KK trainer power question

mcohen

I have a KK Road Machine trainer. I also have the extra 12 lb. flywheel. I also am using the powermeter that KK sells for their trainers. My questions are, first, aside from the extra weight training component to the extra flywheel, am I getting added benefits? If not should I not use it? It does make it harder for me to get my RPMs up, about 10 rpms slower than without it. Does that matter?

Also, what can anyone tell me about the accuracy of the KK powermeter, as compared say to a Powertap? I am saving for a Powertap, but don't have it yet. Probably won't until next spring/summer.

All info appreciated.

mgraffeo

Can't comment on the flywheel. The kk pm is a little interesting, but that is about it. I have one, it's a glorified speedometer, that converts that speed into a power. You can't download anything, and so it's not all that useful for the sort of training we do here. I'd say save the money and put it in the power tap fund. If you really must try it, send me a PM, and I'll sell you mine real cheap.

David R

I have the 12 lb. flywheel.  I only used it a few times.  I didn't think I was feeling anything different, so I did a test one day. Put it on take it off several times throughout the ride.  The last time I was annoid that I had spent the extra money on it and was not getting any bennifit, I stopped abruptly to take it off.  Only this time it shot off the other flywheel rolled across the room at a high rate of speed and put a hole in my wall.  I will never use it again.

charris

I agree with Mike that because you can't download it does limit its usefulness, but I'll give a slightly different viewpoint on accuracy.  I have a KKRM (with the standard flywheel).  I don't have the KK computer (I have a Powertap) but a while back I discovered these links:

http://www.kurtkinetic.com/powercurve.php

http://www.kurtkinetic.com/documents/Power_Curves419.pdf

 

So just for fun (yes, I know, I need to get our more) I did some spreadsheet experimentation.  What I did was ride on my KKRM with my PowerTap, then take the PT csv (which has power and speed every 1s), use the formula Kurt gives you above to calculate power from the speed reading, then compare the derived power esimate to the actual power.

 

Long story short, what I found was that, pretty consistently, it was within ~6% - when you're pedalling consistently/steadily (i.e. it's obviously out to lunch when you're spinning up or coasting down).

 

Now for a few disclaimers.  People will tell you it depends on (in something approximating decreasing order if importance):

a) how much you tighten the resistance wheel

b) what your rear tire pressure is

c) what kind of tube/tire you're using

d) what the ambient/local temperature is and how that changes over time

e) how much you weigh

f) how many cats you have

 

And of course they're right.  But in spite of all that, every time I checked, I was surprised at how accurate it was.  I am somewhat methodical about setting the resistance and tire pressure which probably helps my results.

 

Of course it will be more difficult for you to be comfortable with how "accurate" it is with your setup because you don't have the sanity check of a real power meter.  If you could borrow someone's PM once so you could "baseline" with a "known" resistance setting/tire pressure, that would help a bit.

 

So that's a very long-winded way of saying that it's not necessarily just a bogus number, and I think it could potentially be useful for you until you have a real power meter - as long as you understand what it is/isn't.  Try correlate it with RPE and HR during your workouts and when you do get a true PM, you'll be that much further ahead of the curve.

 

Re: the flywheel, I don't have it, but if you believe this (and specifically #2 - inertial load) it could help.

http://alex-cycle.blogspot.com/2009/01/turbocharged-training.html ;

 

I say if you believe it because some people think that the inertial load theory is, well, a load.

mgraffeo

Craig, I'd love to see some of those spreadsheets. I did the same shortly after getting my PT (I'd previously been generating 'mock' power files using a rear wheel speed sensor paired to my Garmin, and run through those calcuations in Excel before importing into WKO, kinda a poor-man's PT for the trainer). I found some weird swings in the power, where it would start off close, and then diverge, or start off not too close, and converge (don't remember).

I don't argue that it's informative, but I think a rear wheel speed sensor gives exactly as much information, since 20mph is the same power each time on the trainer, so you can train with power using the speed number instead...

Mike

charris

Couldn't find it after a quick search but I know it's around here somewhere - will dig it up.  I'd be curious to see how it matches up for others (and how accurate my recollection is).

charris

Found it!  Uploaded one here:

http://www.sendspace.com/file/cssn6n

I grabbed a random file from last year and ran it through this and it came up with an overall 8.2% difference (totals and calculation at the bottom).

As might be expected, it tends to overestimate: 399 data points were underestimated and 2318 were even or overestimated.

 

Disclaimer: I'm a complete Excel hack, and an even worse statistics hack, so take with a salt shaker handy.

 

If anyone else wants to test - if you have a Kurt Kinetic Road Machine and a PT (other PMs would probably work but would have slightly different columns I'm guessing?):

-From a workout in WKO, choose "Export Copy as" and choose CSV

-Open CSV in Excel.  If yours are like mine, you'll get columns A-H (Minutes,Torq (N-m),Km/h,Watts,Km,Cadence,Hrate,ID)

-From the attached sheet, copy down the formulas in I2,J2,K2

-Copy over (modifying appropriately for the number of rows you have) the average/non-zero average/% formulas at the bottom of the sheet