I've been riding Continental CityContact 26x1.5 tires (stock on my LHT) for 4,000+ miles. They have been great tires. Just two flats, both on the rear tire, for most of those miles .... but in the past two months, I've gone through 5 tubes on the rear tire. My questions:

1) How do I know when I need to replace my tires? I assume that the rear tire needs to be replaced due to the recent frequency of flats. However, although there are small tears in the tire due to prior flats and small cracks in the sidewall, the tread is still good and I cannot see the tire fabric through the rubber, hence, according to Sheldon, the tire "looks" ok.

2) What is a good replacement tire? It appears that Continental has abandoned the CityContact 26x1.5. I'm considering the Continental TravelContact 26x1.75 as a replacement, since I've had a good experience with Continental tires and the TravelContact has good reviews. Would this tire have noticeably higher rolling resistance due to its slightly larger size (1.75 vs 1.5)?

3) If I decide to replace the rear tire with a TravelContact, is it okay to replace the rear tire only, or should I replace both tires as a set since the TravelContact is slightly larger?

Thanks much!