# Tag Info

## Hot answers tagged power

35

There are several different types of power meter on the market and each measures something slightly different in order to make their estimates. In addition, the way that they measure what they measure has implications for their accuracy. Below I discuss what the major models measure, how they measure it, and the implications for accuracy. Power is the rate ...

21

Since you say you're looking to become a triathlete soon it's far too early to be thinking of advanced training aids like power meters. The first few things to do (not necessarily in this order) are join a tri club enter a triathlon or two join a tri training squad observe your (comparative) strengths and weaknesses get a well recommended triathlon book. ...

11

Your question is simple but a full answer is complex. The simplest answer is to point to Part 2 (especially chapter 4) of Wilson and Papadopoulos (2004), or the recent review by Debraux et al. (2011), or the paper by Martin et al. (1998). However, even these papers do not cover approaches that take better advantage of the data available from modern bicycle ...

11

Presuming you are doing a standing start and coming to a complete stop at the top of the hill. The simple requirement is you need energy to move your from the bottom to the top. Most of the energy required will be to raise potential energy of the payload (you and the bike). Essentially you will be creating kinetic energy (moving the bike) by converting ...

8

You don't quite supply enough information in your specific question (that is, "50RPM for 10 minutes with 39x23 with 10% hill") to provide a full answer in absolute terms but, if we assume you're riding a standard sized 700c bike there's enough information to make a good estimate in relative terms. First I'll give a short answer, then a rule of thumb that's ...

8

Generally, you attach a bike computer or a power meter to a bicycle to collect statistics, and/or some sensors to yourself. A bike computer measures the revolutions per minute of a wheel, typically by attaching a magnet to a spoke of the wheel and using a detector attached to the frame which tells the computer every time the magnet passes the detector (so ...

7

I found this image of the first SRM power meter interesting: The crank is rigged up like a lever (rotating around the spindle) - the more forcefully you push the pedal, the more the strain-guage bends, the output of which is used as part of calculating wattage (as is better described in the other answers!) Many modern power-meters are essentially ...

7

Mountain bikers regularly run these low cadences for very short periods, often at much higher power output. The issue with causing damage to knees is more about the duration of the climb and how strong your stabiliser muscles are. (Too much time mushing causes chronic overuse problems, while weak stabiliser muscles can allow injury to happen), however they ...

7

Aside from pacing better, if your cadence drops to 40rpm for too long and you are in your lowest gear at maximal effort for the expected duration, then you could probably use at least a gear 2/3rds or less than you currently have so you are likely to be able to sustain closer to 60rpm. That's possibly not feasible on your bike, but perhaps a 29 rear cog at ...

7

We cannot know exactly unless Dowsett's team releases it, but we can make a reasonable estimate. The most important unknown is Dowsett's drag area, or CdA, so below I have calculated the power needed to average 52.937 km/h for various values of CdA, given the assumptions noted on the figure. Notably, rho is air density in the velodrome and a trackside ...

7

They do help with training and racing but they are also very expensive. As you say you are a beginner I imagine increases in fitness/strength (and therefore speed) are going to come fast anyway, even without a power readout to base training around. I would definitely invest in a HRM though and make sure the bike computer you use has cadence as well as speed....

7

On flat terrain raw power is what is more important than Power to weight ratio. On rolling terrain P/W is important, but the larger rider still has the advantage. On mountainous terrain P/W is the determining factor. You can see this from races in pro cycling. Flat races are won by large strong riders and sprinters. Rolling races are won by mid size riders ...

7

The physics model of cycling power and speed has been validated in the real world. Two examples are this and this. The model embedded in Analyticcyling.com's online calculator is based on these two papers. Whether the amount of difference calculated by the validated models is worth it to Joe and Billy is a question that can't be answered by the physics.

6

I will presume you are asking about the types of trainers that one mounts one's own bike onto, and not a dedicated "bike" trainer such as a Monark ergometer or a CycleOps Indoor Cycle (ergometers such as these are used in exercise physiology laboratories and can be calibrated to be very accurate). Consistency and Accuracy of Speed Measurement Accurate ...

6

The raw pedal force or torque data are difficult to work with but you can extract some information from them. First, note that Stages mounts the strain gages (or gauges) permanently to the crank, so the crank length is constant and they know what it is; that means that there is a one-to-one relationship between the kgf and torque columns. In this case, it ...

6

The short and most direct answer to your question is to use your power meter to pace your ride optimally and Alex Simmons, who has given another answer to your question, was too modest to mention that he is an expert in this and has developed one of the most sophisticated power pacing models for variable conditions. A longer answer is, to paraphrase Prof. ...

6

From what I've read, adding a power meter betters measuring HR only, for some reasons: Heat, diet and stress can affect your HR. A low HR might be an indicator that you are in good shape. You can have a high HR and your power output be low An increase in power implies better performance, but an increase in HR does not necessarily. So it is good to combine ...

5

If I on one ride add 1 kg of weight to the bike, how much slower (in time) will I be? Assuming that you and your bike mass 100kg (in round numbers), an extra 1kg causes a 1% increase in weight, i.e. a 1% increase in the potential energy associated with climbing the hill. If your power output is constant, that implies a 1% increase in time. However some ...

5

According to the FAQ on their website: Note: PowerTap hubs must be laced with a minimum 2 cross pattern to avoid damage to the hub and maintain the warranty." That suggests that making the non-drive side radial could lead to warranty issues. Radial lacing does stress the flange more than tangential lacing so many hub manufacturers do not allow it. To ...

5

If you could find several long hills of different but relatively constant (and not too steep) slope, then determine the slope and your terminal velocity on each hill (assuming that velocity is below some safe speed), you should be able to do the math to determine aerodynamic drag (working on the reasonably valid assumption that rolling resistance is ...

5

There is a new website/download/software package called TrainerRoad that will allow you to train with Virtual Power for the price of a Trainer, ANT+ stick, Speed/Cadence sensor and \$10/month subscription. Checkout the compatible hardware page (linked on the main page) to see if you already have a trainer on their list of known power curves. If not the Kurt ...

5

The Flow appears to be quite consistent though, depending on the mode in which it is used, it can be quite inaccurate. Below is a plot of reported power for speed on the Flow, with each line representing a different "scale factor." All of these data were collected at a coast down calibration of 0, with the same tire, at the same ambient room temperature; ...

5

First, get 'Training and Racing w/ a Power Meter' by Hunter Allen and Andrew Coggan. So incredibly helpful in learning about your device. Second, use WKO+ for analysis. I have been using it for 4 years and it is fantastic. In reference to you question, I typically use the 20 min time trial as a good way of setting my training zones. After a solid warm up (...

5

There are some bike hubs containing an electrical motor inside. If you google "bike hub motor" and take a look at the images, you'll get the idea. I think these ones are ideal since they require minimal changes to the overall bike structure, allowing for normal riding if the motor is not working, and they don't burn evil oil: you just plug the bike to the ...

5

The short answer to your question is, "yes, weight does affect cruising speed on the flat, but not by much." The longer answer to your question is a special case of one of the answers given to this bicycles.stackexchange question: "How can one estimate drag for a bicycle?" There you can find the equation for power given speed, disaggregated into the ...

5

Power output by itself is not a good measurement of performance. Performance of 300W for a 130Kg rider compared to a 80Kg rider is completely different. You should be looking at a combination of Power to weight ratio Time to complete a regular route/segment on garmin connect/strava. Heart rate How you actually feel during your cycle How well your bike ...

5

The following chart can be found in an interesting article on Training Peaks blog. From this you should be able to adjust your power level occordingly.

4

Fundamentally, power meters all work by measuring force (or torque) and a speed. http://en.wikipedia.org/wiki/Power_(physics)#Mechanical_power P(t) = F(t) * v(t) In other words: Power = Force * velocity A pedal or crank based power meter will be measuring either how much torque is applied to the cranks. That combined with your cadence gives you the ...

4

The Tacx Power measurement is accurate in terms of consistency, meaning 200w on Sunday is 200w on Monday, as long as your trainer is set up consistently. It is generally showing a higher number than most other Power meters. My Powertap and my Fortius, when run concurrently differ by about 10%. As for long term accuracy, I've had my Fortius three years. I do ...

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