Fluid 2 Trainer Speed/Wattage

[kb1dqh]

Hi,

On the iBike 2 software there are a bunch of Fluid 2 trainer options. I have a new one with the yellow quick release handles, not the old knob version. Has anyone checked to see if the power profile has changed from the older Fluid 2s? I'm having trouble holding 16-17 mpg, which, per the iBike 2 graphs, is just over 200 watts. My FTP on the road is 285 watts. Seems like a larger gap than expected.

Also, does anyone use a different FTP in the WKO+ software for trainer workouts?

Thanks!

[gregh3285]

You know, I have the same concern. Of the two or three Fluid 2 power curves, I found that even the most conservative curve seems to overstate my Fluid 2's (2006 vintage) power curve (perhaps by 50 watts at 19-20 mph). Before I got my iBike, I emailed the Saris folks (about my 2004 vintage CycleOps Magneto) trying to understand more of the detail about how they came up with the curves they had posted on their web site. The response I got back about the power curves was, "The graphs we have listed on the website is [sic] just a rough estimate of the power curves. They are used to demonstrate the differences between models and can not really be used as a scientific measure of power. There remains some variability in how tight you have the rear wheel placed against the trainer, etc. which may change your power output. These graphs won't show you the information you need."

[kb1dqh]

Thanks Greg. However, even if those aren't right on the Saris site, iBike has power curves that I assume were tested against a powertap or SRM. It just seems that the wattage around 16-18mph is much lower than I expected given my percieved effort on the newer Fluid 2 trainer.

[Velocomp]

New iBike 3 software (about to be posted) will allow you to make changes to any trainer curve to custom fit it to your actual riding conditions.

[kb1dqh]

Thanks John. I guess my real question is, "is there a new curve for the latest Fluid 2 trainers"? I can't develop my own curve because I don't have a powertap or SRM to calibrate against.

[Velocomp]

We don't own this particular trainer but perhaps someone else on the forum can help adjust one of the Fluid 2 Trainer profiles.

[Russ]

One interesting site tested a number of trainers and has curves, including fluid2. Probably not a real new unit. There was some discussion on old topica list about these too. I think basically that the fluid2's weren't highly consistent. I had one and noticed that it seemed to increase the drag once it warmed up to certain amount.

http://www.geocities.com/almost_fast/trainerpower/

Russ

[gregh3285]

If I'm not mistaken, the curves Russ refers to are in the list of options in the iBike software. To the defense of iBike, trainer cal is always going to be tricky. I have to wonder if even small changes in tolerances within the manufacture of trainers, air temp, tire pressure, wheel/roller contact force, and (for fluid trainers) oil temp could all impact the speed/power curves. So, even if a given trainer model is tested, unit-to-unit variations are going to occur.

My thoughts are to consider power performance data. Consider comparing similar intervals run outside versus efforts inside. As an example, on a trainer I saw (over an 8-minute block) an average HR of 158 bpm and an average power of 238 W. Looking for similar blocks of time running consistently at around 158 bpm, I saw one case of 156 BOM at 199 W and 158 BPM at 202 W. I've done CTS Field Tests (but always indoors), so I don't have a good outdoor comparison for an 8-minute all-out block. Lately on the trainer I've seen 280 - 285 W. That doesn't however, seem so out of whack. The comparison requires so good thinking.

[travispape]

There's a couple of new things in iBike3 for indoor training, one of the being that you can tweak your trainer curve if needed. The Fluid model seemed to go through some revisions (or maybe it was just sample-to-sample variations) that resulted in a variation in power vs. speed results. If you don't have another power meter to test it with, what you can do is figure out which of the curves most closely matches your perceived effort and then dial it in by adjusting the B parameter in the new interface as shown below.

trainer coeffs.jpg (96.36 KiB) Viewed 12237 times

Any variations due to rolling resistance, which depends strongly on your type of tires and tire pressure, will mostly show in that B parameter. If your power seems low at your cruising speed, you can bump up the B parameter to compensate. Remember to send the modified values to your unit.

The other thing that is new are a couple of models of rollers that are now supported.

rollers.jpg (83.68 KiB) Viewed 12237 times

Travis

[campycarbc50]

Hey Travis

I just got the Elite Parabolic Rollers. Think the E-motion rollers with the mag setting on 0 would show about the same wattage??

[travispape]

Hey Travis

I just got the Elite Parabolic Rollers. Think the E-motion rollers with the mag setting on 0 would show about the same wattage??

A Google search didn't turn up any resistance data for these rollers.

Unless the rollers have an option for adding resistance (magnetic in the case of E-Motion, fan in the case of Kreitler), the power vs. speed characteristic will depend mostly on the drum size.

I'm not sure if the 0 setting on the E-Motion rollers means that the magnetic resistance is fully disengaged, but in any case, just looking at the pictures that Google turned up it looks like the E-Motion rollers use a smaller drum. The Kreitler 3.0 or 4.5 drum setting might be a closer match to the Elite. Pick the drum setting that is the closest and leave all of the other options turned off.

Note also that since the Elite rollers are plastic, that the tire temperature will be higher resulting in a slightly lower resistance.

So until someone measures resistance for these rollers, the best you can do is pick the one roller curve that most closely matches your perceived effort. I think your best bet is to try either the 3.0 or 4.5 drum setting for Kreitler. You can further fine-tune the curve by tweaking the B parameter up or down.

Travis

[campycarbc50]

Thanks Travis,
I used the 3.0 which shows 151 watts at 18 mph. If I fine-tune the curve by tweaking the B parameter up or down should I try to match the 127 watts average at 18 mph from my last ride, or the 145 watts which was the "normalized power" from the CyclingPeaks software of the same ride? Here's the data from both files.

Thanks again for all your help!!


Dist: 13.02 mi (0:25:37)
Energy: 437.0 kJ
Cals Burn: 417.8 kcal
Min Avg Max
Power 0 285.0 383 W
Speed 0.0 30.5 40.9 mi/h
Caden 19 96.6 129 rpm
HR 93 163.2 181 bpm
164 lbs; 11/18/08 5:48 PM
68 degF; 999 mbar


Dist: 55.29 mi (3:04:03)
Energy: 1397.5 kJ
Cals Burn: 1336.1 kcal
Climbing: 1609 ft
Braking: 22.3 kJ (1.6%)
Min Avg Max
Power 0 126.6 613 W
Aero 0 105.4 1349 W
Rolling 0 15.4 36 W
Gravity -1184 1.2 383 W
Speed 0.0 18.0 42.4 mi/h
Wind 1.2 19.0 40.9 mi/h
Elev 485 573 689 ft
Slope -10.0 0.02 10.6 %
Caden 4 85.6 119 rpm
HR 93 158.1 181 bpm
Aero: 0.292; Fric: 3.50
CdA: 0.288 m^2
Crr: 0.0026
164 lbs; 11/02/08 2:06 PM
74 degF; 999 mbar

[travispape]

If it were me, I would compare the average powers for 20 min of all-out on the road vs. 20 min of all-out on the rollers.

Take your average speed on the rollers, set the yellow cursor at that speed in the trainer window, and adjust the B coefficient until the average power is the same as what you did on the road.

Most cyclists (but not all) don't put out quite as much power indoors as on the road; therefore, I wouldn't use road normalized power. Even if you set the average powers to match, the indoor trainer might slightly over-report power.

[kb1dqh]

Travis,

That's a great point. I can avg about 300 watts in a 20 minute road effort. If I go all out on a good day on the trainer, find average speed, and correlate that to 300 watts, would I be doing the right thing in terms of measuring performance for WKO+? i.e. am I getting the same physical workout on the trainer, or am I really putting out less watts for whatever reason, and overstating my work?

[travispape]

You might end up over-reporting your indoor work. It depends on how cool you keep yourself when you don't have the benefit of the natural wind and whether you are one of those who can "lay it out there" as thoroughly indoors as you do when you are trying to get a good time on one of your outdoor routes.

Keep in mind that even if you get your hands on a DFPM for your indoor work, you would still likely be in a position where you can't directly compare the absolute indoor watts to outdoor watts. You might as well get a good set of trainer coefficients that match up your perceived effort indoors and out, then stick with those coefficients for the indoor training season. You will get very repeatable results even if the absolute watts are slightly different than your outdoor watts, and most people have given up trying to put out as many watts indoors as out just because they find they can't consistently. The fact that the coefficients give you very repeatable results means you have a very useful tool for tracking your training.

[Russ]

The fluid2 was the first trainer I had. After I observed, as many have, that my indoor performance on the trainer seemed lower than my road work, I started poking around the power forums and trainer forums for more information.

What seemed the best explanation, in addition to cooling differences as Travis mentioned,
was that the inertia of the trainer was much lower than the road (and your weight). This resulted in micro accelerations during the peddle stroke that worked your legs differently and possibly harder on an small portion of the peddle rotation basis.

I tried using five pound ankle weights with some perceived improvement. Only problem was some chafing so I had to wear thicker long socks which made it a bit hotter .

Russ