e89 Chassis Secrets revealed by BMW's own chassis guru.

[-=Hot|Ice=-]

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 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 with 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 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 incremental 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…

BMW Z4 chassis secrets richardaucock

[Alext]

SO a mix of 3-series, 1-series and old Z4 then?

[KevinC]

So, they're admitting that runflats on the E85/E86 were a big mistake. Same goes for the rest of the line. BAAAD idea, the technology just wasn't ready for primetime yet. I'm betting it still isn't - give me "real" tires any day. They have no business on a performance-oriented car.

[antzcrashing]

BMW is a luxury car more than it is a performance car, regardless of the fact that it performs better than many other cars.

If you don't believe BMW is following Mercedes in the luxury/prestige pursuit go to the BMW research center in Munich and ask them

Someone at BMW decided its better to market the tires as never requiring roadside swaps than to perform best, to the performance-addict's bane.

This is what I see happening "Warning: Do not replace BMW run-flats with non-run flats, the springs and dampers are engineered for run-flats" or something of the same tune in the Z4 owners manual.

[ik999]

Someone at BMW decided its better to market the tires as never requiring roadside swaps than to perform best, to the performance-addict's bane.

all factors considered, run flats are a good thing. those road-side swaps are not only inconvenient and tedious, but also dangerous. Z4 isn't a pure sports car, and typical Z4 drivers aren't exactly hard line performance aficionados (lol)

as for the comfort and performance aspects, sometimes compromises are beneficial. but don't forget that the M cars still come with standard tires. also, I'm sure that they will make better run-flats over time.

[roburado]

Originally Posted by KevinC

So, they're admitting that runflats on the E85/E86 were a big mistake. Same goes for the rest of the line. BAAAD idea, the technology just wasn't ready for primetime yet. I'm betting it still isn't - give me "real" tires any day. They have no business on a performance-oriented car.

Mistake? More like learning process.

[KevinC]

Originally Posted by roburado

Mistake? More like learning process.

Not if you're one of the unfortunate customers who bought a BMW with the damn things in the last few years. I had an E90 330i with the dreaded things, and they have NO business on a BMW, unless the owner wants them for "safety" reasons.. they should be optional if offered at all.