Radil Pull????

[Sicnarf]

RADIAL pull is what I'm trying to say.....O.K. so I don't type or proof read well.
2006 Buick Lucerne bought new. Currently10,000 miles on vehicle and OEM Bridgestone tires.
A few days after we took delivery we noticed a "pull" to the right and took it back to the dealer.
He fixed(?) we drove car for 9950 miles with no "pull" but got a flat. Took to Firestone to fix where upon I found I needed an alignment as my front tires showed mis-alignment wear.
I returned to dealer, paid for alignment and rotation. (Dealer admonished me for failing to have tires rotated at 5000 miles. Manual says between 5 & 8000.) After alignment car pulled to LEFT (and my air bags needed service).Dealer fixed air bags but says the left pull "might" be Torque or RADIAL pull and could do nothing about either.( Oh yeah, he also mentioned "road crown",I reminded him we're in Houston where ALL roads are crowned RIGHT for drainage.)
Returned to Firestone had them Balance and swap two front tires car NOW pulls to the RIGHT.
The "pull" is more pronounced on excelleration BUT you have to steer to the left to go straight.

Questions:
Which swapped tire would have the "pull", drivers side or passenger?
Since the swapped tire was once on the rear could it have caused the alignment problem to begin with and could the "swapped" tire cause it again?
Would buying a 1 new tire cure it?
Any other advice you might have would be appreciated.
Thanks
Sicnarf

[CapriRacer]

Radial pull is the vector sum of the conicity values of the tires.

I know that's a pretty "jargon" filled sentence.

Tires have a property called "conicity" - root word "cone" - that causes a force to be generating in one sideways direction or the other (or if it is in the middle, the value would be zero.)

If you add the 2 values for the front tires, that is the force pushing the front end of the car sideways. Each vehicle has its own threshold below which the vehicle will not respond to this input.

For example: Let's say your vehicle is sensitive to values above 10 and the values on your tires are +8 and +6 (=+14). Then your car will pull one direction. If you swap tires side to side, the the +13 is pushing the other direction, and since the sentivity level of the vehicle is 10, the vehicle will pull the other direction.

Now let's change one of the tires, so the tire values are +8 and -6 (=+2). Even though the values are the same magnitude, there is no pull (It is below the threshold for the vehicle.)

Now let's change the alignment and use the original tires (+8 and +6). The alignment changes the "centeredness" of the sensitivity, and it could be that the sensitivity level would be skewed like this: Values above +15 to the left and above -5 to the right. In this case there would not be a pull if the tires are mounted with the pull to the right - the alignment is compensating for the tires, but there would be a HUGE pull of the tires are mounted with the pull to the left.

Hopefully you've picked up that it isn't just one tire - it's the pair - and that changing just one tire can change the way the pair "pulls" - and it is possible to set up a vehicle alignment to compensate.

One last thing: It is possible to start with tires that are have no conicity problems, and put a wear pattern into the tires that increases the conicity. This will happen slowly over time.

Unfortunately, vehicle alignment tolerances are pretty wide and even alignment settings within "spec" can cause tires to wear irregularly. That's why I recommend that vehicle alignment be set within the inner half of the tolerance - within "spec" isn't good enough. - and I suspect that is the case here.

Where you sit is that your Buick is currently "square" and the front tires have conicity values that are causing the pull. Move them to the back and the pull will probably disappear.

[Sicnarf]

Capri Racer,
Thanks for the reply. As I indicated I moved the "worn" fron tires to the rear so moving the front to the rear puts alignment damaged tires back in the front.
How does the alignment technician determine the "conicity" of the tire to compensate for it?
Is the "conicity" a mark or value marked on the tire so one could tell what and where it is?
Thanks again for your help

[CapriRacer]

The alignment tecnician can't determine the conicity of a tire (OK, there is one exception), and shouldn't adjust the suspension to compensate (although I think they sometimes do), because it may cause irregular tire wear.

As I pointed out, the conicity value can be changed by wear, so there isn't any point in stamping or indicating what the value is unless the tires are new and being assembled in sets. This is something car manufacturers require, and they each have different methods, but most involve a trailer load of tires being within a certain range, and the next trailer load being a different range, and they don't mix the trailer loads.

If I were in your shoes, I would either live with the pull, or swap tires front to rear, or buy new tires, which ever makes the most sense.