Re: piknockout's STU Auto-x Build - 2006 STi sponsored by Agile Auto: 9/27 SCCA Natio
I'll just leave this here for now.
I don't have any hard data at this point, just waiting to see if the corrupted MaxQ data can be salvaged *fingers crossed*. For this very limited test, we were only looking to understand the impacts to acceleration and top end speed since we couldn't do a true test. The best findings we had was that this 18" setup fit with no rubbing issues and no need to raise the car above our settings with the 17's. Below is more info on what we compared and how we did.
Baseline Wheel/Tire setup: 245/40/17 Dunlop Direzza Z1 (roughly 60ish runs - started full tread) on 17x9 et42 Rota DPT's (19lbs each)
Best time: 48.709 on my 2nd run, could have knocked off at least 0.8-1.0s with two more runs though as I had just jumped out of the Maryland FSAE car, which defies the laws of physics...the STi is a "little" different. It was the 4th run on tires - Shane didn't co-drive on first 2 runs, someone else did. No video unfortunately of that run, but it was not great.
Shifting: Ran out of gear very early in a few places, found two areas that required shifting to 3rd and could use it for a relevant amount of time.
Testing Wheel/Tire Setup: 245/40/18 Bridgestone RE01R's that are roughly 2 years old and a multitude of runs on them. They felt pretty hard/slick when we put them on. Wheels were TR Motorsports MT1 18x9.5 et45 at roughly 19lbs (and only $300 each on Tire Rack). I ran the 10mm spacers up front with this setup as well, so an effective et35 offset up front. No rubbing issues with this setup, but could have been from the lack of grip with these tires. Another note, Dunlops would have been wider and could possibly cause some rubbing.
Best Time: 49.326 on Shane's 5th run overall, 3rd run on this wheel/tire setup. Overall the tires were very slick and had a limited amount of grip. My best time was my 4th run (2nd run on these tires) with a 50.136 - video shows that I was a little too timid with the lack of grip and Shane ran much better lines in a couple of spots.
Shifting: The car still ran out of gear in all the same spots, but didn't run out as quickly. No real noticeable impact to acceleration, other than the extra RPM's needed at the start to get it going. Where the 17's required two definitive shifts to 3rd, the 18's could get by well enough with no shifting, although one spot was debateable as to whether 3rd could be used effectively.
The Verdict: Unfortunately, it's still pretty murky. I think until we can get more runs on equivalent tires, I don't know that we have a real answer. Our MaxQ data was corrupted when we pulled it afterwards and we're hoping to get it fixed. If so, then we can see what the actual differences were in top speed and acceleration to see what the tradeoff would be.
As far as making the car faster overall, I'm thinking with more power on tap next year that we can overcome the acceleration effects of the taller gearing. Also with more power, we should be able to get to the limiter in 2nd at a quicker pace, thus making the 18's a possibly better option, along with another 200 RPM's to help (at Nationals at least: 7400 to 7600).
I think that if I were only running locally/regionally then I would keep the smaller, cheaper, lighter 17" setup and not worry about it. More than likely there's not as much of an issue. But due to the speeds that are being displayed at Nationals the last two years, I don't know that there's much of a choice to go with anything but 18's. I know John Hale is a fan of them and had a raw time on Day 1 that would have put him right in the hunt for the top spot...looks like proof to me. I still haven't decided 100%, but it's currently leaning that way.
Oh yeah, and we can't forget the baller look of the 18's either. :lol: