It is a liability, as a dealer (maybe somewhat more liable than an non-dealer shop?).
People get sued.
We sell 700-800 tires/month at my Lexus dealership, and we will not install tires not specified by Lexus. They must be stock size and specification (load index & speed rating), and, as we learned the hard way years ago, they had better be on Lexus' "approved" list for best service and to minimize handling, wear, and noise concerns over the life of the tires.
I do buy the "bean counter affecting final vehicle delivery specs" theory, but that is not to say that I do not want to trust the manufacturer to conduct all of the testing and research so that I don't have to. I do. Specify the tire, to the tire manufacturers, so that I can buy the tire that works best on my car. Or my bike. And to not be tied too strongly to one tire manufacturer for a particular model car (or bike), share those specified requirements with other primary tire manufacturers, and indeed, fit a variety of tire brands on new vehicles assuring the manufacturers will continue production of said tires to support the vehicles. If tied too strongly to too few suppliers, things like labor disputes, or even price increases can adversly affect product supply, and ultimately the price of the final product, which of course must be competitive in it's own market.
But if I fit an incorrectly sized or otherwise non-recommended tire on a vehicle I will be married to it regardless of what happens.
Think about these smart people who want to take off the stock sized tires and wheels on their land yacht sedans and replace them with tires and wheels that may be several inches smaller in wheel diameter and tire size. And load carrying capacity. And how does that affect safety and handling? And, they are out there driving right beside you every day and night.
As a Lexus dealer, too often I am the last resort when somebody has a problem, and wants a correct diagnoses. You don't have any idea how many times I see cars in telling me they think they are hearing wheel bearings, when all they are hearing is tire whine coming from non-recommended tires. But they never want to pay to have me swap tires and wheels off another car onto theirs, and take them for a ride to prove the point, then swap it all back again. My tech is going to get paid, regardless.
But it would be the tire failure liability that could cost us the most.
