>XSX450 perhaps a better solution, especially with your aftermarket hitch, would be to get a small motorcycle trailer. I think even with the more robust factory hitch, you would be exceeding the recommended tongue weight with that bike carrier. A trailer big enough for a pair of dirt bikes would weigh very little; I'd bet you'd be well under 1,500lbs with two bikes mounted. And the tongue weight woud probably be very low; well within the recommendation.

Just so you know, if there is ever an accident, and that bike comes off and hurts someone or damages property, your insurance will scrutinize your hitch and load before paying any claim. Auto insurers are well know for backing out of massive claims due to overloaded trailers, exceeding vehicle towing recomendations, etc. A favorite out is a vehicle may be rated for 6,000 lbs, but the fine print, (which most owners ignore,) might say over 3,500 lbs you need a weight distribution hitch and electric trailer brakes.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp