One thing to remember when driving in the rain, all that water being picked up and thrown around by your tires is energy being consumed. Since water weighs about 8lb per gallon, think about how many extra pounds a tire is lifting as you drive on wet roads.
At a certain (lower) RPM your tires will be lifting the maximum amount for the maximum diameter of the wheel, at higher RPM they are going to sling that water off faster and generally not "lift" as much as far.
At a certain (lower) RPM your tires will be lifting the maximum amount for the maximum diameter of the wheel, at higher RPM they are going to sling that water off faster and generally not "lift" as much as far.