How fast will a Z4 actually go?

[epbrown]

i've just used an online calculator for the M

using a 3.62 final drive, 6th gear - 0.85 and a tyre 255/40*18

at an 8000rpm rev limit then 201.35mph!
in fifth at 1.1 = 155.59mph

thats obviously not factoring in tyre size changes

That's the theoretical limit. From what I've read, thanks to the drag coefficient our cars can't get much past 180mph. I asked about it when I had my new diff installed. My theoretical limit dropped to 197 or so, but I can't get there either. The 4.10 gears put the limit at 189, so you still don't lose anything real world.

 

[Jas667]

I have not had my M derestricted but on a nice long autobahn I saw 180mph, no limiter kicked in at all. I would say that is as much as the car had, maybe a few more mph with the wind behind but not much more

 

[Screamer]

Jas667: was that in 5th or 6th gear?

 

[fflores]

wow... 135mph only in the US?

I've hit 155ish in teh SRT6, And i hit 157mph in the Neon SRT4.

Where were you able to do this?

Not the smartest thing i've ever done... but there are "Express lanes" here in chicago on the highway, they are extra lanes that are walled off that open and close allowing either north bound traffic or south bound traffic to gain a extra 2 lanes depending on time/congestion direction... Late one night, i happen to catch the express lanes just as the entrance to it opened. There is only 1 entrance and 1 exit at either end of a 12 mile length of the express lanes. There is a 3 mile straight section. I know that before they open the gates to let in traffic, they already have cleared all traffic and have had IDOT trucks threw to make sure that everything is clear, if you are the first car in, you have the run of the entire stretch. The 3 mile straightway is on a little bit of a incline, so you can see whats at the end of the run.

I ran it and hit top speeds.

Like i said, not the smartest things i have ever done. Shortly after that, realized that it simply wasn't worth the risk to drive like that.

I did hit 145mph in the SRT6 when i ran on a road course at the SRT Nationals in Memphis at the end of a 3/4 mile front stretch, at the end of the straight away there was a long 180 degree long right handed sweeping curve.

That was a couple of years back... I don't think i've cracked 85 mph since.

 

[DaveZ4C]

I noticed that the Z4 Coupe 3.0 si sport does 40mph at 1500rpm and 80mph at 3000, which means (taking out tyre changes) an (oversimplified theoretical) top speed of 187mph.

Of course aerodynamics and tyre shape should come into play, but it seems extreme to lose 30mph (someone said the top speed was 157mph) in a 265bhp car shaped like a bullet.

Can 157mph really be right?

Dave

 

[Wondermike]

I noticed that the Z4 Coupe 3.0 si sport does 40mph at 1500rpm and 80mph at 3000, which means (taking out tyre changes) an (oversimplified theoretical) top speed of 187mph.

Of course aerodynamics and tyre shape should come into play, but it seems extreme to lose 30mph (someone said the top speed was 157mph) in a 265bhp car shaped like a bullet.

Can 157mph really be right?

Dave

I would have thought it couldn't be much more than that, you need huge amounts of power at these higher speeds to keep going faster.

Note I am no expert by and stretch of the imagination, but reading here...

...Assuming a more-or-less constant drag coefficient, drag will vary as the square of velocity. Thus, the resultant power needed to overcome this drag will vary as the cube of velocity.

 

[WLH]

A big part of the problem as I understand it is a car driving at say 50 mph might only require 10 horsepower to overcome air resistance. The same car at 100 mph would then requires 80 hp. With the doubling of speed the air resistance quadruples....

 

[Smokin]

Not to mention the 155 is *electronically* limited here in the US. (danged nanny state :x )

 

[20ducks]

fflores, on the Kennedy?

 

[Wondermike]

Not to mention the 155 is *electronically* limited here in the US. (danged nanny state :x )

It's the same everywhere unfortunately, although I'm not so sure I'd want to go 155 anyway, not on our roads :thumbsdown:

 

[WLH]

Not to mention the 155 is *electronically* limited here in the US. (danged nanny state :x )

It's the same everywhere unfortunately, although I'm not so sure I'd want to go 155 anyway, not on our roads :thumbsdown:

Not here either... :thumbsdown:

 

[DaveZ4C]

No need to look any further, I've just done a very scientific test to prove that the Z4 Coupe Si sport will do 165mph. Some of you will be impressed and others appalled.

I plotted a graph of bhp versus top speed for a range of cars with shapes not too dissimilar to the Z4 Coupe and which aren't restricted/limited to a specific top speed. The result was a surprisingly smooth curve.

Audi TT 2.0 197bhp 149mph
Boxter 2.7 245bhp 160mph
Caymen 3.4 295bhp 171mph
911 3.6 325bhp 175mph
Targa 3.8 355bhp 179mph
Aston DB9 450bhp 186mph

Z4 Coupe 3.0 265bhp should do 165mph!!

I avoided cars like Ferraris, Atoms, Lambos, Elises that don't have a similar enough aerodynamic profile, so the results shown will be worthy of any scientific journal. Or at the very least, researchers at Top Gear or Fifth Gear!

Dave

 

[Smokin]

neat. Actually, an easier way would be to plot the cd numbers vs speed/bhp. Some of those shapes are more aerodynamic that they look and vice-versa.

 

[DaveZ4C]

I added the TVR Cerbera and it fitted nicely with the curve. I tried to add the TVR T350 but found two claimed top speeds!

I don't know where to find the cd numbers, so just took the first 7 cars I could find that are in the same broad profile "class" and they seem to fit the curve reasonably well.

Dave

 

[Smokin]

I added the TVR Cerbera and it fitted nicely with the curve. I tried to add the TVR T350 but found two claimed top speeds!

I don't know where to find the cd numbers, so just took the first 7 cars I could find that are in the same broad profile "class" and they seem to fit the curve reasonably well.

Dave

It's probably hard to find the cds. BMW has theirs in their owner's manual. Gonna link that graph??? Sounds interesting.

 

[DaveZ4C]

I don't know how to link you to the graph. You can use the figures and plot it using Excel or similar.

Figures used were:

TT (2.0l) 197bhp 149mph
Boxter (2.7l) 245bhp 160mph
Caymen (3.4l) 295bhp 171mph
911 (3.6l) 325bhp 175mph
Targa (3.8l) 355bhp 179mph
TVR Cerbera 360bhp 180mph
Aston DB0 450bhp 186mph

Z4C at 265bhp comes out at 165mph on the curve

Dave

 

[Top pup]

Note I am no expert by and stretch of the imagination, but reading here...

...Assuming a more-or-less constant drag coefficient, drag will vary as the square of velocity. Thus, the resultant power needed to overcome this drag will vary as the cube of velocity.

That's both wrong and right, the force needed to overcome drag squares BUT the power needed goes up as a cube, ie you need 9 times more power to do 200mph than 100mph.

 

[2dogs]

My brain hurts :? so how fast will it go.....

 

[Dammmittt]

My brain hurts :? so how fast will it go.....

It'll go 155 unless you want to remove the limiter. After that you'll be drag limited.

 

[fflores]

fflores, on the Kennedy?

It runs from Ohio St (I think) til the 90/94 junction on the Kennedy, THe stretch run is between roughly Armitage and Irvin Park, on Addison, there is a entrance which takes you to the Edens (94N)