The Mass Factor
This is what really separates the cars. It isn't just the weight but where it's located. The BMW and the Porsche are similar in heft at 3,230 and 2,976 pounds respectively. The Lotus is a scant 2,077 pounds, but that isn't the whole story.
BMW claims the Z4 M to have 50/50 weight distribution. However, it feels like the car rotates around the engine, which is, of course, forward-mounted. The Porsche has a slight rear bias at 45/55, but feels extremely neutral. There's no real sense that the car wants to pirouette around its center of gravity like most mid-engine cars. The Lotus has a decidedly rearward weight bias at 40/60. It never feels like a pendulum, but it does give an eagerness to turn not found in the others. When exiting turns, the weight in back can be felt pulling the car around, but because everything is so compact near the center, it never feels as if it could get away from you.
The Lotus also takes full advantage of being a smaller vehicle in every way it can. Smaller brakes, wheels and tires all mean less rotating and unsprung mass. What most people don't consider is the much smaller gyroscopic effect of the smaller, lighter tires and wheels. It adds to the already amazing feedback, allowing the car to transmit even smaller nuances in tire/road interface. The giant rubber found on the BMW and Porsche allows for huge amounts of grip, but also numbs steering feel. All that mass just takes the edge off what the tires are doing. -Michael Febbo
Both the Porsche and the Lotus were on factory original tires for the test. The Porsche was on Pilot Sport 2s-one of our favorite tires for fast yet still surprisingly comfortable driving. The Lotus wears Yokohama A048s specifically designed and tuned for this application. The BMW, our long-term tester, had recently received Nitto Invos, which replaced the worn OEM Continental Sport Contacts. The Nittos provided an equal level of grip with a little less noise and improved ride quality.
They performed flawlessly during the canyon running and on the highway. The factory tires led some staffers to believe the car was equipped with run-flats. The Nittos traded the razor-sharp turn-in of the OEM rubber for a touch less sidewall stiffness, yet they still provided accurate feel and were a little more predictable than expected.
The Cayman's PS2s were as grippy and as comfortable as we remembered. It didn't feel as though they had the same high-speed stability as the other tires, but they were definitely the quietest.
The Yokohamas on the Lotus are thinly disguised race tires. It was interesting to drive in different conditions, because the tires really responded well to heat. During slower driving, the tires were slightly cooler and the car moved around a bit more. As temperatures built up with faster driving, the tires kept getting stickier. For race-spec rubber, they provided highly controllable breakaway.
Lotus advises owners not to use anything but the OEM tire on the car. The Exige, being as light as it is, will have trouble generating enough heat to get the most out of other tires. Porsche has a numbers of tires it approves. BMW is a little more open in tire choices but recommends owners stick with tires that meet speed and load indices of the factory equipment. -Michael Febbo