First of all, I want to explain that I get a little self conscious about making suggestions to people who will be spending hundreds or thousands of dollars and making modifications to a perfectly good automobile based on my opinion. However, the question of how to modify for hot lapping comes up often on this forum and is not met with the same truckload of experienced advice that drag racing questions receive. So, I offer my advice to those who can take it with a grain of salt, who won't come after me with a shotgun if it doesn't work out, and who understand that this highly biased advice is (for good or bad) based on my personal experience. This is the path, knowing what I know now, that I would take to modding my Mustang GT for road course duty if I could start all over again. It's not the path most people would choose. It won't earn you many points at the car show, doesn't add much "wow", and some of it will actually make you slower at the drag strip. However, it is based on my experience, not on what I read in a magazine.
The '05 and up Mustang is a very capable car right out of the box, much more capable than the average driver, especially if it's his first day on a track. I'm going to break the mods down into sections assuming that you are getting track time in between mods. Track time is not cheap, especially if instruction is involved, but if you have a choice between doing mods or getting more track time, TAKE THE TRACK TIME. Money spent on track time will lower your lap times more than triple that amount spent on mods every time. No Joke!
Note: If I suggest a particular part/brand name, I do so ONLY if I have personal experience with that particular part and would recommend it to a friend. That does not mean that it's the only available (or best available) choice, only that I've used it and liked it.
Mods for hot lapping round one: (Before your first track day)
1. A full brake fluid flush with a good quality, high temp, DOT4 brake fluid. ( I recommend- Motul RBF600)
2. Replace the brake pads at all four corners of the car with a high performance STREET pad. ( I recommend- Hawk HPS)
3. Mount a fire extinguisher. I don't care if it's a self contained, professional style, three nozzle halon fire suppression system or a 15 dollar, 2 pound Kiddie fire extinguisher from walmart duct taped to the back of the passenger seat. Somehow, somewhere, mount something you can put a fire out with on that car.
Round two:
1. Front brake cooling ducts. (I recommend- one of the kits from Quantum Motorsports)
2. Your choice of lightweight 18x9.5 inch wheels with a 45mm offset. Make sure they will fit a GT500. This will limit your choice of styles but will set you up for round three.
3. Oh God, let the criticism begin! The softest compound, stickiest tires you can live with. (For a daily driver, I recommend- BFGoodrich G-Force KDW in 275/40-18)
Round three: This one's going to make your wallet ache.
1. A big brake upgrade for the front of the car. (I highly recommend- a Brembo 14 inch, one piece slotted rotor kit, part number 1B4.8001A) I got mine at Raceshopper.com
2. Ditch the pads that come with the kit and replace them with a club race pad with a MOT of at least 950-1000 degrees. ( I recommend- Ferodo DS2500)
Round four:
1. Modified racing pedals. When doing this try to move the brake pedal up and to the right so it's in a better place for heel toe downshifting.
2. A solidly mounted, short throw shifter.
3. A properly mounted 6 point racing harness. This is easier said than done. I used a harness bar from Sparco listed as the bar for a '99 to '04 Mustang. Yes, it does fit the S197. Although the hardware package seems to be a little off. A harness bar will let you return the car to stock in between track days.
4. A properly mounted racing seat with harness passthroughs.
Round five: By now, you've done more than a few track days and your car is set up where you can drive it to it's limit, safely and with good feel and feedback. You should have a good feel for what the car is doing and what deficiencies you want to correct. Choose a suspension kit that will accomplish what you want, and that will take you to the limit of what you are willing to spend. Use a manufacturer that races Mustangs and stick to ONE manufacturer for all your suspension components. Want a whole kit that's easy to live with? Use a Ford Racing handling pak. Want to go all out and don't care about NVH? Use Steeda. Whatever you go with, Ford, Eibach, Roush, Saleen, Steeda, remember; these guys don't just throw a bunch of crap on a car and hope for the best. They do development, they do testing, they tweak all of their parts to work together as a system. Use their high dollar testing budgets to your advantage and stick to one manufacturer for everything. You'll thank me later.
Round six: NOW, start adding the mods for more power. And on this one, I'll leave your right foot and your wallet to slug it out. Put me down for $100 on the right foot.
The '05 and up Mustang is a very capable car right out of the box, much more capable than the average driver, especially if it's his first day on a track. I'm going to break the mods down into sections assuming that you are getting track time in between mods. Track time is not cheap, especially if instruction is involved, but if you have a choice between doing mods or getting more track time, TAKE THE TRACK TIME. Money spent on track time will lower your lap times more than triple that amount spent on mods every time. No Joke!
Note: If I suggest a particular part/brand name, I do so ONLY if I have personal experience with that particular part and would recommend it to a friend. That does not mean that it's the only available (or best available) choice, only that I've used it and liked it.
Mods for hot lapping round one: (Before your first track day)
1. A full brake fluid flush with a good quality, high temp, DOT4 brake fluid. ( I recommend- Motul RBF600)
2. Replace the brake pads at all four corners of the car with a high performance STREET pad. ( I recommend- Hawk HPS)
3. Mount a fire extinguisher. I don't care if it's a self contained, professional style, three nozzle halon fire suppression system or a 15 dollar, 2 pound Kiddie fire extinguisher from walmart duct taped to the back of the passenger seat. Somehow, somewhere, mount something you can put a fire out with on that car.
Round two:
1. Front brake cooling ducts. (I recommend- one of the kits from Quantum Motorsports)
2. Your choice of lightweight 18x9.5 inch wheels with a 45mm offset. Make sure they will fit a GT500. This will limit your choice of styles but will set you up for round three.
3. Oh God, let the criticism begin! The softest compound, stickiest tires you can live with. (For a daily driver, I recommend- BFGoodrich G-Force KDW in 275/40-18)
Round three: This one's going to make your wallet ache.
1. A big brake upgrade for the front of the car. (I highly recommend- a Brembo 14 inch, one piece slotted rotor kit, part number 1B4.8001A) I got mine at Raceshopper.com
2. Ditch the pads that come with the kit and replace them with a club race pad with a MOT of at least 950-1000 degrees. ( I recommend- Ferodo DS2500)
Round four:
1. Modified racing pedals. When doing this try to move the brake pedal up and to the right so it's in a better place for heel toe downshifting.
2. A solidly mounted, short throw shifter.
3. A properly mounted 6 point racing harness. This is easier said than done. I used a harness bar from Sparco listed as the bar for a '99 to '04 Mustang. Yes, it does fit the S197. Although the hardware package seems to be a little off. A harness bar will let you return the car to stock in between track days.
4. A properly mounted racing seat with harness passthroughs.
Round five: By now, you've done more than a few track days and your car is set up where you can drive it to it's limit, safely and with good feel and feedback. You should have a good feel for what the car is doing and what deficiencies you want to correct. Choose a suspension kit that will accomplish what you want, and that will take you to the limit of what you are willing to spend. Use a manufacturer that races Mustangs and stick to ONE manufacturer for all your suspension components. Want a whole kit that's easy to live with? Use a Ford Racing handling pak. Want to go all out and don't care about NVH? Use Steeda. Whatever you go with, Ford, Eibach, Roush, Saleen, Steeda, remember; these guys don't just throw a bunch of crap on a car and hope for the best. They do development, they do testing, they tweak all of their parts to work together as a system. Use their high dollar testing budgets to your advantage and stick to one manufacturer for everything. You'll thank me later.
Round six: NOW, start adding the mods for more power. And on this one, I'll leave your right foot and your wallet to slug it out. Put me down for $100 on the right foot.
) Anyway, the SVTOA guys are dedicated open track nuts some of whom have dedicated track only cars. I made it a point to look at the tires they were running and ask some questions. I did not see a single Mustang or talk to a single Mustang driver who was running staggered wheel sizes. There was a guy there in an American Iron Extreme '79 Camero who runs bigger rears but he was also putting down 575 lb/ft to the wheels so I imagine any under steer problems he might have are easily corrected with a slight tap of the throttle. 
Within reach of sitting in drivers seat is best.
