Tire Size worksheet

1. True speed at an indicated 50: 34.21

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{205\text{\hspace{0.17em}mm}\times 0.64}{25.4}$$=5.1654\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $5+2\times 5.1654$$=15.3307\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{190\text{\hspace{0.17em}mm}\times 0.3}{25.4}$$=2.2441\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $6+2\times 2.2441$$=10.4882\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{10.4882}{15.3307}-1\right)\times 100$$=\mathrm{-31.5871}\text{\%}$

6. True speed when the speedometer reads 50: the reading × new diameter ÷ current diameter

   $50\times \frac{10.4882}{15.3307}$$=34.2065$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 10.4882}$$=\mathrm{1,922.94}$

2. True speed at an indicated 52: 83.96

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{342\text{\hspace{0.17em}mm}\times 0.26}{25.4}$$=3.5008\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $25+2\times 3.5008$$=32.0016\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{214\text{\hspace{0.17em}mm}\times 0.93}{25.4}$$=7.8354\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $36+2\times 7.8354$$=51.6709\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{51.6709}{32.0016}-1\right)\times 100$$=61.4635\text{\%}$

6. True speed when the speedometer reads 52: the reading × new diameter ÷ current diameter

   $52\times \frac{51.6709}{32.0016}$$=83.961$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 51.6709}$$=390.32$

3. True speed at an indicated 50: 110.08

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{186\text{\hspace{0.17em}mm}\times 0.33}{25.4}$$=2.4165\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $6+2\times 2.4165$$=10.8331\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{342\text{\hspace{0.17em}mm}\times 0.7}{25.4}$$=9.4252\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $5+2\times 9.4252$$=23.8504\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{23.8504}{10.8331}-1\right)\times 100$$=120.1628\text{\%}$

6. True speed when the speedometer reads 50: the reading × new diameter ÷ current diameter

   $50\times \frac{23.8504}{10.8331}$$=110.0814$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 23.8504}$$=845.61$

4. True speed at an indicated 90: 76.4

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{108\text{\hspace{0.17em}mm}\times 1.29}{25.4}$$=5.485\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $25+2\times 5.485$$=35.9701\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{190\text{\hspace{0.17em}mm}\times 0.37}{25.4}$$=2.7677\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $25+2\times 2.7677$$=30.5354\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{30.5354}{35.9701}-1\right)\times 100$$=\mathrm{-15.1088}\text{\%}$

6. True speed when the speedometer reads 90: the reading × new diameter ÷ current diameter

   $90\times \frac{30.5354}{35.9701}$$=76.4021$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 30.5354}$$=660.48$

5. True speed at an indicated 48: 14.9

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{75\text{\hspace{0.17em}mm}\times 0.88}{25.4}$$=2.5984\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $33+2\times 2.5984$$=38.1969\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{63\text{\hspace{0.17em}mm}\times 1.18}{25.4}$$=2.9268\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $6+2\times 2.9268$$=11.8535\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{11.8535}{38.1969}-1\right)\times 100$$=\mathrm{-68.9672}\text{\%}$

6. True speed when the speedometer reads 48: the reading × new diameter ÷ current diameter

   $48\times \frac{11.8535}{38.1969}$$=14.8957$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 11.8535}$$=\mathrm{1,701.44}$

6. True speed at an indicated 40: 20.76

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{131\text{\hspace{0.17em}mm}\times 0.19}{25.4}$$=0.9799\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $23+2\times 0.9799$$=24.9598\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{259\text{\hspace{0.17em}mm}\times 0.39}{25.4}$$=3.9768\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $5+2\times 3.9768$$=12.9535\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{12.9535}{24.9598}-1\right)\times 100$$=\mathrm{-48.1025}\text{\%}$

6. True speed when the speedometer reads 40: the reading × new diameter ÷ current diameter

   $40\times \frac{12.9535}{24.9598}$$=20.759$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 12.9535}$$=\mathrm{1,556.96}$

7. True speed at an indicated 75: 117.62

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{294\text{\hspace{0.17em}mm}\times 0.16}{25.4}$$=1.852\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $18+2\times 1.852$$=21.7039\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{246\text{\hspace{0.17em}mm}\times 0.26}{25.4}$$=2.5181\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $29+2\times 2.5181$$=34.0362\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{34.0362}{21.7039}-1\right)\times 100$$=56.8205\text{\%}$

6. True speed when the speedometer reads 75: the reading × new diameter ÷ current diameter

   $75\times \frac{34.0362}{21.7039}$$=117.6154$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 34.0362}$$=592.55$

8. True speed at an indicated 45: 16.31

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{410\text{\hspace{0.17em}mm}\times 1.13}{25.4}$$=18.2402\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $22+2\times 18.2402$$=58.4803\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{315\text{\hspace{0.17em}mm}\times 0.29}{25.4}$$=3.5965\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $14+2\times 3.5965$$=21.1929\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{21.1929}{58.4803}-1\right)\times 100$$=\mathrm{-63.7606}\text{\%}$

6. True speed when the speedometer reads 45: the reading × new diameter ÷ current diameter

   $45\times \frac{21.1929}{58.4803}$$=16.3077$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 21.1929}$$=951.64$

9. True speed at an indicated 60: 51.03

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{139\text{\hspace{0.17em}mm}\times 1.17}{25.4}$$=6.4028\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $18+2\times 6.4028$$=30.8055\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{202\text{\hspace{0.17em}mm}\times 0.83}{25.4}$$=6.6008\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $13+2\times 6.6008$$=26.2016\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{26.2016}{30.8055}-1\right)\times 100$$=\mathrm{-14.9452}\text{\%}$

6. True speed when the speedometer reads 60: the reading × new diameter ÷ current diameter

   $60\times \frac{26.2016}{30.8055}$$=51.0329$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 26.2016}$$=769.73$

10. True speed at an indicated 52: 101.12

1. Sidewall of the current tire: width × aspect ratio, converted from mm to inches

   $\frac{64\text{\hspace{0.17em}mm}\times 0.93}{25.4}$$=2.3433\text{\hspace{0.17em}in}$

2. Overall diameter of the current tire: rim + 2 × sidewall

   $10+2\times 2.3433$$=14.6866\text{\hspace{0.17em}in}$

3. Sidewall of the new tire: width × aspect ratio, converted from mm to inches

   $\frac{302\text{\hspace{0.17em}mm}\times 0.36}{25.4}$$=4.2803\text{\hspace{0.17em}in}$

4. Overall diameter of the new tire: rim + 2 × sidewall

   $20+2\times 4.2803$$=28.5606\text{\hspace{0.17em}in}$

5. Diameter difference, as a percent of the current tire

   $\left(\frac{28.5606}{14.6866}-1\right)\times 100$$=94.4671\text{\%}$

6. True speed when the speedometer reads 52: the reading × new diameter ÷ current diameter

   $52\times \frac{28.5606}{14.6866}$$=101.1229$

7. Revolutions per mile of the new tire: 63,360 inches in a mile ÷ circumference

   $\frac{\mathrm{63,360}}{\pi \times 28.5606}$$=706.15$