When talking about tire handling what is tramline mean?

This is the tire tendency to follow road irregularities such as groove left by heavy trucks.

Kind of fighting with your steering wheel to change lane or keep it going straight.

Like you're riding on rails that steer the car instead of you! As tramways do!

Larger (245mm + ) low profile tires are more prone to this effect, when the contact patch is wider than it is long, tramlining is more likely to occur.

I think the main reason for tramlining is the tire design.

Some says that more longitudinal grooves in the tire = more tramlining.

In my case, with a 2000 Mustang GT, no sign of tramlining with new Pirelli P7000 245-45-17, but as they wear, it become present.

With Michelin Pilot MXGT H4 245-45-17, there is so much tramlining that it was dangerous.

Just in between with used Michelin Pilot Sport 225-50-17, they tramline but are not dangerous.

With Toyo Observe G0-2 (winter tire ), 205-65-15 , absolutly no tramlining at all, never, in any road condition.