Sam wrote:
  If somehow you put smaller and lighter tires and wheel into the 15" setup, you could gain power.

Sam has a great point.  The stock steel rims and 185R14 6-ply tires on our van weighed 42.6 pounds each. The 15" Audi 5000 rims with Nokian 205/65R15 XL tires weigh 37.55 pounds per corner. This is a 12% saving in unsprung weight and rotational mass with no change in gearing but with stiffer sidewalls and a larger contact patch.   (I know the Audi rims may not be as strong as stock, but they work well for us and lots of other Vanagon and Eurovan owners.)

George 

'85 Westfalia