Since you can not push RPE to your Headunit and math gets kinda hard with limited oxygen during workouts 
setting your FTP to 100 before riding your outdoor workouts on RPE should be a good idea…
You only have to learn the values here found under “How RPE is Measured”
…RIGHT?!
Good idea? Maybe. But one that comes with some important considerations:
That is a hack I considered suggesting based on previous RPE screen requests. This hack could give the Wattage based on the altered 100w FTP to the head unit.
Example 1: A Threshold effort could range from 90w to 105w on the screen. The rider could interpret that as an RPE (which is usually a single-digit value) but it is not “automatic”.
Example 2: If you want it a bit easier, you could actually use 10w FTP, which would give 9w to 11 (assuming 10.5w rounds up) for the Threshold example above. It would look more like the actual single-digit RPE values in the lists and might be easier to follow.
IMPORTANT: A BIG issue is to make darn sure that you edit the ride after the fact once it is imported into TR (and any other tracking software) to make your FTP for that workout the actual value to are using for the rest of your training. Otherwise you will have bad data for TSS, CTL, ATL and such from an incorrect FTP value.
There may well be other hidden issues that I have not found. That is one reason I never made the suggestion in the past, but I guess we can see how it works if people give it a shot.
right it is not automatic but you could only remember:
'<55 Easy
'>55 Easy Moderate
'>75 moderate
'>95 Moderate-Hard
'>105 Hard
'>120 ALL-Out
I didn’t suggest that on purpose because you still have to convert the numbers and you could get confused having a single digit number which is NOT the RPE
That is indeed a good point. But for me it doesn’t matter. I do not track this numbers when I follow a trainerroad-plan I just do my workouts.
Some people might have a cycling computer and a watch. That could be a complex workaround here.
Think one problem is that a 10 RPE is an all-out effort, and not an effort at FTP. So if you set FTP to 10W, when it tells you 10, you actually have to do an 8 RPE effort? (I think. I don’t get RPE numbers, I had to buy a PM instead).
Yup, it is not an ideal solution and not one I endorse.
Another thought (not fully considered) would be to use 80w as the FTP. That would correspond more closely to the RPE 8 of Threshold at least. Might be a better anchor for the hack, but I suspect it falls short elsewhere. Scaling is likely a problem at one end or the other.
exactly you still have to calculate the RPE but you only have to remember the six numbers I mentioned above
I would love to have a better solution but buying a PM is not an option at the moment 