BMW's latest M Roadster succeeds in two related ways: It grows some, ahem, "whiskers" on the otherwise masculinity-challenged Z4 with butch styling; and secondly, the implicit promise that the body makes is kept with honest-to-M3 muscle. More than a mere dress-up kit or sport pack, the 2006 M Roadster takes the finesse inherent in the Z4's already competent, baseline chassis and infuses it with heart-pounding performance derived from the M division's vast knowledge — with a little help from parts-bin raiding.

Cute goes bad
The M Roadster's more chiseled M-spec styling forecasts its speed and agility with a manly bravado the Z4 donor car only insinuates. Where the Z4 looks like an overreaching design student's idea of a roadster, the M Roadster's unique sculpting identifies it as the epitome of a real one.

At the front, its unique grille and aggressive fascia allow for better engine and brake cooling. Standard self-leveling xenon headlamps (with BMW's "corona" rings) light the way. More than just a fashion statement, the 18-inch M double-five-spoke alloy wheels are surrounded by serious Continental ContiSport Contact tires that are not (thankfully) heavy run-flats. Instead, in the trunk you get a compressor and a can of goo to get you to the nearest shop for tire repair/replacement. The otherwise amorphous aluminum hood features longitudinal creases that must've been painstakingly located to precisely align with the driver's sight lines.

Out back, there's an M-specific bumper ensemble with cutouts for the telltale quad-exhaust tips and a real air diffuser. The '06 M Roadster showcases new, adaptive LED taillamps (also on '06 Z4s) that light more brightly the harder the brake pedal is pushed. The overall effect of the M treatment to the exterior is supremely satisfying. Several times while driving the M Roadster, I saw lesser Z4s and my chest swelled with the satisfaction that comes from the exclusivity that all M variants offer their buyers. Riffing on the Z4's flame-surfacing (on a bar of soap) design netted a shape that looks like the car the Z4 should've been from the start.

Beyond kit
While it's apparent from the outside the M Roadster is more dedicated and antagonistic than the Z4, there's more — a lot more — going on under its taut skin to give it a bite as serious as its bark. The M Roadster's brake system is part of the M3's Competition Package, and standard on the M5. The trick hardware reduces unsprung weight, enhances cooling and resists fading and warping when pushed to the limits this car is capable of producing. The 110-foot stop from 60 mph doesn't begin to indicate how well the brakes communicate and work, repeatedly and consistently.

The widely celebrated cast-iron "S54" DOHC inline-six engine, replete with BMW's steplessly variable valve timing, is transplanted from a current M3. It produces three fewer horsepower than in the M3 (Roadster exhaust particulars), and makes an ample 330 hp to propel our measured 3,277-pound roadster to 60 mph in 5 seconds flat. The 3.2-liter engine has a linear, almost electric quality to it so that any rev range feels as capable as any other right up to the 8,000-rpm fuel cutoff. With its low reciprocating mass, immediate throttle response, high compression ratio (11.5:1) and reedy exhaust note, there's no mistaking the M motorsport connection.

In raw terms, however, compared to the previous Z3-based 315-hp M Roadster, the new car shows only a negligible improvement in outright acceleration. The likely culprit is the Z4-based car's added weight and slightly different gearing. Depending on whose "curb weight" is referenced, the Z4 M is about 150 pounds heavier than the Z3 M. That difference cancels out the additional 15 hp for a no-sum gain. Don't worry. Nobody will ever say the car is slow. It'll convince V8-minded muscleheads and turbo four-bangers of the merits of a BMW inline six with one blast through the gears. The M Roadster still propels about 9.8 pounds with each horse, but how those extra pounds are carried around corners is a different story.

Handled
When our tests focused on handling, the script changed dramatically. Unlike the twitchy, previous M Roadster, the new one is chock full o' costly bits from the M3's suspension and driveline. The effect is, to say the least, pleasingly capable.

To accommodate the M3's burly rear differential, a new subframe was fitted to the Roadster. That differential (fitted to the M5 as well) features a variable locking mechanism that fluctuates the amount of lock-up between the two rear wheels based on their relative speeds. The more one wheel spins, the more locked together they become. While this syst***s wet-weather benefits are obvious, there's also a noticeable improvement in how the car behaves when driven hard out of corners at wide-open throttle. Combined with its M3-derived rack and pinion steering plus front and rear suspension, the M Roadster's at-the-limit control is sharper than an M3's (that always feels like it's on its tippy-toes), head and shoulders above its M predecessor (which comes off as dangerously edgy) and simply in a different world from the commuting-friendly Z4.

A 69.6-mph slalom speed is only a numerical indicator of how confident the M is. Regarding the car's balance, test-driver Josh Jacquot emoted after his slalom runs, "spectacular limit-balance in the slalom test's high-speed transitions," but he continued, "communicative steering and a meaty steering wheel that should be standard-issue on every sports car." Like a circular black banana, the "girthsome" leather-wrapped wheel forces a relaxed grip and supplies volumes of useful tire/surface information to the driver.

Conspicuously absent
We find it exceptionally interesting that this M car features a back-to-basics hydraulic steering rack (no electric assist, no variable ratio, no over-engineered "active steering") and that the company's self-touted auto-clutch manual "SMG" paddle-shifter transmission is not even an option. An evolved version of a ZF Type H six-speed manual transmission completes the man-machine symbiotic relationship. While an SMG might represent impressive "because-we-can" technology, there's nothing rewarding in pulling a paddle for an upshift; no self-congratulations when the car executes one of a thousand perfectly matched-rev downshifts, and we've never driven a BMW SMG that was as smooth as we were from a dead stop in traffic. It seems that when BMW really wants to get it right, old school is still the best way to go. It's redeeming to witness that BMW hasn't forgotten how to "do" a proper steering system and manual transmission.

An excuse to just take a drive
Put all this trick hardware under your butt, lower the fully lined one-touch convertible top, find yourself a winding farm road or mountain pass, and you'll discover why the M Roadster commands an entry-level price $10K over a 2006 Z4 3.0si. The M Roadster inspires a gratifying three-way conversation between the driver, the car and the road that's about as perfect as it gets. Every bend becomes a really good one. Each approaching corner becomes an excuse to heel-toe downshift. Learn to trust it, and the M Roadster becomes an invisible force that carries your consciousness down the road as rapidly as you dare. If you can both afford and appreciate the differences, the M Roadster is worth the extra M-money over a Z4.

Twitchy or responsive?
Even more than the previous-generation M Roadster, the newest Z4-based performance car reveals to its driver all the mindless sloppiness that has crept into his non-rigorous commuting chores. This car feels like the Z4 the BMW engineers and test-drivers originally intended to build before the focus groups electrified the steering, softened its edges and added slop to make it less taxing to drive. The M Roadster's theme is immediacy: quick steering, instant brakes, direct throttle and caffeinated ride.

The M Roadster teaches its driver to tighten up his game. Don't downshift without a proper throttle blip. Don't glaze over in traffic and in a false emergency stand on the brake pedal unless you really mean to stop. Don't even sneeze if you're the type who sometimes uses his knee to steer while you remove the top from your café latte. Driver laziness and ham-fistedness are not only discouraged, they're punished with an immediate response from the car…and we love that. As the enthusiast arm of Edmunds.com, Inside Line has great respect for car companies with the guts to build a car for those who love to drive cars.

Clubbing
With all its intuitive athleticism, the M Roadster gains membership to an exclusive club of sports cars whose interview process weeds out wannabes, poseurs and cars that almost but never quite achieve the complete package.

Oftentimes, sporty cars offer great handling, but lack motivation (Mazda MX-5 Miata). Others provide ample firepower, but can't find their way around corners (any AMG product). Unlimited membership declined to both applicants. The M Roadster is granted true weapons-grade sports-car status with its masterful blend of engine, chassis and design. The whole package works in harmony. The M Roadster is so good that we'd put it in the same club, albeit in a different division, with the Porsche 911 Carrera 4, Ferrari F430 and Corvette Z06.

Respectively, each one of those cars represents the best that that configuration can be. For a sub-100-inch wheelbase, front-engine/rear-drive convertible, the 2006 BMW M Roadster is about as good as it gets. The M division turns the Z4 from a question mark into an exclamation point.

In BMW's 2006 M Coupe, it's all about the steering wheel.

As anyone who's ever driven a BMW knows, the steering wheel represents a crucial element in cars wearing the blue-and-white roundel. In other automobiles the steering wheel merely serves as a directional control device. But in BMW automobiles it's more like an ergonomically shaped syringe — injecting the car's soul directly into the driver's cerebellum.

In the new M Coupe, the strikingly large diameter of the rim is wrapped in supple leather, providing a sumptuous yet brawny place to land your grip. That same luxuriant, meaty feel is maintained throughout every aspect of the car — from its hefty steering effort and shifter action to its heavily bolstered leather seats to its love-it-or-leave-it styling.

Brewed with a 'tude
This overtly edgy character is paired to one of the world's preeminent engines. As an heir to BMW Motorsports' magnificent 3.2-liter, inline-six drivetrain, the M Coupe could rightly be described as the M3's little brother. This choice power plant makes the M Coupe transition with 330 horsepower and 262 pound-feet of torque intact. And it continues to provide unrestrained gyrations up to the 8,000-rpm redline, along with a broad torque band that thrusts the car forward with the immediacy of a 1960s muscle car.

But where the M3 went to finishing school on a full-ride scholarship, the M Coupe dropped out early, told his guidance counselor to pound sand and hooked up with a traveling blues band. This attitude is apparent the moment you fire up the engine. A low-frequency rumble, more in line with Milwaukee V-twins than Munich straight-sixes, has supplanted the M3's high-pitched exhaust squeal. Burly shifter action has long been an M3 hallmark, but the M3's optional SMG tranny is not lurking on the M Coupe's option list to rescue wannabe Villeneuves from the task of actually driving this feisty two-seater.

A track-tive design
We were fortunate enough to do just that around the 4 miles and 14 turns that make up the Road America race circuit in Elkhart Lake, Wisconsin. With an aluminum chassis as rigid as Republican legislation riding on
18-inch M Double-Spoke alloy wheels, the M Coupe offers the kind of instant response and at-the-limit confidence normally associated with track-ready models like the Lotus Exige. Numerous tweaks to the
base Z4 coupe, including a wider front track, stronger rear subframe and hydraulic power steering (the Z4's is electric) conspire with M-specific suspension calibrations to create an incredibly tossable, leather-lined
go-kart wearing BMW badges.

Total vehicle weight is 3,230 pounds, with an aluminum hood and upgraded aluminum front suspension pieces contributing to the car's svelte nature and 50.2/49.8 weight distribution. Slowing the M Coupe is accomplished via the same brake system offered on the M3 Competition Package. That means dual-compound, cross-drilled and ventilated rotors at each corner, with 13.7-inch discs up front and 12.9-inch units in back. Tire specifications are yet another point of deviation between the M Coupe and lesser models, with the base Z4 Coupe's run-flats replaced by traditional Z-rated Continental tires sized 225/45-18 (front) and 255/40-18 (rear).

Techno-savvy
Like many M products the M Coupe features two throttle-response programs. The default "Normal" setting is in use whenever the car is started, but pushing a console-mounted button easily accesses the "Sport" mode. This mode increases the ratio of throttle opening to pedal movement and, in conjunction with BMW's double VANOS variable valve technology, provides nearly instantaneous access to the engine's highest performance levels.

There's a potential dark side to this much power and torque in a lightweight, short-wheelbase coupe, but BMW has tried to ensure those 330 horses cause more joy than sorrow. A mechanical limited-slip differential uses viscous fluid to balance power between the rear wheels, and Dynamic Stability Control can do everything from reducing engine torque to applying individual brake pressure when it senses abnormal understeer or oversteer. Of course the latter feature can be deactivated for those times when you want to experience oversteer, a circumstance the M Coupe seems rather well suited to.

Can't escape its roots
Despite the M Coupe's somewhat gangsta attitude — at least in comparison to the rest of the BMW family tree — there remains a wealth of premium features on both the standard and optional equipment lists. Every car, for instance, comes with automatic xenon headlights,
rain-sensing wipers, heated outside mirrors and automatic climate control. For buyers who like their iron fists in a fully lined velvet glove, there are
fat-cat items ranging from DVD navigation to three-stage heated seats to walnut interior trim. There's even a premium THX-certified audio system with eight speakers and dual subwoofers. Pricing starts at $49,995, which includes the $695 destination charge.

But don't let the Nappa leather fool you; the 2006 BMW Z4 M Coupe isn't a car for posers. Ride quality is about as stiff as any BMW we've driven and, as stated, steering and shifter action require a firm hand — make that a firm hand, arm and shoulder. But if you actually buy ultimate driving machines because you enjoy driving, the car will not disappoint.

In fact, while we know that guidance counselor won't admit to it, little M has made him proud.