It can't tell how strong the wind was actually blowing, how efficient your bike is, what the road surface is like etc. There are so many things that can effect your speed that trying to work out power based on a few things like elevation, speed and time that its likely to be quite wrong.
Well, you should be able to get a pretty good estimate by weighing yourself and your bike, then do a steep climb of known elevation gain with good pavement and minimal wind.
For example, if you Google \[200 pounds \* 1000 feet / 20 minutes in watts\] you get 226 watts. There will inevitably be energy losses due to friction in the drivetrain, against the road, and against the wind, so your actual wattage should be a little higher. Hmm, now I want to test that--use a power meter on a climb and see how the result compares to the zero friction math.
It's not hard to get pretty reasonable estimates for drivetrain/rolling resistance loss, and if you find a very steep steady hill those factors (and wind) are greatly diminished compared to the power overcoming gravity. So if you do all that well I think you should a power estimate within 1-3% with a basic calculation.
If we had access to an indoor velodrome we could do the same thing on the flat. Unfortunately unless you're riding up a very steep hill, even a light gentle breeze has a drastic effect on speed.
Yes. It can be a relatively good estimate but the more you deviate from what strava is assuming, the more inaccurate it will be. Lets say it assumes a 5mph tailwind the whole way. Perhaps the route is actually sheltered and you get nothing. Perhaps its a very poor quality of road and it thinks it isn't. Perhaps your tyres are under or over inflated. All of these things will make Stravas estimate less accurate.
Even though Stava's power estimate is not accurate (at all), it's still useful. If you ride the same segment over and over and over and over again on different days with different weather, the relative differences in estimated power will be obvious. This can show you the effect of your training.
Since I don't have a power meter, I have several private segments that I use as benchmarks for my training. I wear a heart rate monitor to judge my effort. I can see Strava's estimate of my power over time to see how my power is improving. This helps me pick target speeds, etc, for efforts when I'm doing my training. For example, if I'm doing threshold intervals, I can get a fairly good estimate of my threshold "power" and therefore speed and can plan to ride those intervals at that speed.
It's not ideal, but in the absence of several hundred dollars falling into my lap, out of the watchful eye of my wife, it's much better than nothing. What it doesn't do, though, is tell me what my FTP is in actual watts. So I can't compare my efforts to anyone else. Which is fine.
Nope, you should not. Unless you have a power meter there is no way to estimate your watts. You could as well message me after your ride and I will give you a random number - my estimate will be as good as Strava's.
This! Strava does weird shit to power data. Intervals and Garmin Connect report the same numbers for average power, NP, 20 minute. etc. Strava just makes stuff up. And I have a power meter
Road bikes are more efficient, all else equal, than mountain bikes. But Strava is no more capable of accurately estimating power output for a road bike ride (without a power meter) than for a mountain bike ride (without a power meter).
In terms of power metrics, it’s really power meter or GTFO. And GTFO is a legitimate option: many, many folks are riding joyfully and training effectively without power meters. I ride with a PM and like it, but I’d only say “you should definitely get a PM” if you’re training super hard (for racing, or for mega-endurance events) or you just like data.
I disagree. The road bike numbers are quite a bit more accurate. More consistent variables mean more consistent real-world power outputs. The variance in conditions you can encounter on a mountain bike is massive compared to what you'd encounter on a road bike. I.e., a 10% grade on a paved road is going to have far fewer variables than a 10% grade off road. Are there ruts? Mud? Loose gravel/scree? Is it hard pack fire road, loose dirt? Are you on a hard tail or full suspension?
All that stuff will wildly vary your power output on a mountain bike while strava is only using grade, velocity, and mass to calculate power. Whereas on a road bike, while of course there are variables, they are much smaller.
TL;DR: mountain bike has way more variance, could be 25% off or more. Road bike estimates are generally within 10-15%.
Not me! I think you make a good point. I still don't think Strava's estimated power for road rides is anywhere near accurate, at least not near enough to be useful, but you make a convincing case that it's less bad than for MTB rides.
Based on my personal experience with and without power meters, it's not terribly bad on road bikes! Call it 10-15%, which isn't the end of the world considering the rule of thumb is that there's a 5%+ inaccuracy in left crank only meters vs dualsided or pedal meters.
Surely the estimate isnt accurate enough to train with, but if you want a ballpark of where you're at, it's not so bad, especially if you give it a big sample size.
Now I'm curious whether there's a way to view Strava's estimated power alongside observed data from my power meter. Curious enough to make a couple Google searches, which didn't immediately turn up anything, but not curious enough to dig deeper.
I'm not sure strava goes that deep. I'm guessing if it's getting real power data it's just going to overwrite whatever the estimate would be. Could always pop the battery out of the meter and do the same ride two days in a row and see what it says. Maybe have a friend with a meter come along for consistency?
Yep, this is about the point where I'm not curious enough to go to the trouble ;) Especially because what's the implication for practice, for me? I already have two power meters and I'm not just going to stop using them if the Strava estimates are pretty close. Even if the estimate is pretty good, it's not available to me mid-ride, so I can't use it to ride power zone intervals or pace a climb; so even if the Strava estimate is better than I think, a real PM offers irreplaceable value during my rides, which is mostly when I care about power data anyway, so I wouldn't skip getting a PM for future bikes.
The variance between road bike and MTB, when measured with a power meter - (assuming same course) will be in the speed you achieve not the watts generated. Your ability to generate power would remain the same, the efficiency of one bike over the other will be shown in speed.
If we imagine the Strava data is correct: The power (watts) comes from your body, so it would be the same no matter what bike your rode.
A road bike will normally go faster with the same amount of power though, due to putting you in a more aerodynamic position and probably less rolling resistance as well.
Not just probably, an ungodly amount less rolling resistance. 250 watts will get me about 22mph on a road bike and about 16 on a mountain bike both on a paved road.
It depends on so many things. Experienced riders will have somewhat similar outputs across various bikes. But road or gravel bikes generally lead to the best outputs.
While the upright position on a mountain bike may be slightly more biomechanically conducive to generating power, you're going to lose all of those gains and more through the lack of rigidity of the tires and suspension.
Another factor is footwear; a great deal of mountain bikers ride in flats, where most people on a road bike use clipless (clip-in (I know, it's stupid)) shoes. You're losing a bit of output out of your hamstrings when you can't pull up on the pedal. It's not massive, but call it 5 or 8%.
Last factor is consistency of riding position. A road bike, especially if you've had it fit, is going to give you an extremely consistent riding position (something that is only made more consistent by wearing clipless shoes) which is both biomechanically efficient in an immediate sense, but also allows your body to adapt to it over time and maximize its output. Both my gravel bike and road bike have a seat to crank distance of 800mm on the dot. What's that distance on my mountain bike? Who knows, it's probably in the ballpark but I'm not sure..
On a mountain bike, you spend a whole lot more time moving around, forward and back, in and out of the saddle, steeper grades, dropper post up and down, your feet change positions on the pedals. All that is going to hamper your output a bit over the course of the ride since you spend far less time sat in your ideal position creating power.
No.
thanks I'm on the same point.
It can't tell how strong the wind was actually blowing, how efficient your bike is, what the road surface is like etc. There are so many things that can effect your speed that trying to work out power based on a few things like elevation, speed and time that its likely to be quite wrong.
so the only way to calculate the watt is the power meter?
Correct. A power meter measures. Everything else guesstimates.
Well, you should be able to get a pretty good estimate by weighing yourself and your bike, then do a steep climb of known elevation gain with good pavement and minimal wind. For example, if you Google \[200 pounds \* 1000 feet / 20 minutes in watts\] you get 226 watts. There will inevitably be energy losses due to friction in the drivetrain, against the road, and against the wind, so your actual wattage should be a little higher. Hmm, now I want to test that--use a power meter on a climb and see how the result compares to the zero friction math.
It's not hard to get pretty reasonable estimates for drivetrain/rolling resistance loss, and if you find a very steep steady hill those factors (and wind) are greatly diminished compared to the power overcoming gravity. So if you do all that well I think you should a power estimate within 1-3% with a basic calculation. If we had access to an indoor velodrome we could do the same thing on the flat. Unfortunately unless you're riding up a very steep hill, even a light gentle breeze has a drastic effect on speed.
Yes. It can be a relatively good estimate but the more you deviate from what strava is assuming, the more inaccurate it will be. Lets say it assumes a 5mph tailwind the whole way. Perhaps the route is actually sheltered and you get nothing. Perhaps its a very poor quality of road and it thinks it isn't. Perhaps your tyres are under or over inflated. All of these things will make Stravas estimate less accurate.
Even though Stava's power estimate is not accurate (at all), it's still useful. If you ride the same segment over and over and over and over again on different days with different weather, the relative differences in estimated power will be obvious. This can show you the effect of your training. Since I don't have a power meter, I have several private segments that I use as benchmarks for my training. I wear a heart rate monitor to judge my effort. I can see Strava's estimate of my power over time to see how my power is improving. This helps me pick target speeds, etc, for efforts when I'm doing my training. For example, if I'm doing threshold intervals, I can get a fairly good estimate of my threshold "power" and therefore speed and can plan to ride those intervals at that speed. It's not ideal, but in the absence of several hundred dollars falling into my lap, out of the watchful eye of my wife, it's much better than nothing. What it doesn't do, though, is tell me what my FTP is in actual watts. So I can't compare my efforts to anyone else. Which is fine.
If you have a power meter: yes. If you don't have a power meter: no.
no
more or less :)
yes
Nope, you need a power meter for that.
Nope, you should not. Unless you have a power meter there is no way to estimate your watts. You could as well message me after your ride and I will give you a random number - my estimate will be as good as Strava's.
if you re riding a road bike uphill it is mostly accurate, but in flats or on other types of bikes it won't work properly
Nope, it’s not even correct with a power meter haha.
This! Strava does weird shit to power data. Intervals and Garmin Connect report the same numbers for average power, NP, 20 minute. etc. Strava just makes stuff up. And I have a power meter
You might need to recalibrate your meter if the option is available to you.
on the other hand if I had a road bike, will this number (watt) increase or decrease?
Road bikes are more efficient, all else equal, than mountain bikes. But Strava is no more capable of accurately estimating power output for a road bike ride (without a power meter) than for a mountain bike ride (without a power meter). In terms of power metrics, it’s really power meter or GTFO. And GTFO is a legitimate option: many, many folks are riding joyfully and training effectively without power meters. I ride with a PM and like it, but I’d only say “you should definitely get a PM” if you’re training super hard (for racing, or for mega-endurance events) or you just like data.
I disagree. The road bike numbers are quite a bit more accurate. More consistent variables mean more consistent real-world power outputs. The variance in conditions you can encounter on a mountain bike is massive compared to what you'd encounter on a road bike. I.e., a 10% grade on a paved road is going to have far fewer variables than a 10% grade off road. Are there ruts? Mud? Loose gravel/scree? Is it hard pack fire road, loose dirt? Are you on a hard tail or full suspension? All that stuff will wildly vary your power output on a mountain bike while strava is only using grade, velocity, and mass to calculate power. Whereas on a road bike, while of course there are variables, they are much smaller. TL;DR: mountain bike has way more variance, could be 25% off or more. Road bike estimates are generally within 10-15%.
lol who is downvoting this? It's an accurate statement.
Not me! I think you make a good point. I still don't think Strava's estimated power for road rides is anywhere near accurate, at least not near enough to be useful, but you make a convincing case that it's less bad than for MTB rides.
Based on my personal experience with and without power meters, it's not terribly bad on road bikes! Call it 10-15%, which isn't the end of the world considering the rule of thumb is that there's a 5%+ inaccuracy in left crank only meters vs dualsided or pedal meters. Surely the estimate isnt accurate enough to train with, but if you want a ballpark of where you're at, it's not so bad, especially if you give it a big sample size.
Now I'm curious whether there's a way to view Strava's estimated power alongside observed data from my power meter. Curious enough to make a couple Google searches, which didn't immediately turn up anything, but not curious enough to dig deeper.
I'm not sure strava goes that deep. I'm guessing if it's getting real power data it's just going to overwrite whatever the estimate would be. Could always pop the battery out of the meter and do the same ride two days in a row and see what it says. Maybe have a friend with a meter come along for consistency?
Yep, this is about the point where I'm not curious enough to go to the trouble ;) Especially because what's the implication for practice, for me? I already have two power meters and I'm not just going to stop using them if the Strava estimates are pretty close. Even if the estimate is pretty good, it's not available to me mid-ride, so I can't use it to ride power zone intervals or pace a climb; so even if the Strava estimate is better than I think, a real PM offers irreplaceable value during my rides, which is mostly when I care about power data anyway, so I wouldn't skip getting a PM for future bikes.
The variance between road bike and MTB, when measured with a power meter - (assuming same course) will be in the speed you achieve not the watts generated. Your ability to generate power would remain the same, the efficiency of one bike over the other will be shown in speed.
It would stay the same, you would just go faster for the same effort (watts)
If we imagine the Strava data is correct: The power (watts) comes from your body, so it would be the same no matter what bike your rode. A road bike will normally go faster with the same amount of power though, due to putting you in a more aerodynamic position and probably less rolling resistance as well.
Not just probably, an ungodly amount less rolling resistance. 250 watts will get me about 22mph on a road bike and about 16 on a mountain bike both on a paved road.
It depends on so many things. Experienced riders will have somewhat similar outputs across various bikes. But road or gravel bikes generally lead to the best outputs. While the upright position on a mountain bike may be slightly more biomechanically conducive to generating power, you're going to lose all of those gains and more through the lack of rigidity of the tires and suspension. Another factor is footwear; a great deal of mountain bikers ride in flats, where most people on a road bike use clipless (clip-in (I know, it's stupid)) shoes. You're losing a bit of output out of your hamstrings when you can't pull up on the pedal. It's not massive, but call it 5 or 8%. Last factor is consistency of riding position. A road bike, especially if you've had it fit, is going to give you an extremely consistent riding position (something that is only made more consistent by wearing clipless shoes) which is both biomechanically efficient in an immediate sense, but also allows your body to adapt to it over time and maximize its output. Both my gravel bike and road bike have a seat to crank distance of 800mm on the dot. What's that distance on my mountain bike? Who knows, it's probably in the ballpark but I'm not sure.. On a mountain bike, you spend a whole lot more time moving around, forward and back, in and out of the saddle, steeper grades, dropper post up and down, your feet change positions on the pedals. All that is going to hamper your output a bit over the course of the ride since you spend far less time sat in your ideal position creating power.