Formula for working out the "potential" top speed of your car [Archive]

Glenn Butcher

11th February 2003, 01:36 AM

<html><head><title>MPH and RPM Calculations</title><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"></head><body bgcolor="#FFFFFF" text="#000000"><table x:str border=1 cellpadding=0 cellspacing=0 width=807 style='border-collapse: collapse;table-layout:fixed;width:606pt' align="center" bgcolor="#FFFFFF"> <col width=155 style='mso-width-source:userset;mso-width-alt:5668;width:116pt'><col width=64 style='width:48pt'><col width=140 style='mso-width-source:userset;mso-width-alt:5120;width:105pt'><col width=126 style='mso-width-source:userset;mso-width-alt:4608;width:95pt'><col width=122 style='mso-width-source:userset;mso-width-alt:4461;width:92pt'><col width=136 style='mso-width-source:userset;mso-width-alt:4973;width:102pt'><col width=64 style='width:48pt'> <tr height=35 style='mso-height-source:userset;height:26.25pt'><td colspan=6 height=35 class=xl7520137 width=743 style='border-right:0.0pt solid black;height:26.25pt;width:558pt'><div align="center">Calculating your top speed in MPH / and RPM</div></td></tr><tr height=17 style='height:12.75pt'><td colspan=6 height=17 class=xl7320137 style='border-right:1.0pt solid black;height:12.75pt'> </td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=24 class=xl6320137 colspan=4 style='height:12.75pt'>To work out the MPH you will be doing at XXX RPM use this table:</td> <td class=xl2720137 colspan="2" rowspan="2"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=27 class=xl6420137 style='height:12.75pt' colspan="4">Formula #1: mph= (rpm * circumference) / (gear * final * 88)</td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC" valign="top"><td height=37 class=xl6520137 style='height:12.75pt;width:116pt'><div align="center">RPM</div></td><td class=xl6220137 style='width:48pt'><div align="center">MPH</div></td><td class=xl6820137><div align="center">Tyre Circumference (in feet)</div></td><td class=xl6820137><div align="center">Differential Ratio (Final drive)</div></td><td class=xl6820137><div align="center">Gearbox Ratio (Top Gear I.e. 5th)</div></td><td class=xl6920137><div align="center">Var. Conv. Factors (leave at 88)</div></td></tr><tr height=18 style='height:13.5pt' bgcolor="#FFFFCC"><td height=18 class=xl6720137 align=right style='height:13.5pt'x:num="163.06363353584658" x:fmla="=(B9*C9)/(D9*E9*F9)" bgcolor="#99CCFF">163.0636335</td><td class=xl5220137 align=right style='border-left:none' x:num>6500</td><td class=xl5020137 align=right x:num="6.5078746317582059" x:fmla="=B38">6.507874632</td><td class=xl5220137 align=right x:num>4.1</td><td class=xl5220137 align=right style='border-left:none'x:num="0.71899999999999997">0.719</td><td class=xl3020137 align=right x:num>88</td></tr><tr height=18 style='height:13.5pt'><td height=18 class=xl8020137 style='height:13.5pt' colspan="6"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"> <td height=24 class=xl6320137 colspan=4 style='height:12.75pt'>To work out the RPM you will be doing at XXX MPH use this table:</td><td class=xl2720137 colspan="2" rowspan="2"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=28 class=xl6420137 style='height:12.75pt' colspan="4">Formula #2: rpm= (mph * gear * final * 88) / circumference</td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC" valign="top"><td height=37 class=xl6520137 style='height:12.75pt;width:116pt'><div align="center">RPM</div></td><td class=xl6220137 style='width:48pt'><div align="center">MPH</div></td><td class=xl6820137><div align="center">Tyre Circumference (in feet)</div></td><td class=xl6820137><div align="center">Differential Ratio (Final drive)</div></td><td class=xl6820137><div align="center">Gearbox Ratio (Top Gear I.e. 5th)</div></td><td class=xl6920137><div align="center">Var. Conv. Factors (leave at 88)</div></td></tr><tr height=18 style='height:13.5pt' bgcolor="#FFFFCC"><td height=18 class=xl6720137 align=right style='height:13.5pt'x:num="7972.3477995123831" x:fmla="=(B15*E15*D15*F15)/C15" bgcolor="#99CCFF">7972.3478</td><td class=xl5320137 align=right style='border-left:none' x:num>200</td><td class=xl5020137 align=right x:num="6.5078746317582059" x:fmla="=C9">6.507874632</td><td class=xl2920137 align=right x:num x:fmla="=D9">4.1</td><td class=xl2920137 align=right x:num="0.71899999999999997">0.719</td><td class=xl3020137 align=right x:num x:fmla="=F9">88</td></tr><tr height=17 style='height:12.75pt'><td height=37 class=xl3320137 style='height:12.75pt' colspan="6"></td></tr><tr height=17 style='height:12.75pt'><td height=17 class=xl3220137 style='height:12.75pt' bgcolor="#FFFFCC">RX-7 Differential Ratios:</td><td class=xl2520137 bgcolor="#FFFFCC"></td><td class=xl1520137 colspan="4" rowspan="8"></td></tr><tr height=17 style='height:12.75pt'><td height=17 class=xl3320137 style='height:12.75pt' bgcolor="#FFFFCC">Auto</td><td class=xl4520137 align=right x:num="3.9089999999999998" bgcolor="#FFFFCC">3.9090</td></tr><tr height=18 style='height:13.5pt'><td height=18 class=xl2620137 style='height:13.5pt' bgcolor="#FFFFCC">Man</td><td class=xl4620137 align=right x:num bgcolor="#FFFFCC">4.1000</td></tr><tr height=18 style='height:13.5pt'><td height=18 class=xl3320137 style='height:13.5pt' colspan="2"></td></tr><tr height=17 style='height:12.75pt'><td height=17 class=xl3220137 style='height:12.75pt' bgcolor="#FFFFCC">RX-7 Gearbox Ratios:</td><td class=xl4720137 bgcolor="#FFFFCC"></td></tr><tr height=17 style='height:12.75pt'><td height=17 class=xl3320137 style='height:12.75pt' bgcolor="#FFFFCC">Auto(4th)</td><td class=xl4520137 align=right x:num="0.69399999999999995" bgcolor="#FFFFCC">0.6940</td></tr><tr height=18 style='height:13.5pt'><td height=18 class=xl2620137 style='height:13.5pt' bgcolor="#FFFFCC">5th</td><td class=xl4620137 align=right x:num="0.71899999999999997" bgcolor="#FFFFCC">0.7190</td></tr><tr height=18 style='height:13.5pt'><td height=18 class=xl3320137 style='height:13.5pt' colspan="2"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=17 class=xl3220137 colspan=3 style='height:12.75pt'>To work out the circumference of your tyres:</td><td class=xl2420137 colspan="3" rowspan="4"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=17 class=xl3320137 style='height:12.75pt' colspan="3"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=17 class=xl5920137 style='height:12.75pt' x:str="1mm = "><div align="right">1mm= </div></td><td class=xl4120137 align=right x:num="3.9370000000000002E-2">0.0394</td><td class=xl4020137>Inches</td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=17 class=xl3320137 style='height:12.75pt' colspan="3"></td></tr><tr class=xl3120137 height=52 style='mso-height-source:userset;height:39.0pt' bgcolor="#FFFFCC" valign="top"><td height=45 class=xl3520137 width=155 style='height:39.0pt;width:116pt'></td><td class=xl3620137 width=64 style='width:48pt' height="45"><div align="center">Tyre width</div></td><td class=xl3820137 width=140 style='width:105pt' height="45"><div align="center">Profile%</div></td><td class=xl3820137 width=126 style='width:95pt' height="45"><div align="center">Tyre height (incl. Profile)</div></td><td class=xl3820137 width=122 style='width:92pt' height="45"><div align="center">Wheel diam. / wheel rim height</div></td><td class=xl6020137 width=136 style='width:102pt' height="45"><div align="center">1/2 rim height+tyre height</div></td></tr><tr height=18 style='height:13.5pt' bgcolor="#FFFFCC"><td height=18 class=xl3320137 style='height:13.5pt'>Metric (mm's)</td><td class=xl5420137 align=right x:num bgcolor="#99CCFF">225</td><td class=xl5520137 align=right style='border-left:none' x:num="0.5" bgcolor="#99CCFF">50.00%</td><td class=xl5120137 align=right x:num x:fmla="=B31*C31">112.50</td><td class=xl3720137 align=right x:num="406.40081280162559" x:fmla="=E32/B28">406.4008</td><td class=xl3420137></td></tr><tr height=18 style='height:13.5pt' bgcolor="#FFFFCC"><td height=18 class=xl3320137 style='height:13.5pt'>Imperial (Inches)</td><td class=xl3720137 align=right x:num="8.85825" x:fmla="=B31*B28">8.8583</td><td class=xl1520137></td><td class=xl3720137 align=right x:num="4.429125" x:fmla="=D31*B28">4.4291</td><td class=xl5620137 align=right x:num bgcolor="#99CCFF">16.0000</td><td class=xl4520137 align=right x:num="12.429124999999999"x:fmla="=(E32/2)+D32">12.4291</td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td height=74 class=xl3320137 style='height:12.75pt' colspan="2" rowspan="4"></td><td class=xl1520137 colspan="2"></td><td class=xl1520137 colspan="2" rowspan="4"></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td class=xl5820137><div align="center">PI</div></td><td class=xl5820137><div align="center">PI * 2</div></td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td class=xl4120137 align=right x:num="3.1415926535897931" x:fmla="=PI()">3.1416</td><td class=xl4120137 align=right x:num="6.2831853071795862" x:fmla="=C35*2">6.2832</td></tr><tr height=17 style='height:12.75pt' bgcolor="#FFFFCC"><td class=xl1520137 colspan="2"></td></tr><tr height=54 style='mso-height-source:userset;height:40.5pt' bgcolor="#FFFFCC"><td height=54 class=xl3920137 width=155 style='height:40.5pt;width:116pt'>Total tyre and rim circumference in inches:</td><td class=xl1520137 align=right x:num="78.094495581098471" x:fmla="=F32*D35">78.0945</td><td class=xl1520137 colspan="2" rowspan="2"></td><td class=xl1520137 align=right x:num="24.858249999999998" x:fmla="=B37/C35"><div align="center">Calculated Tyre and Rim Diameter:</div></td><td class=xl3420137 bgcolor="#99FF99"><div align="right">24.85825</div></td></tr><tr height=49 style='mso-height-source:userset;height:36.75pt' bgcolor="#FFFFCC"><td height=49 class=xl4220137 width=155 style='height:36.75pt;width:116pt'>Total tyre and rim circumference in feet:</td><td class=xl4320137 align=right x:num="6.5078746317582059" x:fmla="=B37/12" bgcolor="#99FF99">6.5079</td><td class=xl1520137 colspan="2"></td></tr><tr height=17 style='mso-height-source:userset;height:12.75pt'><td height=17 class=xl3920137 colspan="6" style='height:12.75pt;width:116pt'></td></tr><tr height=80 style='mso-height-source:userset;height:60.0pt'><td colspan=6 height=150 class=xl7020137 width=743 style='border-right:0.0pt solid black;height:100.0pt;width:558pt'>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.  </td></tr><![if supportMisalignedColumns]><![endif]></table></body></html>