๎
1๎
๎
Name:๎_____________________๎
DTEC๎105๎
Calculating๎Wheel๎Speed๎
๎
If๎you๎know๎the๎engine๎speed,๎gear๎ratios๎for๎the๎transmission,๎transfer๎case๎ratio๎(if๎applicable),๎rear๎
end๎ratio๎and๎the๎diameter๎of๎the๎tires๎it๎is๎possible๎to๎calculate๎how๎fast๎the๎vehicle๎will๎travel.๎๎This๎can๎
be๎useful๎in๎a๎variety๎of๎ways๎including๎knowing๎what๎speed๎a๎vehicle๎will๎go๎if๎you๎are๎changing๎tire๎
sizes,๎transmissions,๎or๎rear๎end๎ratios.๎๎With๎some๎additional๎calculations,๎which๎we๎will๎cover๎later,๎it๎is๎
also๎possible๎to๎determine๎the๎right๎combination๎of๎engine๎and๎drive๎line๎components๎to๎see๎if๎a๎truck๎
will๎perform๎up๎to๎expectations.๎๎๎
For๎the๎purpose๎of๎this๎exercise๎a๎2๎wheel๎drive๎gasoline๎pickโup๎truck๎will๎be๎used๎with๎the๎following๎
specifications:๎
โข Engine๎is๎turning๎at๎3750๎rpm๎
โข Transmission๎Low๎Gear๎Ratio:๎๎6.23:1๎
โข Rear๎axle๎ratio:๎๎3.73:1๎
โข Tires๎are๎LT265/75R16๎and๎have๎an๎overall๎diameter๎of๎31๎inches๎
๎
Procedure๎for๎calculating๎wheel๎speed.๎
1. Calculate๎the๎gear๎ratio:๎๎๎
a. Multiply๎all๎of๎the๎ratios๎from๎the๎transmission๎to๎the๎wheel๎ends.๎(if๎the๎vehicle๎has๎a๎
transfer๎case๎and/or๎final๎drives๎those๎ratios๎must๎be๎included๎too.)๎
๎
Overall๎ratio๎=๎๎transmission๎ratio๎X๎rear๎axle๎ratio๎
Overall๎ratio๎=๎6.23๎X๎3.73๎=๎23.24๎๎๎๎or๎๎๎๎๎23.24:1๎
๎
2. Calculate๎the๎revolutions๎at๎the๎wheel๎ends๎in๎revolutions๎per๎minute๎(rpm)๎
๎
Wheel๎rpm๎=๎engine๎speed/overall๎ratio๎
Wheel๎rpm๎=๎3750๎rpm/23.24๎=๎161.37๎rpm๎๎๎
๎
3. Calculate๎how๎many๎times๎the๎wheel๎rotates๎in๎and๎hour๎(rev/hr)๎
๎
Rev/hr๎=๎wheel๎rpm๎*๎60๎
Rev/hr๎=๎161.37๎X๎60๎=๎9682.46๎rev/hr๎
๎
๎
๎
๎
