You want to change the tire size on your 2002 astro awd passenger van from 2157515 to 2157015 or 2357015 have used calculators on line but you still have concerns about effect on abs and awd?

As long as all 4 tires are the identical size you will have no difficulties as long as they fit in the wheel wells and don't rub on sharp turns. The ABS looks for a difference in speed between all 4 wheels. If everything turns at the same speed its all good. The AWD will only be affected again if all the wheels ARE NOT the same size. So as long as you keep all 4 corners the same it will be just fine.