One set of rollers and the way it works is one wheel spins normal and the other spins opposite cos of the diffs in theses cars or most 4wd. But the tester has to select 2 or 4wd on the system before he does the test my car was done on the rollers yesterday and no issues.Thats what I mean tho...is there 2 rollers so all wheels are spinning? As far as I seen, one roller, and back wheels on it only