Fea­ture: this is how a 4x4 tyre is made

Car (South Africa) - - CREDITS -

THE rub­ber tted to your 4x4 can make or break your ve­hi­cle’s per­for­mance on- and off-road. How­ever, have you ever given thought to the ex­ten­sive re­search and de­vel­op­ment that goes into pro­duc­ing that tyre? We vis­ited the Con­ti­nen­tal Tyre SA fac­tory in Port El­iz­a­beth (home of Gen­eral Tire; GT) to learn how a 4x4 tyre is de­signed and con­structed.

RE­SEARCH AND DE­VEL­OP­MENT

A tyre com­prises more than 10 in­di­vid­ual com­po­nents and the de­ci­sion re­gard­ing the types of ma­te­ri­als, rub­ber com­pounds and con­struc­tion meth­ods is its own sci­ence. Com­puter sim­u­la­tion work has be­come paramount to the process be­cause ac­tual test­ing with pro­to­type tyres is costly and time­con­sum­ing. Ini­tial tests are con­ducted un­der con­trolled con­di­tions in a lab­o­ra­tory (we cov­ered this in the ar­ti­cle Tech be­hind tyres in the Au­gust 2017 is­sue) be­fore on-road test­ing com­mences.

An in­ter­est­ing sub­ject when it comes to off-road tyres is tread-pat­tern de­sign. The gen­eral per­cep­tion that the to­pog­ra­phy of the tyre is mostly for aes­thetic ap­peal can­not be fur­ther from the truth. Ev­ery lit­tle edge, cham­fer and block is there for a rea­son, and nowhere is this more ev­i­dent than on off-road tyres with bold pat­terns. Be­low are some of the fea­tures on Gen­eral Tires’ X3.

The down­side of an ag­gres­sive tread pat­tern is in­creased road and wind noise at speed, as well as a rolling-re­sis­tance penalty (re­sult­ing in in­creased fuel con­sump­tion). The gen­eral trend is for less-ag­gres­sive pat­terns to meet strin­gent UNECE 30 tyre reg­u­la­tions with­out los­ing of­froad per­for­mance in the process. (Bad news for en­thu­si­asts crav­ing that ag­gres­sive look.)

THE PRO­DUC­TION PROCESS

The smell of fresh rub­ber hangs in the air as I en­ter the pro­duc­tion fa­cil­ity. What grabs my at­ten­tion is how labour­in­ten­sive the process is to cre­ate a sin­gle tyre. This is not be­cause of lo­cal labour law or ab­sence of the lat­est high-tech ma­chin­ery. Ac­cord­ing to Ahmed Boualam, pro­duc­tion man­ager, the same method of tyre pro­duc­tion is em­ployed lo­cally and in­ter­na­tion­ally (Ger­many). The rea­son for this is a tyre – es­pe­cially an off-road ex­am­ple – is a com­plex item with many com­po­nents, and so re­quires ex­ten­sive hu­man in­put.

THE RAW MA­TE­RI­ALS

Ap­proved rub­ber com­pounds ar­rive in bulk at the ex­trud­ers. They are then heated and forced through a speci c die cre­at­ing a green rub­ber pro le (tread or sidewall). The tread con­sists of three types of com­pound: the base, the cap (run­ning sur­face) and the wing strips lo­cated beyond the tread shoul­ders. These three co-ex­truded com­pounds are over­laid to form a con­tin­u­ous assem­bly that is cut into speci ed lengths for the tyre cir­cum­fer­ence.

Al­though each tyre car­ries a bar­code doc­u­ment­ing its pro­duc­tion history, paint of dif­fer­ent colours is ap­plied to the tread in thin stripes as a vis­ual aid to dis­tin­guish be­tween tyre de­signs (ex­plain­ing the colours on the tread of some new tyres). Side­walls as well as tyr­ere­in­force­ment ma­te­ri­als ar­rive in bulk rolls and must be cut to size and speci ed angles be­fore be­ing joined with the tread. Even the hoops of steel wire (bead cores) an­chor­ing the ply and se­cur­ing the tyre onto the wheel rim are cre­ated on site by wind­ing steel wires in a pat­tern and en­clos­ing them with more rub­ber.

ASSEM­BLY

The build­ing of a tyre is done in two stages. Firstly, a cas­ing is made con­sist­ing of an in­ner liner, ply(s), bead, apex, sidewall and, in some cases, re­in­force­ment and shoul­der pads. The cas­ing is then ex­panded on a sec­ond­stage build unit, where the tread assem­bly is ap­plied. The tyre slowly takes shape but still ap­pears alien to the eye; touch­ing the “green” prod­uct re­veals it’s soft and tacky. No ad­he­sive is used be­tween the com­po­nent lay­ers, as the vul­can­i­sa­tion of the rub­ber dur­ing the cur­ing process forms the per­ma­nent bonds.

CUR­ING AND TREAD

The tyre is in ated with a blad­der be­fore it is heated in­ter­nally with steam. The speci c data is pro­pri­etary but it is a func­tion of pres­sure, tem­per­a­ture and time for the tyre to set in its nal form, los­ing that tack­i­ness, with the de­sired rub­ber prop­er­ties. How­ever, it still re­sem­bles a rac­ing slick with no tread. Time for more heat in an oven, where the tread moulds are clamped on the tyre from the out­side, forg­ing the rub­ber into the re­quired shape. More time elapses be­fore a nal prod­uct ex­its the oven in a haze of steam: a tyre is born.

QUAL­ITY TEST­ING

Each tyre goes through a vi­su­alin­spec­tion phase and then en­dures rig­or­ous test­ing be­fore it is al­lowed to leave the fac­tory. This in­cludes mount­ing it on a rim and test­ing nat­u­ral bal­ance at speed. A low scrap rate is es­sen­tial to save both cost and the en­vi­ron­ment.

3 SIDEWALL PRO­TEC­TION LUGS

2 STONE BUMPER BLOCKS TO KNOCK OUT STONES IN DEEP GROOVES

1 MUL­TI­PLE GRIPPING ANGLES

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