Towing, continued: Easier on the tranny in Steptronic mode?
 

Doing my 1st tow gig to the track this weekend with the X5. Do most of you with automatics tow in Steptronic mode? Does it alleviate some strain on the transmission?

I do not have much towing experience with the X5, but I have been towing with many different trucks and SUV's for 15 years. Normally I tow in D and let the trans shift itself. Where I deviate from that is hills - it is better to hold it in the proper gear for a hill so the trans does not keep shifting between gears. Heat is caused by shifting, so avoiding that up a high stress situation like a hill is a good thing. Otherwise, using drive is perfectly fine.

I tow almost exclusively in Step mode. For most highway towing, I keep it in 5th up to 70mph before letting it go to 6th. And even then, for anything more than just slightly hilly terrain, I just leave it in 5th. If I leave it in D or S, at 65 on the highway it's constantly up and down shifting. And shifting is slip which means more heat in the trans.

Pulling my track car on the open trailer, 4300 lbs with tools and tires on the tire rack, I'll get 11-12 mpg at 75-80 in 6th. If I slow it down to 70, I'll get 11.5-12, regardless of whether I lock the cruise in with 5th or 6th gear. At a steady 65, I can't use 6th at all, so have to keep it in 5th for about 12 mpg.

Keep in mind that peak torque on the 4.4 is somewhere around 3400 rpm so you want to be somewhere in the 3000-3500 range for pulling performance. In my X5, 3000 in 5th is about 72, but shift to 6th and it's just 2300, far off the torque and hp curve.

I towed primarily in auto mode, but used manual mode fairly frequently. You want to avoid having the transmission hunt for different gears, that causes additional wear. Equally important, however, is to keep the transmission torque converter in lock up mode on the highway as the torque converter produces significant heat. A long time poster named withidl has summarized this very well over the past few years. Some of his key posts are linked below, have a look:

Xoutpost.com - View Single Post - BMW Towing ?

http://www.xoutpost.com/bmw-sav-foru...-mountain.html

http://www.xoutpost.com/bmw-sav-foru...airstream.html

Xoutpost.com - View Single Post - X5 3.0 Steptronic Question

Thanks for the replies! Great info. I have a 3.0, so I want to make sure I'm towing as 'efficiently' as possible!