Rim and Tires

Auto IVLesson 227

What size rim and tire combination do you use for your ride?

How does this handle on the road?What systems would be effected by the size?

Lets talk tech!

• Lets discuss some right and wrong ways to fit rims and tires under a vehicle.

• Using math formulas you already know can improve your ability to advise your friends and family to Ric Rac your Ride!!

Tire Placard

Solving for x

Sidewall Aspect Ratio• Typically following the three digits

identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91SThe 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm.

SIDEWALL HEIGHTHigher the number = higher sidewall

Lower the number = shorter sidewall

By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.

Terms to remember

Aspect Ratio

Aspect Ratio = (Section Height/Section Width) X 100

• P225/70 R14 • 225 Millimeters of section width• 70 is interpreted as 70 % of the width to equal

section height.

Overall Diameter= 2 x Section Height + Rim Diameter

• Note that there is top and bottom of section height that need to be added to rim size to determine the over all Diameter.

A truck tire has a p-metric tire label of:LT 265/75 R-17

Find the overall diameter

• Section width = 265 mm• Aspect ratio = 75• Section height = x • Section height =

• 198.75 mm• Rim diameter = 17 inches =

• 431.8 mm • Overall Diameter =

• 829.3 mm• 32.65 in

y = 3x + 10•Solve for x when y = 19

• 19 = 3x + 10• 9 = 3x• 3 = x

Shop exercises and Worksheets

Formal Assessment

• Test worksheet