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Strava Average Power estimate


OemD
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If you are training on your own, on a smooth road, normal riding position and the weather was accurately pulled through to Strava:

 

80-85%

 

If you are riding with mates, in bunches, races, road surface changes, riding on your MTB or anything out of the norm:

 

60%

 

 

 

What he said. I'd concur with the percentages too.

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I wouldn't take note of it at all.

OemD if you really keen on power figures, save and buy a power meter.

 

Its a game changer!

 

 

Dr Mike Posthumus disagrees with the gamechanger bit. Studies he conducted at the Sports Science Institute seem to indicate that HR might actually be better but requires more time.

 

A PM provides more motivation to the user as they have found.

 

the biggest benefit is having a plan and being consist in following said plan.

 

that R150 Seminar was a darn good investment!!

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I wouldn't take note of it at all.

OemD if you really keen on power figures, save and buy a power meter.

 

Its a game changer!

Not really interested in the ave power numbers, just the ave power was 200W over 1h30m ride. Which is outside the normal range for me, as I normal range between 150W and 170W per ride. 

 

The higher ave power output does correlate with the fact that I smashed my strava PR's for 8/13 sectors and 5/13 second bests...

 

My question just comes from curiosity and I always compare myself to my previous efforts.

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It's important to understand how Strava estimates your power, with the most crucial part being the rolling resistance coefficient. Road, MTB, Cross all have different values, and the moment you put your MTB on a tar road, that value becomes meaningless. Or if you're riding your MTB up a steep rocky slope. It's all just guessing.

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Its pretty useless IMHO unless you do all your riding in a lab. There are just too many variables e.g the weather/wind/rain, bike type, drafting, terrain, bike position, clothing etc,etc.

 

In general if you ride more - you will get stronger. However IMHO a tailwind will probably make you smash more PRs from 1 week to the next vs the week of training itself  :whistling:. If you want numbers, get a power meter - you can pick up a single sided stages for under 5k now. Do you need it no, does it help to gauge your training if you mostly ride outdoors - hell yes.

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Dr Mike Posthumus disagrees with the gamechanger bit. Studies he conducted at the Sports Science Institute seem to indicate that HR might actually be better but requires more time.

 

A PM provides more motivation to the user as they have found.

 

the biggest benefit is having a plan and being consist in following said plan.

 

that R150 Seminar was a darn good investment!!

 

Interesting, got a bit of the low down of the topics covered. Definitely missed out!

 

From day to day sessions i cant understand how HR could be better if all it takes is an very hot day to through your HR numbers completely out. So would've been interesting listening to that from Dr Mike and co.

 

A PM has has taught me how to train, and yes obviously with a plan and mastermind (coach).

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Snip Snip snip     How Strava Calculates Power

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Rosie
October 31, 2019 21:18
Our Power Equation

The power produced while riding is made up of several components:

  • Power produced to overcome the rolling resistance of forward motion.(Big fat assumption here)
  • Power produced to overcome wind resistance.(Another big fat assumption)
  • Power produced to overcome the pull of gravity (in the case of climbing hills).(This they can get from the weight you tell them (most people lie) and bike (Most bike shops lie here)
  • Power produced to accelerate from one speed to another.( this is Newtonian physics but still has drag and rolling resistance assumptions added in )

The total estimated power produced, P(totalest), is the sum of all four power components.

P(totalest) = P(rolling resistance) + P(wind) + P(gravity) + P(acceleration)

P(rolling resistance)

The power required to overcome rolling resistance can be described by the formula P = Crr x N x v, where

  • P is the power required. (calculated using an assumed rolling resistance coefficient, lets assume its 10% out) 
  • Crr is the rolling resistance coefficient. We define this based on the type of bike (road, mtb, cross) you used. ( there would be tyre pressure assumptions, width assumptions and adhesion assumptions)
  • N is the normal force of the bike and the athlete against gravity. (calcualted accurately as long as the rider doesn't lie about their weight..)
  • v is the rider velocity. (failry accurate if you're not using a Garmin)
For more information about rolling resistance, see http://en.wikipedia.org/wiki/Rolling_resistance.
 
P(wind)

The power required to overcome wind resistance (drag) can be described by the formula P = 0.5 x ρ x v3 x Cd x A, where

  • P is the power required.
  • ρ is the density of air. (assumed value)
  • v is the rider velocity, relative to the wind. (without a pitot tube to measure airspeed this is a massive assumption)
  • Cis the drag coefficient. (highly assumed value since it changes with air density, wind speed, and frontal area)
  • A is the the surface area of the rider facing the wind. (more massive assumptions...)
Because we do not know wind speed or air density during your ride, we assume no environmental wind conditions and an outside temperature of 15C. The drag coefficient is determined by the type of bike you are riding (TT bikes have less drag than mountain bikes). We use a constant for surface area. For more information about wind drag, see http://en.wikipedia.org/wiki/Drag_(physics)
so basically they assume you are riding in a windtunnel where the flow is laminar and not turbulent or transient which would be more realistic and true.
P(gravity)

The power required to overcome the pull of gravity while riding up an incline can be described by the formula P = m x g x sin(arctan(grade)) x v, where

  • P is the power required.
  • m is the mass of the rider and the bicycle.(only wrong if the rider and bike shop didn't lie....highly unlikely)
  • g is the gravitational constant, 9.8.
  • grade is the slope of the hill.
P(acceleration)
The power required to accelerate from one speed to another within a ride sampling window can be described by the formula P = m x a x v, where
  • P is the power required.
  • m is the mass of the rider and the bicycle.(refer to above)
  • a is the acceleration between your starting speed and your ending speed within the sampling window.(does not account for drag and mechanical losses - these are important because for power training we're interested in the force your legs are applying not the power the system outputs after losses. If you want to work with improving drag or bike position then maybe this is ok to a limited extent)
Strava Calculated Power vs. Power Meter

We have seen that in most cases our watts numbers are very close to the numbers provided by a Powertap or SRM. Yes in a windtunnel maybe but based on the number of assumptions to get wrong I'm going to call BS on this statement Note that Strava calculated watts are not the watts produced at the crank but the watts produced by the rider-bike system, this will create a slight difference between the powermeter data and the Strava watts. Lack of good chain lubrication and low tire pressure can rob you of the watts you see on your Powertap or SRM. Other reasons watts can be inconsistent include strong winds and bad elevation data reported by the Garmin. Our calculations are most accurate when climbing given accurate rider and bike weight.

the calculations are accurate mathematically but the quality of the numbers is quite poor I'd imagine. Junk in junk out

Edited by DieselnDust
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Interesting, got a bit of the low down of the topics covered. Definitely missed out!

 

From day to day sessions i cant understand how HR could be better if all it takes is an very hot day to through your HR numbers completely out. So would've been interesting listening to that from Dr Mike and co.

 

A PM has has taught me how to train, and yes obviously with a plan and mastermind (coach).

 

 

Definitely missed out. I think 90% of the people in attendance wanted more and Mike and Andrew definitely wanted to offer more.

 

I train with power and for a long time I didn't .Once my youngest was born and I realised time no longer belongs to me I went back to power because I could focus the workouts more sharply. This is where the biggest advantage lies. 

The message was that when training with HR we need to allow more time for recovery between load repeats. Give your body that time to actually recover. With a PM based training plan they assume that 5min is enough but sometimes you need 10 so HR is actually a better indicator of when you are ready for the next load.

 

Another take away from the session was that I'm training too hard and therefore tired before most of my races. Dr. Mike was saying that 20% of your training time should with intensity (Z4-Z6) and 80% zone 2. That kind of blew my a little but after just 10 days of tweaking my plan to work the drills to align with that I've found i'm more productive.

 

I think most of us are overthinking training and especially the tools we use. That was another takeaway BTW.

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