This question has been answered many times throughout the years but i cant find a definite or straight forward answer.

If I am getting an oem set of 19" rays 8" in the front and 8.5" in the back and I already have 240-45-19's for the back, what would be the closest to the same rolling diameter for the front?

Just looking for what size tire i need in the front.

 

240-45-19

 

so the tire widths wont make this different?

 

I think you meant to write 245/40/19. Stick with that size all around or if you want a little skinnier tire up front you can run a 225/40/19 and that will work fine on your X.

 

http://www.rimsntires.com/specspro.jsp

 

I believe theres a 3% tolerance

Option 1: 235/40/19 & 245/40/19
Option 2: 245/35/19 & 255/35/19

I have found those sizes to be ok with X, If you want to be 100% safe then just do 245/40/19 on all 4.

 

Could the difference in rolling resistance cause any problems?

 

I ran stock setup (rays) directly off a coupe (225/245) with zero issues, the stagger limits are ~5* before vdc has any issues. Unless you go nuts you should be fine

 

Keep in mind, while the electronics limits are 3-5%, there are mechanical limitations as well.

The transfer case will experience more slip than usual due to differences in rolling distance. It is designed to take some as in a turn, the front wheels turn a larger distance than the rear wheels. Slip translates to heat, and that's never good for clutch systems. You may want to consider increased fluid changes to your transfer case here.

However, in 50/50 split situations, the extra diameter and rolling distance while in a straight light needs to be absorbed somewhere. Fortunately for us, this situation usually exists when the tires are on low traction surfaces such as snow and ice. I would also think that someone engaging snow mode probably has a set of OEM wheels as their winter wheels and isn't doing so on 19's. Then again, I could be wrong.

Still, it's in your best interest for your vehicle to try and match overall diameters front and rear as best as you can. You make even want to consider selling the rear wheels and buying another pair of fronts to have the same wheel diameter and width front and rear.

 

man speaks the truth.

some of these guys replying are only speaking in terms of VDC and not AWD since they own RWD models. just saying... =P

245/40/19 is your best bet all around.

 

Okay. I'll thread jack a bit haha I have 18x8 and 18x9 +32 offset all around rims. I was thinking buying a set of 225/40/18 for all 4 rims. Is that okay for my X? I looked at http://www.rimsntires.com/specspro.jsp and if I put 225/40/18 tires the max width for rims it will allow me is 8.5".

Should I be okay with that size of tires? 225mm is 8.5 something so it's just a tad stretch for the 9" right?

 

225mm is about 8.8"

Close to 9" but you'll have a slight stretch

 

Cool then. It shouldn't affect the diameter right?

 

Nope, not if you are running 225/40/18 at all 4 corners.

 

Awesome! Now I'll buy that set then. Thanks a lot!