# strava calculated power vs another riders power meter

#### exiged

##### New Member
Hi Guys,

I was out with a friend earlier who has a PM fitted, his average over the ride was 196w, whereas strava calculated mine at 138w when he added me to the ride (i didn't record it on strava on my phone and i dont have a PM fitted). Is this purely down to a difference in w/kg (he's 5st heavier) or just stravas calculation of my power over GPS?, or a combination of both perhaps?

#### 13 rider

##### Guru
If Strava has your weight it's a calculated guess without your weight it's a wild guess . If any hills were involved in the ride and you rode up them at the same speed your friend would have to have put out more power to keep up with you hence the high average .

#### Edwardoka

##### Guest
Hi Guys,

I was out with a friend earlier who has a PM fitted, his average over the ride was 196w, whereas strava calculated mine at 138w when he added me to the ride (i didn't record it on strava on my phone and i dont have a PM fitted). Is this purely down to a difference in w/kg (he's 5st heavier) or just stravas calculation of my power over GPS?, or a combination of both perhaps?
It's both; Strava's virtual power calculation is a very rough guess, it works by periodically sampling your position and elevation (roughly once a second) and then calculates a "speed" value for each sample by comparing the new position with the previous one, and it compares its previous "speed" and "elevation" values vs the new "speed" and "elevation" values to calculate acceleration and elevation difference, which are then used to provide a number in watts. It doesn't take factors such as GPS accuracy, wind, surface or weather into account and so it's not really that useful a value on its own.

However, if he's 5 stone heavier than you he will need to put out a lot more power than you on climbs to keep the same pace.

OP
E

#### exiged

##### New Member
Makes sense guys thanks

#### cougie uk

##### Über Member
As has been said if he's 5 stone heavier than you then he needs to put out a lot more power than you.

But how did you ride ? Were you side by side ?

If he was in shelter on your wheel then you might have been putting out more Watts than him.

Really you need a PM or we are just guessing.