMA has been saying! We can accept properly regrooved tyres, but cannot accept a situation where some 35% of tyres are indiscriminately regrooved subjecting the haulage operator to possible prosecution under the Construction & Use Regulations.
It is interesting to note that, Michelin's recommendation for regrooving the 11 R 22.5 XZA has increased from 4 to 5rnin without the addition of elxtra undertread. Incidentally, the Michelin Technical Data Book recommends 3mm at present and this represents therefore, a 2mm increase.
Having regard to the present "State of Art" on regrooving, one questions the advice given. With no extra undertread available the safety margin has been dramatically reduced and it is likely to lead to significant increase in the 35% of tyres unsatisfactorily regrooved.
The reality of the situation is that neither Michelin nor the RMA wish to promote indiscriminate regrooving.
The RMA have never recommended that tyres should be retreaded when the original depth is 3mm, and we are at a loss to understand where this comment came from. We do not wish to deprive the user of any mileage potential from his tyres. We do, however, wish him to take extreme care with the regrooving of tyres in order to maximise on the retreading potential of the expensive new tyre and to avoid the possibility of prosecution.
We trust that the above comments clarify the RMA's position with regard to regrooving and would be grateful if you would inform your readers accordingly.
B J Lawton Technical Executive Retread Manujaclurers' Association