If your treadmill only has a max incline of 12%, you could still use the treadmill simulation for the PPA. You could raise the front supports of the treadmill by 3%. Measure the distance between the front and rear supports on your treadmill and multiply the distance by 0.03. If the distance is 60 inches between supports raise the front support by 1.8 inches (60" x .03 = 1.8 inches). Raising the incline actually reduces the strain on the motor.
If you just want to use your treadmill at 12% max; here is an alternate simulation:
Start to top of the Ws = 10%
Top of the Ws to Barr Camp = 11%
Barr Camp to the top = 12%
That will give you an elevation gain of 7,788' which is slightly more than the 7,815' of the PPA.
A simply simulation is 11% for 13.32 miles, which results in an elevation gain of 7,736 ft.
Other than doing the actual PPA, the most realistic training is on a treadmill (if you can stand the boredom). It will give you a good idea of the time it will take you to complete 13.32 miles with an elevation gain of 7,815'. If you are at low altitude, add 30 minutes to your treadmill time to compensate for altitude. If you keep a record of your times on the treadmill, you will see your improvement as you build up your stamina for the long haul.
In response to:
I know this has been posted before, but I can't seem to find it.
Can someone please post the treadmill simulation for the Ascent that includes the distance and percent grade between the different landmarks (Hydro St, top of the W's, No Name, etc).