[PaulOinMA]

Sites like Tirerack will show stock sizes. 235/50-18 is correct.

My '14 Ti came with 19s. I bought 18s on here from a member in NJ for more sidewall. Bought 235/50-18 Continental CrossContact LX25 after I used up the OE tires. Great tire.

 

[PaulOinMA]

Look at the tire pressure sticker in the door frame. Lists tire size.

 

[PaulOinMA]

... or drive on terrible pot holed roads ...

I'm in New England. That's why I went -1 to 18s. Much better ride.

I blew out two tires on the passenger side on my '03 Audi A4 Avant. First wondered if I blew out a tire or bent a rim. Then huge pull to the right. Yup.

Called AAA and said I needed a flatbed because I blew out two tires and it's AWD.

Tow truck shows up.

"Is that Quatto?"

"Yes."

"You need a flatbed."

 

[PaulOinMA]

Tire size calculators available online show differences in tire size and effect on speedometer unless circumference in mm is changed.

F-150 forum has a thread on how to go in and change circumference.

Tirerack can be used to quickly find tire sizes Ford used for different wheel sizes.