Project Update for May 23, 2012: We've done a bit of work to the car since the last update, and had another autocross to test changes before the Lincoln "Spring Nationals" event this weekend.
The defacto R compound DOT tire in SP is a Hoosier A6, but we had been doing well with a Kumho V710. The Kumhos have plenty of life left but work better as a road course tire than in autocross, so we pulled the V710s off of the 18x11/18x12 Forgestars and ordered some HoHos...
Go Big or Go Home!
Looking at the
2012 Hoosier Tire Listing for the A6, the obvious choice up front is the 315/30/18 size, which has 11.8" of tread width and 12.5" of section width. The problem is the height, which is only 25.6". That's short for this car, and even with our "tallest Ford made for it" 3.31 rear gear ratio, this height shortens the speed range in 2nd gear significantly. The goal is to at least be able to reach 70 mph in 2nd, and with the relatively short 2.43 ratio in 2nd, this means we have to watch rear tire height closely. When we ran STX last year (*twitch! shudder!*) we saw noticeable improvements going from 265/35/18 tires to a taller 265/40/18 size, which softened the rear ratio and extended 2nd gear speeds a noticeable amount.
The real goal for me is to avoid EVER having to go to 3rd gear in an autocross run (which inevitably means another downshift to 2nd), as the up/down/up shifts cost so much time. Gear the car right, including tire height, and you never leave 2nd. This 5.0L engine has torque
everywhere so even if it doesn't have as much "snap" at lower speed corners it still has "more than enough". So, all that said...
I picked a pair of 345/45/18 Hoosier A6 tires for the rear and a 315/30/18 for the front. The 345 is
the biggest 18" tire Hoosier makes in the A6 and has 13.25" tread width, massive
13.9" section width, and a big 26.8" tire height (the stock tires are 27" tall on this car). That's a 14" wide rear tire... the same relative size that CP cars use. This tire height allows for an insane 77mph top speed in 2nd gear at 7800 rpm, and 75mph at 7500 rpm. No more 3rd gear in a parking lot with this tire, ever.
Trying to fit a 14" wide tire under factory sheet metal car sounds insane... and went against my own better judgement as well as the recommendations of others. But I've taken some leaps of faith on this build using the "bigger is better" mentality that have paid off already. The car was also experiencing enough wheel spin in slow speed autocross corner exits with the 315mm Kumhos that I was willing to give this larger 345 mm wide tire a chance out back. Of course this tire would never fit up front without major fender surgery, so I went with a non-square 315F/345R combo - again, against my own recommendations. We had to space the 12" rear wheels outboard another 10mm to have the same clearance to the rear swaybar and inner fender structure as the 315 had on the same wheel as before. It was a gamble but I tossed the dice,
hoping we could make them fit.
Yea, not a chance. These things are redonkulous. HUGE. So now the rear tires needed more spacer and protruded past the fenders a solid 1/2 inch, which I dislike both aesthetically and functionally. First, it widens the rear track, making the differential work that much harder and making slaloms/transitions that much more difficult to navigate. Secondly, it adds a potential rub point at the outer fender lip itself, if there is enough roll movement in the rear of the chassis to let it roll over and touch the tire. I was hoping that this wouldn't be a problem, and with a known amount of axle movement in cornering it could even tuck under the fender lip on the outer tire in turns. I also hoped the stiffer 275#/in rear and 550 #/in front springs (installed when we put on the Motons a week earlier) would keep the roll down enough to keep the rear tire away from the outer fender lip.
Other prep this week before this SCCA autocross was a swap to the rear spoiler (wing isn't legal in this series/class), and we could uncover the hidden SCCA stickers (something NASA requires). I didn't even add any fuel to the car from the last event - we loaded it into the trailer Thursday night and it sat there until the race on Sunday.
This next autocross would tell us a lot about this round of changes...
Texas Region Autocross # 3 at TMS
We're trying to make as many of our local "Texas Region" SCCA events this year as we can, and using each event as a test session. Amy was out of town on business this week, so I ran this event by myself. Hey, maybe I could win this time!
Just like the autocross a week before, this event was set-up in the same sealed asphalt "Bus Lot" at Texas Motor Speedway, with the same course designer, but this time with the SCCA region running the show. This is my favorite group to autocross with - they put on an excellent event, every time. Well organized, great courses, good competition, great announcing (except when they let me do it, ha!), and final results are posted within hours. Things run smoothly, safely, and consistently. Its no coincidence that our Solo REs are also the event masters for the 2012 Solo Nationals - Jen and Brad Maxcy. (Jen whipped some ass on Sunday in their STX BMW, beat Brad, and PAXed right on my tail in Heat 1, with Brad 3rd in PAX for the heat)
Here are the event particulars:
The results don't tell the
entire tale, of course. This is where I begin my excuses.
So, as I've said before, this TMS site currently has construction happening right at the edge of the lot surface, with Jersey barriers holding back a mountain of fine, silty dirt from the lot. Every time it rains (which has been often here lately) it washes this dirt/mud mix onto the surface of the lot. So early drivers get to clean off the driving line, mid-day drivers get a cleaner line with some added track temperature, and afternoon drivers tend to see the cleanest line but the most track heat. If its a cooler day the afternoon runs are quickest. If its a warming day the mid-day drivers are fastest. That last scenario happened on this day - 2nd heat drivers were fastest by a good margin. It helped that our top National drivers ran that heat also!
Left: Run #1 was quick. Right: Run #5 was my fastest
I ran in the first heat along with about 1/3rd of the 109 racers. The first run in Mustang was with the stickers still on the tires, but that didn't seem to slow the car down
at all. On that run I had trouble with braking in all of the higher speed stopping zones (super hard pedal - no power assist?) but put in a respectable run. My 2nd through 4th runs were either slower or not much better, with continued braking problems. My 5th run I finally adjusted my braking zones back significantly, went slower into most turns, and dropped 3/4 of a second from my first run. It wasn't pretty but it was faster. This was the only 42 second run of the heat and put me #1 in PAX for that 1/3rd of drivers as well.
This was short lived, as Heat 2 drivers put in some phenomenal times and I dropped to 18th in PAX. There were two significant problems in my runs, and one "missing" problem. Well, other than my regularly crap driving, which goes without saying.
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