Quote:
Originally Posted by JCL
There is not a 2:1 relationship between weight-distributing hitch capacity and non-weight-distributing hitch capacity. There may be such a relationship for a specific model of hitch drawbar, but that doesn't change the vehicle's towing capacity. If it did you could put a class 4 hitch on an X5 and tow 10,000 lbs, which you can't do. You can't extrapolate and say that the chassis can handle 12,000 lbs, that would be extreme for a unibody.
There is a chassis limit, a braking limit, a transmission limit, a cooling system limit, and so on. Whichever one you hit first defines the vehicle towing capacity Early 3.0 X5 models had a 5000 lb published towing limit with the automatic, until 2004. European models had either a 7700 or 7900 lb towing capacity with a special factory towing code option, as I recall.
I think you are brave to tow 7700 lbs with a significant aero drag, with a 3.0. Perhaps you don't have any hills. I wouldn't be as worried about stability, with your Hensley hitch, but I would worry about power, clutch life, and the smaller 3.0 brakes.
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Perhaps I wasn't clear about the 2:1 relationship. What I meant to say is that GENERALLY speaking, that is the relationship. Of course, towing 12,000lbs with an X5 would be utter stupidity.
You make a good point as to the aero drag. However, I think we can say that aero drag would be an inconvenience rather than a safety concern if it's not affecting stability, correct? At least that's how I see it - if it was stability, I could see it being a safety issue, but I don't see a lack of sheer power being a safety deal. We're also talking about 65mph, not 80. But, I digress. If you have any counter opinion I'd be interested to hear it (I'm serious - not trying to be snide).
I've considered the brake issue. Brakes are upgraded with Carbotech track pads and Motul fluid so I'm not worried about overheating or anything. If the towing goes well, I will upgrade to a large brake kit for extra peace of mind.
Your European numbers are actually quite interesting. Where did you hear about that? If that's true, I may be better off than I thought. Of course, the drag issue still exists, but as far as stability and safety, there should be no question if the 7,700/7,900lbs figures are correct.
As far as aero goes, time will tell. I'll be sure to report as soon as I experience the first tow.