Lace wheels are stated as '...needing maintenance'. This maintenance is generally considered to be the usual cleaning, but also includes 'inspection' to assure that spokes have not loosened up. Why? Well, simple: Spokes can loosen up!! Think about it; all that riding 'stretches' the spokes over time. Granted, in most cases this is negligible, and most people never have a problem. However, this is not to say it can't, or 'won't' happen! The issue involved in pulling a trailer with spoke wheels is simply the added weight can exacerbate the problem, causing spokes to loosen up more quickly if they're going to at all. As most folks are NOT in the habit of checking their spokes regularly, this can simply create even more of a problem when pulling a trailer. I might add that it's not uncommon to either 'break' a spoke, or have a spoke nipple simply strip and become loose as well. Due to corrosion in the hub and rim, often a broken spoke will remain in a fixed position from this.......but if not, the tell-tale 'clinking' of the spoke hitting the swing arm and more can be pretty easily recognized unless your pipes are really loud (which again is not uncommon). This 'broken spoke' issue, when masked by loud pipes, can also lead to problems with damaged drive belts or brake lines. Again, more potentially 'unsafe' issues to be concerned with. A properly built and adjusted wheel will likely not produce any kind of a 'handling' problem from lateral weakness when towing that most people would notice. But,there is 'flex' that can occur, and this flex is what leads to problems down the road......or 'can'. Add all this up, and you see why the MoCo made it's recommendation to use a cast wheel if towing a trailer. In reality, it's not a difficult process to find a cast wheel that will fit most any bike....many with no modification at all. I recently replace the 'spoke' wheels on my '05 Ultra just because I'm tired of them, plus the chrome on the HD 'Profile' rim went to hell in a hand-basket! And, I'm now replacing the spoke wheels on my '01 Road King because, again, I'm just tire of cleaning spokes. I'll also add that as stated above, the simplicity of a 'plug' in a flat when on the road is a LOT more advantageous than having to deal with wheel removal and inner tube patching!! But, I just wanted to end by saying that I'm putting '07 Airstrike wheels on my '01 RK....and this requires both the replacement of the the wheel bearings, as well as replacement of the inner bearing sleeve (a factor often overlooked until you get around to doing this, then have an 'o-schitt' moment. Anyway, cost of these wheels on the 'used' market was all of about $200, and another $20 for bearings, $10 for the sleeve, and $20 for a cheap bearing puller! I can probably get $50 to $100 'back' in selling my RK's spoke wheels....which are in near mint condition! So, for the safety aspect of pulling a trailer, and for the few hundred bucks it can cost to swap out a wheel...... I'd go with the 'better safe than sorry' approach. Not fun to have a breakdown on the road!! WC