The original tire fitted on all new 1993-2000 Eurovans was either a 195/70-15, 205/65-15, or 205/70-15—which range in diameter from 25.5" to 26.3". The original tire on all 2001-03 Eurovans was a 225/60-16, which is 26.6" in diameter. The tire that GoWesty recommends for all Eurovans is the 235/60-16, which measures 27.1" in diameter. This change represents as little as 1.9%, and as much as 4.3%, difference compared to the original tire size.
This change means that your odometer will read FEWER miles—and your speedometer will read SLOWER—by those percentages, depending on what tire is size is being replaced. To put this in perspective: at 50mph, this represents a change of between 0.95 and 2.15 MPH. Keep in mind that the original reading is not perfect and most likely reads a little too high. So, in many cases, this change will actually make the readings more accurate. But even in the worse-case scenario, the change is not severe.
GoWesty feels the benefits of the larger 235/60-16 tire size vastly outweigh the relatively minor error that the tire size change may induce.