Having a discussion between some people about whether or not one should go in for an alignment on old or new tires. I hold that excepting some unusual circumstances, it doesn’t matter whether you have brand new tires or tires with some miles on them. I’ve basically been told I’m a complete moron and know nothing for stating this.

And yet, none of the people who’re telling me you NEED to have brand new tires on your car when going in for an alignment can tell me why. Just that old tires will mess up the alignment process. I’m sure this is mostly nonsense, even though online, this seems to be the general consensus.

Since most alignment tools mount to the rim, and have nothing to do with the tire, I cannot understand how old, worn tires would have any effect on the measurements. I concede that if the rims and tires were mismatched this would through off measurements - but that’s the only thing that makes any reasonable sense to me.

One could take the tires off the car, and put it on axle stands, and still do a proper alignment. So what the heck do the tires have to do with it? Is this just something shops tell people to scam them into a new set of tires?

I’ve done front end alignments myself, and I remember learning to do four wheel alignments, ages ago, using rim mounted laser tools at a Subaru dealer, and I just cannot fathom how having not brand new tires would screw it up. The “experts” who disagree with me haven’t given any reasons behind why, just that the tires do matter, and old tires will mess up your alignment. Are there any experts here who have an answer? (I’m assuming if it is true, it must be something fairly fundamental, just that supposed mechanics telling me otherwise aren’t actually mechanics and so don’t know the real reason).