Silken fluidity perfectly describes the character of the powerplants, steering, and brakes on the 2006 BMW 3 Series. We sampled the new 325i Sport with a six-speed manual transmission and the 330i Sport with a Steptronic six-speed automatic transmission on public roads. At Pennsylvania’s BeaveRun raceway, we also flogged a 330i Sport with a six-speed manual around the road course.

That car was our favorite. It pulled strongly and smoothly all the way to redline, it’s 18-inch Bridgestone run-flat tires gripped extraordinarily well with a slight tendency toward understeer in tighter hairpin turns, and its Active Steering system, which reduces the degree to which the wheel must be turned to negotiate sharper turns such as when parking, proved its mettle in the slalom course. Even the brakes worked flawlessly, lap after lap, never hinting at fade or suffering pulsation in the pedal. Of course, it was in the mid-40s and windy at BeaveRun, so the rotors and pads had plenty of time to cool between applications.

Our 325i Sport with a manual was quite entertaining, and returned 24 mpg during our trip to BeaveRun from downtown Pittsburgh, despite the fact that we drove it like somebody else was paying for the gas. Though the 325i now makes almost as much power as the old 330i, the redesigned 3.0-liter inline six manages just 185 lb.-ft. of torque, making it feel a bit sluggish. Gratefully, rowing gears to access the power is sheer bliss, the stick gliding from gate to gate and the clutch delightfully light and easy to engage, unlike with previous BMW manual transmissions which had a hair-trigger clutch and a bit too much resistance at the gates. BMW has even added a hill-holding feature to prevent excessive clutch slipping on hills. The 325i Sport’s 17-inch Pirelli Eufori run-flat tires were a little loud, and we detected more wind noise than expected right where the windshield pillar meets the roof, but otherwise there’s little to complain about. The 325i is just as much fun to drive as the 330i, it’s just not as fast.

Our least favorite, the car that most people are likely to buy, was the 330i Sport with the Steptronic automatic. And just to clarify, labeling this our least favorite 3 Series is like suggesting that Chubby Hubby is our least favorite of the three best Ben & Jerry’s flavors lining the freezer case at the local Trader Joe’s. This car rode on 18-inch Bridgestone run-flat tires that were quieter than the 325’s Pirellis but provided a harsher ride thanks to slightly lower sidewall profiles. Plus, when driving hard, this car’s transmission sometimes delivered downshifts that came a split-second later than we wanted. We could have shifted for ourselves using the Steptronic feature, but BMW insists on using a non-intuitive tap-up for downshifts and tap-down for upshifts, so we left the selector in fully automatic mode. Nevertheless, we extracted a 20.2-mpg average from the 330i, which makes 40 more ponies and 35 more pound-feet of torque than the 325i’s respective 215 and 185 ratings.

No matter which 2006 3 Series we drove, the Sport suspension setup proved a gift to enthusiast drivers and a curse for luxury seekers. The car doesn’t ride roughly, but it does ride stiffly, and every little ripple in the road gets telegraphed to the cabin. Another trait we disliked was the tendency, on undulating or heavily patched road surfaces, for the front tires of the both the 325i and the 330i to tug from side to side. If you’re not planning to drive the 2006 3 Series in the manner for which it is intended, we’d recommend skipping the Sport package and sticking with the smaller standard tread.

BMW also offered a chance to drive a 330i Sport with one of the run-flat tires deflated. Though we guessed right off which tire had no air, we wouldn’t have been able to tell on the short road course designed to prove that, even when running on a flat, the new Three is a secure performer.