Towing with my 35D- load leveling?

[FunfDreisig]

@ spyro235 Thanks for following up on your original post. I look forward to hearing your experience with the air suspension add on.

We recently bought an AirStream NEST (4,000 lbs & 400 lbs tongue weight). It is light enough that we have very little squat. But I'd still like to smooth out the minor hobby horsing over railroad crossings, etc. So I'm very interested in your future posts.

Funf Dreisig

[spyro235]

Just want to update this thread- towed 2300 miles over last thursday, friday, this monday and tuesday. The 2 weekend days were the drift event at the wonderful USAIR track in Shawano WI.

The drive was GREAT. The bags in the rear basically completely eliminated squat, with 600-625# of weight on the ball. The ride was splendid. Other then slightly longer acceleration and braking distances, the ride just felt like a normal X5 rolling down the road. Averaged 18.9 mpg through the entire 2300 miles, and didn't have a single issue the entire time. The 75+ mph downhills with crosswinds and lots of truck traffic made it a bit squirelly, but I rechecked the tongue weight and found I had only weighted about 525 lbs on the ball accidentally. Bumped it up to 600 even a few hours into driving by tightening the front straps and loosening the rears, and it became super stable again. By my estimation my trailer was anywhere form 6200# to 6600#, a bit over USA's rating, but well within my trailer's 7k rating, and the oem bmw EU rating.

Overall, the trip was a supremely comfortable one. Wasn't white knuckled, and had my brake controller set up to brake bias the trailer slightly, and I encountered one REALLY heavy braking situation along the way, in which I basically panic slowed from 75 to 30ish when a semi just didn't check his mirrors and came into my lane. Car remained super stable and tracking straight, while DUMPING speed. I was honestly impressed with the whole setup, especially with my continued confidence in the build quality of my Big Tex 18' trailer. I'm happy to answer any questions!

For reference, I ran my bags at 41PSI the whole trip. After the first day, I checked and found them at 36PSI, but I attribute that to the loaded wear in stretching of the bags. They have held 41PSI since then. The instructions say "for spring pitch gaps of over 1", use max 35psi, and for under, use up to 50PSI, and my gap measures aarroounnndd 1", so I set myself a 43psi limit. It still squatted a bit at 30psi, so I went to 41-42ish, and it just took the weight without issue.

[bfeng]

Great review and feedback. I only get about 13 mpg towing my 5500lbs race trailer at 65-70moh, but it is big tall flat-front box. When I had a 850lbs Trailex open trailer I got closer to 16.5mpg on the highway. You should be very happy with almost 19mpg!

[spyro235]

I'm sure if I cruised at your cruising speeds, mine would go down to the same. I'm still heavily considering trying out the 50i diff swap, which would lower the final drive from 3.46 to 3.15. If I remember correctly when I did the math, this would make the new 5th gear 5% shorter than our current 6th gear, so at worst case, towing would be done in 5th instead of 6th. For every day use, I'd love to have the longer final drive, but the car is geared phenomenally right now for towing. 95% of my driving is just highway commuting, in which I would absolutely love to see the 3-5 mpg gain that the 8 speed in the f15's get on the highway. I love the 27mpg I get with a heavy foot, and the 28.5-29.5 I get wiht a light one, but netting 32-35mpg on pure highway would be really beneficial for me over the next few years. I'm well on track to run about 40k miles a year, so it wouldnt take long to recoup the $3-500 in parts I'd spend on the differentials.

[bfeng]

That is also phenomenal highway mpg when not towing. I average 27mpg @ 70mph actual (indicates 72mph on cruise control). The only time I break 30mpg is cruising on flat roads w/o traffic between 40-55 mph.

[spyro235]

Oh man, I’ll get 27mpg if I’m real highway cruising at a real speed of 75-80. I’m deleted with dudmd stage 2.
I usually get 28.5-29.5 at 70 real speed on cruise control. I’ve gotten 31.4 when spending an entire tank at 68 real speed, and I haven’t had the patience to try slower.