To my knowledge BKool trainers don't need to know your rolling wheel diameter which, seeing as we all use 700c wheels is down to your tyre size.
It may not need the info. But it does make use of it in other areas. There is a box for the wheel diameter, as well as chainring and cassette sizes, in bkool when setting up training plans iirc. It is used to set the work areas.
Your tyre simply rotates the roller and the circumference of the roller is 'the road'.
The quicker the road is moving the more power BSim indicates (relative to incline and weight etc = conditions).
It therefore baffles me that a tyre can change the power displayed for a given speed, person and conditions.
Not saying it doesn't, it just mystifies me a bit mathematically but I agree with Bill, if a certain tyre gives you more speed (forget power) then use it for leagues and shine brightly (be brill).
But as you say it does not affect speed then that is pointless other than giving better stat's but baffles me even more because BSim uses your speed and the conditions to calculate power and hence same speed and conditions should equal the same power.
Maybe it was badly written.
I have not compared speed from tyre size to size. I have compared speed from bsim to garmin on the same tyre size.
I am not that consistant or poweful enough, when pedalling, to be able to note down cadence, gear and speed. Then repeat it with little to no variation to do a direct tyre size comparison.
However my perceived effort on the smaller tyre is higher with a lower power reading, the 23 was inflated to its max of 140psi. I have not tried the 25 tyre yet so there may be a more accurate power comparison with only a slightly higher PE using a middle size tyre, a 25. This is comparing bsim power, to a set of vectors.
I hope that makes more sense
)
and my little legs were going like beeswings - i demand a hill !! well done 
