jas278 Posted August 26, 2006 Share Posted August 26, 2006 Subject: Tyre Report A long story but here is a factual report on 4 tyres which belonged to me ..... Report on 4 Tyres: branded ‘BRONCO’ Grizzly Claw Ref: SAG / 05 / 12 / LTS Ref: SAG / 05 / 12 / LTS Report prepared for Marcus Sabin, Leicester Trading Standards Report prepared by S.A. Green – HND, ONC. INTRODUCTION I am currently employed by ‘Starco’ Europe, which is part of the ‘Scandinavian Tyre and Rim Company’, as Technical Director. In addition to my responsibility for technical matters in the UK, my role extends to technical support for all 13 plants around Europe and Russia. The Company manufactures wheels, tyres and wheel assemblies for supply as Original Equipment to vehicle manufacturers. Previously, Goodyear had employed me for fifteen years until May 2000. My final position as Technical Training Manager, gave me responsibility for all Technical Training of company personnel operating throughout the UK, Europe and the Middle East. Prior to this position I was Manager of Product Performance and Service department for six years until 31st December 1994. In this role I had occasion to examine many thousands of tyres having failed either in service, or as a result of systematic destructive testing. I began my career with British Leyland as an apprentice and gained extensive experience in all aspects of automotive engineering in both design and practical skills. I hold an HND qualification in Mechanical Engineering and an ONC in Electronics. Following my apprenticeship I worked for 11 years in research and development, specifically dealing with axles, brakes and suspension systems as part of a vehicle design team. I specialise in all aspects of vehicle design and behaviour, and in particular, tyres, their performance, and the interaction between tyres and vehicle suspension design. I have been asked to examine the subject tyre(s) with the purpose of identifying the reasons for their current condition, the nature of any structural failure and any possible implications to the merchantable and safe condition for sale. I was given the information that the wheels and tyres were fitted to a ‘Landrover Discovery’ 4 x 4 vehicle and had only travelled for a relatively short distance since they were supplied. THE TYRE(S) I examined 4off wheel and tyre assemblies at a private address in Hinckley, at the request of Mr Marcus Saban of Leicester Trading Standards, the details of which were as follows: Tyre size: LT 265/75R16 Service description: 112Q Brand: ‘Bronco’ Grizzly Claw TDR: 14mm centre-line – 17mm at shoulder Production date / Serial No: No markings Other markings: Retread made in England – conforms to BSAU 144 EXAMINATION Following a careful examination of the wheels and tyres, the following details were noted: Wheel Assembly No. 1 The first of four tyres was examined having been fitted to the front of the vehicle, to reveal a structural failure in the shoulder area of the tyre such that complete and catastrophic deflation had occurred. There was clear evidence of rubber degradation and cracking due to overheating and rubber reversion at the base of the large shoulder blocks and also at the junction between these blocks and the carcass where there are naturally uneven stresses due to the heavy lug design. The carcass showed clear signs of distress at these same points and had suffered separation between radial cords and also belt edge, resulting in structural failure. The carcass had suffered from severe abrasion and overheating in the shoulder areas as was evidenced by the inner liner condition. I was unable to detect any evidence of a penetration which might have caused the deflation. The deflation appears to have been caused by the break-up of the tyre structure, the evidence of overheating being such that it had occurred over a relatively short distance including the time taken for the driver to pull over and stop when it was realised that the tyre had failed. Wheel Assembly No. 2 The second tyre, also having been fitted to the front of the vehicle, was also showing similar signs of rubber reversion in the shoulder blocks with some cracks beginning to appear. However, this tyre remained intact insofar as it was still inflated and no major structural failure was immediately apparent. Wheel Assembly No’s 3 & 4 These two tyres remained in apparently sound and inflated condition. Balance Weights The following quantities of balance weights were seen to be fitted to the wheel assemblies, having been balanced by the tyre shop who supplied the new wheels and tyres; Wheel assembly #1 – 225 grams Wheel assembly #2 – 200 grams Wheel assembly #3 – 190 grams Wheel assembly #4 – 100 grams TERMS OF REFERENCE There are standards laid down within European Directives ECE108 / ECE109 regarding the manufacture and testing of such remoulded tyres. These performance requirements are specifically to ensure that process quality is consistent to the original development of the remoulded product, and that any such product is capable of being operated within the performance suggested by its service description. The markings ‘conforms to BSAU 144’ are out-dated and obsolete for two reasons (i) They are now superseded by ECE 108 / 109, & (ii) In any event, there were several suffix additions and revisions to BSAU 144 even when it was current, no such suffix is marked on these tyres, this means that these markings were insufficient even when last BSAU 144 was current. The remoulding processor is totally responsible for ensuring that the carcasses gleaned from tyres having previously worn-out treads, are in suitable condition for both the re-moulding process and the subsequent safe operation with the new re-moulded tread. A further requirement is dynamometer testing (sometimes referred to as ‘drum’ testing) for the required duration to prove that the tyre tread design, rubber compounds used and re-manufacturing process are all of such integrity that they are safe for continuous operational use up to the full load and speeds indicated by that service description. The above mentioned dynamometer tests are required to be repeated during production runs to ensure that each subsequent batch also complies with the same requirements. CONCLUSIONS The tyres fitted to the front axle of the vehicle whilst it was lightly loaded (as was the case according to Mr Stray), would be subjected to a higher load than those on the rear axle due to the un-laden weight distribution of the vehicle, additionally, the steering forces would also load the shoulder areas of the tyres more than those at the rear. This is therefore a fair indication that the loads at the front axle, although being far below what the tyres are able to carry according to their service description, creates the differing results. Both front tyres were showing signs of distress, with one of them having failed completely, both rear tyres being in better condition than the front ones. The two front tyres showed clear evidence of overheating and rubber reversion in the shoulder areas and as the tyres were not carrying their maximum load, this tends to indicate a small safety margin with regard to heat generation and satisfactory running temperature. Mr Stray informed me that he had operated these tyres in the same way as on previous sets of tyres and at the same correct recommended pressures for the vehicle, and I am unable to detect any collaborative evidence for under-inflation prior to the complete deflation of the tyre due to the carcass break-up. The quantity of balance weights fitted would give concern regarding the uniformity of the re-moulded tyres; generally, re-moulded tyres have very good uniformity as the action of buffing off the worn-out tread tends to reduce any run-out within the original carcass. It is interesting also to note that the worst offender in this regard, was in fact the same tyre on the front of the vehicle which had failed. It would be a matter for further investigation as to whether the remoulding manufacturer has in fact dynamometer tested the original remould design and/or the subsequent production batches, to prove the ability of the tyres to be operated safely at the rated load and speed in accordance with ECE 108 / 109. These tyres do not carry the required markings to indicate that they comply with the required testing procedures for the above mentioned standards. It is therefore my considered opinion that these tyres do not comply with the necessary regulations, governing the sale of such tyres for use on the public highway. Stephen Alan Green – December 2005. IT DOES WHAT IT SAYS ON THE TIN... Forums powered by WWWThreads v5.0.9 Pro © Copyright 2005 Emap Automotive - all rights reserved. Quote Link to comment Share on other sites More sharing options...
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