NA top speed limiter

[m3f_norris14]

What's up people! I just got back from a 4 hour trip to St Louis, and set a couple personal top speed records. On the way there, I hit 132. Very nice, but on the way back, I passed this guy, going significantly faster than him. Then I look in my rearview, and he starts catching up, to ride my coattails. Well, I think if you're going to speed, have the balls to do it on your own. So I look at my bud in the passenger seat, and say, "let's lose him!" No cars for a mile ahead of us and straight highway. I put my foot to the floor, and we started climbing. In what seemed like just a few seconds, his car was almost out of sight behind us. I was thinking the limiter would kick in at 137, but I actually hit 140, according to the speedometer. I know it's normal for that to show a couple miles per hour faster than reality, but I think the last time I tested it, at a more reasonable speed of 60, the speedometer only showed about 2 MPH faster. Is that difference increased as the speed increases?



Anyway, it was awesome!!! :dance: I wish I had my digicam, so my bud could've taken a picture of it. I'm sure it will happen again, at some point, but it's hard to find long stretches of empty straight highway where I live.

[m3f_maxxedout9_a585527231]

Most cars have an increased difference at higher speeds.....my maxima has accelerated after the needle was burried before at 140...but I doubt I was going that fast.....but since I just got the M3 yesterday I've yet to take it more than like 105

[m3f_Sirius_880bd69485]

BMW raises their spedo readings by 7%. So were going slower than you thought. So, if you were reading 137, you were going only 127ish....

[m3f_Drifter_23d8df4bc6]

ah were did you get that info?

[m3f_Sirius_880bd69485]

My service manager at work, he actually completed my sentense when I was asking him before I could finish it up lol.

[m3f_m3-dude]

Here is how I found out that the speedo is faster than what you really are going. If you have the cruise on, on a flat road. On your OBC, push the average miles per hour button, then reset it. Mine is like 4-5mph under what the speedo says at 75.

[m3f_Drifter_23d8df4bc6]

OH sorry i was thinking about the e46 speed diffs at high speeds but I also have been up to 140 and it did kick in at around 135 to 140.

[m3f_Sirius_880bd69485]

OH sorry i was thinking about the e46 speed diffs at high speeds but I also have been up to 140 and it did kick in at around 135 to 140.



The e46 top speed regulator is higher I believe. All late-model, modern BMWs have that 7% mod to them.

[m3f_98technovlt]

the "intentional" +7% statement is a falsehood. Electronic spedometers have virtually 0% error. The variation, which is almost always a higher indicated speed vs actual speed, is the result of the changes in "rolling" diameter that are a function of tire wear and tire pressure. The programmed calculation is based on new tires and correct tire pressure. As the tire wears, or the pressure is lost (tires only go spontaneously down in pressure not up) the linear travel/revolution is reduced, fooling the calculation into indicating a higher speed.

[m3f_Sirius_880bd69485]

the "intentional" +7% statement is a falsehood. Electronic spedometers have virtually 0% error. The variation, which is almost always a higher indicated speed vs actual speed, is the result of the changes in "rolling" diameter that are a function of tire wear and tire pressure. The programmed calculation is based on new tires and correct tire pressure. As the tire wears, or the pressure is lost (tires only go spontaneously down in pressure not up) the linear travel/revolution is reduced, fooling the calculation into indicating a higher speed.



Its built into the programming. Even though it may have a 0% error, its built into the system to do it automattically.



Edit: Pondered this on my drive.... from what your saying, if your tire loses air pressure/wears, the "rolling" diamater changes right? So, going off that, wouldn't it be true if you got a larger/smaller rims, it would change your spedo reading also? Isnt' this why they put the speed sender in the diff, so you don't have to worry about that problem? Because its geared to the gearing of the diff?

[m3f_Max M3]

the "intentional" +7% statement is a falsehood. Electronic spedometers have virtually 0% error. The variation, which is almost always a higher indicated speed vs actual speed, is the result of the changes in "rolling" diameter that are a function of tire wear and tire pressure. The programmed calculation is based on new tires and correct tire pressure. As the tire wears, or the pressure is lost (tires only go spontaneously down in pressure not up) the linear travel/revolution is reduced, fooling the calculation into indicating a higher speed.



That's absolutely correct.

[m3f_genner21_b0df9c1cac]

yeah, i thought the limiter was like 130ish..i hit 142 i believe. I sure wasn't trying to stare at the speedometer going that fast.

[m3f_Flybry07_aa2e46014a]

My e30 318is was always off by 5mph all the time. I figured the M would be off by a few but I dident know as much as 7%.



Does this mean in order to cruise at a true 70mph I need my speedo to be indicating about 75mph???? (70 X.07 = 4.9)

[m3f_98technovlt]

Dark,

You are correct in that if your wheel/tire diameter changes your spedo will indicate that error. However, because of the fact that the wheel RPM is sensed off the diff. the calculation is unaware of the linear distance/revolution change - hence the error.

As far as there being a "fudge" factor in the calculation, I posed the question to BMW on their website. We'll see what they say....

[m3f_98technovlt]

Also I believe that there are multiple sensors that contribute to calculating speed, it would seem that there would be wheel sensors front and back in order for the ASC to work.



BTW: IIRC the stock software limiter is 137mph.