I just bought a pair of Continental Top Touring 2000 700/28 tires. Even though both tires have the size clearly marked on the sidewall it has become apparent to me that they are not exactly the same size. At first glance one looks to be narrower and shorter than the other. I took my metal ruler and spread the tires flat and measured the width from bead to bead. One tire is 5mm narrower than the other. Also when you lay one tire on top of the other it is apparent that the wire beads are not the same diameter. One is about 5mm smaller in diameter than the other. I have not mounted either of these tires. They still have the tags on them and I plan to take them back.
If I had bought them from any other shop taking them back would not be an issue. But of all the shops I called and visited this was the only one that had them in stock and these were the only two he had. When I pointed out to the manager that one tire looked different he swore that they were identical. When I got them home and looked again I realized my first impression was right. Based on my previous experience with this shop I know the manager is going to argue with me about taking at least the smaller one back so I thought I would get all my ducks in a row in order to present a clear case for either a refund or a replacement.
1) My argument will be that the smaller tire is not the true size stamped on the side. It is either a defect from the factory or a much older tire that was made to different standards or specifications (it does look like itís been on the shelf for a long time when compared to the other)
2) The smaller tire will have a somewhat harsher ride than the bigger.
3) The smaller tire will be harder to mount and dismount for changing flats when compared to the other tire.
4) With the tires uneven the bike will not sit level.
5) If he will not give a refund then I want him to replace both tires. The reason I would prefer both to be replaced is that it would be more likely that they would be the same size if they were shipped form the factory at the same time.
Take the tires back and physically show him the measured difference. There should be no problem exchanging them if the LBS has a habit of conducting good customer service.
As for you reasons, the 5mm difference is not going to cause any issues with the bike not being level. Most of your weight is over the rear and would most likely even it out. There will be no issue with a harsher ride. It's not like going from a 70 series passenger car tire to a 40 series performance car tire.
I would just take them back with receipt in hand and ask to exchange them for another set. This way the LBS still makes a sale and you get a set of tires that match.
Some call it God's country. I call it Acton, Maine
Too Many - 7 or 8
As long as you did not mount and ride the tires, no excuse or reason should be needed in order to return them. And in this case, even if you had mounted and run them, they were not what you were told they were, so taking them back should be no problem either.