How fast will a Z4 actually go?

[DaveZ4C]

I have a Z4 Coupe 3.0si Sport. I know the car is restricted to 155mph. Does anyone know how fast the car could go if it wasn't restricted? Has anyone been able to remove the speed limiter and try a high speed run? or has anyone been able to calculate whatthe top speed would be?

Dave

 

[Smokin]

limited to 135 here in the States. There is a youtube of someone hitting 160 mph on the autobahn. I have no idea if they've reached the rev limiter or if they've just milked all out of the stock intake/exhaust, etc they can. I'm sure if you let someone like DINAN get hold of it, it may go a bit faster.

 

[2 Zero]

How about faster than you should go in any small car!!

 

[plowy]

mine is de-limited, part of the remap, fastest i've seen is a GPS verified 158mph, so the truth is not much more than 155mph in reality

 

[Breaker]

limited to 135 here in the States.

Really!! That's a bit low!!

 

[sp3ctre]

limited to 135 here in the States.

Really!! That's a bit low!!

LOL, my old Nissan Micra just about did 135

 

[BlackSapphireZ]

135 is as fast as mine goes...

feels rock solid at that speed.. could go lil faster

 

[Smokin]

limited to 135 here in the States.

Really!! That's a bit low!!

I think it's because the state troopers didn't want more people outrunning them! :evil:

 

[plowy]

I think it's because the state troopers didn't want more people outrunning them! :evil:

With all the evidence i've seen on camera you could do that in a 116i....... :rofl:

 

[Screamer]

Anyone got any ideas about the M Coupe's 'natural' limit (and the roadster for that matter)? I'm also intrigued to know more about the limiter: sure I read a while back that it enables itself with the 5th-to-6th change, but apparently beyond 155mph is fair game in 5th with the M..! Does that mean the car will happily exceed 155 in 5th, and then the change into 6th will be like hitting a brick wall..?!

 

[ZetaTre]

You can do the math if you have all the parameters:

Take the redline limit and multiply it by the various ratios in tranny and diff and you'll get how many RPM the wheels are doing. If you multiply it by the circumference of the tires and convert it into MPH or KmH you get the max speed... I think...

 

[WLH]

My previous Z4 which was a 2003 3.0i I had up to 145 on one occasion for less than one minute. It would have gone faster but I was running out of straight and level road.

The video on youtube that Smokin mentioned is below and the driver was Mark from the old Z4um. The car as I recall was a 2003 3.0i.

[youtube]pRQRMuqJyd4[/youtube]

 

[pvr]

I had 163 (GPS) top down with my old 3.0 in Germany. I was running out of free road, but the car was still accelerating. I did have the SE Cai in my car though.

 

[ZetaTre]

You can do the math if you have all the parameters:

Take the redline limit and multiply it by the various ratios in tranny and diff and you'll get how many RPM the wheels are doing. If you multiply it by the circumference of the tires and convert it into MPH or KmH you get the max speed... I think...

Here's what I figured, please tell me if I'm on the wrong path (I know there might be some approximations, but directionally it should be right)

My wife's 2.5i is an M54B25 with readline at 6,500RPM
In 5th grar the transmission gear ratio is 1:1, so no RPM changes there
The diff is 3.25:1 so the wheels are spinning at 2,000RPM which is 120,000 revolutions per hours

Now, Michelin says that a 225/50-16 makes 834 revolutions per mile so the circumference of the tire is 1/834 miles

If I do 120,000/834 I get 144MPH.

 

[plowy]

You can do the math if you have all the parameters:

Take the redline limit and multiply it by the various ratios in tranny and diff and you'll get how many RPM the wheels are doing. If you multiply it by the circumference of the tires and convert it into MPH or KmH you get the max speed... I think...

Here's what I figured, please tell me if I'm on the wrong path (I know there might be some approximations, but directionally it should be right)

My wife's 2.5i is an M54B25 with readline at 6,500RPM
In 5th grar the transmission gear ratio is 1:1, so no RPM changes there
The diff is 3.25:1 so the wheels are spinning at 2,000RPM which is 120,000 revolutions per hours

Now, Michelin says that a 225/50-16 makes 834 revolutions per mile so the circumference of the tire is 1/834 miles

If I do 120,000/834 I get 144MPH.

The theory above is all pretty correct but where the theory falls down is the wind resistance that is generated at these sorts of speeds can make the theoretical speed unachievable...I think..

 

[JamesF]

You can do the math if you have all the parameters:

Take the redline limit and multiply it by the various ratios in tranny and diff and you'll get how many RPM the wheels are doing. If you multiply it by the circumference of the tires and convert it into MPH or KmH you get the max speed... I think...

Here's what I figured, please tell me if I'm on the wrong path (I know there might be some approximations, but directionally it should be right)

My wife's 2.5i is an M54B25 with readline at 6,500RPM
In 5th grar the transmission gear ratio is 1:1, so no RPM changes there
The diff is 3.25:1 so the wheels are spinning at 2,000RPM which is 120,000 revolutions per hours

Now, Michelin says that a 225/50-16 makes 834 revolutions per mile so the circumference of the tire is 1/834 miles

If I do 120,000/834 I get 144MPH.

The theory above is all pretty correct but where the theory falls down is the wind resistance that is generated at these sorts of speeds can make the theoretical speed unachievable...I think..

Yep battle becomes wind resistance vs raw horsepower above a certain speed I think. The Alpina is claimed to be able to hit 169mph with the roof up.

 

[cj10jeeper]

The theory is not bad as a start point, but you'd need to factor in that the rolling radius of a tyre changes based not only upon the weight of the car but the speed it's travelling at and these 2 make a massive difference. We used to do a lot of this stuf with Jeeps where running big 37" tyres we'd have to juggle final drive ratios to work correctly at 5psi off road and still be drivable aired back to 24 psi for the motorway at 70mph plus.

Interesting debate though as to how fast in stock because as soon as you start to mess with mapping, engine, exhaust, intake, gearing then it's really a different car and frankly you can choose your top speed within the limits of wind resistance gearing and power usualy trading against acceleration

 

[ZetaTre]

The theory is not bad as a start point, but you'd need to factor in that the rolling radius of a tyre changes based not only upon the weight of the car but the speed it's travelling at and these 2 make a massive difference.

Absolutely: that's why on the Michelin website they say that the number of revolutions per mile is measured at 45MPH. I would guess at 140MPH as the tire expands it makes less revolutions per mile... I'm not sure how many less: next time I get at that speed I stick my head out of the window and start counting...

 

[DavidZ4]

Okay, Im trying to understand this.......but....... :sos: :sos: :sos: :sos: .........my head is gonna explode!!!

 

[Top pup]

Anyone got any ideas about the M Coupe's 'natural' limit (and the roadster for that matter)? I'm also intrigued to know more about the limiter: sure I read a while back that it enables itself with the 5th-to-6th change, but apparently beyond 155mph is fair game in 5th with the M..! Does that mean the car will happily exceed 155 in 5th, and then the change into 6th will be like hitting a brick wall..?!

The limiter simply kicks in at an indicated ~168mph, you can get there in 5th or 6th. I don't know the coupes real top speed but someone posted this on the old z4-um and it looks about right to me.