I know if 245, it's gonna be 245/40/R17, but what about 235? 40 or 45?

 

Look at the "revolutions per mile" on the spec sheet and compare to the stock tire.

 

Neither is very good, but choose the one closer to your front diameter.

 

I have 225/45 17 in the front

 

225/235 isn't much stagger. A 245-40-17 will stretch onto an 8" wheel with 45+ offset. If you do insist on a 235, maybe drop down the front to 205 or 215.

 

If front is 225/45-17, then rear should be 255/40-17

 

I was running 245 and 255 rears, felt I bit understeering, so put 235s to try.

 

For daily driving and long commutes a 215/45/17 or 225/45/17 fronts and 235/40/17 or 245 or 255 rear will suffice. I have had all of the above.

Currently I am running 225/40/17 fronts and 245/40/17 rears. Works great with the R compounds..

But in all honesty you want to stick with a 245 or higher if your on a 17x8 or higher width rear wheel.