2003 acceptable tire sizes
 

I was hoping to get insight on to how large a tire size I can go without having to alter or mess up my transmission. I’m not looking to go to big like 20 inch tires, but I was hoping to go to about 17 or 18 inch tires safely without having to modify anything. Anyone here have insight to this. Just an easy tire swap.

Unfortunately,, it is not all as simple as that.

For example , if you install a larger tire on the front . will it contact the chassis part of the vehicle and cause problems when the steering wheel is turned to a sharp turn?

Then in the rear. when the car body comes down as when hitting a bump will the tire hit the inside of the fender well?

Some tire places can better answer what they were able to change without incurring problems.
They may also be reluctant to change anything due to the vehicle having been certified with a particular size tire.

Not sure what your motive is here, but if you would like to explain, maybe we might be able to save you some problems.

Update
 

This does explain a lot. My motive since I have had the car in original form for about 9 years or so is to jazz it up a bit. Put some nice looking all black rims and have the car sit a few inches higher. The wheel well has some room so I figured replacing the original 16’ tires with 17 or 18 would be nice aesthetically and hopefully within the realm of an even tire swap with no mechanical adjustments being made and without causing issues with the transmission.

I was looking to get all four of the same tires, I was looking specifically at 215/60R or 65R 17. That is the size I’m am hoping to install instead of the regular P205/70R15.

Hopefully someone here has trailblazer that path or has insight before I spend the money and get the tires and rims and have issues soon after.