Another Power Question - CycleOps Trainer
 

OK, someone asked in another thread how to calculate power without a power meter while riding out on the road. That seems to be a complicated task. However, what I would like to do seems like it would be simpler. I would like to calculate my power output when riding on my CycleOps fluid trainer, based upon the speed of my rear wheel (a standard sized road wheel). It seems to me that this should be much simpler - no wind resistance, grades, or variable friction. The only factor is the resistance of the fluid trainer. The one complication I can think of may be if different CycleOps fluid trainers have different resistance levels.

It would be nice if someone else who owns a CycleOps trainer and a power meter could simply publish a graph of power readings to wheel speeds, but I haven't been able to find such a thing on the net. From what I hear, the trainer is designed to simulate outdoor riding, in that the faster you go, the more power it requires to increase your wheel speed by a given amount. So the graph would be a non-linear, exponential one.

It still depends on your tires, pressure, weight, whether each unit is calibrated to have exactly the same resistance, how well that calibration holds up over time, etc.

The tire pressure, it seems like, is something that one could set at a standard value fairly easily. However, I don't see how weight makes any differences though, or tires. As long as the tire doesn't "slip" when it's on the trainer, it seems like that shouldn't matter. The internal resistance of the trainer seems like it's the only variable, as long as the contact between the trainer and the tire is tight enough such that the wheel doesn't skid. What am I missing?

This has been established here already w/ the fluid trainer. Can't claim for its accuracy but it's on here somewhere. You can try searching but the new search sucks.

I found something but really, who cares? Estimated power is stupid. You might as well go off PE or HR.

Interesting, I shall try searching. If anyone else has any of their own data, I'd be interested to see that as well.

Ah - this is cool - thanks!

Cycleops publishes this..

http://www.saris.com/comparison/trainers.pdf

I eMailed them to see if they could share how they developed this and any raw data and they (Jerrod) said this...

Unfortunately, we don't have any raw data for those. The numbers can change fairly dramatically depending on the bike and the rider, so we just used an average of the results we had here with different riders and powertap setups. What you may want to do if you can't extrapolate good numbers from the online graph, is to find a friend with a PowerTap hub and jot down power output #'s at different speeds.

I did a regression calc in Excel based reading data from the chart for my wind trainer and got this... doesn't mean all that much perhaps, but it's what I've got.

y = 0.8369X^2 - 3.0409X (y is power in watts, x is wheel speed in mph).

I may try an borrow a power meeting to calibrate, but once all this friggin snow melts I think I'll just go out and see how I'm doing on an actual road!!!

Too bad you don't have a Kurt Kinetic trainer.

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

http://www.kurtkinetic.com/documents..._Curves419.pdf

Great information you all - I especially like the trainer.pdf file.

Tires, pressure, and weight all affect rolling resistance.

Edit: I guess weight wouldn't because the weight is held by the skewer, but the pressure and tire certainly would matter.

Keep this in mind (it was posted awhile back)


http://i443.photobucket.com/albums/q...Untitled-1.jpg

Answer by WR:
Edit: In the graph, blue is speed (sensor in the rear wheel, obviously) yellow is power. Red is HR.

I don't know about the CyclOps, but I've been using the numbers from Kurt with their road machine.

I have the wattages with corresponding speeds taped to my top tube. I know it's not as accurate as a true power meter, but it's also better then going by HR alone. HR can vary greatly, same with PE, or at least it can for me....Depends on how I feel that day in general...The speed of the rear wheel does not lie. It gives me a more measureable constant to go by and range to work within.

I really think this has improved my indoor training this winter. The true test will come in about 4 weeks whne I head to Georgia and do some real road riding and then at the beginning of April when I do my first race. By that time I wll be in possesion of a Powertap and I can see how close my numbers on the trainer are in reality...

The KK power curve does not correlate w/ my Ptap.