Got the wrong tire installed- 245/40/18 instead of 245/45/18

[fooitm35x]

I know, I know - should've checked before leaving the shop... The place is very reputable and I never ever crossed my mind such thing is possible...
I have already emailed the shop quoted me the right size but installed the wrong size, and I will give them a chance to fix it.

Anyway, how much worried should I be with 245/40/18?
And what can I possibly do if the shop will refuse to replace it?
It's been only two days, and it seems that Continental has Customer Satisfaction Trial program, so I hope that would cover it.

[The00Dustin]

You shouldn't be too worried. Your speedometer will say you are going slightly faster than you are, and your car will sit slightly lower than it did. Many people with aftermarket rims probably aren't any closer than that in circumfrence/diameter. However, if you want anything about the correct size back, they should fix it for you if you have it quoted right on paper and especially if they don't have it invoiced wrong (if the invoice is for the right size even though you got the wrong size) and you noticed that soon. They will probably be taking a loss, though, unless they are dishonest and put the slighly used tires on another car as new or use the satisfaction warranty even though it's not really a satisfaction with the tire issue.

[autoengr]

Specifically:
245/45R18 is 26.72" in diameter and the tire has a 4.34" profile
245/40R18 is 25.68" in diameter and the tire has a 3.86" profile

So as Dustin said, the car will sit 0.5" lower and the speedometer will read 3.6% faster than your actual speed based on the circumferential change.