I worked in the tire and service business till retiring in 2012 and never heard of a 3 psi extra in winter recommendation. Al manufacturers tire pressures are based on cold tires, at the lowest ambient temps expected. Of course, most of us don't air up the tires when it's 15 degrees at 4 am. We might wait till later in the day and say, 35 degrees. In this case, you would ideally add a few pounds to the manufacturers cold pressure.I understand the direct correlation between temperature and tire pressure, i.e., rise in temperature increases pressure; however, what I find confusing is the recommendation to increase tire pressure by approximately 3 PSI in the wintertime. It seems logical to me that the decreased resting tire pressure associated with cold weather would be corrected by increasing the resting pressure to "NORMAL", and adding ~3 PSI is actually overcompensation.
I would appreciate a logical explanation of the rational for increasing the recommended resting tire PSI during wintertime.
The common "one psi for each 10 degrees F" is close enough but the actual fudge factor is closer to .8 lb/10 degrees F. To figure it precisely, convert the temperatures you're working with to Kelvin and calculate the percentage difference.