Well I bought another complete set so I’ll have both on hand if I’d get a flatI don't carry a spare, even though we may be 30 miles away from the truck in the foothills, I do carry an airpump and had to use it once to help a friend out, we have also had one flat that required a trip back to the truck. I do carry a portable air compressor.
If you think you need a spare go with the 11", you will have the correct tire for the back and no problem steering unless you have a lock up type of front end.