Just bought a 2015 4x4 Expedition with 20" wheels and noticed the spare is 18". Looks like they couldn't get a 20" underneath if they wanted to. How will this affect driving to the nearest tire repair shop if I have a blowout? How far would you drive on it?

 

Just need to compare tire diameters...... although you will feel a slight difference at the steering wheel, overall it should be the same in terms of handling, driving (temp)

Tire Size Calculator

 

.2 difference.

 

Forgot, thanks for the calculator

 

I've had the 18" spares on my 20" equipped F150 twice. You can't tell the difference in normal driving.

 

Wheel size doesn't matter, it's the tire diameter, which are the same.