BMW must think its recent cars strayed too far from its sports car ethos, as it is bringing back the "s"--denoting sport--to select models. We previously reviewed the, and now get a look at the new sport roadster, the 2011 BMW Z4 sDrive35is.
This roadster comes loaded to the gills with BMW's performance technology, all surprisingly standard for a company that charges extra for every little convenience feature. But the Z4 sDrive35is also makes a few compromises for comfort that undercut its sporting nature.
The Z4 is a good-looking little roadster, and we noted a lot of attention from bystanders. Its retractable hard top is a best-of-both-worlds solution, offering the security and weather protection of a hard top plus the fun of open-top driving. The top folds into the trunk with Transformers-like mutability.
The retractable top doesn't come without consequences, however. First of all, when folded away into the trunk there is very little storage space left, and what there is can be explored only with the type of robotic equipment being used on BP's Gulf oil gusher.
And although BMW takes its sports car dynamics very seriously, the retractable top throws off the car's balance one way or another. If BMW engineered the car for a 50/50 weight distribution with the top up, the front will be light with the top down, and vice versa. A soft top would have had less impact on the car's weight distribution.
BMW compensates for the weight change with its dynamic suspension, an option on just about every other BMW car, including the M models, but standard in the Z4 sDrive35is. When set to Sport or Sport Plus, the suspension lowers by almost half an inch. This suspension uses sensor input to adjust each of its dampers independently, making them softer or more rigid depending on the road and what the driver is asking of it.
As with other recent BMWs we've tested, the Z4 sDrive35is exhibits a dual character; it's perfectly comfortable to drive over a variety of roads on a daily basis, and is willing to get down and act mean on a track or in the twisties. In Normal mode, the suspension is loose and compliant, but far from soft. Going to Sport or Sport Plus mode, we didn't notice a sudden, dramatic difference, but the car becomes more rigid.
We threw the Z4 sDrive35is into corner after corner, finding that it offered so much grip and such good control that we could maintain very high speeds. The car encouraged us to push harder and harder, and we were impressed by how well it stuck to the pavement, without allowing much of the tail wag that larger BMWs use to rotate in a turn.
But getting close to the limit, we repeatedly found understeer; the car headed toward a wall or cliff instead of going in the direction we pointed the wheels. This was surprising, and not something we would expect in a BMW. As it happened with the top up and down, we ascribe it to BMW finding a less-than-perfect compromise to the moveable top's weight distribution changes.
Along with suspension settings, the Sport and Sport Plus modes put the throttle at a more aggressive level, the latter also turning down traction control. The Z4 sDrive35is gets the same engine as the 335is, a 3-liter direct-injection straight-six with twin turbochargers. Each low pressure turbocharger forces air into a set of three cylinders.
Tuned for the Z4 sDrive35is, this engine produces 340 horsepower and 332 pound-feet of torque, which is significantly more than the standard Z4's 306 horsepower. And like the 335is, the Z4 sDrive35is has an overboost feature, which temporarily pumps the torque up to 369 pound-feet, putting 0-to-62 mph acceleration at 4.8 seconds.
The exhaust note was higher pitched than that of the 335is, and was not to everyone's liking on the Car Tech staff. It is quite distinct.
Another surprising standard feature is the seven-speed double-clutch transmission (DCT). A traditional manual transmission is not even available in the Z4 sDrive35is.
In standard drive mode, the DCT reaches for the gas-saving higher gears, and feels a lot like an automatic transmission. In Sport mode, it keeps the engine revs higher, and shifts down a little more aggressively, but not enough for our tastes. Powering out of a corner, the DCT had only dropped down to fourth gear, leaving the engine far from peak power at 3,500rpm.