Wow, I got a pair of 45mm sks longboard fenders for my crosscheck w/ 35mm tires because my usual preference PB Cascadia I couldn't get in that size in any kind of timely manner. The mudflap on these things is spectacular, but after my 1st commute (this morning) I fear it might actually be too much of a good thing, which I wouldn't have thought possible. The flap, which goes down past 5 o'clock on the front wheel, has enough vibration that accelerating makes it whap into the tire (and so do crosswinds). It only buzzes on the tire, does not bind, but it is kind of grating. May play w/ the stays before the ride home today to see if I can either stabilize it or move it farther out.

I just installed a set on my LHT, and I agree that the huge front fender + mudflap does seem to jiggle in the wind quite a bit. I've got it mounted pretty tight to the tire, not enough for it to contact, but I am getting more toe overlap with the fenders on. I guess I'm not super happy with them right now though they look nice...

Maybe you should stiffen the mudflap with a wire (a spoke or a coat hanger) or maybe some plastic such as a milk jug.

Never had any rubbing issues with mine after 18 months, and I've got it fit fairly snug. However, you won't want it too close to the tire because you'll be getting every little twig and acorn caught up in there.