It sounds like the tread width in millimetres
No, a 245 tire is 245 mm wide. A 275 is 275 mm wide.
If you mean a 245 tire there is not enough information to answer. Things that you left out of the question like, year and model Jeep.
Doubtful, since the radial is bigger on the r17...
There were two original tire sizes for this car. 245/70R16 245/75R16
It is 245 mm wide at tread.
Yes you can
Yes you can
The biggest stock tire I have seen is a 245/70/16
117
3996
NO, the 245 tire will be smaller in overall diameter and your speedometer will be off. Handling, ride, power, and fuel economy will be effected.
245/70/17 Most models come with 245/65R17