Anyone have Kurt Kinetic PM and another PM?

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Wondering if anyone here has the Kurt Kinetic trainer and PM and also another PM like a Power Tap for example. When you ride your trainer how close are the two pm's or more specifically how close it the Kinetic PM to something like a Power Tap?http://cyclingforums.com/images/smilies/smile.gif

Wondering if anyone here has the Kurt Kinetic trainer and PM and also another PM like a Power Tap for example. When you ride your trainer how close are the two pm's or more specifically how close it the Kinetic PM to something like a Power Tap?http://cyclingforums.com/images/smilies/smile.gifI have the Kinetic trainer and the power computer. I do not have a power tap, so I do not know how they compare, but according to the reviews, they do compare pretty closely. I care more about improvement in my ability to sustain an output level than what the actual level is, so I do not care how accurate it is as long as it is consistent, which it seems to be.

The first power computer I had died after about 1200 miles. I e-mailed Kurt Kinetic, and they sent me a new computer the next day without asking for a receipt or the return of the broken one. I thought that was excellent service. I have not put many miles on the new computer, yet, so I do not know if there is a reliability issue or if I just got a bad unit. As long as they are willing to replace it so quickly, it does not matter to me.

I have the Kinetic trainer and the power computer. I do not have a power tap, so I do not know how they compare, but according to the reviews, they do compare pretty closely. I care more about improvement in my ability to sustain an output level than what the actual level is, so I do not care how accurate it is as long as it is consistent, which it seems to be.

The first power computer I had died after about 1200 miles. I e-mailed Kurt Kinetic, and they sent me a new computer the next day without asking for a receipt or the return of the broken one. I thought that was excellent service. I have not put many miles on the new computer, yet, so I do not know if there is a reliability issue or if I just got a bad unit. As long as they are willing to replace it so quickly, it does not matter to me.
Well Rick, I guess if we wanted to really be great posters, we could arrange a meeting and set-up an experiment....seeing as I have a kinetic & powertap, but no KK computer :D

Well Rick, I guess if we wanted to really be great posters, we could arrange a meeting and set-up an experiment....seeing as I have a kinetic & powertap, but no KK computer :D



Hey Rick, she's asking for a date I think.
:rolleyes: ;) :D

Well Rick, I guess if we wanted to really be great posters, we could arrange a meeting and set-up an experiment....seeing as I have a kinetic & powertap, but no KK computer :D

Lucy, you don't need the KK PM. Kinetic gives out the calibration formula, and also a representative graph.

Here's the formula for the Kinetic Road Machine AND several other trainers where X = speed in MPH.
http://www.kurtkinetic.com/calibration_chart.php

And the graph for the Road Machine
http://www.kurtkinetic.com/pdfs/Power_Curves419.pdf

So I plugged in some speeds and came up with this for you to check against your Power tap if would could be so kind:)

Kurt Kinetic speed

17 mph = 185.8 watts
18 mph = 209 watts
19 mph = 234.6
20 mph = 262
21 mph = 292

Wondering if anyone here has the Kurt Kinetic trainer and PM and also another PM like a Power Tap for example. When you ride your trainer how close are the two pm's or more specifically how close it the Kinetic PM to something like a Power Tap?http://cyclingforums.com/images/smilies/smile.gifYou have to be slightly more precise in posing this question. There are two variables that will cause differences between the KK power computer and the PT. One is the tires you are using. I think this could easily account for 10W due to the difference in rolling resistance. The second is the elapsed time on the KK trainer. The PT/KK power ratio is going to decrease over time until the KK is fully warmed up (~10mins) after which I think it will still decrease as a function of time but not as much. If one wants the most accurate estimate of power, these two issues should be standardized.

Wondering if anyone here has the Kurt Kinetic trainer and PM and also another PM like a Power Tap for example. When you ride your trainer how close are the two pm's or more specifically how close it the Kinetic PM to something like a Power Tap?http://cyclingforums.com/images/smilies/smile.gifI have both PT a the kurt computer. I had promised I would do a comparison but never did. For me I am at threashhold at about 20.5 mph. PT is about 250 there. Sorry for the guesses, but I am mostly concerned with power of 1 min or less. I think Whoa has both and would be a much better resource for info than I am.

You have to be slightly more precise in posing this question. There are two variables that will cause differences between the KK power computer and the PT. One is the tires you are using. I think this could easily account for 10W due to the difference in rolling resistance. The second is the elapsed time on the KK trainer. The PT/KK power ratio is going to decrease over time until the KK is fully warmed up (~10mins) after which I think it will still decrease as a function of time but not as much. If one wants the most accurate estimate of power, these two issues should be standardized.

Yes, waiting til the KK is warmed up is important.

About tires....well KK recommends a cheap hard tire inflated to it's proper pressure.

Here is a good blurb from a KK dude.

This is Aaron Kadera from Kinetic again. I figured I'd drop some new information on what the power computer is and the procedure to calibrate our computers.

Tire pressure is irrelevent. Our computer measures power at the rubber, not at the hub. As long as your tire is not slipping, the Kinetic PC is accurate to +/- 3% of a PowerTap reading at all reasonable speeds (0-40 mph). To avoid tire slippage, use a cheap, hard-rubbered tire filled with proper pressure and make sure the roller is pressed against the tire firmly.

The following will eventually be posted on our website. I also have the calibration results and procedures for other trainers if anyone is interested.

The Kinetic Power Computer was designed to work with the Kinetic Road Machine. However, it is not limited to use only on our trainer. Here’s how it works:



The Kinetic PC operates on the principle that the Road Machine’s resistance is speed sensitive and ONLY speed sensitive. Some people don’t buy into that, but if you think about it, the only factor that has any impact on the resistance unit is how fast the roller is spinning – independent of rider weight, cadence, crank length, etc. After riding one of our trainers, you are, no doubt, aware of a relationship between speed and effort. The faster you go, the harder it is to pedal. The beauty of the Kinetic Road Machine is that we have tweaked and studied this relationship to a further extent than any other company.



We have used our test robot, Crank Armstrong, to analyze the forces experienced by a rider on our trainer. Specifically, we analyze the amount of wattage needed to sustain any given speed on our trainer. Once we get the data from Crank, we send it over to Tom Compton at Analytic Cycling. He uses a computer program called Mathematica to fit the data to a mathematical formula. The end result is a very accurate power curve and a mathematical formula that describes it. The best-fit formula for the Kinetic Road Machine is in the form P = Ax + Bx3, where P is power in watts, x is speed in miles per hour, and A and B are constants. With this formula, we can calculate how many watts a rider is producing on our trainer if we know how fast the bike’s wheel is turning.



The Kinetic PC has a rear wheel sensor that picks up speed off the rear wheel and then converts speed to power using the formula provided by Tom. The end result is an accurate estimation (+/- 3% of a PowerTap reading) using some very simple and inexpensive hardware.



Our computer is not a strain gauge and does not measure torque, so there are a few things it will not do. Unlike the much more expensive PowerTap and SRM systems, our computer will not register a spike in wattage prior to a sudden acceleration. With our computer, the wheel must turn faster before a higher wattage reading is observed. Likewise, our computer will register positive wattage while coasting even though no force is being applied to the pedals. Furthermore, wattage readings while not riding a trainer are obsolete because all those variables that are insignificant on a trainer (rider weight, cadence, crank length, etc.) are no longer controlled.

About tires....well KK recommends a cheap hard tire inflated to it's proper pressure.I believe the specific tire and not just tire pressure matters.

On the issue of tire, I've found that the Conti UltraSport Hometrainer tire produces more accurate and consistent power output results. And they're more stable and responsive on Kreitler Rollers, too.

jla

I believe the specific tire and not just tire pressure matters.

Wondering if anyone here has the Kurt Kinetic trainer and PM and also another PM like a Power Tap for example. When you ride your trainer how close are the two pm's or more specifically how close it the Kinetic PM to something like a Power Tap?http://cyclingforums.com/images/smilies/smile.gifi just ordered a kk computer from 1-up should be here next week , i will ride with powertap and compare and post results here.

now if i could just figure out if its my old sweet spot or my "winter sweet spot" to train in

I have a Kinetic Trainer and PowerTap. I dont have the Kurt computer but I do the math as mentioned above. I did a 20 min. time-trial effort and my average watts on the powertap was 317. I suppose I could have used the powertap to get speed values, but for whatever reason I just used my EDGE 305 which has a rear wheel sensor. My avg. and max speed was 22.0 and 28.8 respectively. This puts my kurt calculated watts at 325 avg, 621 max.

I expect to do a few more trainer runs in the upcoming weeks, I'll try to remember to post more results here. By the way, buy a kinetic and don't look back. EXCELLENT customer service! I got mine used and love it. Will most likley be selling the powertap in a couple months. I never seem to ride solo outdoors, so I only ever care about power training when indoors.

EDIT: I should note that I did a 20-min warmup and my tire was a new Panaracer Stradius Elite

Tonight's numbers....

CP12:
-PowerTap 350
-Kinetic 375 (23.4)

... 5 minute recovery, then ....

CP1:
-PowerTap 547
-Kinetic 579 (28.0)


hope this helps . . . . . .

EDIT (again, sorry..).. for the CP1 my edge305 display screen shows avg speed 28.0 but when I look at this effort in the History section it shows avg speed 27.5 which would be 554 watts. Just reporting it as I see it..

Tonight's numbers....

CP12:
-PowerTap 350
-Kinetic 317 (23.4)

... 5 minute recovery, then ....

CP1:
-PowerTap 547
-Kinetic 579 (28.0)


hope this helps . . . . . .That's quite a different slope - under reads on CP 12 by 9% and over reads on CP 1 by 6%....

That's quite a different slope - under reads on CP 12 by 9% and over reads on CP 1 by 6%....
Yes, I noticed that too. Please also note that I mistyped the 317 that you quoted, the correct calculation is 375. This is Kinetic formula I use:

=(F4*5.24482)+(0.01968*F4*F4*F4) where F4 is avg.mph

So, what does it all mean??? beats me. Means power devices aren't accurate. I don't care so much about accuracy between systems (I know others do...) as long as the system I end up going with is repeatable, I'll be a happy camper.

Yes, I noticed that too. Please also note that I mistyped the 317 that you quoted, the correct calculation is 375. This is Kinetic formula I use:

=(F4*5.24482)+(0.01968*F4*F4*F4) where F4 is avg.mph

So, what does it all mean??? beats me. Means power devices aren't accurate. I don't care so much about accuracy between systems (I know others do...) as long as the system I end up going with is repeatable, I'll be a happy camper.As long as your PT is in good order and torque has been zeroed, then it will be pretty accurate.

Accuracy is helpful but precision is more desireable (but often go hand in hand anyway). OK - after typo correction then it over reads at both CP levels (which is much more desireable than before). That suggests to me that the constants in the formula just need a bit of tweaking and you'll have it closely match the PT.

Here's a guesstimate - try 4.56299 & 0.01905

Should get you within a watt. Interested if same constants work at lower power levels....

No doubt some smart cookie out there can solve the equations instead....

I don't know what else influences these formula on this trainer (tyre pressure, heat, clamping etc since I don't have one).