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I work for a tire company and was a test driver for 8 years so I have a pretty good background on these issues. I will try to explain a couple of similar types of vehicle pull behavior that you guys are discussing.
Normally, "Crown Sensitivity" has a lot to do with how much caster the front alignment has - the higher the degree of caster the less sensitive the vehicle is to crown changes. High Caster causes increased steering efforts too.
A different behavior that we call "Truck Rut Wander" describes how tires can "wander" when encountering ruts in the road that were made by heavy vehicles. This is caused when the tire is entering or leaving the rut and can cause the car and even the steering wheel to suddenely dart left or right. This is mainly influenced by the shape of the tire shoulder (whether the shape is somewhat square or if it has a rounder shape). I am talking about the tire's profile and trying to describe the shape where the sidewall turns into the tread. Wide, high performance tires are much more square than an old 14" base tire, for example. If you are wondering, square shaped tires are usually worse for truck rut wander.
The tread pattern of the tire can also cause pull issues. Some tires have what is called an "S" type pattern. This means that when looking at the tread that all of the blocks look like they lean in the same way. In other words, if you looked at the lateral grooves they would have the similar orienations - i.e. when looking down at the tread the groove could look higher on the left and lower on the right. This type of tread can cause a pull in one direction under acceleration, and a pull in the other direction under deceleration.
One last thing to remember: If you are trying to determine if your car has a pull problem never check it from the left lane of a freeway. All roads are crowned, and all vehicles are set up to have a slight left pull on perfectly smooth roads. This is so that when travleing on normal 2 lane roads (or the right lane of a freeway) the vehicle will track straight despite the small amount of road crown (the inherent left pull cancels out the right drift due to the road crown). Road crown is there so rain will drain off of the road. The left lane of a freeway usually has a left crown and coupled with the vehicle's inherent mild left pull will cause a fairly strong overall left pull.
I hope that this helps clear somethings up and does not create a lot more questions...
posted by 198.208.22...
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