You use the RIGHT side arms on our street cars to eliminate the need for excessive shims (which can push the factory a-arm into the pass header under full articulation, or be very close to your steering shaft on the drivers side). I went looking for this post to update after my alignment after installing my Speedway arms 1-1/2yrs ago (both RIGHT side). They have been doing just fine. I decidedf to finally get down to the alignment shop last week. You may not believe this, but my car required NO shims. I didn't believe it, but I was in the bay with him and read the machine for myself and saw the results.