Changing Tires Activity

By Alex Wilhelm and Stone Ormand

Tire size

Our original tire size was 20 inches and we decreased our size to 18 inches

Factory and replacement

The factory tire information is 20 inch p275/65r20 width 10.8 ar 65%. Height is 7.02 dia 34.04 circum 106.954. New Tire is 18 inch p275/70r18, width 10.8 , ar 70%, height 7.56' da 33.12 circum 104.0

Miles per gallon

The Standard tires Have 14.7 mpg

The New Tries have 14.26 mpg

Chart and "K" ratio


Old New

Width 10.8in 10.8in

Ar. 65%. 70%

Height 7.02in 7.56in

Dia. 34.0in 33.12in

Cricum 106.9in 104.0in

K ratio 0.97

Our statements

1. If your odometer is reading is 50,000 (miles) you have travails 48500 miles on the new tires

2. If your speedometer reading is 70 your speed is 67.9 miles per hour with the new tires

3. If your mile per gallon with factory tires is 14.7 what is your miles per gallon with the new tires

K Ratio= 0.97