I wish that could be done, but the Roval hoops are drilled for 2:1 drive-side to non-drive-side spokes. Not sure they make a Powertap hub drilled that way.
Edit: Just went and looked at my Roval’s. 21 spoke rear so I guess you could lace a 28 hole G3 using every other hole on the NDS.
If it doesn’t work then just sell the rear and put a powertap on a new wheel with a disc cover. The depth of the backwheel is irrelevant anyways with a disc cover for aerodynamics.
I wish that could be done, but the Roval hoops are drilled for 2:1 drive-side to non-drive-side spokes. Not sure they make a Powertap hub drilled that way.
Edit: Just went and looked at my Roval’s. 21 spoke rear so I guess you could lace a 28 hole G3 using every other hole on the NDS.
Per the PowerTap website, the NDS must be 2 cross, and I think from talking to them on the phone, they also said must be at least 12 NDS spokes for accurate measurement.
You can get a powertap build into a suitable rear, covered, for $800 or less. You can get a high end used front race wheel for 400-500. $1200 = power + nearly the fastest wheels regardless of price. Why every power and aero seeking triathlete on a budget doesn’t do this is beyind me.
Your Roval carbon clinchers are worth more than the PowerTap wheelset you are considering trading for. I was in a similar situation as you and chose to sell my race wheels, but I ended up buying a Zipp 808/404 wheelset used with PowerTap. They are the older generation but I got the wheelset for a great price and it even came with a disc cover. Just keep your eye out on the classifieds.
Getting the PowerTap wheelset and $400 cash, so I think it evens out the value. The g3 should really help with my training and maybe now I can put the cash into an aero helmet and wheel builder cover.