Z4m coupe top speed 300km/hr

[Nikitas_Z4mcoupe]

Originally Posted by GuidoK

I don't think the z4 roadster gets unstable at high speeds, but its more that a fabric hood gets a pretty big beating above 250kph.
Especially hoods with a big curvature. Hoods on supersportscars mostly are much flatter as their base sits higher.

Surely there is a great improvement over Z3, but still its lagging a lot from the coupe.
Pistonheads
‘’Scoring 14,500Nm/degree in BMW’s torsional stiffness test, the M Roadster is pretty stiff for an open car, and despite its wide 225/45 and 255/40 rubber on 8.0J and 9.0J x 18-inch alloys rubber, scuttle shake on poor roads in minimal. Even so, it does not come close to the Coupé’s impressive 32,000 Nm/degree, which is more than double the Roadster’s rigidity’’

You have to drive a coupe to see what I mean....

[pokeybritches]

Originally Posted by Nikitas_Z4mcoupe

Surely there is a great improvement over Z3, but still its lagging a lot from the coupe.
Pistonheads
‘’Scoring 14,500Nm/degree in BMW’s torsional stiffness test, the M Roadster is pretty stiff for an open car, and despite its wide 225/45 and 255/40 rubber on 8.0J and 9.0J x 18-inch alloys rubber, scuttle shake on poor roads in minimal. Even so, it does not come close to the Coupé’s impressive 32,000 Nm/degree, which is more than double the Roadster’s rigidity’’

You have to drive a coupe to see what I mean....

I've driven both extensively. There's very little difference. Certainly not night and day.

What I have noticed is the steering rack on the coupe is quicker, which I prefer. The extra steering input required on the roadster makes the car feel slightly hesitant compared to the coupe, even though mechanical grip is pretty much identical.

[GuidoK]

On high speeds you don't need that much rigidity. You need a stable platform. Both aerodynamically tuned as in terms of alignment tuned.
Rigidity is something you need in corners and under braking, so that wheel alignment doesnt suffer under torsional stress.
There is not much stress on the chassis when going in a straight line.

I think the z3 has more issues on high speed aerodynamics. That mostly result in a light feel in the nose and less responsive steering.
That is somehting I haven't noticed in the z4. Although the hood has a slight tendency to bulge a bit, so there is some low pressure there.

[Steeler]

Originally Posted by GuidoK

Although the hood has a slight tendency to bulge a bit, so there is some low pressure there.

Guido,
At what speed did you experience the hood bulging
I must admit I have been into triple figures MPH and have not noticed that.

I have often thought that a couple of tasteful hood vents would help the heat escape and would also be an aerodynamic aid at higher speeds.

Sorry for the hijack OP

[GuidoK]

Above 250kph. say 260 or 270kph (so above 160mph)

I can see it a little bit at the front of the hood on the sides that there is aerodynamic pull from low pressure above the hood. It wobbles a bit. So I don't think it's pressed down but pulled up. Airplane wing effect or so.

Maybe on facelift cars it is less obvious because the hood latch changed on facelift cars.

[Nikitas_Z4mcoupe]

Originally Posted by pokeybritches

I've driven both extensively. There's very little difference. Certainly not night and day.

What I have noticed is the steering rack on the coupe is quicker, which I prefer. The extra steering input required on the roadster makes the car feel slightly hesitant compared to the coupe, even though mechanical grip is pretty much identical.

Don’t get me wrong, night and day comparing with my old Z3 a 2000 model car......
Z4 roadster is a vast improvement and a great car.
I have driven both cars on the track so probably not a fair comparison as most of our time we spend it on the streets.
Z4m coupe steering ratio 12.8:1 compared to Roadster 13.7:1 and a 1mm thicker rear anti-roll bar makes it sharper