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Ask Anything - August 2014

Mustang Handling

Bob Albert; via CarCraft@CarCraft.com: I have a building problem and need some of your advice. I have been rebuilding a '00 Mustang GT 4.6 auto for four years. It came home to me running on five cylinders and two gears. I've replaced the cooling system and front brakes, and I repaired the rear brakes and had the top of the engine rebuilt. I replaced the front and rear springs and struts dropping the car 13⁄4 inches, and repaired the power steering. I junked the 15-inch tires and installed 18s so the car turns much better now. With these systems done, the car handles, runs, and stops much better. Where should I be going to improve the car for track day?

Jeff Smith: Any production car that will be subjected to aggressive cornering will need good shocks and springs. This goes for both the front and rear suspension, but especially for the front. Production cars compromise handling in exchange for a comfortable ride. Here is where you will need to move that compromise much more toward improved handling and sacrifice a little bit of ride quality. The problem with a generalized recommendation is that we have to assume that this car will still be daily driven on the street, but that you'd like to improve the handling without getting too aggressive.

You did not mention the specific tires and wheels that you installed, which is worth discussing because of all the components that can make a big difference, and tires are certainly at the top of the list. Just like in drag racing, the softer and stickier the tire, the better the car will handle—even if the suspension is not completely optimized. The good news is that you upgraded to 18-inch wheels. Assuming a similar overall tire diameter to stock, 18-inch wheels reduces the tire sidewall height, which is good because shorter sidewall tires are stiffer and less prone to rolling over under high-load cornering. Wheel choice is critical because a wider wheel is required with a wider tire to properly load the tire on the pavement. A rough rule of thumb is to use a wheel the same width as the tread.

We did a little research and looked at the '97 Mustang driven by Brett Lindert who has competed at several of our Real Street Eliminator events at the Car Craft Summer Nationals. Brett runs a set of 275/40R17 Nitto NT05 tires on the front and massive 315/35R17 Nittos on the rear, mounted on 17x9-inch front and 17x10.5-inch Bullitt wheels on the rear. If you would rather have a set of tires that you could rotate, then the same size wheels and tires on all four corners is an advantage to making the tires last a little longer. Generally, the front tires tend to take more abuse on autocross and road courses, and having the ability to rotate the tires front to rear could make them last longer. Most of the current autocross events now require a street tire with at least a 200 treadwear rating. You can find this rating on the tire's sidewall or in the tire specs on any of the tire company websites. The ratings gauge treadwear, so a lower rating means the tire is softer, while a higher rating (a larger number like 500) means the tire is a little harder and will last longer. The tires currently in vogue in autocross racing are the BFGoodrich G-Force Rival, the Falken Azensis, Dunlop Direzza Z-II, Hankook Ventus R-S3, and the Nitto NT05, among others. All of these tires meet or exceed the 200 treadwear rating.

Once you have a set of tires and wheels to your liking, a good suspension alignment is essential to improve handling. The Mustang uses a strut front suspension, which isn't factory adjustable, so you might look into a set of adjustable upper strut plates. These plates offer adjustment for both caster and camber. These plates are good for both setting the alignment and compensating for lowering the car, which usually accompanies a change to stiffer springs. You mentioned that you've already lowered the car, so an alignment is critical. We'd suggest going with something close to a negative 3⁄4 degree of camber and between 4 and 5 degrees of positive caster to induce more high-speed stability. This added caster will increase steering effort, but that's not necessarily bad. Finally, a slight amount of toe-in, perhaps 1⁄32 inch, will improve tire wear. You may hear about racers adding much more negative camber to increase lateral g-force. This can be helpful at the track, but this will also radically increase inside tread tire wear by increasing the inward tilt of the tire, which loads the inside of the tire. Also, while negative camber helps cornering, few realize that this also reduces tire footprint under braking. That's why we like to maintain the static negative camber at around 3⁄4 degree.

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