TREAD PAT­TERN DE­SIGNS

Fast Ford - - All About… Tyres -

Aside from the com­pounds used, the sec­ond big­gest dif­fer­en­tial in tyre de­sign is the tread pat­tern. There are thou­sands of tread pat­tern de­signs al­ready avail­able, and as tyre re­search and de­vel­op­ment con­tin­ues man­u­fac­tures are con­stantly pro­duc­ing new styles.

Ar­guably on smooth dry roads, slick tyres will of­fer the best per­for­mance be­cause all of the tread area is in con­tact with the road. How­ever, our roads are sel­dom to­tally dry, there­fore the tread pat­tern needs to have the abil­ity to clear wa­ter from un­der the tyre in wet con­di­tions whilst still re­tain­ing as much dry per­for­mance as pos­si­ble.

The dif­fer­ent tread pat­tern de­signs avail­able for road tyres can be eas­ily split into three main cat­e­gories; sym­met­ri­cal, asym­met­ri­cal, and di­rec­tional.

SYM­MET­RI­CAL TREAD PATTERS

Start­ing with the most sim­ple, a sym­met­ri­cal de­sign is ex­actly as it says and fea­tures the same pat­tern across the whole tyre. This means the same tyre can be fit­ted the same way to any of the four wheels.

ASYM­MET­RI­CAL TREAD PAT­TERNS

An asym­met­ri­cal tread pat­tern dif­fers across the width of the tyre, mean­ing the de­sign has an in­side and an out­side edge and needs to be fit­ted ac­cord­ingly. Asym­met­ri­cal tread pat­terns of­fer a cou­ple of ad­van­tages over sym­met­ri­cal de­signs. The first of which is the outer edge and shoul­der area of the tyre usu­ally fea­tures larger, stiffer tread blocks to help with cor­ner­ing sta­bil­ity. This is be­cause the outer edge of the tyre is sub­jected to higher loads than the in­side when cor­ner­ing hard. Asym­met­ri­cal pat­terns also tend to have an in­ner edge that fea­tures more tightly packed and more ag­gres­sive grooves. This helps with wa­ter dis­per­sion and gives bet­ter per­for­mance and grip in wet con­di­tions. Fi­nally, asym­met­ri­cal de­signs can also fea­ture a fairly wide con­tin­u­ous cen­tre rib, which aids high-speed straight line sta­bil­ity too.

DI­REC­TIONAL TREAD PAT­TERNS

Di­rec­tional tread pat­terns dif­fer again from both sym­met­ri­cal and asym­met­ri­cal de­signs. They are sym­met­ri­cal across the width of the tyre (mean­ing they have no spe­cific in­side or out­side edge) but have a de­sign that only works in one di­rec­tion of ro­ta­tion (hence the name). This means the tyres can only be fit­ted to a pair of wheels (ei­ther left or right handed) and need to be turned around be­fore fit­ting to the op­po­site pair.

Di­rec­tional tyres of­fer dif­fer­ent per­for­mance ad­van­tages to asym­met­ri­cal pat­terns, the main one be­ing wet weather per­for­mance. The ag­gres­sive nature and num­ber of grooves typ­i­cally used on a di­rec­tional pat­tern means it of­fers greater wa­ter dis­per­sion than an asym­met­ri­cal de­sign.

Th­ese deep di­rec­tional grooves lit­er­ally pick the wa­ter up from the cen­tre of the tyre and throw it out of the sides, giv­ing very im­pres­sive wet grip. In the dry the ag­gres­sive grooves have no wa­ter to dis­perse but the larger tread blocks of­fer a greater con­tact patch with the road than sym­met­ri­cal tyres, there­fore of­fer­ing more grip.

The di­rec­tional grooves used on this type of tyre also help re­duce road noise and straight­line sta­bil­ity, when com­pared with an asym­met­ri­cal pat­tern.

It is also pos­si­ble to com­bine both asym­met­ri­cal and di­rec­tional tread pat­terns to have a de­sign that has both an in­ner and outer edge and a di­rec­tion of ro­ta­tion.

Th­ese style tread patters usu­ally fea­ture a stiffer tread block on the outer edge, sim­i­lar to that of an asym­met­ri­cal tyre, but the pat­tern tends to in­cor­po­rate ag­gres­sive grooves as with a di­rec­tional tyre.

SHOUL­DER BLOCKS

While talk­ing about tread pat­tern de­signs it’s also worth not­ing the shoul­der block area of the tyre. This is the area be­tween the tread pat­tern and the side­wall, and takes the brunt of the car’s lat­eral forces dur­ing cor­ner­ing. As a re­sult th­ese tend to be fairly chunky in their de­sign, to max­imise the con­tact patch with the road as the tyre moves around un­der heavy cor­ner­ing forces. The grooves be­tween the shoul­der blocks are known as sipes, and their job (as well as help­ing to dis­perse wa­ter in wet con­di­tions) is to help keep the tyre cool. The po­si­tion of th­ese sipes de­ter­mines the size of the shoul­der blocks, and th­ese are de­lib­er­ately spaced to en­sure the shoul­der blocks are not uni­formly sized. In­stead, the size of the shoul­der blocks dif­fers all the way around the cir­cum­fer­ence of the tyre, as this al­ters the har­mon­ics of tyre and can ac­tu­ally re­duce road noise. If the shoul­der blocks were all the same size the tyre would pro­duce an ir­ri­tat­ing hum when driv­ing at a steady speed.

Sym­met­ri­cal tyres are con­sider the ‘norm’, and are gen­er­ally cheaper than asym­met­ri­cal or di­rec­tional de­signs

Asym­met­ri­cal tyres have a de­sign that dif­fers across the width of the tyre

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