I used them on my 40 foot Kenworth box truck and a one ton GMC cargo van. They added noticeable stability. The best benefit to me was causing rain and tire spray to flow straight back from the vehicle rather than fanning out all around the back. It improved wet weather visibility tremendously. On the truck it increased my mpg about 10%. That's a huge savings. I don't know in the van as I put them on immediately after purchasing the van. If I were to get another boxy vehicle I would absolutely use them again.