Calculating your top speed in MPH / and RPM | |||||
| To work out the MPH you will be doing at XXX RPM use this table: | |||||
| Formula #1: mph= (rpm * circumference) / (gear * final * 88) | |||||
RPM | MPH | Tyre Circumference (in feet) | Differential Ratio (Final drive) | Gearbox Ratio (Top Gear I.e. 5th) | Var. Conv. Factors (leave at 88) |
| 163.0636335 | 6500 | 6.507874632 | 4.1 | 0.719 | 88 |
| To work out the RPM you will be doing at XXX MPH use this table: | |||||
| Formula #2: rpm= (mph * gear * final * 88) / circumference | |||||
RPM | MPH | Tyre Circumference (in feet) | Differential Ratio (Final drive) | Gearbox Ratio (Top Gear I.e. 5th) | Var. Conv. Factors (leave at 88) |
| 7972.3478 | 200 | 6.507874632 | 4.1 | 0.719 | 88 |
| RX-7 Differential Ratios: | |||||
| Auto | 3.9090 | ||||
| Man | 4.1000 | ||||
| RX-7 Gearbox Ratios: | |||||
| Auto(4th) | 0.6940 | ||||
| 5th | 0.7190 | ||||
| To work out the circumference of your tyres: | |||||
1mm= | 0.0394 | Inches | |||
Tyre width | Profile% | Tyre height (incl. Profile) | Wheel diam. / wheel rim height | 1/2 rim height+tyre height | |
| Metric (mm\'s) | 225 | 50.00% | 112.50 | 406.4008 | |
| Imperial (Inches) | 8.8583 | 4.4291 | 16.0000 | 12.4291 | |
PI | PI * 2 | ||||
| 3.1416 | 6.2832 | ||||
| Total tyre and rim circumference in inches: | 78.0945 | Calculated Tyre and Rim Diameter: | 24.85825 | ||
| Total tyre and rim circumference in feet: | 6.5079 | ||||
Example Tyre Circumference calculation: You can estimate the rolling circumference from the tyre-width, profile and rim height. For example, a 195/60R-15 tyre will have a section height of 60 percent of 195mm, (195 x .60) = 117mm, which converts to 4.6063 inches. Add 4.6063 to one-half of the 15-in. wheel diameter (4.6063 x 7.5), and you get 12.11inches. Multiply by 2pi (12.11 x (3.141593 x 2) = 76.0661 gets the circumference using inch units; then dividing by 12 gets you to the circumference in feet (76.0661 / 12) = 6.3388.
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