A poor economy can be a good thing. It means supply is up, demand is down, and cars are dirt cheap. So we went in search of a new project car and the original B5 Audi S4 grabbed our attention. It's got everything; all-wheel drive, twin-turbos, a bulletproof bottom end and a cornucopia of parts both OEM and aftermarket to throw at it. But there's a downside; most cars are either abused beaters you should avoid or heavily modified, high-dollar cars with their share of problems.
After a long search, we found a pristine, garaged '02.5 S4 with only 35k miles under the diligent care of wealthy grandmother who was tricked into buying it by her son. For the price of a new Hyundai, we had ourselves an all-purpose project but instead of the usual 700hp route every S4 owner aspires to, we're going to build the car for daily reliability and fun, yet fast enough to bitch-slap unsuspecting BMWs and Infinity G35s.
Before throwing aftermarket parts at it, we wanted a baseline of the stock car's performance since we'd be addressing the handling first. So we tagged along with Motor Trend to put the stock S4 through their figure-8 test.
As the name implies, it's a mini-autocross comprising two 200ft circles that's an easy way to evaluate acceleration, braking, transitional handling, understeer and oversteer, while obtaining an average lateral g-force number to measure grip.
Out of the box, the S4 lived up to its nose-heavy reputation. The stock suspension allowed the car to wallow through minor dips, making it impossible to maintain consistent cornering speed with any confidence.
We achieved a 26.355sec lap time, according to our vehicle telemetry system, averaging 0.87g of lateral acceleration in both directions.
The grip numbers are good on account of the Michelin PS2 tires on the car, but the overall lap time is slow for an all-wheel drive car with decent power.
First: Tires
Tires are the most important aspect of any car. All too often, car owners don't consider tires until the wheels are purchased and are stuck with fitment issues or simply skimp on the rubber. So there's a benefit to doing our homework first, picking the right size tires and selecting the type of tire to meet our needs.
One of the drawbacks of the B5 platform is the limited real estate in the fenders wells. The car comes on 225/45 R17 tires and we also knew that (depending on the brand and shoulder profile) a 255-width tire would require fender rolling and cutting of fender liner. So we chose 245-width. And also decided on larger 18" wheels.
We then needed to opt for the aspect ratio (or sidewall height). Having more sidewall is good for comfort and avoiding bent wheels, but at the cost of steering response and clearance issues (especially with wider tires on different wheel offsets) with the double A-arm suspension.
As a rule of thumb: play it safe and don't exceed the overall diameter of the OEM equipment. There are plenty of tire size calculators online to help find the right size.
As it happens, the perfect tire for us would be a 245/35 R18, which only increases the stock tire diameter by 0.89% - easily within the 3% tolerance that OEM traction control and ABS systems allow for tire wear, etc. This would also keep our speedo accurate.
Picking tires first becomes more critical if you decide to run staggered wheels on an all-wheel drive car, which can upset differentials, traction control or ABS.