Un­rav­el­ling the mys­tery of tire side­wall num­bers, let­ters

Truro Daily News - - SALTWIRE WHEELS - BY RICHARD RUS­SELL WHEELS

The side­wall of a tire has a lot to tell you — if you know how to read it. Let’s take, for ex­am­ple one that says 215/55/R/17 98H.

215: This num­ber tells us the width or cross sec­tion of the tire as mea­sured in mil­lime­tres from side­wall to side­wall. Ob­vi­ously, the larger this num­ber the wider the tire. Some high-end sports cars have tires up to 335 mm wide on the rear wheels.

55: This is known as the as­pect ra­tio or height of the side­wall from rim to road ex­pressed as a per­cent­age of the sec­tion width — in our ex­am­ple 55 per cent of 215 mm. This is a fairly com­mon num­ber to­day. Older car tires had as­pect ra­tios of 70 and even 80.

As this num­ber goes down, so does the amount of rub­ber vis­i­ble from the side of the tire. Those ul­tra-wide sports car tires men­tioned above could have an as­pect ra­tio as low as 30 and be des­ig­nated as 335/30. This num­ber can comes in in­cre­ments of five i.e. 60, 55, 50 etcetera.

R — Ra­dial con­struc­tion: Most com­mon pas­sen­ger ve­hi­cle tires are of ra­dial con­struc­tion to­day. There are very few bias belted tires avail­able — or wanted.

17 — Wheel di­am­e­ter in inches: The size of the hole in the cen­tre of the tire. Don’t ask why this mea­sure­ment is uni­ver­sally given in inches, while the re­main­der are met­ric.

98 — The load rat­ing or in­dex: This num­ber refers to a chart used in the tire in­dus­try and in­di­cates the max­i­mum amount of weight this par­tic­u­lar tire is de­signed to carry. The num­bers on the chart range from 71 to 111. Your tire dealer will have a copy of this chart show­ing the amount in pounds or kilo­grams.

Our ex­am­ple of 98 means a load rat­ing of 1,653 lbs. per tire, or a to­tal of 6,612 pounds. A rat­ing of 111 cor­re­sponds to 2,403 pounds mean­ing a ve­hi­cle so-equipped could carry 9,612 pounds.

These weights in­clude ve­hi­cle, pas­sen­gers, lug­gage and ev­ery­thing else. Find­ing a tire with a higher load rat­ing than oth­ers of the same size is im­por­tant when car­ry­ing heavy loads or tow­ing.

H— Speed rat­ing: This num­ber comes from an­other stan­dard in­dus­try rat­ing sys­tem and re­sul­tant chart. The let­ter in­di­cates the max­i­mum sus­tained speed the tire is de­signed to cope with. The let­ters range from H to Z but not nec­es­sar­ily in or­der. The let­ters are their cor­re­spond­ing speed rat­ing in km/h are: Q-160, S-180, T-190, U-200, H-210 (our sam­ple), V-240, W-270, Y-300 and Z-over 300.

In ad­di­tion to the in­for­ma­tion out­lined above most tires also com­ply with UTQS — uni­form tire qual­ity stan­dard — that pro­vides con­sumers with in­for­ma­tion on three cat­e­gories — tread wear, trac­tion and tem­per­a­ture.

Each tire maker con­ducts its own tests, fol­low­ing pre­scribed pro­ce­dures and the in­for­ma­tion is for com­par­i­son only, not a safety rat­ing and not a guar­an­tee of how long the tire will last. The in­for­ma­tion is lo­cated on the tire side­wall and on a sticker at­tached to the tire when new.

Tread wear: The num­bers typ­i­cally range from 50 to more than 600 in­di­cat­ing how long the tire is ex­pected to last un­der con­trolled con­di­tions. For ex­am­ple, a tire with rat­ing of 400 should last twice as long as one car­ry­ing a 200 rat­ing. It is im­por­tant to note each man­u­fac­turer uses dif­fer­ent rat­ing sys­tem, so do not com­pare a 200 from one with a 200 from an­other.

Trac­tion: These num­bers in­di­cate a tire’s abil­ity to stop on wet pave­ment, un­der con­trolled test con­di­tions on as­phalt.

Twenty mea­sure­ments are taken on as­phalt and 20 more on con­crete. The rat­ings range from high­est or best to low­est, AA through A, B and C.

Tem­per­a­ture: These rat­ings in­di­cate a well-main­tained tire’s abil­ity to re­sist and dis­perse heat. Tires are tested on a rolling in­door test ma­chine start­ing at 121 km/h and in­creased in eight km/h in­cre­ments un­til the tire fails. The rat­ings are based on a tire that is prop­erly in­flated and not over­loaded — the chief causes of tire fail­ure. The rat­ings range from high­est (A) to low­est (C) – the min­i­mum re­quired by fed­eral stan­dards.

Other in­for­ma­tion con­tained on a side­wall in­cludes:

Max­i­mum pres­sure: The max­i­mum rec­om­mended tire pres­sure.

De­sign us­age: M+S or MS or M&S in­di­cates an all-sea­son tire. A lit­tle peaked moun­tain with a snowflake in­di­cates the tire has met spe­cific snow trac­tion per­for­mance re­quire­ments and is de­signed specif­i­cally for use in se­vere win­ter con­di­tions. A tire with nei­ther of these mark­ings is des­ig­nated for sum­mer use only.

Tires also carry an ap­proved code that identifies the man­u­fac­turer, plant, tire make and model, date of pro­duc­tion.

The next time you think of curl­ing up with a good book, con­sider curl­ing up on the garage floor and read­ing a tire.

RICHARD RUS­SELL PHOTO

The next time you think of curl­ing up with a good book, con­sider curl­ing up on the garage floor and read­ing a tire.

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