WTF?? Why diff part numbers?

[Donner]

Confused to say the least - please help explain the rim/tire ratio v. part number. Same strut manufacturer...

Strut part no. xx1 is used for a tire rim combo 265/75/16
Strut part no. xx2 is used for a tire rim combo 265/70/17

What would be the reason for diff part numbers? I'm having this prob as we speak. Why would there be two part numbers if there was no diff?

http://www.explorerforum.com/forums/showpost.php?p=1896722&postcount=32

 

[Donner]

The manufacturer assumes the stock rim is 16" Therefore, the application cannot be used on the stock 17" REGARDLESS of what year, it cannot be used or it will bounce like a basketball.