Tire Sizing and Ratings

Tire Sizing and Ratings

Auto Theory

Today's Learning Goals

• You will be able to read a tire and determine its size

• You will be able to read/translate tire ratings

• You will be able to select the correct tire for a vehicle based on size, driving conditions, and cost

Before we start...

• Write Down the information shown on this tire

• As we go through a new item label its meaning.

• 
  

It will look something like this at the end.

Starting with tire sizing...

Tire Type (Intened use)

• P = Passenger Tire

• LT = Light Truck

• T = Temporary (Spare)

• ST = Special Trailer

• No Letter = Euro-Metric (Passenger)

Multiple Choice

What is this tires intended use?

• Passenger

• Light Truck

• Temorary

• Trailer

Tire Width

• This is the width of the tire measured in millimeters (mm)

• The larger the number the wider the tire

• Standard tire width 215mm - 255mm

• Spare Tire Width 80mm - 110mm

• Race/Performance Tire 275mm - 355mm

What is this tires width?

Multiple Choice

True or False: You can put whatever width tire you want on a rim.

• True

• False

The tire width is dependant on the rim width.

Aspect Ratio / Section Height

• Ratio of the tire diameter and the tire width.

• Basically a measurement of the sidewall thickness

• The Lower the number the thinner the sidewall

• The Higher the number the thicker the sidewall

Low section width tires can also be called low profile.

Multiple Choice

A lower aspect ratio tire would effect my tires ability to _____________.

• Provide Cushion and smooth out the ride

• Provide grip in snow and ice

• Do smoky burnouts

• Provide grip to the road surface

Tire Construction

• R = Radial (Most Common)

• B = Bias Ply

• D = Bias Ply

Most Passenger Vehicles will use a Radial tire.

Rim Diameter

• Rim Diameter: Measured in inches

• The larger the number the taller the rim

• The lower the number the smaller the rim

Multiple Choice

True/False: A tire labeled P225/55R17 will fit a 16in Rim.

• True

• False

Now let's change to tire ratings.

• Tire Load Rating

• Speed Rating

• Treadwear Rating

• Traction Rating

• Temperature Rating

Load Rating

• The higher the number the more load the tire can carry.

• For example: 88 = 1235lbs (Maximum)

• 4 Tires = 1235lbs X 4 = 4940lbs

• The car is able to carry 4940lbs safely.

• Do not exceed your tires load ratings

Load Index Chart

• You will not have to memorize this chart.
• When looking up load index just Google the chart.
• When selecting a tire ensure the load rating will meet the demands of your vehicle.

Multiple Choice

A 2005 Honda Civic has a weight rating of 2782lbs. The tires have a load rating of 71 which translates to 761lbs. Are these tires adequate for the load of the vehicle?

• Yes, all four tires load ratings are greater the weight of the vehicle

• No, all four tires load ratings are less than than the weight of the vehicle

Speed Rating

• The maximum speed a tire is rated for

• For Example (S) = 112 MPH

• When selecting a tire the speed rating should be close the vehicle max speed.

• Limiters on cars are dependent on the tires.

• Obey all speed limits!!!

Speed Rating Chart

• Do not memorize the chart

• Select a tire with a speed rating that fits the type of vehicle you drive.

• There is no need to put a Y rated tire on a car that only goes 100 MPH

• As the speed rating increases so does the cost!

• 
  

Example: A McLaren P1 has a top speed of 217 MPH. What speed rating would be correct for this car?

• Option 1: T = 118 MPH

• Option 2: Z = 149+ MPH

• Option 3: Y = 186 MPH

• Option 4: (Y) 186+ MPH

Multiple Choice

Select the tire for the McLaren P1...

• L

• Z

• Y

• (Y)

(UTQG) Uniform Tire Quality Grading

• Treadwear Rating

• Traction Rating

• Temperature Rating

• 
  

Treadwear Ratings

• Tread wear Rating: 300 (example) comparative rating based on testing on a government test track.

• For Example: A 300 Treadwear tire will last three times as long a 100 Treadwear Tire.

• The higher the number the longer the tire will last

Open Ended

What do you think manufactures change to make a tire last longer than another tire?

Traction Rating

• AA, A, B, C Scale

• Traction grades are an indication of a tires ability to stop on wet pavement.

• AA is the Highest

• C is the Lowest

• Higher the grade the more expensive.

Temperature Rating

• The tires resistance to heat build up at speed.

• Temperature A, B, C

• A = Best

• C = Worst

• Tires with an A rating dissipate heat up to a maximum speed that greater than 115 MPH

Let's Put this all together!

• Write Down the rating on a piece of paper or screenshot this image.

• We will start the decoder activity in 1 minute.

Multiple Choice

What is this tires intended use?

• (P) Passenger

• (LT) Light Truck

• (S) Sports Car

• (R) Radial

Multiple Choice

What is the tire width?

• 75mm

• 185mm

• 82mm

• 14 inches

Multiple Choice

What is the tires aspect ratio?

• 82

• 14

• 185

• 75

Multiple Choice

What is this tire construction type?

• (B) Bias Bly

• (P) Pias Ply

• (R) Radial

• (S) Sporty Ply

Multiple Choice

What rim diameter will this tire fit?

• 14 Inch

• 185mm

• 82 inch

• 75 mm

Multiple Choice

What does the 82 on the tire represent?

• Speed Rating

• Load Rating

• Temperature Rating

• Traction Rating

Multiple Choice

What does the (S) represent on the tire?

• Speed Rating

• Traction Rating

• Load Rating

• Treadwear Rating

Open Ended

What is the treadwear rating, traction rating, and temperature rating?

Homework Over the Weekend

• Using any tire record, and decode the information found on the sidewall.

• The assignment will be found on Canvas under the Day 13 Module!

Multiple Choice

Extra Bonus Point: What is the tires maximum tire pressure?

• 110 PSI

• How am I supposed to know?

• 75 PSI

• 30 PSI