Quote:
Originally Posted by Jawnathin
I sent over my logs. << snip >>
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Just based on the video, I took a look at the CAM event data first because it looked like it would have a lot of interesting analysis opportunities. Looking at the video and through the data, I pulled 9 distinct full throttle zones from the run. The first plot below (should be a clickable thumb) shows all the data as recorded by solostorm and the second plot shows just the 9 FT zones. I analyzed zones #2 and #4 as constant FT even though there are very momentary ‘lifts’ of the throttle – even if the data is good, we’ll say these could’ve been 100% on the later, quicker run
One thing I noticed right away is that you have a lot of ‘repeats’ in your RPM data and a fair amount in your speed data as well. I think your OBD dongle is reading at a lower rate than what solostorm is recording at. The data required a little more interpretation, but it still provided a good sampling of initial speeds and distances.
The full results are in the table/image at the bottom of the post. The various columns show the results from each pull and the total FT acceleration time is in the next to last column. The rows show the baseline 245/40-17 R-S3’s with the shifting as driven as well as various other comparisons. To summarize:
Code:
gears used tire
1-2-3-2-3 245/40-17 R-S3 18.317 sec
1-2-3-2-3 235/40-17 ZII* -0.001 sec
1-2-3-2-3 225/45-16 ZII* +0.004 sec
1-2-3-2-3 225/45-17 Rival +0.004 sec
1-2 245/40-17 R-S3 -0.026 sec
1-2 225/45-16 ZII* +0.121 sec
1-2 235/45-17 RE-71R -0.061 sec
These results turned out a bit differently and even closer than I would’ve guessed. Over 9 zones the closeness of the different sizes using the shifting pattern driven is remarkably close. Seeing that you slowed down after shifting to 3rd at the 14 sec mark, the second shift to 3rd is quite close to the line and in general not a lot of the run is at speeds above the 2nd gear limit speed, I wondered what the calcs would show for just holding 2nd throughout the run.
Those 2nd-gear-only results are shown in the bottom 3 rows. I decided to go with the baseline tire and two extremes in the 225/45-16 and 235/45-17. To my surprise, holding 2nd was a bit quicker for the baseline size and also the tall 235/45-17, which I wouldn’t have guessed. Even more surprising is the 225/45-16 is only 0.121 slower despite being on the limiter for a total of 5.4+ sec!
So this is indeed a case where taller is better. But for a fairly fast course with ~18 sec of full throttle acceleration over an ~60 sec run, the differences are small. My conclusion is still to make a reasonable choice and drive! I’m really suspicious that the gearing advantage is not worth the compromise in overall cg height and sidewall stiffness (though you could mitigate the latter with 235/40-18’s
).
Definitely an interesting data set to look at. I do plan to also look at the AAS data as well, but I'm not sure when I'll get to it.
