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      07-09-2009, 09:43 AM   #1
apollner
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Did you feel a "bump" from behind while at a traffic light?

It's happened to me a few times. I'm at a traffic light, I have a car behind me, and I sense what feels like someone bumping me ever so slightly from behind. Then I look in the rearview mirror and see that the person behind is not close enough for them to have actually bumped me.

I think what is happening is some sort of resetting or rebalancing of the torque distribution between from and back wheels. I'm just guessing, I really don't know.

So the last time it happened, I took conscious note of surrounding variables.
a) I had my foot firmly on the brake pedal.
b) I did not feel any modulation on the brake pedal.
c) The car had the Sport button depressed.

I state the above, because on previous occasions when this happened, I did not remember if my foot possibly had released some pressure off the brake pedal.

The feeling is somewhat similar the the slight "nudge" you get when putting the car from park into drive.

Anybody else experience this? Any further thoughts on what could cause it?
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      07-09-2009, 09:56 AM   #2
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Are you sure you are not feeling the car going into neutral? All modern BMW's with auto trannys go into neutral at stops when your foot is left on the brakes for a few seconds. Once you release the brake the tranny engages again. I think it is designed to lower RPM's and reduce fuel consumption.
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      07-09-2009, 12:31 PM   #3
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I've experienced this too. It doesn't matter what mode you're in. But you feel it when you're stopped at a red light a couple of seconds after coming to a complete stop. It's a little less subtle than shifting from Park to Drive, well at least on my car. The feeling is ever so slight and you must be a sensitive person to feel it. I've always wondered what that was because it's never happened on any other BMW that I've driven. It kind of bothered me not knowing what it was.
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      07-09-2009, 11:25 PM   #4
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What I have felt is something like this, lets say Im driving the car in manual mode, then I get to a traffic light going down on the gears, the car stops and Im in second gear, nowm if I put the car into 1st gear when Im still standing, I feel a little movement like the gearbox is engaging 1st gear, but never experienced what you are saying here
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      07-10-2009, 04:36 AM   #5
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Mysterious Bump

90% of the time i engage the auto hold/magnetic brake hold, so that my right foot is over the gas pedal & does not have to waste time moving over to the accelerator when traffic moves. This saves time & allows me to enter traffic flow 1/2 second faster when a slot opens up in the lane next to the on ramp.

I'm mindful that should i get rear ended or bumped, the auto hold may disengage, so i'm always ready to jump back onto the brake.

During this past year that i've been driving the x6, i'm fortunate to say that i've not experienced any bump in stop & go traffic.
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      07-10-2009, 09:55 AM   #6
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I frequently feel a bump as I take my foot off the brake at a traffic light and step on the gas gradually to move forward. It has always felt to me like the car started to roll backwards when I took my foot off the brake and then jerked when the transmission engaged to move it forward.
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      07-10-2009, 10:08 AM   #7
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Quote:
Originally Posted by Kojak View Post
I frequently feel a bump as I take my foot off the brake at a traffic light and step on the gas gradually to move forward. It has always felt to me like the car started to roll backwards when I took my foot off the brake and then jerked when the transmission engaged to move it forward.
FYI, the tranny will not go into neutral with the brake pressed if you are in sport mode.
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      07-10-2009, 01:45 PM   #8
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I only put it in sport mode when I'm planning on driving agressively - ie about half the time
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      07-14-2009, 02:43 PM   #9
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Quote:
Originally Posted by apollner View Post
It's happened to me a few times. I'm at a traffic light, I have a car behind me, and I sense what feels like someone bumping me ever so slightly from behind. Then I look in the rearview mirror and see that the person behind is not close enough for them to have actually bumped me.

I think what is happening is some sort of resetting or rebalancing of the torque distribution between from and back wheels. I'm just guessing, I really don't know.

So the last time it happened, I took conscious note of surrounding variables.
a) I had my foot firmly on the brake pedal.
b) I did not feel any modulation on the brake pedal.
c) The car had the Sport button depressed.

I state the above, because on previous occasions when this happened, I did not remember if my foot possibly had released some pressure off the brake pedal.

The feeling is somewhat similar the the slight "nudge" you get when putting the car from park into drive.

Anybody else experience this? Any further thoughts on what could cause it?
yup I noticed this too and turned on the camera to see if the guy behind had hit me but he was 3 ft back. I notice it does fell like someone nudged you, I didn't experience this on my X5 which was a couple of years old or on my wife's 330.
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