Does anyone else question the way wahoo/garmin calculate average speed on outside rides? I just find it weird. For instance my ride today, fairly flat, 2K climbing over 62 miles. My average speed after 40 miles was 18.8 mph (it was an endurance ride ) The next 21 miles is fairly flat and I keep it about 22/23 mph…my avg speed raises to 19.6 mph…then I have a one mile climb back to my house, not steep at all but about 1415 mph…in that 78 minutes my avg speed drops to 19.3…it sure seems to go down way faster than it goes up. I know it just is calculated by mileage and time but is just seems weird that it goes up so slowly but drops so fast.
https://www.strava.com/activities/2455645344/analysis
Average speed calculations
Power data! I ride a lot of flat and the wind heavily influences average speed. Speed is really situational, that’s why it’s all about power
You did 61.56 miles in 3hrs 11mins. 61.56 divided by 3.1833 = 19.3. Your average speed is correct. Where is the problem?
I know, it is just math. But for some reason it seems off in my head.
One way I’m seeing it is your using distance for the first two comparisons of average speed and time for the final climb.
Then I looked at your Strava, not sure if the elevation graph is correct but I can’t relate it to your description, so maybe in your mind they terrain is different from what the elevation graph shows.
I myself would break it into 5 segments…
mini descent & flat 9 miles
climb 12 miles
flat 20 miles
descent 12 miles
flat & mini climb 9 miles
Workout the averages from these segments, using time taken, not distance or mixing them and then see if it still seems weird?
Just an idea
I was just curious if anyone else had similar feelings…I guess I should buy a house down in the valley instead of in the hills.
Seriously guys, this is classic just overthinking things. Your average speed for the ride is correct.
Consider the following conundrum…
You have a journey of 20 miles. The first half of the journey is uphill, the second downhill. You travel at an average speed of 30 mph for the first 10 miles, taking 20 mins to cover the distance. What speed do you need to travel for the remainder of the journey to maintain an average speed of 60mph for the entire journey?
You need two trains travelling towards each other at different average speeds and that’ll be a starter in an old O Level maths paper!
Add in some braking…
I think that’s because it’s much easier to go less than half your threshold speed than to go twice your threshold speed, especially when the gradient turns up. If your average is 19, you probably see more 12’s and 13s (and for longer) on the hills than you see 26’s and 27’s on the descents.
Better get your teleporter out.
Mike
I don’t think there’s anything necessarily wrong with the math, although on the surface, 0.3 mph does seem like a bigger than expected drop in average speed over one mile.
However, I’d point out a few things:

It looks like more than a 1 mile climb back to your house (eyeballing the elevation profile). If the distance is more like 1.5 miles, this has a noticeable impact on the math.

Strava rounds to one decimal place. 19.6 could be 19.55 and 19.3 could be 19.34. Again, seems like a small effect, but this would have a noticeable impact on the math.
From where your speed drops below average to the finish is 2.3 miles according to Strava.
Your Wahoo is reporting average speed based on moving time (as is Strava).
The correct numbers are as follows:
 To bottom of final climb  59.2 miles in 3:11:15 at 18.58 mph
 Final Climb  2.3 miles in 0:09:44 at 14.17 mph
 Overall  61.52 miles in 3:20:59 at 18.36 mph
The true reduction in speed over the last 2.3 miles is 0.22 mph.
You should turn off auto pause as it inflates the average of parts of the ride that have plenty of stops and, comparatively, makes slower parts with no stops pull down the average faster than you’d expect.
Mike