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Old 01-30-2013, 09:35 AM
kpgray's Avatar
kpgray kpgray is offline
Location: Rochester, Michigan
Join Date: Oct 2012
Posts: 522
Mein Auto: 2014 335i M-Sport RWD
Originally Posted by Taeksoo View Post
I'm no engineer (obviously) but just wanted to ask if this is right.
I noticed when I'm in Drive and braking my rpm goes down then up and then down then up.
It seems like it's down shifting while stopping.
I would have thought that this would waste more gas.
I'm just curious if anyone can explain why this is and why it would be more gas efficient? Or it's not gas efficient but help stop faster?

Sent from my SCH-I535 using Bimmer App
I just came out of an Acura TL to a 328i xDrive and I also noticed the engine drag seemed greater than my Acura. My Acura almost seemed to coast in comparison (or disconnect from the engine) when I let up the gas, my Acura would certainly would coast further upon deceleration, however, upon further investigation, BMW has a Brake Energy Regeneration System (link below) that shows it as one of the Performance and Efficiency items on the 3-series features and specs page. I notice when you decelerate, it takes just a moment after you release the accelerator (about the same amount of time you wait for the auto stop/start to turn the engine off at a stop light) and then you will feel a slight perception of the engine downshifting, I believe that is the regeneration system taking the momentum energy and using it to charge your battery. I have found that I can utilize the drag to coast into a red traffic light with less braking and not irritating the person behind me. I am not real familiar with the system, but I had inquired about the deceleration and was told by one of the experts from BMW at the local summer Olympic Drive event last year that is what I felt.
Kenneth P. Gray
2014 Black & Tan 335i M-Sport/SAT/PP/TP/CWP/DAP/HK/403M
2010 Cadillac SRX Performance, Platinum Ice/Ebony (Wife's drive)

2014 Black/Tan 335i M-Sport/Sport Automatic Transmission/Premium Package/Technology Package
Cold Weather Package/Driver Assistance Package/Harmon Kardon sound/19" Wheels 403M HP tires

Last edited by kpgray; 01-30-2013 at 09:39 AM.
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