Why does the Forecast AI where you pick a race, include the speed as a metric? Obviously, speed is dependent on a lot of external factors (wind, drafting etc.) that are not know to Xert. And the race file already has all the power data in it, which is really all that matters. So why does it also consider speed and why does it have such a big impact on the achievability when I change the speed?
Thanks for pointing out our latest feature. 
What you can do with the speed value is increase (or decrease) and Xert will calculate how much additional/less power is needed to achieve that average speed. It takes into account the power, speed and gradients of the source and runs an analysis to determine the power changes needed and then determines whether you can achieve the new speed and the training required.
It does a lot of intelligent adjustments to power. If you’re coasting down a hill, the speed can’t be increased, for example. If you add weight, it will add additional power on steeper gradients in order to achieve the speed.
The method presumes you will maintain the same riding patterns and conditions - drafting, coasting, wind, riding positions, etc. and simply scales the power appropriately. If you plan on racing or riding differently, you’ll need to account for that indirectly.
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Thanks for clarifying! So the speed you enter is relative to the speed of the original activity. I think it would be a good idea to clarify this in a help text, as I understood it differently.
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I just wanted to say that I have just used this new “adjust speed” feature of RaceAI to re-target a 1 hour hillclimb in my area.
One tip (and thanks to @ManofSteele for help on this aspect). I used fitfiletools.com to trim my FIT file from last year to just the climb - so then the speed was specifically relevant to the effort.
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Hmm… I hadn’t thought about using it that way. Makes sense.
I tested the new speed feature by selecting my Mt Washington ride from last year which is a climb from start to finish.
Race AI is spot on at predicting what TP is required to break 100 minutes at my weight.
That was my time goal in 2023 when my TP was 10+ pts higher, but event got cancelled.
I doubt I’ll hit the same numbers again but now I know my time goal was possible. 
That Mt Washington climb looks epic (and brutal)! Congrats!
I grew up in new england, and skied Tuckermans (in July ;-)) but never rode up Washington.
My local climb is a lot easier 12 miles at 5% average.
Rist or Poudre Canyon?
Rist!
I stay off 14 (too many RVs and folks that still think txting and driving is OK)