I've read that having an even number chainring and an even number cog increases wear on the components. I have an odd number chainring (45 T), should I worry about having an even or odd number cog (either 17 or 18 T).

with the 17 you have 17 skid patches

with the 18 only 2 since 45-18 equals to 5-2

have fun with math

sheldon suggests the opposite about even-even here.

i can't help you with the drivetran wear theory, but 17t will give you 17 skid patches. 34 if you skid with either leg. 18t will give you two patches, 4 for ambiskidding. (proof here)

With an even/even combination, only every other tooth experiences wear (you'll have to read Sheldon if you want an explaination as to why). At any rate, and even/even combo could be interepreted as good or bad. If you want your chain and drivetrain to wear out together, the drivetrain will wear together better with even/even. Your drive chain will work smoothly as it wears and you can get a lot of miles out of the same chain+cog+chainwheel. This only works if you pay very careful attention to how you put the chain on everytime you remove your wheel.

With odd/odd, all of the teeth will experience wear, but will probably wear more slowly overall, especially if you replace the chain when it becomes stretched. As the chain stretches, your drive train may become rough. If you have odd/odd, or a mix of even/odd (or even even/even but don't pay attention to how your chain is put back on when you remove the wheel) then its probably best to replace the chain frequently, and you'll get a lot more mileage out of the rest of your drivetrain.

Either way, drivetrain wear is just inevitable. My advice would be don't buy expenxive chains (Izumi or other NJS chains) (in my experience they wear almost as fast as chains that cost 5-8 times less), replace your chain often, and don't worry about whether you have even or odd numbers of teeth (although skidpatches are something to consider). Go with what ever gear ratio works best for you.

really?!! I would not have imagined in a million years that this was even an issue. Thanks, guys!