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I haven't driven the HDC, but ... (archive)

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Posted by here's the pic - MicahO on October 19, 2001 at 15:52:22:

In Reply to: (damn).. posted by Dragos on October 19, 2001 at 12:38:56:

I have read reviews that talked about overheating the brakes on off-road tests. If it only works up to 5 mph, I have to agree, I don't know how one could overheat the brakes at that speed.

Granted, I haven't had to hold my van steady at 5mph on long descents, but I have had to hold it in check on a number of occasions that required a LOT of engine braking and a fair amount of brake. On a 5000lb+ vehicle with an 8800lb gvw, I was able to move it through some ridiculously long, steep, twisty and narrow passes in the North Vermont mountains without overheating the brakes or tranny. These roads were paved or at least dirt/gravel (not real off-road), but the vehicle had much more weight, and I bet much less brake than the X5, so maybe the x5 could deal with most hills no problem on brakes alone.

I will have to see what my old Car and Drivers said about that system and the circumstances that led to the overheat. I still don't like the principle much.


Finally, and on a semi-related note, what the hell was BMW thinking with the Hill Descent Control in the X5? A system that slows vehicle progress ONLY by engaging the brakes, thereby massively overheating them on a longer slope??? If I can't figure out how to downshift and do it my-damn-self, I'll take what GM/Allison have done on their new intelligent transmissions.

(I guess my post didn't help at all in the end..)
As for HDC, there's what BMW was thinking :
- they got an awesome deal of getting the "technology" (probably co-owners of the patent now) from LR before dumping it to Ford. Now Ford can't quite liberally use it for their own purpose.
- HDC works up to 5mph and that is no speed that can overheat your brakes, even given the steepest and longest ramp. The beauty of the system is that it works so smooth - at such low speeds any excessive braking (engine or mechanic/hydraulic - you know what I mean) inputs disrupt the balance of the vehicle.

I seriously doubt that you could keep a car going down a steep slope at a constant 5 mph.

doesn't know how a LSD presents itself but has one anyway

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