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Garry
September 25th, 2006, 12:38 AM
Stupid question - how can I calculate the effects a different gear ratio has - I know there are things like 3:23, 3:43, 3:73, 4:11 ... and I know that the higher I go, the better the takeoff and the lower the topspeed ... but what are the (mathematical) effects of e.g. going from 3:43 to 4:11?
TAQuickness
September 25th, 2006, 01:00 AM
What do you mean? How do you adjust your calibration by hand? Or how to project your RPM for a given speed?

At one point in time, I found a bunch of good formulas on Google.
Garry
September 25th, 2006, 01:04 AM
The latter ... effects it will have on the speed (and therefore fuel efficiency) of the car ...
roy
September 25th, 2006, 05:52 AM
Garry
Do you mean like this excel spreadsheet on fbodyEurope (http://www.fbodyeurope.org/gallery/8_Book1.xls) ?
Garry
September 25th, 2006, 05:57 AM
:) Tnx Roy!
roy
September 25th, 2006, 06:52 AM
Maybe you can improve on it. I usually keep a hard copy in the car due to the limited speedometer to see what top speed I reach by gear and rpm.
joecar
September 25th, 2006, 07:01 AM
You mean this formula...

RPM = MPH * 336 * AxleRatio * TransRatio / TD

where TD = tire diameter in inches

Rearrange if you want MPH from RPM.

Edit: Like this:

MPH = RPM * TD / (336 * AxleRatio * TransRatio)