Definitely. Tires pull to the side and two identical tires pull against each other equally. It is unrealistic to expect a car to go straight with mismatched tires. That applies to all older computerized alignment equipment but if the tires have the same circumference and width, the car can still be aligned. It is the suspension system that is being adjusted, not the tires. Understand that the alignment will address tire wear issues and can make the steering wheel straight, but don't be surprised if it doesn't go straight when you let go of the steering wheel.
Newer aligners that use wall-mounted cameras can take mismatched tires into account. The car may still pull after the alignment, but the settings will be correct after four new, matched tires are installed. The camera alignment systems are the first in the world that do not require the car or hoist it's on to be perfectly level, in fact, with the right adapters, the car can be aligned with NO wheels or tires on it. This technology has only been around for a few years.
I preferred to align cars just before people bought new tires so I could "read" the tire wear. That helped me to be sure I was seeing anything that needed correcting.
November, 23, 2010 AT 7:28 PM
I should add that many alignment shops refuse to align vehicles with mismatched tires because they know there will be customer complaints afterward due to tire pull. You can sit on a chair with legs of different lengths but it won't be pleasant. You can align a car that isn't sitting level, but the numbers will only be correct when it is sitting on a level hoist. It will not address the pull caused by different tires, and the angle changes as the suspension travels up and down over uneven roads.
Besides mismatched tires, weak springs are a bigger reason to not align a vehicle. Ride height is critical to proper handling and tire wear. When the suspension sags, it changes the geometry of the control arm(s) and spindle. To show what I mean, stick your arm straight out to your side. Notice how far away your fingertips are. If you raise your arm up six inches and down six inches, that would mimic your van's suspension going up and down as you peddle down the highway. As you do that, do you see how much closer your fingertips get to your body? Not much change in distance at all. Now, to visualize weak springs, lower your arm halfway down, then move it up and down six inches again. Now you can see because of the arc, your fingertips are moving a lot closer to your legs and further away. That is what happens to the bottom of a tire as the car goes up and down. The alignment numbers can be perfect, but you will still have terrible tire wear from it scrubbing sideways on the road surface. It will also be tilting back and forth causing it to run on the edges a lot. That will increase inside and outside wear.
A five year old van should not be suffering from weak springs yet but a conscientious alignment specialist will still measure ride height. Ford has always been notorious for not providing some alignment adjustments, especially on their front-wheel-drive cars, so ride height is particularly important. Some of their cars have extremely bad tire wear built in that can not be corrected. The '80s models Escorts are perfect examples. The front tires tilt out on top so much that it looks like something is broken, and there is no way to adjust it. It made them ride real smooth compared to other brands of small cars so they sold a pile of them, but you had to be pretty lucky to get more than 15,000 miles out of a set of tires. Got'cha! The alignment industry came up with some modifications that would correct the rear tires from being tipped in way too much but due to the design of the front suspension, there was nothing that could be done on the front except keep buying tires.