Assertion: tractor's axle | /r/HasAspect | single wheels
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Source sentences:
text: In the UK, some semi-trailer trucks have eight tires on three axles on the tractor; these are known as six-wheelers or "six leggers", with either the center or rear axle having single wheels which normally steer as well as the front axle and can be raised when not needed (i.e. when unloaded or only a light load is being carried; an arrangement known as a TAG axle when it is the rear axle, or mid-lift when it is the center axle).