Out of curiosity I've been out an done a little experiment.
Cateye Enduro 8 V Garmin Edge 500 set to use manual wheel circumference.
The Garmin was set for a manually entered wheel circumference of 4192mm - double the Auto wheel circumference it was originally set for which was 2096 mm.
The Cateye was set to the std wheel circumference for a 700/23c wheel of 209 cm.
According to the Cateye I cycled a distance of
1.18 km (on a flat route)
As expected whilst cycling along the Garmin showed my speed and distance travelled to be twice that recorded by the Cateye.
When uploaded to Strava, contrary to my thoughts earlier the reported distance was still twice that of the Cateye at
2.3 km, max speed and average speed were both double as well.
When looking at the analysis of the ride it starts at 0km and finishes as 2.3 km as I don't have privacy zones set (I crop at start and finish of ride instead)
Therefore it would seem that if you took the Strava upload at face value there would be no indication that there was something wrong with it and
you could easily believe someone had cycled further than they actually had.
I then exported the GPX file from Strava and uploaded it to Ridgewithgps - where the distance ridden was shown as
1.2 km (I think this is similar to how Jo discovered the initial problem)
When uploaded to Garmin Connect the distance is shown as
1.23 km.
So it would initially seem a problem with Strava as other websites aren't fooled by playing around with the wheel sensor circumference data.
(I know Kurts Garmin connect data was always under distance compared to his Strava data by as much as 1.5km per day but mostly less than this so I'm sure his distance data is as good as you can get with GPS.)
Here is Bruce's Garmin connect page
https://connect.garmin.com/profile/cycle_dr1Based on what I had seen above I was expecting to see a difference between this and Strava but there isn't any so that would appear to dispel the wrong wheel circumference theory.
I can't seem to be able to look at the Garmin Connect analysis of Bruces ride as the website comes back with a timeout error - may be because I'm not 'connected' with him.
All very confusing.
Jo, how are you able to get the GPX data for Bruces ride on the 4th - are you a Strava Premium Member?