How we pick an all-round win­ner

Auto Express - - Winter Driving Special -

AS ever with our tyre tests, each de­sign is as­sessed over a num­ber of key cri­te­ria, al­low­ing you to focus on the area that’s most im­por­tant to you when buying. There are 13 cat­e­gories, but we’ve put the em­pha­sis on wet per­for­mance, with snow grip count­ing for a smaller, but still es­sen­tial, part. Price makes up a small el­e­ment of the over­all rank­ing.

The scores for each test rate the win­ner at 100 per cent, with the rest ranked rel­a­tive to that. Then, to cal­cu­late the over­all champ, we add up the scores, and weight them to en­sure that a test with a big dif­fer­ence in per­for­mance counts for the same as one in which the tyres are evenly matched.

To en­sure we test what you can buy, we ask the mak­ers to nom­i­nate a tyre, which we then pur­chase. How­ever, stock prob­lems meant this wasn’t pos­si­ble with Falken, Kumho, Nexen and Toyo.

Snow brak­ing

THIS test repli­cates that heart-stop­ping mo­ment when you hit the brakes while driv­ing on snow and all you get is a jud­der­ing from the pedal. We do a se­ries of max­i­mum-brak­ing stops from 26mph, mea­sur­ing the dis­tance taken to de­cel­er­ate to 3mph, then take an av­er­age to form the over­all re­sult.

Snow trac­tion

WE do this test, which as­sesses how likely you are to get up that snow-cov­ered hill, at the same time as the brak­ing test. In it, we mea­sure the dis­tance taken to ac­cel­er­ate from 3mph to 26mph us­ing trac­tion con­trol. We start at walk­ing pace then ac­cel­er­ate at full throt­tle. An av­er­age makes up the re­sult.

Snow cir­cle

PURE lat­eral grip is mea­sured here with­out other fac­tors, such as ac­cel­er­a­tion or weight trans­fer, play­ing a part. The test cir­cle has a di­am­e­ter up to four times big­ger than that of the wet test, but the tech­nique is the same. Tuck the nose in to the in­ner edge and ac­cel­er­ate un­til it runs wide. An av­er­age of lap times is used.

Snow han­dling

THE han­dling track is a real test for tyres be­cause it com­bines big el­e­va­tion changes with tight turns and open sweep­ers. Climb­ing turns ex­pose any trac­tion prob­lems. An av­er­age of lap times is used and the cir­cuit is graded af­ter each run to en­sure con­di­tions are the same.

Straight aqua­plan­ing

OUR aqua­plan­ing tests mea­sure how well tyres cope with deeper wa­ter and how ef­fec­tively the tread pumps out wa­ter from un­der the tyre. The car is placed on a rail sys­tem with one wheel in wa­ter. It is then ac­cel­er­ated hard un­til the tyre is spin­ning 15 per cent faster than the one in the dry.

Curved aqua­plan­ing

A FLOODED strip on a large tar­mac cir­cle is at the heart of this test, which looks at how well tread works when cor­ner­ing. The car is lapped at ever-higher speeds with lat­eral G mea­sured as it passes through the wa­ter. The test is com­pleted when all grip is lost.

Wet brak­ing

THIS test is tem­per­a­ture-sen­si­tive, so we do it in win­ter and sum­mer con­di­tions. We do mul­ti­ple stops mea­sur­ing the dis­tance taken from 50mph us­ing the rail sys­tem, which en­sures the same piece of track is used each time. The cold tem­per­a­tures were a lit­tle higher than ideal this year, but were still less than seven de­grees Cel­sius.

Wet han­dling

LIKE wet brak­ing, wet han­dling is af­fected by tem­per­a­ture, which is why win­ter tyres have dif­fer­ent com­pounds from sum­mer ver­sions. Again, as with the brak­ing test, we rate this sep­a­rately at above and be­low seven de­grees Cel­sius, then take an av­er­age of the lap times around the track.

Wet cir­cle

AS in the snow cir­cle ex­am­i­na­tion, this test pro­vides a mea­sure of the lat­eral grip each tyre can gen­er­ate, this time in the wet. Lap times are at the heart of the rat­ing, so we do mul­ti­ple laps with the nose of the car track­ing the in­ner kerb, ac­cel­er­at­ing un­til the line can no longer be held.

Dry brak­ing

OUR tests are done in spring or sum­mer tem­per­a­tures, al­though the test is not as sen­si­tive to heat as the wet ver­sion. Sev­eral stops from 62mph are av­er­aged out to get the fi­nal re­sult.

Dry han­dling

WE mea­sure lap times around a 1.6km sec­tion of the han­dling track then take an av­er­age. The sec­tion pro­vides fast di­rec­tion changes and long turns where the tyres are heav­ily loaded.

Rolling re­sis­tance

THIS test mea­sures the force re­quired to turn a tyre, which di­rectly af­fects your car’s fuel econ­omy. The more power needed, the more fuel re­quired. Our test is done to in­dus­try stan­dards with an av­er­age of two tyres used. To cal­cu­late the dif­fer­ence be­tween two tyres, a five per cent change in rolling re­sis­tance roughly equates to one per cent in fuel econ­omy.

Cabin noise

THIS is not the same test as that used for EU tyre la­belling, which mea­sures pass-by noise. Our ex­am­i­na­tion is car­ried out in­side the car with a sound me­ter mea­sur­ing noise lev­els as the car coasts from 50mph over three sur­faces.

Price

OUR fig­ures are sup­plied by the win­ner of our test of on­line tyre re­tail­ers, Black Cir­cles. The fig­ures are fully fit­ted prices and are what the com­pany charges (or would charge if a tyre is not part of its range). It plays a small part in the re­sult be­cause the em­pha­sis is on per­for­mance.

SNOW TESTS: Tyres are rated on how quickly they can stop, ac­cel­er­ate and turn car on the white stuff

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