1

Tire FundamentalsTire Fundamentals

R. BortignonR. Bortignon

2

Tire FunctionTire Function

Provide traction (friction) with the road surfaceProvide traction (friction) with the road surface

Provide cushion between the road and the metal wheelProvide cushion between the road and the metal wheel

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Tire SizeTire Size

Letter designates tire type:Letter designates tire type:

“ “P” Passenger tireP” Passenger tire

“ “LT” Light truck tireLT” Light truck tire

“ “C” Commercial tireC” Commercial tire

“ “T” Temporary/spare tireT” Temporary/spare tire

4

Tire WidthTire Width

Tread width in millimetres This tire’s width would be 235 mm

5

Aspect RatioAspect Ratio

Tire height-to-width ratioTire height-to-width ratio Aspect ratio = 75Aspect ratio = 75 Sidewall height is 75% of the tire widthSidewall height is 75% of the tire width Aspect ratio of this tire is 235mm X 75% = 176mm tall sidewallAspect ratio of this tire is 235mm X 75% = 176mm tall sidewall

6

ConstructionConstruction

““R” designates the tire is a R” designates the tire is a radial tire radial tire

Radial tires have plies that Radial tires have plies that go from bead to beadgo from bead to bead

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Rim DiameterRim Diameter

Rim diameter is given in inchesRim diameter is given in inches 13 = 13”13 = 13” 14 = 14”14 = 14” 15 = 15” etc.15 = 15” etc.

8

Load IndexLoad Index

2-digit # that determines the 2-digit # that determines the tire’s maximum load carrying tire’s maximum load carrying capacitycapacity

82 Load Index = 1047 lbs82 Load Index = 1047 lbs

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Maximum Load RatingMaximum Load Rating the weight a tire can carry at the recommended air pressurethe weight a tire can carry at the recommended air pressure e.g. 1300 lbse.g. 1300 lbs Are the tires needed for a minivan or delivery van?Are the tires needed for a minivan or delivery van? Don’t do what this person did!Don’t do what this person did!

10

Speed RatingSpeed Rating

maximum allowable road speed a tire can safely withstand maximum allowable road speed a tire can safely withstand without failurewithout failure

letter systemletter system

for example “H” speed rating = 130 mphfor example “H” speed rating = 130 mph

11

Mud and Snow RatingMud and Snow Rating

M+S stands for mud and snow (used on all-season tires)M+S stands for mud and snow (used on all-season tires) good all-weather performancegood all-weather performance may not be suitable in heavy snowmay not be suitable in heavy snow

driving in snow? tire should have the driving in snow? tire should have the mountain snowflakemountain snowflake symbolsymbol

meets severe snow standards set out by RMAmeets severe snow standards set out by RMA

12

Treadwear RatingTreadwear Rating

treadwear is given as a numbertreadwear is given as a number the higher the number, the longer the tire will lastthe higher the number, the longer the tire will last 100 = Baseline100 = Baseline more than 100 = Bettermore than 100 = Better less than 100 = Poorerless than 100 = Poorer

13

Traction RatingTraction Rating

traction (wet braking test) is given as an A, B, or C ratingtraction (wet braking test) is given as an A, B, or C rating• AA = best tractionAA = best traction• A = intermediate tractionA = intermediate traction• B = acceptable tractionB = acceptable traction• C = poor traction ratingC = poor traction rating

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Temperature RatingTemperature Rating

Temperature is also given as an A, B, or C ratingTemperature is also given as an A, B, or C rating A = bestA = best B = intermediateB = intermediate C = acceptableC = acceptable

the higher the rating the more resistant to temperature the higher the rating the more resistant to temperature build-upbuild-up

the more a tire heats up, the quicker it wearsthe more a tire heats up, the quicker it wears

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Inflation & Wear ProblemsInflation & Wear Problems

• under inflated: under inflated: excessive wear on excessive wear on outer treadouter tread

• over inflated: over inflated: excessive wear in excessive wear in middle of treadmiddle of tread

wear bars flush with tread: tire needs replacing!

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17

Tire RotationTire Rotation

ensures maximum tire lifeensures maximum tire life

evens out tire wearevens out tire wear

tires should be rotated every tires should be rotated every 10,000 kms10,000 kms

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Split RimsSplit Rims

• used on many ¾ ton pick-ups into the early 70’sused on many ¾ ton pick-ups into the early 70’s

• DO NOT demount, inflate or install in a high school shop!DO NOT demount, inflate or install in a high school shop!

19

Wheel BalanceWheel Balance

wheel trampwheel tramp wheel shimmywheel shimmy

imbalance causes vibration in the vehicle or a steering wheel that shakes

wheel balancers correct this imbalance in the wheel/tire assembly

20

Center Post Tire MachineCenter Post Tire Machine

refer to ShareOut’s Equipment folder for instructions

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