New 6-speed manual transmission

While the 2.5i model's standard transmission is a 5-speed manual, standard in the 3.0i is a brand-new 6-speed unit.

Weighing no more than the 5-speed of the previous Z3 3.0i, this "gearbox" incorporates refinements for even greater driving pleasure (and BMWs are already known for excellent manual transmissions):

• New, even more effective synchronization of shifting
• Sportier shifting, via a 20-mm (0.8-in.) shorter shift lever and 10-mm (0.4-in) shorter shift "throws" from neutral to each gear.

Optional Steptronic 5-speed automatic transmission

Available for both models is the 5-speed STEPTRONIC unit that has garnered repeated praise from auto critics.

Like all other current BMW automatics, it incorporates a Sport mode that programs automatic shifts at higher engine speeds; like nearly all of them, it also includes the STEPTRONIC system, which lets the driver choose shifts manually by "flicking" the lever rearward or forward.

Though basically similar to the transmission offered in other BMW 6-cylinder models, it has been specially tailored to the Z4 with a "tighter" torque converter (thus a more direct response feel) and specific shift characteristics.

Optional Sequential Manual Gearbox

Last year saw introduction of the Sequential Manual Gearbox (SMG) as an option for M3 models; since its debut, SMG has become popular with M3 buyers.

To be offered in both models as of April '03 production, the Z4's SMG differs from the M3 unit in several respects:

• In its Automated shift mode, labeled D , it offers a single shift mode vs. M3's five.
• In its Manual mode, there are two shift programs vs. M3's six.
• In contrast to the M3's program selector, a Dynamic Drive Control button on the console selects the Sport mode for manual shifting.
• The Neutral position is labeled N instead of 0 3.

Thus the Z4 SMG is engineered for performance, convenience and (above all) driving pleasure in the context of these high-performance "regular" BMWs, as contrasted to the super-performance M3s with their exotic BMW M 333-hp engine.

Yet the fundamental concept is the same: electrohydraulic shifting applied to a 6-speed manual transmission and offering the driver a choice of automated or manual shifting. In D, shifts are programmed for "normal" driving, with the accent on a relaxed, unaggressive style - though the SMG automatically adapts its shift points to brisk driving. "We worked long and hard," says drivetrain engineer René Chlumsky, "to develop the appropriate characteristics for a sport roadster."
In M, basic operation is as with the M3 SMG: The driver shifts gears at will, either by tipping the shift lever or actuating shift "paddles" on the steering wheel. As in D, electronic controls and electrohydraulic action let off the accelerator, declutch, change gears, re-engage the clutch and "step on the gas" - all in a perfectly orchestrated sequence tailored to how gently or hard the driver is driving at the moment.