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      04-25-2012, 06:45 PM   #47
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mjh93sa's Avatar

Drives: M135i
Join Date: Dec 2005
Location: Gloucestershire

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It's an often disputed subject and on the whole I think that everyone is right... and talking bollocks.

If you leave the 'box in drive then you are applying power to the drivetrain. This must be overcome by either the foot brake or the handbrake. BMW handbrakes are not the best, but can certainly hold against the creep of a modern 'box (my 135i certainly could and i would use it for a stop of say a single traffic light cycle to avoid blinding the guy behind).

Additionally, with the drive all hooked up the torque converter is doing work to apply power, so given the usual frictional losses etc it will be heated by this action and without motion there will be less cooling airflow. But it's in the most lightly loaded state and for a short period of time, certainly no worse than creeping through dense traffic chewing on the exhaust gases of the car in front with little cooling airflow. The granny in the Fiesta next to you doing 3k revs and using the clutch for speed control is going to have problems, not you.

Shifting into neutral will casue wear by engaging and disengaging drive, selectors are moving, gears are engaging, etc, etc. But, properly designed and manufactured all of these moving parts can do so over and over again for one hell of a long time.

A quick example. The gear teeth within a gearbox are subject to all sort of loads. As they mesh and disengage each gear flank is rubbing over it's counterpart in the mesh. It is then subject to the absolute forces being transmitted through it as well as the effects of cyclic loading (fatigue). However, with the correct material selection, surface hardening and general design they can be expected to last the life of the car. Just think how many times those parts are engaging and disengaging. It doesn't mean of course that they do design for infinite life in a car (BS ISO 6336 is a riveting read if you want to start to look at gear design ).

So, back on topic, and in short. Yes all methods have their advantages and drawbacks, but with modern designs you shouldn't have a problem with either method.

Personally my preference in the 135i was to use the footbrake for short stops, the handbrake (with a foot hovering over the brake) for slightly longer stops, and only shift to neutral if it was clear that you would be stopped for some time.

Gone: Fiesta - Focus - E46 320dSE - E91 330dMSport - E82 135iMSport - R55 JCW Clubman
Now: M135i with lots of toys