Tramlining:
I'm assuming a right hand drive car here. Imagine you are going around a left hand bend and want to cut the apex of a bend, so you approach the bend with your wheels close to the white line on the right side of your lane and you plan to 'cut' the apex by moving across to the verge at the left side of your lane before moving out to the outside of the lane on the exit of the bend. When you tramline the car follows the curve of the road instead of cutting the bend as you tried to steer it. You apply what you think is enough steering lock to do it but nothing happens so you have steer more to get it to move but now you have too much lock on and have to un wind again to make your apex. Now I'm not talking tyre smoking understeer here, the car just follows 'ruts' in the road until you apply extra steering angle to get them through it.
A similar experience is found as described above where you are driving along the inside lane in the undulations (ruts) left by HGV's and you try to change lane but you find you have to steer more lock than you expected to get it to begin moving and then have to wind that lock off again as soon as it stops tramlining.
Certain tyres suffer worse from tramlining than others, normally there is a trade off between off-road grip, road handling characteristics, tyre wear and road noise. You need to try different tyres to find what suits your driving.
I run 255/55/18 as well
