Miata Mailing List: January 1994, Message #13
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   From: MISSERTD@delphi.com
Subject: Miata Shift Points
   Date: Mon, 3 Jan 1994 17:38:15 -0500

Question was asked about horsepower, torque, and shift points.

Road and Track recently had a piece on calculating shift points. The
object is to shift at the RPM that results in the maximum torque
for the gear that you are shifting INTO. Calculate it this way:

1. Calculate the ration between the two gear ratios.
2. Multiply the result by the RPM at which your torque peaks.
3. The product is the RPM at which you should shift.

For example, if 1st gear is 3.136 and 2nd gear is 1.888, then
3.136/1.888 equals 1.661. If your torque peak is at 5500 RPM, then
1.661 times 5500 equals 9136, the RPM at which you should shift
from 1st to 2nd.
 
If my calculations are correct for my 90 Miata, all of the
torque-maximizing shift points are well above the redline, so
the practical result is to shift at the redline.
 
Here is how I calculated:
 
1st gear = 3.136
2nd gear = 1.888
3rd gear = 1.330
4th gear = 1.000
5th gear = 0.814
 
Ratio of 1st to 2nd = 1.661 times 5500 = 9136 RPM
Ratio of 2nd to 3rd = 1.420 times 5500 = 7808 RPM
Ratio of 3rd to 4th = 1.330 times 5500 = 7315 RPM
Ratio of 4th to 5th = 1.229 times 5500 = 6757 RPM