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Further analysis. Our torque curve is relatively flat from 4500 to 5200 - meaning this is the range where the car pulls hardest. If we look at this 700rpm sweet spot range:

With 25.5" tires:
Sweet spot torque:
1st: 26-30
2nd: 45-52
3rd: 66-76
4th: 87-101
5th: 113-130

From the video, you can see the car accelerates well up to about 100mph. I am shifting from 4th to 5th at around 100, just as the toque curve is dropping off. But when I get to 5th, I am well below the sweet spot of the torque curve and the car falls flat - damn 0.733 5th gear!! :mad:
I think your dyno run was clipped off at the low end and high end. I found another 6S dyno plot that is clean from 2500 to 6400, and is much like Mazda's advertised power curve:

I used that torque curve as an input to my "shift points" Excel program, as well as the gear ratios, and the tire diameter. The result is the torque at the front axle vs speed for each gear.

I created jpeg picture files ( on smugmug ) of the plots from Excel, but I can't make a picture here. ---- Any ideas?

The bottom line is it's best to stay in the lowest gear possible, and when I ran a 6 speed (common in Oz), you have more axle torque in 3rd, 4th, and 5th. They hit 6400 sooner in each of those gears: 3rd is 82 vs 90, 4th 104 vs 120, 5th is 127 vs 155, and 6th is like a continuation of 5th, hitting 6400 at 142.

More later ...


2,883 Posts
Ok, I'll just try links to where the Excel "shift points" reside. The first is for the as built 5 speed with CR's last tires at VIR.

Note that the last two points on each gear's curve represent 6250 rpm and 6350 rpm.

Since each curve shows the axle torque with full engine available hp based on rpm, there is no case where you would upshift before max rpm, in any gear. Since the plot is axle torque vs rpm , and rpm is expressed by evenly spaced dots on each gear curve, this is actually a 3 dimensional plot for a family of gear curves.

One main point is that it is hard to find a sweet spot of significance based on the engine's torque curve.

1st --- 3.153
2nd -- 1.842
3rd --- 1.258
4th ---- 0.947
5th ---- 0.733
final -- 4.133
tire 275 35 18, 24.81" dia


I also tried the 6 speed available from austrailia:

Note that my base Excel program is based on a 5 speed, so for the 6 speed I input data for gears 2-6 .

You still should hit max revs before shifting, excepth at 125mph, you should barely "short-shift" at 6250 rpms in 5th to 6th.

As expected, more axle torque in all gears (1st?), and less max speed in each gear.

2nd ---1.842
3rd --- 1.310
4th --- 1.030
5th --- 0.837
6th ----0.755
final -- 4.388

tire 275 35 18, 24.81" dia

I know a person that uses shipping containers to ship british parts, and cars, overseas. The way to get a 6 speed would be to find a place the gets your 6 speed into a container in australia, and then to you in Va.

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