I'm assuming that the factory spare tire is useless while running 19s.

Any one have any insight?

Thanks in advance.

 

I don't think the factory spare tire is useless based on your specs. Consider the following:

Stock tire is 225/50/17, which means 112.5mm of space from edge of rim to edge of tire. When converted to inches, that means 2*(4.43)+17 = 25.86 inch total diameter.

Moving on to 19, yours (and mine) tire is 245/35/19, which means 85.75mm of space from edge of rim to edge of tire. Using the same formula as above, the diameter of our wheels/tires is 2*(3.38)+19 = 25.76.

So, that is a .1 inch difference, and actually a smaller diameter with the 19s. If our spare tire was meant to be used with the stock 17s, then I think they'll be OK with the 19s.

One idea I had was to keep one of my 17s in the trunk to use as a spare. It would definitely ride better if/when I ever got a spare tire. It would fit nicely in the trunk, too, as that's where the manual tells you to put a flat tire (just flip the adapter).

Edit: I think I got all the math right, but someone please correct me if I'm wrong.

 

Just run the same wheel/tire in the front and you're fine.

(If you get a flat in the front, you have to make two changes. One for a good rear to the front, then another for the spare to the rear.)

 

If they're roughly the same size and fit in the wheel well, it wont matter much. Think of it this way... the corner with the spare will act like it's making a turn; the smaller side would be on the inside of the turn.

If you have a LSD, you'll want the same size tires on that axle. That may only apply to actual lockers, as that knowledge comes from the off-road world.

 

Thanks for all the help gentlemen.

 

You're not wrong

 

Just put on 19's with the same wheel ratio's. Thanks for all the input guys.

So should I throw one of my stock wheel/tires in the trunk instead of the spare? I am assuming the spares are usually much smaller. Haven't had a chance to check yet.

 

OD is the only consideration. Even without a Limited Slip Differential front end, still, put the same size tires on the front on a FF car.