Cycleops Fluid2 Power curve?

[ZimboNC]

I've never raced before and I've been cycling about 1 year. I don't have a power meter... yet... so for now I'm doing HR-based training, but I'm curious to know if there's an accurate simple mapping from MPH on the Cycleops Fluid2 to power output in Watts.

I've found two different mappings on the Internet (one is a graph the other is an equation) that appear be based on the same formula. The formula for the Cycleops Fluid2 is apparently

p = 0.74715x + 0.0466912x^3

where x is the speed in MPH and p is the output in Watts. However, this formula seems unlikely to me because I'm able to hold 20mph on the trainer for 30 minutes, which gives a whopping 388 watts. Yeah, there's a lot of suffering involved to maintain that speed but frankly, I really don't think that number is accurate even though I am allowing 10 minutes for the fluid to warm up and I'm tightening the back wheel the recommended 2.5 turns. I would believe 250 watts, maybe, but 388 seems quite high. At 75kg, that would put me at 5.17 w/Kg for 30 minutes. Um, I don't think so.

Is there anyone here with a PowerTap and a Cyclops Fluid2 who can tell me the amount of power needed to hold 20 mph (after a 10 minute warmup) when the back wheel is tightened exactly 2.5 turns?

--Steve

 

[Woofer]

You are almost never going to get an accurate number from this method until you actually use a power meter. I get different numbers when I change *tires* on a trainer, much less riders and trainers and everything else.

Instead of attempting this, why don't you just climb a known hill, time yourself, and use www.analyticcycling or the german equivalent? Both of those are pretty accurate when I compare them with known climbs, time to finish, input all the relevant known data, and compare with recorded power meter outputs.

 

[frenchyge]

Well, you can peruse the curves here:

http://cycle-ops.com/products/fluidsquared.htm# --> click comparison chart, then view power curve.

-or-

here: http://www.1upusa.com/1uptrainerpowercurves.htm (which doesn't come anywhere close to the above curve, but is probably more accurate)...

...but neither is going to be anywhere near the formula you presented. As was mentioned above, there are differences in speed v. power from one ride to the next, which makes using a curve difficult unless some checks are done to ensure consistency (ie, timed coastdown from a specific speed to adjust tension properly).

 

[ZimboNC]

Well, you can peruse the curves here:
http://cycle-ops.com/products/fluidsquared.htm
-or-
http://www.1upusa.com/1uptrainerpowercurves.htm

YIKES! The formula says 388 watts @ 20mph, the Cyclops site says 330 watts @ 20mph, the 1upusa sites says 185 watts @ 20mph. Hilarious!!

All's I can say is if 20mph is 185 watts then I suck suck suck. If it's 388 then I'm a genetic freak. But there's a whole lot of room in between.

Guess I'll have to save my pennies for a PowerTap SL.

--Steve