I had a flat tire tire yesterday on the drivers front. My current wheel / tire set up is 18", my factory original spare is the OEM 17". Will I be causing any harm to the drivetrain by running the off size spare for a day or 2 or 3 ?

 

No, as long as the spare is on the front and you do not engage 4wd.

 

Just a little more info. Wheel size does not matter, its the tire diameter/circumference that does. When your tire size does not match it really only matters if you have a LS differential, but as kingfish stated since its on the front your in good shape.

 

Thank you for the reply's, I feel less concerned now. There is some differance in tire sizes. Three of the tires are 275/65/18 and the OEM spare is 235/75/17. I will plug the flat today and get it put back on tonight or tomorow, Monday at the latest. Unless I get called out on Sunday the truck shouldn't even be leaving the yard. I just need to get through todays work schedule with the spare.