How fast will a Z4 actually go?

[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.

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...

That's a good site then if they are giving a true rolling radius as so many calculations are based upon the manufacturers advertised tyre size that's rather arbitrary (a 35" Simex is usually around 33.5"!! as an extreme example).
I have no idea of the change in radius caused by an extra 100mph but suspect it will stay within low single digits so you may be fairly close

 

[DavidZ4]

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...

That's a good site then if they are giving a true rolling radius as so many calculations are based upon the manufacturers advertised tyre size that's rather arbitrary (a 35" Simex is usually around 33.5"!! as an extreme example).
I have no idea of the change in radius caused by an extra 100mph but suspect it will stay within low single digits so you may be fairly close

:? :? Can anyone explain this in normal person speak :? :roll: :tumbleweed: :| :| :| :| :| :| :|

 

[Smokin]

You have several factors going on here:
1. Diameter of the tire depends somewhat on inflation pressure.
2. At speed, there are two opposite factors occurring--the increase in downward air pressure making the tires "shorter" and wider due to increased "weight" of the car and the opposite happening, that is, the spin of the wheel will make the tread try to move outward like things in a centrifuge. Won't move much, but it MAY be enough to throw any calculations off.

You also have to factor in the expansion of the tire due to heat, etc, but ZetaTre's calculation should be "close enough for government work".

 

[IMZ4N]

On a 10,000 foot runway, breaking at 9,000 foot marker.

04 3.0i steptronic, sport mode not used ( steptronic will not shift to 5th gear if in sport mode ) top up ( best times was with the top up ).

 

[Aebous]

I'm luvin the mpg on the speedo of the M.

 

[pmeloche]

limited to 135 here in the States.

Really!! That's a bit low!!

I just checked the BMW USA site and the Z4 is electronically limited to 155 mph. :driving:

 

[marriedblonde]

I thought the acutal restriction was 259kph so 161mph and not 155mph?

 

[cj10jeeper]

I thought the acutal restriction was 259kph so 161mph and not 155mph?

I've never heard that figure before. In Europe the accepted self regulated limit always quoted is the 155mph. That said I've no idea if any of them actually trigger at that.

The new Japanese Nissan GTR (IIRC the model) uses GPS which is neat in that it knows when the car leaves a public highway and the speed restriction software then releases the very low legal limit....

 

[pvr]

And once off-road, shield the GPS aerial so it thinks foreever it is off road

 

[GerryM]

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.

LOL, 1.9 MPG!!!!

 

[pvr]

Better state that it was outside the UK otherwise half the police force would be allocated to catching this criminal :?

 

[Breaker]

I'm luvin the mpg on the speedo of the M.

Blimey, I thought the M was bad on fuel when opening it up, but I didn't think it was that bad!!!

 

[Breaker]

Better state that it was outside the UK otherwise half the police force would be allocated to catching this criminal :?

That just about sums up our police system in this country! :roll:

 

[Smokin]

limited to 135 here in the States.

Really!! That's a bit low!!

I just checked the BMW USA site and the Z4 is electronically limited to 155 mph. :driving:

All I know all the paperwork for my 2007 3.0Si Coupe says 135 mph. Kind of a moot point anyway as I don't intend to find out just how fast she goes.


edit: Brochure *does* say 155 mph, electronically limited. my bad........

 

[Doh]

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

 

[pm@wybo]

well if it's correct, a review of Hamann Z4 M says 273 km/h for a derestricted standard engine which is 170 mph

http://www.conceptcarz.com/vehicle/z12452/BMW_BMW_Z4_M.aspx

 

[fflores]

wow... 135mph only in the US?

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

 

[20ducks]

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?

 

[Smokin]

Check my post--I did some digging and edited my post to 155mph electronically governed. I'm still not going to find out *just* how fast she can go as the speed limits around here are in the 60-75 range.

 

[ZetaTre]

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?

On a drag strip oke: