The success of 5-series was driven by Wolfgang Reitzle, the product development head then. This perfectionist asked everything to be done to the highest satisfaction - engines, suspensions, controls, build quality .... but what separate the 5-series most from other BMWs is the forward-thinking styling, which does not show any trace of aging after 6 years. This is very unusual for a sedan. Think about it, other than the 5-series which car have a styling last so well ? one of the secrets of its resistance to aging must be the superior build quality - also thanks to Mr. Reitzle who was in charge of the production side as well. Exterior or interior, the car feels solidly put together while material used in the cabin is first class. Audi might surpass the BMW in this respect, but it can't match the BMW's design - trademark driver-oriented center console, warm colour trimming - and absolute comfort. 

Although not as roomy as the class-leading E-class, there is a lot of space up front and rear for all kinds of people, but it is the ride quality that makes it more comfortable than its German arch-rival. The aluminium Z-axle rear suspension attaching the rigid body provides supple ride over variety of roads. British journalists (and public) particularly praised its ability to smoothen bumpy B-roads underneath. Until now, there is still no rivals can deliver this kind of ride quality. At the same time, the 5-series is of course renowned for handling - again, none ever come close. Without tuning the suspension too firm, it is amazing that the 5-series feels so nimble in twisty roads. It suppress roll well and grips hard in corner. The steering for six-cylinder models are so communicative, direct yet free of kickback. Other controls are tuned so precise to keen driver's like - throttle, brakes, superb manual box (Steptronic is good but not so tempting as the manual) ... all these are packaged in a well insulated cabin. 

But the beautiful engine note is not insulated to the extent that you cannot enjoy them. As always, BMW's inline-6 produces lovely music as well as good performance. The new M54 series undoubtedly push that to higher level, especially is the 3.0 unit which pumps out a class-leading 231 horsepower and 221 lbft of torque (do you really believe Jaguar's 240 hp rating ?). Not only as smooth as before, now it pushes the car to 60 mph in 6.8 second (Autocar even said they measured that in wet). You might remember the early 528i was nearly as quick but note that after 6 years BMW has added 135 kg extra equipment (including ESP, more airbags and navigation) and other enhancement to the car !  

In contrast, V8 models - 235 hp 535i and 286 hp 540i - are quite unnecessary to me. Not only because of small gain in performance, the main reason is that they employ recirculating-ball instead of rack-and-pinion steering for space reason thus compromise a bit steering feel. Bigger engines also make them less sharp to handle. However, compare with V8 rivals they are still capable to retain the top spot. 
 

BMW M5

The latest generation is no longer powered by the M1-derived straight six. Base on the 540i's 4.4 litres V8, engineers enlarged the bore and stroke thus obtain a displacement of nearly 5 litres (4941c.c.), raise the compression ratio to 11.0 : 1, then add the Double Vanos variable valve timing which was originated in McLaren F1's V12 and has been already standardised in the latest straight sixes. Still, this is not a real M power (no relationship with motorsport experience) thus I'm slightly disappointed with its average 80hp/litre specific output. Considering a '85 Testarossa managed just 10 horses short from the same capacity, I believe there's still space for improvement without needing to enlarge the V8 again.  

However, capacity compensates the lack of efficiency. Who dare to say 400hp as insufficient ? The supercharged Jaguar XJR has 370hp while Mercedes' 5.5 litres E55 has 354hp. Although the extra capacity of the Mercedes gives it some advantage in torque (391lbft versus 369lbft), the BMW has 6 speed manual transmission instead of 5 speed automatic, so the M5 still accelerate faster. I expect it could sprint to 60mph in 5.1sec, versus Mercedes' and Jaguar's 5.3sec. At higher speed, the power advantage of the high-revving V8 could probably widen the gaps. Top speed, well, are all electronically limited to 155mph for all of them.  

Apart from the engine, M5 differs from the normal 5 series in many aspects. First of all, as seen in the pictures, it has an aggressive air dam and air intake in the front, also side skirts, different rear bumper and a tiny rear spoiler at the boot lid. Ride height has been dropped 15mm in front and 10mm in the rear. The new air dam alone generates 40-45kg down force when the car is travelling at 150mph. Even with wider tyres, M5 still managed a reasonably good drag coefficient of 0.31.  

Then, as expected, the suspensions are stiffened. Tyres enlarged to 18 inches, 245/40ZR18 in front and 275/35ZR18 in the rear. To cope with the increased weight (Engineers did not try hard to keep fit, thus result in 1720kg, or 135kg in addition to 540i), large diameter brakes - 345mm in front and 328mm in rear - were employed to provide 911-level of stopping power.  

However, the most interesting feature of the new M5 is the "Sport Mode". When you turn the switch in center console to Sport Mode, the electronic damping suddenly turns to hard setting, steering's power assist reduces, and moreover, the electronic throttle sharpen its response. From close to full open it takes just 120ms, faster than any driver could manage manually. Switch off the Sport Mode and the car will becomes more civilised and comfortable.  

According to sources who tested the M5, driving the car is an exciting experience. The powerful V8 is flexible at low speed thus requires less gearchange from the slick Getrag 6-speed than say, M3. When driving in Sport Mode, the  engine is very responsive. Once the rev enters 5,000 rpm, the engine goes wild and this could be the best moment of your life until the 7,000 rpm cut-off.  

The car handles suprisingly well even if you ignore its weight and dimensions. It seems to have unlimited grip, especially the DSC stability control is very well sorted that it only assure you're inside the cornering limit safely, unlike some system which intervene too much and ruin the driving pleasure. The body control and balance are first class, steering is the most responsive and communicative among rivals. Not only that, one tester even said its steering return to the level of the original M3, making the current M3 feels undesirable. When compare to E55, the BMW seems like a mid-engined supercar while the Mercedes obviously feels bulky. Even so, M5 rides more supple than E55, thanks to the 5-series' aluminium suspension arms which reduce unsprung weight.  

Besides, the normal 5-Series also donates many good things to the M5, such as the supreme driving position and seats, the spacious rear seats and the good look.