Right now I have stock 16" tires and it looks like they will wear out this year so I'm thinking of putting winter tires on my stock rims and getting a set of 17x8 rims, the one question I still have is tire size.
I played around with some tire size calculators and this is what I came up with:

16" stock vs 17" stock: 2.16% error
16" stock vs 235/45R17: 0.06% error
16" stock vs 245/45R17: 1.46% error

The thing is i really want the 245s, and I need a second opinion on whether you think 1.46% spedometer error is that much?

My excuse is that at 65MPH it's going to be a litttle less that 1MPH of error and that doesn't seem that much considering the spedomoter needle is about 2MPH thick and at 100MPH the error would be 1.5MPH but taking into account that the spedometer is suppose to have an internal discrepancy of 3-4% or 4MPH at 100MPH the 1.5MPH doesnt seem to matter that much.

 

Who cares how far off the spedo is? As long as you know that when you see 65 you are really doing 67 that is all that really matters.

 

I made a calculator for MS Excel while back:

http://www.glue.umd.edu/~nauman/tire.xls

 

Making your diameter smaller or larger will affect your gas mileage slightly.

 

Thanks for your input,
245s it is