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How fast will a Z4 actually go?

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DaveZ4C
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Re: How fast will a Z4 actually go?

Post by DaveZ4C » Fri Sep 12, 2008 9:06 pm

Smokin wrote:Actually , that only took a minute. Interesting part of the graph is noting the great increase in horsepower but a much smaller increase in speed. Are any of these other machines electronically limited and are the mph numbers the theoretical top speed? I'll have to expand the x axis a bit to see exactly where the Z fits but it does look very close.

I only used cars that are not limited/restricted.

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Re: How fast will a Z4 actually go?

Post by DaveZ4C » Fri Sep 12, 2008 9:07 pm

Being fair your other figures do seem about right to me :)[/quote]


I like to think of them as very scientific

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Re: How fast will a Z4 actually go?

Post by Smokin » Fri Sep 12, 2008 9:10 pm

DaveZ4C wrote:
Smokin wrote:Actually , that only took a minute. Interesting part of the graph is noting the great increase in horsepower but a much smaller increase in speed. Are any of these other machines electronically limited and are the mph numbers the theoretical top speed? I'll have to expand the x axis a bit to see exactly where the Z fits but it does look very close.

I only used cars that are not limited/restricted.
Then the change in the slopes for increase in bhp and increase in top speed are even more interesting.
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Re: How fast will a Z4 actually go?

Post by DaveZ4C » Fri Sep 12, 2008 9:22 pm

Didn't someone say that wind resistance increases exponetially with speed?

This would mean, for example, that at 150mph you need much more power to get a 10mph increase in speed than you would at 100mph.

This would cause the curve.

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Re: How fast will a Z4 actually go?

Post by DaveZ4C » Fri Sep 12, 2008 9:25 pm

To go any faster, you would need much more horsepower (Bugatti Veyron 1000+ bhp) and/or a change in aerodynamics, ie. move from a coupe shape to a race-car shape (ferarri, lambo, robin reliant).

Dave

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Re: How fast will a Z4 actually go?

Post by ovrkll » Sat Sep 13, 2008 2:33 am

hmmm, just to throw into the equation that the //M is still pulling very hard at 120'ish,,,, very hard. :thumbsup:
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Re: How fast will a Z4 actually go?

Post by Smokin » Sat Sep 13, 2008 3:13 am

ovrkll wrote:hmmm, just to throw into the equation that the //M is still pulling very hard at 120'ish,,,, very hard. :thumbsup:
Yeah, but that next 30-40 hp is *much* harder to get than the first 120!
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Re: How fast will a Z4 actually go?

Post by ovrkll » Sat Sep 13, 2008 3:16 am

I have seen several other documentations that the //M will do 168 in fifth, bypassing the 155 electronic limiting in 6th gear :)


I may try this one day,,,,so keep an eye on the news :lol:
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Re: How fast will a Z4 actually go?

Post by Smokin » Sat Sep 13, 2008 3:20 am

Yeah, but you're gonna have to be away from Hotlanta traffic!
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Re: How fast will a Z4 actually go?

Post by ovrkll » Sat Sep 13, 2008 3:30 am

Actually, 120'ish is easy in this area. Just have to find a time, and place, a little more open for 150+. I know of a few areas, but the traffic during my awake and driving times, leave no wiggle room for idiots. You know the kind that want to shoot all the way across to the left lane upon merging, without looking :x
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Re: How fast will a Z4 actually go?

Post by Smokin » Sat Sep 13, 2008 3:37 am

ovrkll wrote:Actually, 120'ish is easy in this area. Just have to find a time, and place, a little more open for 150+. I know of a few areas, but the traffic during my awake and driving times, leave no wiggle room for idiots. You know the kind that want to shoot all the way across to the left lane upon merging, without looking :x
Know 'em all too well. RTP traffic is horrendous (that's why I don't work there nor head for Raleigh during rush hour!)
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Re: How fast will a Z4 actually go?

Post by epbrown » Sat Sep 13, 2008 4:32 am

DaveZ4C wrote:To go any faster, you would need much more horsepower (Bugatti Veyron 1000+ bhp) and/or a change in aerodynamics, ie. move from a coupe shape to a race-car shape (ferarri, lambo, robin reliant).

Dave
I don't know the robin, but even some Ferraris aren't slippery enough. I've been doing some comparos to the 360 and its performance specs are very similar to my M Coupe with 3.91 gears. The 360 is drag limited to 184mph, I've read (in the Evo/Octane Ferrari anniversary article compilation).
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Re: How fast will a Z4 actually go?

Post by DaveZ4C » Sat Sep 13, 2008 4:35 am


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Re: How fast will a Z4 actually go?

Post by Dammmittt » Sat Sep 13, 2008 4:44 pm

This thread is pretty funny. I like the VSG talk :lol:

Some notes.

Pressure drag increases with the square of the velocity (assuming all other things are constant). Viscous drag is more difficult to predict and at low mach numbers viscous drag is on the same order of magnitude as pressure drag, so you can't ignore it. Most people use the coefficient of drag as a way of characterizing the shape of the car and the viscous drag at a certain Reynold's number. But the coefficient of drag the automobile industry gives is completely useless for any sort of drag prediction calculations.

The one thing you can count on is that at a given engine RPM and gear ratio, you'll be doing a specific velocity in the car.

Expansion of the tires isn't really worth determining since it'll be very small compared to the actual tire radius.

Of course RPM limiters also get in the way, along with speed limits and police. Then you also have to worry about speedo error which in BMWs always indicates higher than actual speed.

So, what does this all mean? In a vacuum you can easily calculate the maximum theoretical speed of a car. In reality, it's much harder to predict, depending on weather conditions and wind directions and whether you're going up/down hill or on flat ground, are all going to affect the maximum speed you can achieve in the car.

So the best way to figure out how fast your car will go is take it some place without speed limits and find out for yourself and take your GPS to measure it :)
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Re: How fast will a Z4 actually go?

Post by epbrown » Sun Sep 14, 2008 4:38 am

Going forward, a simple "Duh" will suffice, Capt. Obvious. ;)
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