Help on power/watts

The short answer to your question is that yes, you can estimate power as a function of rider, speed and resistance. For example, Strava has an algorithm that will estimate power. And, the iBike computer (now marketed by Velocomp) derives power from speed and estimated resistance.

The problem is the accuracy of the estimate. The reason there is a wide variance in accuracy is because it is extremely difficult (actually, it's impossible) to estimate resistance. The logic of deriving power from speed is that power is required to produce speed given total resistance, so if I know total resistance then I can impute the amount of power required to produce the speed. And, that's true because it's simple physics. But, here's the rub. Total resistance includes some variables that are relatively constant, such as the weight of the rider and bike, rolling resistance from the tires, frontal area resistance due to the rider's position on the bike, and the frontal area resistance of the bike. But, then you have variables that change constantly, such as grade and wind. The truth is that road gradient changes constantly and wind direction and velocity changes constantly. So, no matter what values you use, they are only accurate some of the time. So, the bottom line is you should use any estimates of power not based on an actual power meter with the knowledge that the accuracy of the estimate is subject to a large variance.

If you want to play with the assumptions and estimate power based on assumptions, here's a site where you can do that: http://www.analyticcycling.com/

Wow, overload of variables. Lol

Very informative and very knowledgeable you are.

Thank you for the site adress, I'll have a look

The site is very informative, overwhelming. Thanks

I found a section that shows cadence at a given speed and gear ratio you in.

Is it possible to get watts from such a model.
I've got an entry level giant indoor trainer, magnetic one.
I put my cycling clock on so I can keep track of my training, speed, distance,time.

Out of scanning the web I don't get any graphs for the idt giant.
But every other idt on the planet I can.

Thank you

It's virtually impossible to develop a reliable formula to translate resistance & speed to watts for any trainer, and here's why. Even at the same resistance setting and speed, there are other variables that greatly affect watts. For example, power is very sensitive to tire, tire pressure, tire wear and heat. Most trainers and tires heat up and the watts required to produce a given speed at resistance will change as the trainer heats up and as the tire heats up.

What you can do is to calibrate your trainer with a power meter. If you know someone with a PowerTap hub (or any other power meter), see if they will help you calibrate your trainer. In other words, develop a table of the relationship between resistance, speed and power. But, take note that the calibration is only valid if you use the same tire, with the same tire wear and the same tire pressure and the same trainer warmup duration. The bottom line is that there is no simple, painless way to estimate watts without a power meter.

Thank you...

Getting someone with a power meter and running my idt at certain speeds will give me a good idea where I'm heading when training.

Thank you for speedy reply and informative information.

Hi

I found this.

See the attachment.

Kind of all what i was looking for..

What's your take

Such broad assumptions about the relationship between power and speed are basically worthless. You have to ask yourself why you want to know your power. If you use a number that is at best an approximation with huge variance, then I say it's a worthless number. Do some reading at the link I gave you and you'll understand the variables that determine total resistance. It's a long list.

I'll go over the information, dive in abit deeper this time..

Thank you

Strava can provide power estimates based on your speed, weight, and gradient, but it may not be entirely accurate. For precise wattage, a power meter is necessary. Regarding your accident, ensure your bike is properly fitted to minimize risk of further injury.

Strava can provide basic data, but it's not designed for medical analysis. How did your doctor assess your wattage post-accident? Sharing Strava data might be interesting, but it won't replace medical expertise. 😉

tim_hal516 said:

Strava can provide basic data, but it's not designed for medical analysis. How did your doctor assess your wattage post-accident? Sharing Strava data might be interesting, but it won't replace medical expertise. 😉

Went to a lab in cape town, so it's a fresh start with new numbers and from there out it's just collecting data.

Lab tests are crucial, but data without context is meaningless. How did your numbers change post-accident compared to pre-accident? Without baseline data, analyzing progress will be like spinning wheels. 🚴

Lab test conducted under same conditions and equipment is vital, which I didn't have. So it's a fresh start. The test will be a constant ftp throughout regardless of what training I'll be doing. But a rough idea 150-180 watt down.

While understanding your circumstances, it's crucial to note that a "fresh start" with lab tests doesn't equate to accurate progress tracking. Without pre-accident data, you're essentially comparing apples to oranges. Your FTP (Functional Threshold Power) range of 150-180 watts down is a start, but remember, cycling performance isn't solely about power output. Factors like endurance, recovery, and mental strength also play significant roles. Let's not overlook these aspects in our discussion. 😄

Absolutely! While a fresh start with lab tests might not provide an exact comparison, it's a starting point, like standing atop a new mountain range. True, FTP is just one piece of the puzzle, but it's like having a solid base camp. Endurance, recovery, and mental strength are indeed vital, each a challenging climb on its own.

Remember, even if you're comparing apples to oranges, both fruits have their unique qualities. So, don't be disheartened. Instead, view this as a chance to conquer a different peak, perhaps one more challenging and rewarding than before. Keep pedaling, and let's see where this new route takes us!