So..... I've performed alignments since 1981 professionally. I've used just about every type / brand of equipment and aligned just about everything that would fit on the rack. Further, I've studied this in depth and have attended a lot of training courses over the years. To the point that I taught other technicians 'the rope's' of the business of aligning vehicles. My specialty was problem vehicles that had been to other shops and end result was not satisfactory-or-where vehicles were heavily modified, like a 4x4 truck that was lifted with tall tires, which throws everything off from the manufacturer's original engineering of all the planes of angles working in unison. Specifically steering axis inclination along with axle centerline ( height) point of intersection with the center of the tire tread as it meets the road.

While the summation of this part of my career may or may not qualify me as an expert, at least possibly very experienced. One thing to remember is that when the vehicle is on the rack, all 4 wheels/ tires are sitting on 'floating' plates that allow the suspension to settle naturally.

Remember that the tire wear you see is a direct result of 1 or more angles out of spec, it is a reflection of what is wrong with the settings. Installing new tires w/o changing any mechanical settings will yield the exact same readings/ measurements as before as the vehicle is sitting on floating plates on the rack.

To the OP, depending on the amount and severity of the wear on the tires, the old tires CAN affect how the vehicle drives AFTER a proper alignment if not changed.

^^ Agree, it's just a question of degrees. F1 versus my daily driver.

^ this is why I ask questions on Pelican rather than just look them up on the internet. (also why I preface things I have an opinion on with "I'm not an expert" since there probably is one here)

I've always wondered just what can be adjusted on the suspension of your average daily driver with MacPherson strut front suspension, other than toe in? I've put brakes on my Infiniti FX35 a few times now and I don't recall ever seeing anything that could be shimmed or adjusted other than the tie rod ends.

Cool. Did not know that.

Assuming nothing bent, all part are good, you can easily add camber adjustment by slotting the upper bolt hole in the strut stem to knuckle attachment point. Some aftermarket manufacturers offer camber/ caster adjustment plates on top where the upper strut mount attaches to the tower.

These types of modifications are for the driver that wants more aggressive settings for better handling that are not attainable otherwise.

So when I take my daily driver in for an alignment, they're checking everything, but if anything other than the toe is out of spec. worn or bent parts need to be replaced. Or possibly some time on the Celette bench.

Have to agree to disagree with that last part.. I'm in the same boat though. Professional ASE Master Tech and have been wrenching since 1982.. (you got me beat by one year..lol.) I've also been to numerous classes etc and then taught at the manufacturer level for many years...etc.
I agree about the floating plates obviously as that accounts for the suspension to settle etc, but that doesnt account for a tire that is not sitting flat/straight/true because of wear. Even with the suspension settled, if the inside of your tire has no tread and the outside is full (for whatever reason) then the entire wheel is tilted inward, even with the suspension settled, - alignment angles with it. So if you align the car in that situation, when you put new tires on later, your angles will be incorrect...

It is rather diffcult to try to explain this over text!! I do remember watching a training video on this exact thing WAY back when though and I guess it just stuck with me..

Exactly. I had a F100 back in the '80's that had been hit in the front. Would get it aligned when I bought tires. Then one day the shop that had been aligning it for years told me that it was too badly damaged to align. Steering box was out of whack, yada yada yada. I said you have been aligning it for years. He said yeah, I know but we got this new computerized machine that won't let me. I drove it for few more years without alignment before trading it in. Tires never wore uneven.

Toe and camber for sure. Toe via tierod ends. Camber is usually either via an eccentric bolt where the upright bolts to the strut or via the strut top mount (like a 911).

I think caster is also usually adjustable on the front.

Modern vehicles are so much better engineered, tighter tolerances, tight manufacturing tolerances, tighter assembly tolerances. So unless something is worn out or taken a hit / damaged - camber / caster is usually within range

But, ugh, "within range" can be total crap. I've had plenty of alignments over the years that were "within range" but resulted in a steering wheel that was off (due to laziness, I assume), or required constant tension on the steering wheel to drive a straight line (we aligned it for crown in the road), or had each side of the vehicle at extremes of the range like positive camber on one side and negative camber on the other side.

I just try not to use places that are likely to give that sort of alignment any more.

Thanks again for explaining my question, so that even I can kind of understand.
You guys are great!!
Gary

My Cayman has always handled incredible but even when new it felt a little off in the rain. A few months ago I was driving in heavy rain and it felt like the back end wanted to step out in a scary way. So I took it in to check alignment. Turns out the rear alignment was just a little off. I wonder if it was like that from the factory? All good now but point is even new a car could be out of tolerance.