Hi, I just ordered a set of 4x 18" rims. Its 18x8, I believe the recommended size is 245/40R18. Can anyone give me a tire size that I can Staggered in the rear?

I don't think you can truly stagger if all the rims are the same size. If you are trying to put wider tires in the rear, it wouldn't be recommended if the rim size is the same as the one in front. The reason being, if you use a wider tire on the same rim, it will actually have a different rolling diameter than the other rim with a smaller tire size. The abs sensor/traction sensor may get a little "freaked out" and act up.

For example bridgestone potenza re-11 has a 235/40R18 with a measured diameter of 25.4" and a revolution per mile of 820.
A wider tire with the same height. 265/40/18 has a measured diameter of 26.3" and a revolution per mile of 792.
You can get close by getting a wider tire with a lower profile like 265/35/18 and that will give you a diameter of 25.3" and rpm of 823.
However the overall look may not be pleasing since the front wheel is gonna look "thicker" than the rear.

If you really wanna go stagger, get a wider rim on the rear.

cool then, thanks for answering... I will get the same. I think 18" is wider for my daily ride. Just want to get an idea how to do it.

why stagger tires on non-staggered wheels>?

im confused with the OPs reply...

You can stagger the tires. 215 or 225 on the front and 235/245 on the back . Actually 245 may be the max size for 8". Not 100% sure tho