Project Update for July 22, 2013: Dang, has it been six weeks since my last post in this thread? So much going on at the shop, been to the track 3 different times, lots of new S197 Development, our production E46 LS1 swap launched, and I got behind again. I started writing this post several weeks ago, then two of my guys went to support a racer at Pikes Peak and that put the picture and video processing from recent racing events behind schedule, and I put off finishing my post. But the longer I wait the more it keeps snowballing, so I am going to break this up over several smaller posts and just get started.
More Race Prep for the Vorshlag TT3 2011 Mustang GT
We almost never run the car the same way twice, as we're always trying to develop new parts to make the car faster. Hopefully some of them turn out to be parts we can sell - which is always a driving force in any of our Vorshlag project cars. Anyway, before the NASA event at Hallett, June 22-23, I wanted to work on a few front grip improvements. One thing I keep complaining about as we run at faster and faster tracks is a front end push in high speed corners. That 125mph entry into
Turn 8 at NOLA was pretty hairy, and had significant understeer. The rear wing seems to be producing plenty of downforce, but the ABS plastic, OEM front Leguna Seca splitter isn't keeping up on the opposite end.
We didn't get to fix any of that aero imbalance just yet (we will have more on this in a future update this summer), but I've suspected that we have had a
mechanical grip imbalance on the car for a while. This could be from a number of factors, such as a track width difference front to rear, as well as a wheel width deficiency on the front axle. As most folks know, even with the same
tire width, the width of the
wheel that the tire is mounted to can affect usable grip at the road surface. And while the 12" wide wheel on the back of our car seems
to some as a bit of a stretch for the 315mm tires we run, the same 315 on the 11" wide front wheel looks a bit pinched. The shoulders of the front tire tread are significantly more curved when you look at them closely, when mounted. And I don't want to stick with 315mm tires forever, either - every time we've increased tire width the car gets faster.
Our 2011 GT with 18x11" front and 18x12" rears - can't fit much more without flares
As I have discussed in previous updates, we are running a set of Forgestar F14s in 18x11" front and 18x12" rear this season and part of the last, with the 315/30/18 Hoosier A6 (and R6) or Kumho V710 in 315/35/18 tires at both ends. As you can see in the picture above, those are extreme fitments on the S197 chassis, without fender mods. Any more wheel or tire width up front and the wheel would poke outside the fenders. Same for the rear, which is pretty much maxed out. But I still felt we could gain some front grip (and potentially room for more front tire) if we went with 18x12" wheels up front, but only if we were then willing to cut and flare the fenders. Well, that time has come. We also needed a second set of wheels for race weekends, so we could test and learn the track on a more cost effective, durable tire than the Hoosier A6 (super sticky autocross tire) and then mount the A6 set for one session (hopefully) of faster laps. So Jason, Ryan and I took some measurements and we ordered up a set of 4 more custom 18x12" wheels, again, with different front and rear offsets. We tweaked the rear wheel backspacing but essentially kept the front backspacing the same as the old 11's.
Originally we had this 18x12" wheel built to fit a 345/45/18 Hoosier, but sadly this 13" wide tire rubbed like mad out back. Someday...
To fit this rather large 18x12" out back on a Mustang under the stock fenders takes a lot of parts and some compromises, and I think for the more extreme S197 racers an 18x11" would be better fit at both ends. For that wheel width I think the optimum tire size would be something in a 295-305mm width, as the 315mm tire is a bit squeezed. Not a lot of R compound tires to choose from in that size, but we ran across some 305/650/18 racing slicks and bought a bunch of them recently. I will discuss a potential "mounted and balanced" race tire/wheel set in one of my next posts. We've got a set of 18x11's coming in here next week and we will confirm our sizing measurements on my 2013 GT (which is for sale,
here - more on that in a bit). For most track guys the 18x10" wheel is an even better solution, as this wheel can work without spacers and still rotate front to back.
New set of 18x12" Forgestar F14 wheels in gunmetal with a "flat clear" + a new set of Hoosier R6 "practice tires" (winnings from NOLA weekend)
Forgestar was able to quickly build the new 18x12" set for us to our new specifications, but they were backed up a couple of weeks in powder coating so we had the set sent to us in the raw machined form. I took the raw wheels to our local powder coater, who does lots of wheels and knows the temperatures that you must stay under to avoid ruining the heat treat of the alloy (which we confirmed with Forgestar). He showed me some sample boards and then convinced me to try a new clear coat finish called a "flat clear". So on this set we kept the same gunmetal gray color code that Forgestar used on the first set of F14s, but went with this new flat clear coat final finish, which came out pretty damned good. This is different than a typical "flat" powder coat finish, which is flat in the base coat and doesn't have a clear coat at all. Those finishes can stain more easily but since this set-up has a separate clear coat (just one that has a flat finish) it should hold up better. Pretty slick, looks cool, and we'll see how it holds up to the heat and stresses of track abuse (2 events on them so far, and it looks perfect).
I knew all along we would have to trim the front fenders to clear these now 1" wider wheels, as the entire extra inch of wheel width is
all outboard (we already had the wheels tucked right up to within 3mm of the strut on the inside). This increases the front track by 2" total now, and also means the tire is going to poke past the fenders about 1" per side. More front track generally adds more grip at that end, too. All part of the plan.
Left: The original fender is now "wall art". Right: Sometimes these crazy ideas do involve alcohol
We searched and found a slightly lower cost fender for the '10-12 Mustang online, but once you factored in shipping it was cheaper to get two new fenders from Ford. Fine with me, as I like to use factory sheet metal whenever I can. After those arrived in black e-coat, it was time to measure and cut up the brand new fenders. First we pulled off the OEM fenders (which Amy wanted to keep unmolested, and are now Wall Art - soon to be joined by the OEM hood and front bumper cover), pulled off a front spring, installed the new wheel/tire combo, reassembled the front suspension, loosely attached the new fenders, and compressed the wheel and tire up to full bump travel on the Moton struts. Then we marked this spot (the loose fenders were pulled out of the way of the compressed tire), transferred this mark to the new fenders and cut a 1/4" above that. The plastic fender liner was trimmed to the new outer fender contour as well.
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