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n00b - understanding Strava data

Old 05-04-20, 07:51 PM
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lykbutta
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n00b - understanding Strava data

Hello all,

im new to the group and just got into riding back in mid March due to the gyms being closed. Picked up a trek Marlin 6..had an 820 for years however never rode it. Sold it and upgraded.

Biking has been amazing for me and trying to learn as much as I can. Started off with 4-5 mile rides now pushing 20. I decided that Iím only doing the paved greenways and 0 trails so I even bought a GIANT Contend AR1 because I am feeling road biking would be better.

I am using Strava and want to understand the data. Did a 20 mile ride yesterday ..said I was at 99W and burned about 665 calories. Today I was feeling good so after work I did the same 20 miles but saw my results today and I was STUNNED. The watts were 212 and the calories burned were at 1376!!! I know I made an effort to pedal at a better pace and take fewer breaks. Can someone help me understand the data. Of course itís better but just trying to learn. Any help is appreciated.
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Old 05-04-20, 08:46 PM
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Seattle Forrest
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Watts are a measure of power (the rate work is being accomplished). You see car commercials about horses under the hood, a horsepower is about 750 watts. Like a car, a bike requires power to move. As you can see from your data, a bike requires drastically less power than a car, because a bike is one of the most energy efficient forms of transportation.

More power gets you more speed, but the relationship isn't linear at all. People buy things like aero wheels and supple tires because they waste less power, letting you go faster for the same # of watts.

Strava uses physics to estimate how much power is required to move your bike at the speed it says you were going, over the hill conditions the GPS knows about. We just talked about how things like tires are important, and Strava doesn't know which ones you're using. It doesn't know about the wind either. So it's power estimates are "for entertainer purposes only" but you can use them to get an overall sense as long as you remember they can be off. (Some people buy hardware to actually measure watts.)

If you know how many watts you've put out, it happens that you have an extremely accurate calorie estimate. I have no idea how well Strava's estimates work for calories.
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Old 05-04-20, 09:04 PM
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My boy that rides suggested I get a bike computer. Is it worth the $$$$$
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Old 05-04-20, 09:14 PM
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Originally Posted by Seattle Forrest View Post
If you know how many watts you've put out, it happens that you have an extremely accurate calorie estimate. I have no idea how well Strava's estimates work for calories.
I did a ride yesterday (with a power meter) and it was 4,237kJ for total work but their calorie count was 5,517 for the 6h13m I was riding. I always eat back the total work number. I find on zwift rides the total work kJ number is always really close to the calories, but it seems outdoor rides factor in the heart rate data? I dunno but ever since I started using the power meter numbers it's been a lot easier to cut weight.
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Old 05-04-20, 09:30 PM
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Without a power meter, heart rate sensor, etc., Strava offers a rough guesstimate based on neutral conditions, rider weight, bicycle weight and type, etc.

Add a heart rate sensor, use the Elevate browser extension with Strava, and it'll provide a little more detail. But it's also a guesstimate. Elevate depends on an accurate FTP for relevant data, and without a proper test on a bike with a power meter, I'm just guesstimating.

I usually average 125-150 Stravawatts, around 1.5-1.65 w/kg, which aren't real, just a factor that makes sense only within the Strava universe. Whenever I see a lower power estimate, it corresponds with my reduced effort. But a week or so ago Strava claimed I averaged more than 300 Watts or 3+ w/kg over 30-40 miles. No way, not at my age and my health. Turns out something in the app or website reset my default bike from my 25 lb road bike to my 40 lb upright hybrid. Yeah, if I averaged 16 mph over distance on that 40 lb comfort hybrid on roller coaster terrain, sure. But not on my road bike. After resetting my defaults the reading was more in line with my usual effort.

Lots of variables can influence actual work done, which Strava doesn't account for. In my area wind is a significant factor that Strava doesn't factor in. But the data is a little less inaccurate over time, distance and repetition.

There are other online calculators for estimating power based on speed, rider and bike weight, bike type, etc., and which also factor in wind. I've tried 'em a few times, including plugging in data for the headwind vs tailwind. Turns out the end result was the same as Strava's estimate without accounting for wind. In my case that's because my workout routes are always loops that tend to average out wind effects -- tail, head, cross wind.

It's possible Strava is slightly underestimating my power but not enough to matter. I've ridden with folks my size on similar road bikes who do use power meters. Strava's estimates are usually pretty close to the data they get from power meters. I might, on my best day, average 200 watts for 20-30 minutes, tops. I don't need to spend money on a power meter to tell me what I already know -- I'm never gonna be fast, or even competitive in the masters division in races and time trials.
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Old 05-04-20, 11:08 PM
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Originally Posted by clasher View Post
I did a ride yesterday (with a power meter) and it was 4,237kJ for total work but their calorie count was 5,517 for the 6h13m I was riding. I always eat back the total work number. I find on zwift rides the total work kJ number is always really close to the calories, but it seems outdoor rides factor in the heart rate data? I dunno but ever since I started using the power meter numbers it's been a lot easier to cut weight.
Are you using a Wahoo? The kJ and kCal numbers should be very close.
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Old 05-05-20, 09:24 AM
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Originally Posted by Seattle Forrest View Post
Are you using a Wahoo? The kJ and kCal numbers should be very close.
Yeah, the wahoo bolt... it's always been way off from the kJ numbers. I think strava just takes the calorie number from wahoo instead of using its own calculation?
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Old 05-05-20, 01:06 PM
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Many of us here probably built ourselves up to 100 mile or better rides with little to no data collection at all. Just ride longer and more often is all you have to do. Helps to do some short segments of the same ride at full throttle, then relax for a bit, then go at it again. Knowing why you did bad or good with data sometimes just shows you aren't were you want to be and tells you you need to ride more.

Numbers mainly just give us stuff to argue or boast. In the end it's almost always been the person that gets from point a to b first wins. So a watch is all that is needed.

Trends to me are more useful than anything, So I just look at times for certain segments of my ride. However if you are going to get obsessed with numbers, a power meter can make less confusing and keep you more focused on the right things for training. Though if you are recreational, what are you training for? ............... Though I say the that with sarcasm, cynicism and other stuff because I still do pretty much the same as others here, though I haven't made the leap to power meters yet.
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Old 05-05-20, 01:12 PM
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Originally Posted by Iride01 View Post
Many of us here probably built ourselves up to 100 mile or better rides with little to no data collection at all. Just ride longer and more often is all you have to do. Helps to do some short segments of the same ride at full throttle, then relax for a bit, then go at it again. Knowing why you did bad or good with data sometimes just shows you aren't were you want to be and tells you you need to ride more.

Numbers mainly just give us stuff to argue or boast. In the end it's almost always been the person that gets from point a to b first wins. So a watch is all that is needed.

Trends to me are more useful than anything, So I just look at times for certain segments of my ride. However if you are going to get obsessed with numbers, a power meter can make less confusing and keep you more focused on the right things for training. Though if you are recreational, what are you training for? ............... Though I say the that with sarcasm, cynicism and other stuff because I still do pretty much the same as others here, though I haven't made the leap to power meters yet.

i figure thatís what Iíll do. Just continue on with Strava now, getting my road bike soon, and once I start seeing the 40 and up mile trips then Iíll start investing in a power meter.
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Old 05-05-20, 01:20 PM
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Originally Posted by Iride01 View Post
Numbers mainly just give us stuff to argue or boast. In the end it's almost always been the person that gets from point a to b first wins. So a watch is all that is needed.
Years ago I dated a lady who was an excellent cook, able to whip up delicious things at the drop of a hat. I was riding a lot, but started getting slower. The numbers coming from my HR strap told me it was because I was eating too much fat and not enough carbohydrate, I couldn't hit my LTHR.
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Old 05-05-20, 02:59 PM
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Originally Posted by Seattle Forrest View Post
Years ago I dated a lady who was an excellent cook, able to whip up delicious things at the drop of a hat. I was riding a lot, but started getting slower. The numbers coming from my HR strap told me it was because I was eating too much fat and not enough carbohydrate, I couldn't hit my LTHR.
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