Can't afford SRM or PT right now, other power measurement tools?

Rideastrong

I am not in a position to purchase a PT or SRM right now. Maybe for next year. I do need a new trainer for those bad days outside. Are there any trainers that have a somewhat accurate power meter? I know it won't be as good as a PT or SRM, but i would like to get a temp fix right now. I also use a Polar 720i, but the power interface looks kind of weak in the design and have read too many mixed review. Any suggestions? Thanks.

RapDaddyo

This is a good question, but I'm not sure there is a low-cost answer. I don't have personal experience w/ them, but CycleOps' top two trainers purportedly have power. I don't know if they are discounted, but the MSRP is $700 for the low-end model and $900 for the high-end model. For that money, you could almost get a PT Pro. Maybe somebody knows if there are cheaper trainers with power.

P.S., It looks as though the CycleOps trainers are discounted -- $600 for the Electronic model and $750 for the Electronic +.

Flatscan

The reviews that I read specifically say that the Polar works poorly on a trainer; it's suspected that the vibrations from training in place interfere with its sensing.

Performance Bike has 2 trainers with power displays, the Travel Trac Mag Force Plus ($260 list) and the Fluid Force Wireless ($350 list). Much cheaper than the PowerTap, but pretty steep as you can get a Cycleops or Kurt Kinetic fluid trainer (no power, but solid name-brands) for that price.

cbjesseeNH

Published peer-reviewed scientific literature suggests that Polar and Computrainer systems deviate sufficiently from "gold standard" laboratory cycling ergometers that significant training difficulties can arise if comparing actual laboratory data (ergometer, blood lactate, ventilation, etc) and data from these systems. Studies suggest SRM Pro to be quite good but there are no studies on Powertap yet.


Most of these studies show that a given unit (Polar, Computrainer), if properly configured and used, give reproducible results. Data from these systems differs from lab data, and data from one system may differ from another system. It seems that if you define your own power zones, ventilation thresholds, etc., using a specific system with your bike, you can get data of sufficient quality to gain training benefits. The numbers may not be accurate (comparable to lab standards) but may be precise (comparable with your system and bike), if you repeat the same tests the same way (same tires, pressure, cadence, gears, etc.)

What this means is that if you go to a lab and they hook you up to air tubes and take your blood while you pedel madly on a $10,000 ergometer cycle, the Lactate Threshold Wattage they give you may not be comparable on your trainer/bike system at home. If your LT is 270W in the lab, you may ride at home at 270W but be above or below your LT.

The best solution is probably not lab tesing and the most expensive and accurate bike, trainer and power meter with you charting and graphing numbers. The best solution is a decent bike, trainer and power meter and some good coaching by someone familiar with power. Heck - a good coach not familiar with power at all will likely get you farther than $25k worth of hardware/software, but I'd bet you can do very well with a trainer costing under $500, a power meter costing under $1000 and coaching at somewhat above the CTS entry level cost. A coach that gives you a plan and looks at your testing data once a month to adjust the plan according is a decent start. And there are plenty alternatives to CTS that may be more economical and effective for you.

This from a scientist who rides a bike and listens more to those who ride bikes and coach cyclists than to my fellow scientists!

MichaelB

We develop low volume highly differentiated electronic equipment and I asked a while back whether people thought there would be much of a market for a cheapish power measuring device.

I have some basic designs for a simple chain mounted pickup device and would be willing to make a few prototypes if I thought there was a market. Measuring chain tension was a the cheapest and easiest way to measure crank load although it isn't brilliant due to interference with the gears, your feet and chain wear.

We would aim at around the £100 but it would be tricky.

beerco

um...haven't you seen the polar power unit? At least in the states, it's protected by patents.

LimShady

I am in the same situation as you. I was thinking of getting the Kurt Kinetic trainer and adding the computer module to it. Another complication is that I would like to get a downloadable data from the power meter. Anyone have suggestion for this type?

ric_stern/RST

I think you need to look at your fellow scientists as well... there's a few papers on PT...

Ric

__________________
http://www.cyclecoach.com

Bruce Diesel

I have a Tacx trainer. What is interesting is that the trainer provides a booklet with power graphs for the various resistance settings. For my one they are linear and for the flow version it is exponential. I simply worked out the equations for the various resistance settings, imported my polar data into a spreadsheet, and calculated my power output - poor man's power meter.

Flatscan

I read that the Kurt Kinetic computer is a regular cyclocomputer that has the trainer's speed/power curve programmed into it. "* Power output only accurate when riding trainer." implies that it will function while the bike is removed from the trainer, just not correctly. Since you mentioned that you have a Polar, look at the suggestion below.

I have the published speed/power curve for my 1Up trainer. I'm planning to further calibrate the curve with my PowerTap (when it finally comes) so that I have the option of leaving an outdoor tire on my PT wheel and running a normal wheel with magnet and trainer tire.

palewin

Normally I avoid posting the "I read on another board" second-hand info, but in this case it may be useful. On the bicycling.com racing thread, one of the posters (coppi1) owns a shop in Colorado, races in France every summer, and is, I believe a cat2. With those credentials, he uses and recommends the Polar power unit, with the proviso that it has to be set up correctly. In fact, he prefers it to the PT, because he can use it with the various sets of carbon race wheels available to him (he has mentioned both the Zipp202s for climbing and one of the deeper-rimmed Reynolds for other events). Therefore given your cost parameters, the Polar power unit might really be a good way to go. Again, with apologies for trying to paraphrase other's experience, I've heard that the Polar's weakness (other than a lot of wires and a "picky" set up) is that since it measures power via chain vibration, it has problems on a trainer because the vibrations are quite different from those on a real road.

Rideastrong

More info please.. So are you saying there is a way of combining the info from the Tacx trainer module into the Polar unit and calculating/estimating power? I would prefere to not have to design spreadsheets to do the math.

Does anyone have any expereince with the electronic cyclops trainers? How are they calculating power? There does not seem to be any connection or interface to the bike drivetrain.

I do not want the polar power unit. I have seen it in action and seen to many freinds get frustrated with it. I don;t want to spend that much money and be frustrated with my purchase.

Flatscan

Bruce Diesel said that Tacx provides power graphs (I assume versus speed) in their booklet. From that, he was able to work out speed -> power equations for his trainer. The Polar records the wheel speed during the session, and he uses a spreadsheet to convert speed -> power. He doesn't need any session information from the trainer. I don't think there's any way to avoid using a spreadsheet to do the conversion. If the trainer has a non-linear curve, the process is a little more complicated.

I assume they measure power at the resistance drum, since power there is the same as at the hub or at the cranks, less relevant losses. I assume further that cheaper trainers use a programmed table to convert drum speed -> power, instead of measuring with strain gauges, which accounts for their typical inaccuracy.

Rideastrong

after reading more and more info from RD, frenchi and ric i think i may just have to postpone the PT purchase till next year and do it right the first time. It really seems like this is truly the best way to go.

I was looking at the teax trainer, and it does seem interesting, i am concerned about the accuracy. Does anyone here use it and has anyone compared the readings to a PT or SRM?