Need some help for choose tire size between 235/45/18 or 245/40/18?

What should I go on the rear between 235/45/18 or 245/40/18? on the stock wheel.

Thank you for you all

 

You want the same size tire all the way round. I have 245/40/18 they have more grip but can be a little more expensive and will make the car feel a little less agile.
Wider tires is my choice 245 all round.

 

In my opinion.....the actual tire choice makes a bigger difference than the size. For example, a 225/45 Kumho XS will perform better on a track than a 245/40 XXXXX (insert all season tire here).

I wouldn't suggest a 235/45 since it is larger in diameter than stock. Actual section width is greatly dependant on manufacturer and model. There are some 225/45 tires that have a wider tread width compared to some 245/40 tires. In general though, wrightcomputing as it correct, 245 will have a wider tread patch but will have a little less steering response (comparing 245/40 to 225/45 of same brand and model). Once you start comparing across models or brands though, you can't make this generalization.