[kro$s]

Originally posted by Luke@tirerack
you can use different size tires but, the overall diameter must be the same and a 225/55-17 is physically taller than the 225/50-17 size ... this diameter difference will alter scrub radius and ackerman angles wich are 2 of the alignment angles whci his why the dealer told you they wouldn't do the alignment until you had the correct tire size or atleast the correct diameter .... Pep Boys guys know very little about tires in general and they gave you bad advice

Basically!!
check: http://www.miata.net/garage/tirecalc.html