Wheels spacers are used when fitting wider wheels with larger offsets. To place the wheel centre line back over the centre line of the hub. Use of them on standard wheels just to increase track is not advisable as it imposes extra load on the wheel bearings. It also changes the steering geometry. Making it more likely that in the event of an high speed puncture or a wheel hitting a pothole the steering wheel will be snatched to that side. On PAS vehicles not that noticable, but a lot of extra strain is applied to steering gear, which could result in a sudden failure.