California State Route 198. When we discovered that beautiful ribbon of road during the first Best Driver's Car competition in 2011, we knew the combination of fast sweepers and slow hairpins, on- and off-camber turns, chattery pavement and big midcorner bumps, all clustered on a traditional hill climb and staged in triple-digit heat, would be the ultimate test of a performance car's mettle.

Conversely, Route 198 is exceptional at revealing a car's flaws. Undersized brakes, inadequate transmission calibration, and unfinished suspension tuning have all been exposed here.

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In the Supra's case, it was the latter. Driven to the limit, the Supra's rear suspension couldn't cope with 198's rough asphalt, braking-zone undulations, and midcorner bump-steer moments. Under such duress, the Supra felt nervous and unsettled—always trying to regain its footing rather than preparing for the next corner. Those rear-end oscillations made the steering twitchy and nervous. Even pro racer Randy Pobst had a "moment" on 198, which really tells you something.

The M2, by contrast, shone brightly. It easily absorbed and ignored those same grip-challenging bumps as it charged up and down the hill. Where the Supra was busy chasing its tail, the M2 was already showing its taillights. When the going got tough, the Bimmer dug in and drove like that Competition badge means something.

This is precisely the opposite of our experience during a previous comparison test, held on another one of California's mountain highways, State Route 39. Although no one would accuse SR-39 of having perfect pavement, it has none of 198's big bumps in the worst places. Rather, its small ripples of cracked pavement got the M2 Competition out of sorts but didn't faze the Supra.

Although we found the Supra to be tail-happy on Route 39, two of the three judges in that previous comparison agreed it was predictable, easily controlled, countered with slower, more deliberate steering inputs, and, most of all, fun. All three judges felt the opposite about the M2. In short, we judge the cars we get on the roads we drive them.

Foul play between tests? None we could find. We tested the same M2 both times. The Supras were different, but after 198, when we worried there might be something wrong with the BDC Supra, we sent it to a dealer. The dealer found no mechanical or alignment issues, which some judges were certain existed.

With a clean bill of health, we put the Supra on the nice, smooth Laguna Seca, and suddenly the old Supra, the comparison winner, was back. We can only conclude, then, that the new Supra is particularly susceptible to large bumps in the braking zone and midcorner, and it took a road like 198 to expose this nasty shortcoming.