no idea really, all i know is that when i had the car i took it in to see if the tracking was out, and they had put the front wheels on the wrong way, they are directional tyres and the tread has to face in a certain way, he changed them over and the steering was a lot better for a couple of days, now it has gone crap again. I know the front tyres need changing very soon think they are just above legal limit. Im no mechanic but i wouldnt think the tread would make much difference to the heaviness of the steering