Road Tests

Comparison Test: 2007 Audi RS 4 vs. 2007 BMW M5

Introduction

By Jason Kavanagh, Engineering Editor
Date posted: 03-04-2007

You asked for it, and now it's here. The 2007 BMW M5 is available with a conventional manual transmission, and it's all because of American drivers like you.

BMW will make only 2,000 BMW M5s with a six-speed manual transmission this year, and they will all come to the U.S. BMW purists were outraged when the mad Germans didn't include a manual transmission in the model mix when the new-generation M5 arrived here in 2006, and their outcry forced the hand of the disapproving Bavarians.

Now that the 2007 BMW M5 is here, it turns out that there's just one other German sedan with both a manual gearbox and an engine that makes more than 400 horsepower: the 2007 Audi RS 4.

The 2007 Audi RS 4 and 2007 BMW M5 are practical four-door sedans, yet they are also dedicated high-performance machines. They are sports cars disguised as everyday transportation.

It's the kind of comparison we live for. Never mind sensible transportation; this is all about fast driving.

"M" is for meddling
As soon as we drove it over our favorite test loop in the Santa Monica Mountains, the M5 impressed us. Its variable-ratio steering is precise, and so unlike the active steering of the civilian BMW 5 Series. And the stupendous 500-horsepower V10 gives the M5 the ability to inhale straight sections of road.

Even when the M5 is grinding its tires in the acute corners of the mountains, the car's suspension is in such control that body roll is practically nil, so the transitions between corners are made gracefully and rapidly. When you're driving below the absolute limit, the M5 has few peers in terms of both composure and out-and-out pace.

The 2007 BMW M5's ZF-built, six-speed manual gearbox has slightly different ratios than that of the regular 540i, but it has the same long shift throws and notchy-yet-positive gear engagement typical of BMW manuals. The clutch pedal effort is surprisingly light despite the challenge of controlling the V10's 500 hp and 383 pound-feet of torque.

Press on harder and the BMW M5's Dynamic Stability Control (DSC) takes hold smoothly yet sternly, and finally the fun bleeds away just when the going gets good. "M Dynamic Mode," the most permissive setting for the M5's DSC, allows the M5 to be driven right up to the limit until you might get a whiff of understeer as you turn into a corner. But the slip angle of the rear tires (let alone any wheelspin) is kept resolutely in check by DSC's manipulation of the throttle and brakes.

Oh, but we switched off the stability control, right? Sour news, Jack; the DSC cannot be defeated in a BMW M5 when it's equipped with the manual transmission. No powerslides or burnouts, and you can also forget about the kind of throttle inputs that might influence the M5's cornering attitude.

Suddenly any notions you might have of flinging the BMW M5 around a local road circuit at a track day turn to vapor. Apparently the Germans are unaware that track days are pretty common in America, and that a BMW M5 driver is just the sort of guy who knows this.

So forget about a big rear-drive sedan that is keenly responsive to your throttle foot in the corners. When you're driving with extreme commitment, this car's a dud.

A sheep in wolf's clothing
BMW tells us that the DSC in the six-speed M5 can't be disabled because of warranty concerns associated with aggressive launches.

If BMW was worried about the effect of wheel hop on drivetrain durability, we would have preferred that the system simply limit wheelspin (or launch rpm) in 1st gear only. As far as at-the-limit driving, we think BMW has messed with the idea of what the M5 concept is all about.

The likely explanation might be that a low-volume afterthought like the M5 with manual transmission doesn't carry much weight when it comes time to commandeering BMW's engineering resources. Simply removing a line of code from the DSC menu in iDrive might have been a temptingly fast (and cheap) way for BMW to mitigate any risks associated with bringing this niche model to market in the U.S., where the Germans are fearful of litigation.

With no workable way to defeat DSC, we selected M Dynamic Mode for all of our performance testing. The M5 manual achieved 0.83g on the skid pad and 68.4 mph in the slalom, 0.1g and 0.8 mph shy of the performance achieved by the SMG-equipped M5 we tested a year ago.

These are decent results, but the Audi did better. The RS 4 posted 0.88g on the skid pad and turned 69.0 mph through the slalom cones.

Two engines, 72 valves, 16,500 revs
When you match up the BMW M5 six-speed in a speed test with the Audi RS 4, it's no contest. The 3,903-pound RS 4 gets to 60 mph in 4.5 seconds, and then sprints to the quarter-mile in 13.0 seconds at 107.3 mph. Yet the M5's unrelenting thrust borders on lunacy, as the 4,122-pound sedan tears to 60 mph in 4.4 seconds and then covers the quarter-mile in 12.7 seconds at 113.6 mph.

In fact, the manual M5 is quicker than the SMG-equipped M5 we tested. With the SMG, the M5 hit 60 mph in 4.8 seconds and ran the quarter in 12.8 seconds at 115 mph.

Though the M5 SMG seven-speed has a faster trap speed in the quarter-mile thanks to its closer-ratio seven-speed, the brutal clutch takeup in the SMG-equipped M5 renders it difficult to produce a clean launch, hurting its elapsed time. So the SMG can be beat in a straight contest of speed.

Unleashing this sturm und drang puts tremendous demands on the brakes of both cars, and neither one disappoints. The M5 comes to a standstill from 60 mph in just 114 feet, and the RS 4 stops in just 2 feet more. The ABS system in each car cycles with rapid-fire speed.

The Ingolstadt upstart
Audi's RS 4 is a tweener. In terms of physical size, it competes with the BMW M3, though there's not yet an M3 sedan available in the U.S., of course. Meanwhile, the RS 4's base price splits the difference between a BMW M3 and an M5, and the same goes for its horsepower rating.

Tweener or not, the 420-hp RS 4 had almost no trouble keeping up with the 500-hp M5 on the real-world roads of our mountain test loop. More grip and confidence in the Audi's chassis is part of the reason; the other is the combination of all-wheel drive and a stability control system that can be fully switched off when you like.

While you're charging into a tight corner, you can chop the RS 4's go pedal aggressively to help pivot the nose toward the apex, dial out some steering lock, roll in a lot of throttle and then just hang on. When it comes to exiting 2nd-gear corners, the Audi has explosive acceleration on tap, nullifying its 80-hp deficiency compared to the M5.

Audi's short-throw close-ratio gearbox delivers blazingly quick shifts and is a perfect match for the heroic V8 engine. This 4.2-liter jewel revs effortlessly, delivering a broad swath of torque across the rpm range and producing a spine-tingling exhaust note besides.

Like a Mitsubishi Evo, the Audi's faithful, communicative chassis goads you into leaning on the tires ever harder until the limit of adhesion is only a memory. You discover varying degrees of understeer, but the RS 4 responds well to balancing the chassis at the limit with the throttle, and a rear-biased 40:60 torque split helps out.

The RS 4 is enormous fun, and a much more engaging drive on our favorite roads than the M5. There's an honesty to the RS 4, a willingness to play that cannot be elucidated by bench-racing its specification sheet.

In comparison, there's a sense of artificiality to the BMW M5, even as fleet and composed as it is. Maybe it's the extreme measures taken by BMW's engineers to keep their 4,000-pound sedan from not feeling like one, but after driving the RS 4, the M5 felt strangely detached from the road. Fast, but aloof.

Hand me your cape and scepter
It's a terrifically bad idea to design a car with the weight of a V8 engine hung entirely over the front axle. It hurts weight distribution, generates a lot of polar moment of inertia, overworks the front tires and brakes, upsets ride quality and makes the steering heavier.

None of this seems to matter in the 2007 Audi RS 4. Using just such a layout, Audi has managed to out-fun the 2007 BMW M5, one of the world's most respected driver's cars. And it's done so for tens of thousands of fewer dollars.

The RS 4 didn't succeed all alone, though. It had help from the competition.