And when I say testing, consider that I typically run the fuel tanks dry of any car two or three times during a session. Most cars can run 30+ laps at Tsukuba Full incurring between 20-30% tire wear and still perform quite well. One adjustment per lap and each lap time compared against the previous one. If I can reproduce the lap time consistently, the adjustment is, usually, kept.
If I'm going to make recommendations, I don't want to be doing anyone a disservice. Even if that service is free. LOL!
Don't worry Choccy, I don't think you're doing anyone a disservice (and my apologies if I came across that way at any time). You just need to see the testimony from barumba to see how important your input has been to him, and I believe Pete found it useful too. For me, it's certainly been interesting to see how the different pressures panned out - it's just that I couldn't replicate the improvements. But that could well be down to driver preference as we've both mentioned through this thread.
One thing I certainly can't deny is that you put much more testing into your tunes than I do. It's very rare that I run more than about 8 laps tuning, even at short tracks. If I'm tuning for a long track, feel becomes much more important as it takes so much longer to get a representative set of times. But even then, you get a feel very quickly for what is a nice consistent tune.
Well then, let me testify.
I tune my cars with a calc created by SLAVE MUNKY. His default psi is 28.5 front and rear. This has always proved serviceable, but quite a while ago, very early in this thread, I asked Choccy about the concept under discussion, Light Weights and Handling. My thought was, why does a light weight handle poorly? What has the weight got to do with how a car handles, if the car's suspension is tuned according to common convention. That is when Choccy first advised me of the BF Goodrich Engineer's best starting point for treaded tires. That little widget I created based on that formula has been posted a few pages back in this thread.
http://www.mediafire.com/download.php?ykdwrf7apxd7a69. Go to the second sheet in that link. I also included FD's advice for Tire Pressures, for legacy tunes and calcs he had influenced. To Choccy's point, was that the tires and how you tune them have a significant impact on how a car handles, even before suspension and differential tuning. So off I went, retuning cars I had built. I went back to treaded tires if I had slicks. Why, 'cause I wanted to test the theory. I changed the tune in the calc to insure integrity of the formulae, heavily reliant on tire dynamics. I re-ran laps with the calc derived 28.5 psi. Took note of the times and handling characteristics. I then adjusted the tire psi that were derived from the widget. In all the cars under 2200-2300 pounds, I found that when I used the widget values I was able to best my times achieved with the default 28.5 psi. Cars felt rooted, road feedback was improved, therefore confidence, therefore lap times.
The cars in the 2500-3000 pound range were a toss up, could not really define which psi was better, the 28.5 or the 27 or 30 psi from the widget. When I re-tuned cars in the 3000 plus weights, most mid weight sedans, I found that the 28.5 default in the calc performed well, and in many cases the FD derived psi from the widget yielded better handling and better times. Then I took the big leap, went up to 4500 pound tanks. In this case, I was quite surprised. Even though the default 28.5 was very stable, the sCHOC values from the widget were great. Better than the default and better than the FD values.
One thing that became quite apparent, the lightweights with slicks may have been running on skates. The temperatures needed to optimize these tires could not be reached, not enough load to bring the tires up to temps. So, the narrower, treaded tires needing less static weight and driving load to bring them up to temp, and the streets and sports came into their range quite effectively.
So, the long and the short of it, light weights on lower range treaded tires worked best, for me, with the lower psi. The mid range sedans, on the treaded tires fell within a range that both my calc defaults and the widget yielded similar results. Once back out of the range of my calc, over 28.5, the widget again yielded better times, sometimes a toss up between the sCHOC and the FD values from the widget. So, for now, I tune my car with the SM calc (have for a few years, including the latest release), run at least 5 test laps to acquaint myself with the feel and bring the tires up to ultimate temp and hot psi. I then apply the sCHOC values from my widget, run another three laps (so tires can reach new equilibrium), then adjust to the FD widget values, run 3 more laps. Which ever psi deliver the best times, I save as my tune for that car/class. In any of the above, I adjust psi a wee bit more or less 0.5 pounds front or rear to balance any slight US/OS I might sense, rather that adjust the suspension, which for the most part is pretty well balanced.
That is my testimony. And now, I want to thank Choccy and Spiny and all the others who contributed to this thread for all their input, and yes, influence to how I tune my cars. Much gratitude, guys. Another great and FUN learning experience!
Cheers
