I have them on my 37 foot triple slide TT and my brother has them on his 36 foot DP. Not a lot of mileage improvement but the difference in handling is like night and day. The air tabs break up the bow wave from passing semis before it can move the trailer around. My brother carries a scooter on the back of the DP and can run all day in the rain. The scooter is as clean as when he starts out. Back of my TT stays clean. I also installed 6 Air Tabs on the sides of the TT midway to help counteract the side winds. 35/40 mph plus side winds have no affect on the TT. 60foot rig. Best $220.00 we both spent. Highly recommend this product. Good company to deal with.