So in your dealer's estimation only the center of the tread matters and it doesn't matter if the edges of the tire are showing cords? What a moron. You definitely need an alignment if on tire's edge is wear significantly faster than the center and opposite edge. I'd get it checked out when you put your new tires on or if you still have a lot of tread left on the Ecopias then get it done now.
Thats were people measure the tire depth. I guess i missed the part about "cords showing". The middle groves are alot deeper than the small groves. I have the same tires as the OP and have over 47k on them, and I'm thinking about getting some new ones before a trip up north in a few weeks.
I definitely don't have cords showing. On one tire, the wear bars are getting close to the surface on the edge, but there is definitely still tread. I'll try to get some photos this weekend, if time and weather allow.
When I said cords showing I was trying to make a point that just because you have good tread in the middle doesn't mean your tires are fine if the side or sides are worn down. Tread depth should be fairly uniform.
I just replaced my OEM yokahoma tires on my 2010 prius. Guess how many miles? Go on, guess.... 24,400 (ish) The guy at firestone shewed me, the bottoms had tears with peices of rubber hanging off, bad news! We keep them inflated, rotated, and drive safe (although we do use the 75mph highway about 200 miles per week). Oh well! I'm sure I'll save that $600 back in gas.
Rebound no surprise I got 30k out of my Yokohama's they were horrible, I replaced them with Nokians which are still great.
I replace my tires long before they are worn out. Why? Because they lose traction as they age. Good tires are cheap insurance. Tom
TireRack.com agrees with you and REV. Tire Tech Information - When Should I Replace My Tires? Video: What Honest Abe Doesn't Tell You About Minimum Tread Depths