Racing power levels

[ecandl]

I think it's sort of hopeless and pointless to try to guess your wattage outdoors or speed outdoors from the speed of the kk, except under a very narrow set of conditions. Also, I have noticed divergance between my powertap readings and the expected kk power at higher power levels which I believe has to do with power losses between the tire and the roller (i.e. slippage). My pt reads pretty much spot on with the kk until about 230 watts and then reads progressively higher as power rises. I believe the extent of this divergance depends on tire choice, inflation and tension on the roller so, if you keep those factors constant, you can tell whether your getting stronger or weaker by the speed of the kk.[/QUOTE]
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?

 

[wiredued]

If I remember it right at analyticcycling you need to know your frontal area(hard to calculate) and rise/run grade level. On the KK if you weigh 165 lbs it feels like a 1% uphill grade would feel with nuetral wind with hands probably on the brake hoods. My weight is 196lbs back in October outside on flat 0% grade rail trail I could do 20mph for twenty minutes and on the KK I could manage only 18.6 because of the slight uphill feel.

Why are the watt numbers from KK so much higher than analytic cycling. It shows over 400 watts to go 25mph. No way did I average over 400 watts in my last 40k. Analytic puts it closer to 300w which would make sense. Tell me I only have to bring my watts up only 50 until race day, and not 150

 

[cclarke]

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.

 

[Piotr]

You have to remember that the KK numbers are based on a hypothetical 165 lb rider going up a 1% grade and I'm guessing they didn't base the expected air resistance on a rider in aero position. So how many watts does it take you to go 25 mph slightly uphill while riding on the tops? Can you sustain 25 mph on the kk?

On the flats with aero bars, it takes me about 250 watts to go 25 mph but I'm sort of small.

I think it's sort of hopeless and pointless to try to guess your wattage outdoors or speed outdoors from the speed of the kk, except under a very narrow set of conditions. Also, I have noticed divergance between my powertap readings and the expected kk power at higher power levels which I believe has to do with power losses between the tire and the roller (i.e. slippage). My pt reads pretty much spot on with the kk until about 230 watts and then reads progressively higher as power rises. I believe the extent of this divergance depends on tire choice, inflation and tension on the roller so, if you keep those factors constant, you can tell whether your getting stronger or weaker by the speed of the kk.

This is regarding the divergence in readings at higher power (or rather speed) on the KK. I'm quite small and sprinting at around 850W is probably all I can muster. OTOH, I've been known to sprint up to 37MPH on the KK (1165W!). I've never done that outside without a serious tail wind, and certainly not up a 1% grade road. Yeah, the KK is great, but I wouldn't trust it for 5 sec. max. power testing.

 

[wiredued]

Timan and Catabolic Jones say if roll down is 13.4 seconds it is dead on above 100 watts http://www.cyclingforums.com/t386350.html maybe your sprint improved

This is regarding the divergence in readings at higher power (or rather speed) on the KK. I'm quite small and sprinting at around 850W is probably all I can muster. OTOH, I've been known to sprint up to 37MPH on the KK (1165W!). I've never done that outside without a serious tail wind, and certainly not up a 1% grade road. Yeah, the KK is great, but I wouldn't trust it for 5 sec. max. power testing.

 

[Piotr]

Timan and Catabolic Jones say if roll down is 13.4 seconds it is dead on above 100 watts http://www.cyclingforums.com/t386350.html maybe your sprint improved

Thanks for the vote of confidence. I took a 3rd once in a pack sprint at 36 MPH, but I was in the winners draft and at the end of a crit racing season, and... I was 25. 37 MPH in the middle of Sweet Spot off-season training at close to 40 y.o. seems a bit of a stretch. Here's to a dose of reality!

 

[cclarke]

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.

If anyone is still interested, I looked at the files and the difference between the whole five minute block and just the last four minutes was minimal, maybe 1-2 watts. So I guess I really don't know why my powertap and the reported kk power/speed differ. I did a 1 hr tt at 283 average watts tonight and the rear wheel speed was 20.4 mph. Per the kk chart, 287 watts should get you 21 mph. Maybe I'll bring the kk upstairs and see if the warmer temperature gets me closer to the chart.

I forgot a little how nice and smooth the kk trainer feels. I have a very old Velodyne with an electro-magnetic brake that I've been mostly riding for the past six months when indoors and, compared to the kk, the resistance is much more variable. The Velodyne brake seems to overcorrect as I spin up by applying additional resistance so the power files are noticeably more erratic even though the average power tends to match the set power pretty closely. I have to change my pedalling cadence or force to match the changing resistance which is the opposite of what I had expected using ergo mode. Still, the Velodyne's ergo feature where you can just set the power level and grind it out is pretty cool. Also, you can set the virtual gradient which seems to offer more specific resistance for climbing simulation than the kk but I'm not sure it matters that much as long as you are doing similar power/cadence training on the kk as you'll do on outdoor climbs.