Gears and shafts G87.01 Mainshaft Illustration # 303-00
Shorter or Longer Gearing Explained
A number of customers inquire about short gearing but do not grasp the concept. The lower gears need the largest spacing between shifts and then the spacing needs to be made shorter to allow the torque of the motor to "pull" or overcome the taller gears as the driver approaches top gear in a progressive manner. So in a perfect racing world of trying to move the car forward in distance in the shortest amount of time one would like the shift between first and second gear to be about an 3200 RPM Ill # engine revolutions per minute drop, the shift from second gear to third gear about 2500 RPM drop, the third to fourth gear shift about a 1700 hundred RPM drop and then the shift into Fifth Type Top gear about a 1400 RPM drop. When graphed out on a gear chart this will look like a half of a Christmas tree split down the middle like this graph which is of the stock ratios for an early Porsche 911 of A, F, M, S, X.
If the gearing is not made progressive and the initial shifts are spaced too closely time is lost as each upshift with a synchronizer transmission loses about a half of a second and each downshift loses three quarters of a second. So if the lower gearing is too short then you are wasting time making shifts from one "granny" gear to the next "granny" gear. As the car approaches 60 MPH it is covering about a hundred yards a second. The car with the longer initial gearing has only made one shift to get to 60 MPH and has only made one shift that will only cost him 40 or fifty yards in rolling distance. The "Granny" gear car has made two shifts with each losing about a half a second each and thus losing about 100 yards in rolling distance. The engine of the car with the longer initial gearing is also not struggling to "pull" or overcome the taller gearing with torque and the shift RPM drops are getting progressively shorter and this car is driving away from "Granny". So the gearing may be made longer or shorter depending on the desired top speed one wants to reach but the shape of the gear graph must remain to look like the half of a Christmas tree.