shifting gears down - but following which rule?

[Helmuth]

Guys,

I am going downhills really often and long and sometimes she helps me avoiding to step on the break because she shifts one gear down - nice behavior !!

BUT:

I have never found out when she does that. Like an iPhone - great app but nobody knows how to use it. Tried to use the break several times sometimes she shifts down - see that on the RPM - but not always .... ??

Any advice or hint?

Sorry for not beeing an english native speaker.

Best regards,

Helmuth

[JCL]

Which gear the vehicle selects will be due to a combination of vehicle speed, throttle position, engine temperature, and so on. I am not sure that it is worth trying to figure out why it shifts on any particular hill, but it should be repeatable.

If you are going down a long hill, and want to use the engine to slow you down:

• Use the lever in manual mode, ie to the left, to select a lower gear. You can see how long the hill is, and the computer can't. Take control.
• Don't shock the engine and driveline by throwing it into a lower gear, apply a little throttle to ease the transition (like matching revs with a manual transmission)
• Keep the rpm at a reasonable limit, paying attention to whether the engine has been warmed up or is still cold. Cold engines shouldn't see as many rpm for best life
• The wear to the clutches in the automatic transmission happens on each shift, not with distance. So, while it is reasonable to use a lower gear on a long hill, using it at every stop sign is just silly.
• Reasonable use of the gears to slow you down will not wear things out, and you generally won't burn more fuel
• Unreasonable use (high revs, abusive shifting, etc) will cost you money by wearing things out
• Remember that in general, brakes are cheaper than engines

Hope that helps.

[Fraser]

What model E53? Diesel or petrol?

[rayxi]

Judging by the numerous posts about the infamous tranny slam, I don't think the ZF engineers even know how it works.

[bgsquad]

I noticed that it downshifts when you really slow down... i mean like 30 kph to select 2nd gear, or 40-50 kph to select the 3rd gear... once you are on the desired gear, release the brake and let it roll down hills, it will hold that gear for you. the slightest touch of the throttle will make it shift up...

So yes, as JCL said, it's better to take control with the manual mode... btw, thnaks JCL for the great advices...

[motordavid]

Many/most auto trans cars do it, in my experience...it isn't a BMW "feature".
We do a 4+ mile, slower speed, curvy downhill, coming down the Mtn: our
previous POS Honda CR-V did it, and theCEO's new Hyundai Tuck does it,
and a previous old beater co. car did it here, too. Nice, for a bit of engine braking.
JCL nailed it: all dependent on those factors, and the "why" is just what it is...
GL, mD

[Helmuth]

Thanks guys for your great advices - especially JCL
@Fraser: it is a 3.0d - just updated my profile - silly me.
All the others - thanks for your replies.

Had a Chevrolet Trans Sport before - it never shifted down - always up only. Additional I was reading that manual gear shifting in an X5 would be bad for the X.

Main reason for asking that question is that my brakes which are new (rotors and pads) are not able to do their job on long - really long - downhill roads (if you have Google Earth installed here is the Link: http://toolserver.org/~kolossos/eart...me=Plöckenpass)
After driving that road the brakes are really smelly and dark blue..... !?!
Front Pads are EBC yellowstuff and back pads EBC redstuff. Rotors are new but I am afraid not the original ones.

Best regards,

Helmuth