Mike;
Not sure what you mean by "add on " to the formula. I use the formula in
the following form;
MPH = ( 0.002973 x TD x RPM ) / OGR
where TD = tire diameter in inches
OGR = overall gear ratio
where OGR = tran ratio x axle ratio
The 0.002973 is a Conversion Factor Constant (CFC ) which converts tire
diameter into circumference, inches into feet, feet into miles, and minutes
into hours, or;
CFC = (3.14 x 60 ) / (12 x 5280) = 0.002973
Using my Corvette as an example;
RPM = 5850 at fuel cutoff Axle ratio = 3.45
Tran ratio = 0.75 in 5th gear OGR = 0.75 x 3.45 = 2.5875
TD = 25.95 inches
So, MPH = ( 0.002973 x 5850 x 25.95 ) / 2.5875 = 174 MPH ( I wish !)
Lance
----- Original Message -----
From: "Mike Meierle" <mike.meierle@alcatel.com>
To: <land-speed@autox.team.net>
Sent: Thursday, March 25, 2004 1:14 PM
Subject: Gear Ratio Formula?
> I have the standard formula below.....
>
> mph = rpm x tire diameter / differential gear ratio x 336
> 76.468 = 4000 X 27.106 /4.22 X 336
>
> Can I simply add on to this formula for calculating speed in specific
gears
> of the transmission by doing the following:
>
> mph = rpm x tire diameter / differential gear ratio x 336/transmission
gear
> ratio
>
> 20.556 = 4000 X 27.106 / 4.22 X 336/3.72<- First Gear
> 34.758 = 4000 X 27.106 / 4.22 X 336/2.2<- Second Gear
> 50.979 = 4000 X 27.106 / 4.22 X 336/1.5<- Third Gear
> 76.468 = 4000 X 27.106 / 4.22 X 336/1.0<- Fourth Gear
> 96.795 = 4000 X 27.106 / 4.22 X 336/0.79<- Fifth Gear
>
> Or do I need a Math refresher? Mayf you out there?
>
> Oh yeah, I'm building a Speed Table in Excel which incorporates the Tire
> Diameter Calculator
> slap in the basics, P205R75/15, and you get your speed at RPM and Gear.
>
>
> Mike Meierle
> 36 Technology Drive
> Suite #110
> Irvine, CA 932647
> Phone: (949) 450-9160 X8031
> www.alcatel.com
|