so they are equal in roll out when mounted.... putting the wider tire on a 10" rim is equal to the smaller tire on the 9" rim. So you don't always have to have the same series tires front and back then on a vehicle because you're going by the mounted measurements and not just by what the tire says.
no you can have significantly different tires front to rear, however on a modern vehicle with brake anti lock, traction control & stability systems, the roll out must be close in order to prevent system issues, in most case they dont have to be exactly the same, however they need to be close
in the set we are selling , the roll out front to rear is nearly the same eliminating any computer system issues, the aspect ratio has to be different in order to achieve the same roll out
on some 4 wheel drive vehicles like the Grand Cherokee, wheel roll out is extremely important, in some case even replacing tires, should only be done in sets of 4, with identical tires being installed.....we have seen issues on GC for example where axle have overheating issues, and even locked up at hwy speed caused by mismatched tires