Theoretical top speed of Z4M?

[lucid]

Originally Posted by BTM

Additionally, comparing cars deregulated top speed with similar power won't tell much without comparing their cD to the Z4's. Coupe or roadster will also make a difference, since it's aerodynamic footprint is not identical.

Right, that is what I meant by specs of the car: Cd, frontal area, whp, etc.

[tarheel91]

Originally Posted by BTM

Exactly. That is about top speed assuming that the car's power can overcome all the friction (atmosphere, contact patch, etc).

Additionally, comparing cars deregulated top speed with similar power won't tell much without comparing their cD to the Z4's. Coupe or roadster will also make a difference, since it's aerodynamic footprint is not identical. You would even expect things such as ambient temperature, elevation (air density), tire pressure, and road surface to have slight effects.

The maximum speed the gearing will allow is about 193. All of the above factors are going to work against achieving that MPH. How much of an effect each variable will have is also dynamic, meaning that they might never be exactly the same, lending to the reason that official top speed runs are an average of 2 back to back runs in opposite directions.

Even then, I tend to think of top speed in a similar way I do lap times, or baseball statistics. They are only 100% accurate in reporting what has happened, and can give a general idea of what a car (or player) is capable of, but is no where near a perfect predictor, as there are too many uncertain, unmeasurable, and unreproducible externalities not only built into the numbers already recorded, but any subsequent numbers as well.

This should be at the top of every forum. I can't tell you how many times I've tried to explain why a 1mph higher trap speed or 1 second faster on the Nurburgring doesn't really tell you anything.

[MIKe86]

Why do I feel foolish when reading about the speed limiter? I thought M's were not speed limited... hmm.

Originally Posted by pal

I did 155.4 mph in the standing mile at Texas last March - measured by their equipment; 156 mph on a Garmin GPS inside the car as I let off a bit after the mile I was in 5th gear and the car was still pulling but not as hard as it was in the first 1/2-3/4ths mile. Even got a little famous

that looks fun!

[BTM]

Originally Posted by MIKe86

Why do I feel foolish when reading about the speed limiter? I thought M's were not speed limited... hmm.

They are electronically limited to 155mph. There are ways to get around this though, such as running a tune

[MIKe86]

Originally Posted by BTM

They are electronically limited to 155mph. There are ways to get around this though, such as running a tune

Well mine has gone well over an indicated 155 and I was 99% sure I didn't have a tune. Was a lease car that I purchased cpo, PO had an rpi scoop on it... Hmmm...

This might be why my sport button does not behave anything like my buddy's e46m. His physically bumps the car revs up instantly and lurches the car forward while cruising. Mine doesn't change anything while cruising, you can just feel the difference in pick up next time you blip the throttle - little more snap and squat more instantly. If I'm cruising and I turn off sport mode I feel like a little wind was let out of the sail and throttle response is back to normal.

This sound indicative of a tune or does everybody's e86m behave this way like I thought?

[ga41]

Originally Posted by MIKe86

Mine doesn't change anything while cruising, you can just feel the difference in pick up next time you blip the throttle - little more snap and squat more instantly. If I'm cruising and I turn off sport mode I feel like a little wind was let out of the sail and throttle response is back to normal.

This sound indicative of a tune or does everybody's e86m behave this way like I thought?

That's normal behaviour. Mine operates like that too.

[cmark8]

I somehow dug this out from the back of my mind, but you can actually overcome the speed limiter at 5th gear, but if you try it at sixth, the limiter kicks in. I'm not sure if this only applies to e46 m3 or it also applies to the z4m.

[BTM]

Originally Posted by cmark8

I somehow dug this out from the back of my mind, but you can actually overcome the speed limiter at 5th gear, but if you try it at sixth, the limiter kicks in. I'm not sure if this only applies to e46 m3 or it also applies to the z4m.

Strange...today using the same online calculator I'm getting the following:

1) 4.35:1 = 39MPH
2) 2.50:1 = 67MPH
3) 1.66:1 = 101MPH
4) 1.23:1 = 137MPH
5) 1.00:1 = 168MPH
6) 0.85:1 = 198MPH

Still using 25" tire diameter and 8200 fuel cutoff, 3.622:1 final drive. Maybe I had a small typo yesterday which gave 193 in 6th gear. If you can in fact bypass the limiter in 5th (though this is the first I've heard of it), 168 definitely seems attainable.

[pokeybritches]

There is no limiter in 5th. That's a fact.

[BTM]

Huh...seems strange but ok

[BTM]

Originally Posted by BTM

Strange...today using the same online calculator I'm getting the following:

1) 4.35:1 = 38MPH
2) 2.50:1 = 66MPH
3) 1.66:1 = 99MPH
4) 1.23:1 = 134MPH
5) 1.00:1 = 164MPH
6) 0.85:1 = 193MPH

Still using 25" tire diameter and 8000 fuel cutoff, 3.622:1 final drive. Maybe I had a small typo yesterday which gave 193 in 6th gear. If you can in fact bypass the limiter in 5th (though this is the first I've heard of it), 164 definitely seems attainable.

NVM I was using the 8000RPM cutoff which is correct. Not sure why I was thinking 8200 today

Corrections in bold

[cmark8]

Originally Posted by pokeybritches

There is no limiter in 5th. That's a fact.

Originally Posted by BTM

Huh...seems strange but ok

So yeah, if you're somewhere in Mexico with no aftermarket tune trying to reach top speed, 5th gear!

[Serious]

Very basic calculation here.



drag coefficient 0.35
Frontal Area 1.91 m^2
mz4 power = 248kw
air density = 1.225kg/m^3 @15C
assuming ~20hp to overcome friction.

82.75m/s or 185.1mph

that said I've done ~160 in my MZ4 and 167 in my e46 m3 and I don't think it would make it to 185.

[Nhopkins1394]

Originally Posted by lucid

Why is that relevant?

And the glove box must be COMPLETELY empty!

[The HACK]

Originally Posted by Serious

Very basic calculation here.



drag coefficient 0.35
Frontal Area 1.91 m^2
mz4 power = 248kw
air density = 1.225kg/m^3 @15C
assuming ~20hp to overcome friction.

82.75m/s or 185.1mph

that said I've done ~160 in my MZ4 and 167 in my e46 m3 and I don't think it would make it to 185.

That formula fails to take into account drag lost to tire spinning as well as frictional heat as energy lost between the tire and the road. Even unlimited the MZ4 is not going to hit 185mph. As I said earlier, the ONLY way to get here is if you drop the MZ4 off of an airplane and make sure it goes nose down. Terminal velocity (which I haven't calculated) would likely be the fastest the car would go in real life.

And those of you going by the car's speedometer, they're anywhere from 5-10% PLUS 10MPH too optimistic. When you say "I did 1XX mph at [name the place]," if you're going by what the speedometer tells you you're likely at least 10 mph slower than your actual indicated speed. A case in point, if you ever watch that video of Hans Stuck driving the M6 on the Autobahn and the MPH heads up display showed 192 mph and he was still pulling? If you did the same theoretical top speed calculations I think you'll find that given the M6's CD and frontal area that it would peter out right at the 194-195 mark. There's no way that car can continue to "pull" even at 192 like that.

EDIT: Nevermind. You took out 20hp to account for friction. My bad.

[BTM]

Originally Posted by cmark8

So yeah, if you're somewhere in Mexico with no aftermarket tune trying to reach top speed, 5th gear!

Then it's a question of do you run out of RPM before you run out of power

[BTM]

Originally Posted by The HACK

And those of you going by the car's speedometer

Absolutely. At triple digit speeds where percentage error has a larger effect, ANYTHING will throw your speedo off. Aside from the fact that it reads on the high side by design, it is virtually impossible to get a precise reading from (is that 151 or 152? 151.5?), and simple variances in treadwear and tire pressure (as air expands with heat) will affect indicated speed. I guess you could use nitrogen or another gas that's volume is not related to temperature to combat this, but it doesn't address everything else that is affecting the reading.

Also, loving the "BMW enthusiast does not equal car enthusiast" headline

[Serious]

Originally Posted by The HACK

And those of you going by the car's speedometer, they're anywhere from 5-10% PLUS 10MPH too optimistic. When you say "I did 1XX mph at [name the place]," if you're going by what the speedometer tells you you're likely at least 10 mph slower than your actual indicated speed. A case in point, if you ever watch that video of Hans Stuck driving the M6 on the Autobahn and the MPH heads up display showed 192 mph and he was still pulling? If you did the same theoretical top speed calculations I think you'll find that given the M6's CD and frontal area that it would peter out right at the 194-195 mark. There's no way that car can continue to "pull" even at 192 like that.

I never used the speedo to check top speed. I ran my e46 m3 to the rev limiter in 5th gear and using known tire diameter & gear ratios went back and calculated the speed. Surprisingly the speedo was very accurate in my car at those speeds (1-3%).

[MIKe86]

Originally Posted by ga41

That's normal behaviour. Mine operates like that too.

Ok, cool.


Re: speed limiter in 6th only... How about if one surpasses the 155 mark and THEN shifts into 6th? Speed limiter kick or stay bypassed? Food for thought..

[esqu1re]

Originally Posted by MIKe86

Ok, cool.


Re: speed limiter in 6th only... How about if one surpasses the 155 mark and THEN shifts into 6th? Speed limiter kick or stay bypassed? Food for thought..

My guess is that it kicks in.

Operating under a few assumptions / train of logic:
1. Car doesn't limit speed to 155 in any other gear except 6--therefore you can surpass 155 in 5th.
2. Car doesn't care about limiting engine power in any other gear except 6.
3. Car only cares that 155mph shall not be passed in 6th gear.
4. When you shift into 6th gear, the car becomes "aware" of the speed for the purposes of limiting top speed.
5. Shifting car to from 5th to 6th gear when doing greater than 155 will activate the limiter, as the car is now "aware" that it has surpassed 155 for the purposes of limiting top speed.

[Shipkiller]

You also have to remember that its 155MPH plus or minus 10%.............

Also, there is no switch to tell the car is in 6th. Its a just a function of Speed...

[MIKe86]

Originally Posted by esqu1re

My guess is that it kicks in.

Operating under a few assumptions / train of logic:
1. Car doesn't limit speed to 155 in any other gear except 6--therefore you can surpass 155 in 5th.
2. Car doesn't care about limiting engine power in any other gear except 6.
3. Car only cares that 155mph shall not be passed in 6th gear.
4. When you shift into 6th gear, the car becomes "aware" of the speed for the purposes of limiting top speed.
5. Shifting car to from 5th to 6th gear when doing greater than 155 will activate the limiter, as the car is now "aware" that it has surpassed 155 for the purposes of limiting top speed.

Eh, I don't necessarily agree with that logic. If it's all electronically controlled, it can be programmed to do whatever.

Originally Posted by Shipkiller

You also have to remember that its 155MPH plus or minus 10%.............

Also, there is no switch to tell the car is in 6th. Its a function of RPM vs. Speed...

Threw me for a loop with that plus or minus 10%. Plus 10% puts you at 170, the car will BARELY get there (stock) and I think that's only on a downhill or tailwind and talking indicated speed type of situation.