ecandl said:
Just out of curiosity, what is the difference in watts between your pt and kk at 287.65 watts?
Also, I know the KK is set for 165lb rider, sea level, etc. Would there be much difference for me at 155lbs at 3000ft?
I'd have to go look at my file from last night to see what the speed difference was at 287.65 watts on the pt vs. what the kk chart would indicate. Not that I could actually cut it that finely anyway.
Last night out of curiosity, I did a "workout" varying speed on the kk in one mph increments for five minute blocks somewhat randomly using 15, 16, 17, 18, 19, 20, 21 and 22 mph. For 22 mph, I just did 2 minute blocks. IIRC, 287 watts would fall between 20 and 21 mph. 20 mph took 271 watts and 21 mph took 310 watts based on two five minute blocks of each. It was cold in my garage which, while it might not impact the fluid in the kk, does have an impact on the tires. Also, power levels required for a given speed dropped during the first couple of blocks but then stablized for the rest of the ride as a result, I suspect, of the tires warming up. Those numbers are pretty close to what I typically see when it's cold. When it's warm, wattage is lower at the same speed or, to put it differently, the kk speed is faster for my intervals at the usual power levels.
It's beyond my experience to comment on how altitude might change the way the fluid in the kk behaves but your weight shouldn't make any difference as long as we are talking about wheel speed on the trainer.
Also, I haven't done the roll down test as suggested on another thread as I usually just guide my workouts by the pt power and perceived effort. I don't have a strong opinion one way or the other about whether additional tension on the roller would raise or lower the power needed to go a given speed but I use the suggested 2.5 turns of the tension knob once the roller makes contact with the tire. Powertap was zeroed.
My pt numbers also include the effort needed to accelerate to the block speed (for example from a block at 16 mph to a block at 21 mph) which takes additional power above the amount needed to maintain a given speed on the kk. So this additional effort would skew the pt numbers upwards, particularly on shorter efforts. I'll go back and look at the file to see if the last 4 minutes of each five minute block are closer to kk's chart.
Finally, I'm measuring speed at the rear wheel which may differ, again based on slippage, from the actual roller speed on the trainer.
FWIW.