I'm considering carrying one of my winter tires (on 19" wheel) with me as a spare. The winter tire is a 255/60R19 and the summer tire is a 275/50R20. The diameter difference is 0.2" and 5 revolutions per mile (675 vs 670) between them. I'd like to know if using it as a spare for lets say 150 miles is within the tolerance of the AWD system or will it cause damage. The mini spare that comes with a GL450 is a T165/90D19 and is spec'd at 677 revs per mile. I carry a compressor, plug kit and slime but there are some wide open spaces where I live.