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      07-19-2009, 01:50 PM   #1
drft92
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Stock limited top speed ?

I was under the impression that the M3 was limited to 155 mph. Yesterday on a private track I broke 160 and never hit the limiter, I had limited track time and was only able to achieve this once. Any thoughts ? Malfunctioning speedo ? My googly eyes ?ha ha

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      07-19-2009, 02:04 PM   #2
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Nothing wrong with your speedo, they're just reading fast by some percent. Maximum indicated speed should be about 168 mph which actually translates to a real speed of 161 mph.


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      07-19-2009, 02:14 PM   #3
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Quote:
Originally Posted by drft92 View Post
I was under the impression that the M3 was limited to 155 mph.
Not on M cars. I've seen between 168 and 171. The speed limiter is always set at indicated speed, but it's typically lower than real, as noted. With 19" wheels, which are slightly smaller in circumference than 18s, error is about 4% on my car, which is not bad at all. With 18s should be about 3% (most cars are between 3 to 5%). Hope your 'track' didn't start with an 'I' . Good day.
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      07-21-2009, 02:38 PM   #4
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Quote:
Originally Posted by southlight View Post
Nothing wrong with your speedo, they're just reading fast by some percent. Maximum indicated speed should be about 168 mph which actually translates to a real speed of 161 mph.


Best regards
south

Thanks for your insight South !


Quote:
Originally Posted by elp_jc View Post
Not on M cars. I've seen between 168 and 171. The speed limiter is always set at indicated speed, but it's typically lower than real, as noted. With 19" wheels, which are slightly smaller in circumference than 18s, error is about 4% on my car, which is not bad at all. With 18s should be about 3% (most cars are between 3 to 5%). Hope your 'track' didn't start with an 'I' . Good day.

Thank you for your input also elp. No my track did not start with an "I".



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      07-21-2009, 02:45 PM   #5
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When you change wheels or final drive ratio it does NOT change the error in the speedo. I've got 18" wheels, 19" wheels and a 4.10 final drive. None of those changes will change the speed registered through my local radar traps. That's because the speed is measured at the wheel hub, based on it's absolute revolutions. Mine's about 8% optomistic, which I think is fairly typical.

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      07-21-2009, 03:42 PM   #6
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Quote:
Originally Posted by dcstep View Post
When you change wheels or final drive ratio it does NOT change the error in the speedo. I've got 18" wheels, 19" wheels and a 4.10 final drive. None of those changes will change the speed registered through my local radar traps. That's because the speed is measured at the wheel hub, based on it's absolute revolutions. Mine's about 8% optomistic, which I think is fairly typical.

Dave
But surely the diameter of the wheel/tyre combinations would have to be identical in order for the error to remain the exact same?
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      07-21-2009, 03:47 PM   #7
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Quote:
Originally Posted by dcstep View Post
When you change wheels or final drive ratio it does NOT change the error in the speedo. I've got 18" wheels, 19" wheels and a 4.10 final drive. None of those changes will change the speed registered through my local radar traps. That's because the speed is measured at the wheel hub, based on it's absolute revolutions. Mine's about 8% optomistic, which I think is fairly typical.

Dave

How does your car run with the 18" wheels and a 4.1 final? Also compared to stock 19" wheels did the 18" wheels with the 4.1 final make a difference?
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      07-21-2009, 03:51 PM   #8
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Quote:
Originally Posted by stylinexpat View Post
How does your car run with the 18" wheels and a 4.1 final? Also compared to stock 19" wheels did the 18" wheels with the 4.1 final make a difference?
Good point, it probably does, but it's less than 1 mph, so I can't decern it. I've got BMW's stock tire sizes on both the 18s and 19s, which I'm certain have slightly different diameters.

The FD difference is over 6% different from stock, yet no difference in speed shows up.

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      07-21-2009, 04:01 PM   #9
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Quote:
Originally Posted by dcstep View Post
Good point, it probably does, but it's less than 1 mph, so I can't decern it. I've got BMW's stock tire sizes on both the 18s and 19s, which I'm certain have slightly different diameters.

The FD difference is over 6% different from stock, yet no difference in speed shows up.

Dave
So it just feels quicker with 18" wheels and a 4.1 final but really isn't any quicker, right??
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      07-21-2009, 04:45 PM   #10
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Quote:
Originally Posted by stylinexpat View Post
So it just feels quicker with 18" wheels and a 4.1 final but really isn't any quicker, right??
Quicker and speed are two very different things. It IS quicker with the 4.1, meaning that it's mid-gear acceleration is superior (faster than) to the stock 3.85 FD. As for 18" wheels/tires, I DO plan to get some lower profile rubber for some 18" autocross wheels that will make the car quicker for AX, but slower in speed at the same engine rpm. Stock 18" wheels with larger diameter tires than 19" stock wheels will actually be faster at the same rpm, but not as quick.

Everything's relative. A 4.10 is probably quicker in an 1/8-mile drag than a 3.85, but it may or may not be quicker in the 1/4-mile, although I suspect that it will be very marginally quicker.

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      07-21-2009, 07:50 PM   #11
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How many people have the upgraded ECU? Does it make a significant difference in performance/fuel consumption?
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      07-22-2009, 08:30 AM   #12
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Just some more info to confirm:

On my US M3 I went 168 according to the dash, but my GPS said I was only going 162.
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      07-22-2009, 03:38 PM   #13
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Quote:
Originally Posted by mikewads View Post
On my US M3 I went 168 according to the dash, but my GPS said I was only going 162.
That's a 3.7% error; very typical. And you did that on a 'track', correct?
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      07-22-2009, 04:08 PM   #14
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My UK E92 M3 just stops accelerating at exactly 170mph on the speedo.

Cheers

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      07-22-2009, 04:39 PM   #15
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Quote:
Originally Posted by mikewads View Post
Just some more info to confirm:

On my US M3 I went 168 according to the dash, but my GPS said I was only going 162.
That was before you upgraded your exhaust and ecu ?

Quote:
Originally Posted by elp_jc View Post
That's a 3.7% error; very typical. And you did that on a 'track', correct?
elp whats with you and the "track" ? your making me wonder !
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      07-23-2009, 02:39 PM   #16
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Quote:
Originally Posted by drft92 View Post
That was before you upgraded your exhaust and ecu ?
yes
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