My ramp also has a heavy "Sandpaper" finish and is usually OK to drive up unless it's wet. What happens is the front tire hits the break between the door and garage just after the back wheel has cleared the first bump coming off the ground and onto the ramp. As stated elsewhere you need the right speed hitting the ramp to get up while measuring your hard stop precisely at the wheel chock. If the wet rear wheel spins just a little I loose my momentum, so wet or damp I recommend extra care when loading. Also, as others have noted, raising the ramp door and driving up an extra supplemental ramp will help as well as raising the front end of the RV a few inches by lowering your front stabilizers. Hope this helps if you're getting up the nerve to load that big cruiser for the first time.
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