So, there we were in Alicante. Heinz Krusche opened his technical discussion on the E89 Z4 with a little background behind the project. This was revealing in itself.

We spoke in the lobby of the launch hotel. Once we’d got drinks (Krusche: cappuccino. Me: OJ. PR men: water), it was down to business. When did development of the E89 start?

3 years ago, said Krusche, but they only started drilling down to production finites 18 months ago. Prior to that, they were assessing 2 types of car – both ‘flexible’ roof and hard top. Interesting… as was the revelation that there was a philosophy change with the E89, towards ride.

This had to be balanced with an internal BMW edict, that every single car has a different concept to one another. Crucial point, this: just as the 5 cannot simply be a shrunken 7 or a big 3, so the Z4 should not be a quasi-M, or a 135i Coupe with 2 less seats.

Much of the on-road testing happened in Munich – specifically, the country roads around the factory. They’re twisty enough to be a good base. Sweden’s Arjeplog was for low-friction testing, while Miramas was the base for dynamic stuff.

‘We also visit the Italian Dolomites 4 times a year, for big department handling tests.’

Specifics on that new chassis philosophy, explained Krusche, centred on a shift in thinking within BMW, that has been in place since the 1 Series Coupe. In a nutshell, to go softer on the springs, but stiffer on the dampers.

The ICM chassis controller helps, especially on cars with Adaptive M suspension. Krusche says that here, ICM is not as all-encompassing as on the 7 and X6, but is still a trick bit of chassis software centralisation. Bosch’s latest ESP 8.0 also brings finer finesse than ever.

2 different chassis setups were engineered; standard and Adaptive M. the fact that ‘Comfort’ Adaptive M is even more comfortable than the standard suspension, yet ‘Sport +’ even sportier than the E85 Z4, is crucial to its appeal.

‘It widens the breadth of the car’s abilities,’ says Krusche. For just £930? Tick the box for me, definitely…

Before we got into the real deep stuff, I asked Krusche who’s responsible for testing it all and pulling it together. Driving gods, such as him? Partly, he answered.

‘But we also have people who are not such good drivers. They are brilliant engineers, yet drive more like the average guy on the street. Their input is crucial, too.

‘This is how we make cars that are great to drive by everyone, not just race car drivers.’

Krusche. The most savvy dynamics engineer in the industry?

BMW chassis secrets

NEW: BMW Z4 photo stream on Flickr

Pre-launch impressions: BMW Z4 2009

Heinz Krusche is BMW’s chassis guru. I’ve met him several times, and always enjoyed top insight from him (not least his tales of how he keeps DSC turned on for the road – but ‘always’ turns it off when on track…).

Such people exist in every car company, but they don’t always have the power of Krusche.

He wields the same sort of influence as Jost Capito at Ford. There’s another genial genius – and look at how well Fords drive. Lotus, too, has Matt Becker, ensuring that every single model drives sublimely.

So, speaking to Krusche is always enthusing. Here, then, are five reasons why the Z4 is another tick against his name.

1. Stiff Body In White
The basic bodyshell is 25 percent stiffer than before. Vital, said Krusche, for the entire driving experience. This torsional rigidity is the starting point, the vital gear in the cog. Without such a good starting point, he said, it is impossible to make cars drive well.

‘It is a big step down if the tolerances are too great.’ You can’t turn a fundamentally bad car into a good one by tweaks alone.

2. 3 Series front axle
The new Z4 uses the 2-joint front axle from the E90 3 Series (and also the various iterations of 1 Series). It’s vital, said Krusche, not least for improving feedback to steering.

With it, BMW can independently tune directional stability, steering feel and lane change stability. Curing a major flaw of the E85 Z4: its wearisome camber steer.

The rear axle, incidentally, is a development of the old Z4 (and is also on the X3). ‘There was no reason to change it,’ said Krusche.

3. Axially parallel layout electric power steering
The new Z4 also uses the axially-parallel EPAS system from the 3 Series. It means the engine isn’t sat on the steering column, so mass is reduced and a purer feel from the road is allowed. The electric motor is in parallel to the steering rack.

The EPAS system has also allowed Krusche to tune the frequencies from the road surface. Basically, you want to isolate high frequencies, but allow through low frequencies. Cumulative learning from the old, oft-criticised Z4 EPAS has allowed BMW to do this.

‘You can vary steering torque with the switch in the car,’ said Krusche. It means it can be (over) light in normal mode, meatier in Sport +.’

He’s also tuned it so there is no resistance for when you need to make steering corrections – tidying up snap oversteer, for example. ‘We also vary the feel for when you come to the limit, adjusting the Servotronic function for more feedback.’

4. Greater understanding of run-flat tyres
The E85 Z4 was a run-flat pioneer, and earned much criticism for being so. The tyres’ necessarily stiff sidewalls, and greater weight, both counter ride fluidity. Almost a decades’ learning, plus BMW’s close collaboration with tyre maker Bridgestone (the rubber’s bespoke for the new Z4) mean big improvements.

The evidence of this learning is illustrated by driving the E60 5 Series alongside the newer E90 3 Series, for example. But for greatest contrast, feel how the E85 and E89 Z4s deal with impact harshness and sudden surface imperfections.

Krusche makes a further revelation here, though: again, close work with the Body In White team has led to yet more improvements. By working out the intricacies of where run-flats need compliance in the structure, and where they’ll benefit from extra stiffness, BMW’s been able to tune and filter the natural frequencies of the bodyshell to dramatically improve ride quality.

It’s all about iterative understanding, he said.

5. Change in BMW setup philosophy
Since the 1 Series Coupe, BMW has subtly tweaked its basic chassis setup to improve comfort. Spring rates are slightly softer, and dampers a little stiffer. This has been influenced, again, by knowledge from the characteristics of run-flats.

The secret to doing this well, says Krusche, is in damper tuning. By playing with internal baffles, the size of the holes within them, the rates of flow between the three internal champers – goodness, even the material of the plunger on the strut! – depth is engineered in. Fine art? Call it black magic…

Despite all this, though, Krusche says he doesn’t get the final sign off. It’s always down to the BMW Board – who, at least thrice a year, will drive test cars and give the final say-so.

Krusche can only do so much. The final Z4 we drove on the launch was not one chosen by him, but the good Dr. Ings. You have to say, all have not done a bad job…