Is it possible and common for front wheels to have a different alignment?
An example: could my front left be 1mm toe-in and my right 2mm toe-in.
I know wheels are connected through the steering rack.
The car I'm thinking about only has toe-in and out, other adjustments like camber are not possible.
You are correct that the two wheels are conected, and in practice, when driving, usually they will try to centralise themselves, so the running toe will equalise.
However, alignment should always be done with the steering wheel pointing straight ahead, to centralise the rack. As the wheels turn for corners, each wheel will turn different degrees, to allow for the outer wheel taking a larger curve. If the rack is not centralised, the wheel angles will be incorrect. The wheel with the greater incorrect reading will tend to show the most wear, as its angle on corners will be the most incorrect.
Measurements are taken from this central position, resulting in possibly different readings each side, then proper adjustments should be made to align each wheel, to maintian the straight ahead.
A general rule was that rear wheel drive cars had toe in, and front wheel drive had toe out. The reason for this is that with RWD, as the car is pushed, the front wheels have a tendency to turn outwards, so the toe in is supposed to compensate for this, accounting for the play in suspension bushes and flexibility of the tyre. As we moved to radial tyres, toe in/out changed. A FWD car tends to pull its wheels inwards as the wheels are driven, so used to have toe out. Of course, nothing is as simple as that, and manufacturers have to test and calculate accounting for suspension bushes, movement on bumps, vehicle loading, etc.
Excessive toe in tends to make the car turn into corners more abruptly, but with the wheels not working as a team, grip can be lost sooner. With excessive toe out, turning into corners becomes vague, as the outer wheel has to move further before it starts the affect the turn. This can be a little worrying as hedges, or oncoming traffic seem to come at you, while the car refuses to change direction.
Handling is the best reason to get them aligned properly, uneven or excessive wear is the usual iincentive to fix it, as it hurts the pocket.
Never try to move the steering wheel to correct it not pointing ahead. This used to be common practice, and still occasionally it is done, makign the alignment process longer, and more expensive. Most cars nowadays seem to have a master spline to prevent this.
Sadly, even with correctly aligned steering, many cars will still pull to one side. Suspension geometry is complicated, and different designs and setups can tend to pull more or less than others. Rear wheel alignment can affect the pull, and many Panda 169s appear to be afflicted, due to poorly aligned hub carriers on the rear axles. Correcting this needs patience, and lots of experimentation with shims. Sadly, aftermarket axle manufacturers have copied their sample so exactly, theirs are misaligned too.
