Rep Power: 0

Will it affect my engine if I put the wrong size tires on the car?

I bought some 17's and the Tire Rack says that the proper replacement size is 205/45. The tire calculator says that 205/45's will throw off the speedometer so that when it says 60mph I'm actually traveling 60.2mph. Now 205/40's throw off the speedometer so that when it says 60mph I'm actually going 58.9mph. I've found the tires I want and the 205/45's are $105 a piece and the 205/40's are $78 a piece. My gut is telling me to get the proper size but my wallet is telling me to get the cheaper size. Will it affect the car if I put on the 205/40's?

 
Rep Power: 311

It will only effect the speedo. I have 215/40/17 and I barely even notice the difference. What is it off...like 3%? That's nothing. I wouldn't worry at all. The ride quality will suck with 40's tho.

 
Rep Power: 449

i would recommend 215/40...but if your set on the 205, then go 205/45