Back when I started driving OEM bias ply tires were only good for 12k miles and you would do a 5 tire rotation for that first year and buy 4 new tires of better quality that would last 16-20k and keep the best of the original tires as the spare.
When winter arrived you would buy 2 studded snow tires and 1 used steel rim and have them mounted for the winter season on your spare and that used rim.
When summer arrived you would dismount the snows and put one in your garage and one in the trunk as your spare.
From then on you did a 4 tire rotation. Things progressed over the next few years first with belted bias-ply tires that would last 24-30K miles and then steel belted radials that lasted 30-40k.
My first radials in 1974 was a set of Kelly's that had 4 body plys and 3 steel belts. The ride was punishing but the handling was phenomenal
As has been mentioned before the early radials were rotated front to back. I don't recall ever asking why but just followed their instructions.
For a few years there were a variety of radial construction ideas. Steel, polyester, nylon, rayon, fiberglass, aramid, and even Kevlar was used in the radial's construction.
I don't know when the rotation changed back again to one of the cross rotation methods but I am guessing about 15 years ago as I am fairly sure the OEM Vectors that came on my '84 Dodge Aries were still rotated front-back.
After that I had 2 T-Birds, an XJ, and 2 Audis. The T-Birds and Audis had direction performance tires and has to be rotated front-back which had been my practice for many years. I bought the XJ while I still had the 2nd T'Bird so I rotated the OEM Wranglers in the same manner.
What does this have to do with ProComp you say.... If the ProComps are directional they will say so on the sidewall. If by any other quirk in their construction they require a specific rotational method the manufacturer will advise you. They may not have an incentive to maximize your tires longevity but in this modern litigious society they absolutely WILL NOT advise you to do anything that would lead to early catastrophic failure as shyster lawyers would have them in court until they drove ProComp into bankruptcy with both real and fraudulent claims.
For what it is worth my WJ's manual and the factory manual (on CD) recommend forward-cross back rotation. on section 22 page 5 STANDARD PROCEDURE - TIRE ROTATION
Tires on the front and rear operate at different
loads and perform different steering, driving, and
braking functions. For these reasons they wear at
unequal rates and tend to develop irregular wear
patterns. These effects can be reduced by rotating
the tires at regular intervals. The benefits of tire
rotation are:
² Increase tread life
² Maintain traction levels
² A smooth, quiet ride
The suggested method of tire rotation is (Fig. 10).
Other rotation methods can be used, but they will
not provide all the tire longevity benefits.
(Figure 10 shows four tire rotation with the rear tires to the front on the same side and then the front tires crossed and mounted on the rear)
My Conclusion: Your spare is a spare, it is just meant to last until you are able to get the flat tire fixed or replaced. I have a brand new OEM Wrangler ST as a spare and it is going to stay there. When I bought the WJ a part of the deal was a replacement of the tires with ones of GOOD quality. I got a set of 4 highly rated Kumhos for an additional $125 to replace the Wranglers