"It" refers to the power referred to earlier in the sentence - I think it's a standard English usage of the word.
I can't see how you have a problem understanding it. Why would max revs or max power have anything to do with what I stated?
Because if "it" means the previous power, then what you are saying is
shift when you're far enough into the power to not drop below the previously mentioned power in the higher gear.
Im not quite sure what the previous power is? The power you have in the current gear?
That still seems to me to say you want the power after the shift to be at least equal to before the shift.
The only time you can shift gear and the power in the higher gear is equal to the power in the lower gear is when you shift after max power.
Maybe we are on completely different wavelengths on this.
Im an engineer and use the term power probably a bit more technically than most.
But your sentence seems very ambiguous.
The "it" references a power that isnt clear, its either self referential (power after shift is not less than before the shift) or its unspecified (power that after shift that not below some other power which itself isnt specified)
I took the meaning as self referential - which implies shifting after max power.
walks away dazed - amazing how such a simple sentence can cause so much confusion!