I trailing arms. I bumped into a tree at a few miles an hour on my 2005 Ski Doo Freestyle and it sent the right ski 6" behind the left one. After that the sled was junk because the frame was bent. Someone said I could put it on a frame machine at the body shop but that's rediculous. On my other trailing arm sled I plow over trees, bushes and stumps, and the sled is straight as an arrow...