100km is not 100km in event

Happy Holidays all,

Rode a fast “100km” event from start pen to finish banner for over 2 and a half hours and got the leader board. A dialogue then appeared saying event was completed and do I want to stay on the CRIT course or I will be exited in seconds. I hit “remain” on computer. Then, seconds later, with no further riding, I exit the ride and save on the computer.

Now I see that the activity distance is listed as 99.4 Km. Several others in our grupetto also got 99.5 Km, another one seems to have 101 km. Was the banner incorrectly placed? Did I exit the event incorrectly and cause the distance to be altered? Is Zwift bonkers?

Zwift support said I may have entered the event late. (Incorrect, in start pen) or I should reboot my router. (Gigabit wired network, gigabit internet connection, fast business grade router. Fast and rock stable. ) which seems like an unlikely problem,

Something is wrong here and it’s not likely local to me. Several people with different setups from across the country got shorted. (East coast and West Coast.) A “100km event” is not 100km start to finish on Zwift.

Of course, I will hit “remain” and add an extra KM at end of the next ride. But, something needs to be fixed. Zwift should have interest in supporting users who ride 100k.

Event: Group Ride: USMES Christmas Hawaii Torturefest Special 100K sub 2 hours Thursday December 29th 11:30 CT
Windows 10, Intel i7, 32 Gb memory, NVIDIA 1650Ti, 8Gb graphics, Zwift Version 1.32.1 (106405)
Zwift Companion Android app Version 3.42.0 (1477), Server Version 1.307.1

Random thought… over that distance, could the course be 100km depending on whether you take the turns on the insides/outsides, etc? I think in the older steering device conversations, courses can end up with lesser or greater distances based on the path chosen.

One article that discusses a bit:
ht tps://zwiftinsider.com/steering-alpe/

1 Like

Interesting idea. Thanks. But, none of us had steering enabled.

So 0.5km/100km=0.5% error in distance lines from automatic steering events…

You might hope that Zwift checked the distance before ending a “100 km ride”. Obviously not…

I agree. But in a group event someone is arbitrarily put on the inside of a turn and someone else is taking the longer outside line. Is the lap distance on that crit course based on the shortest, middle, or furthest lines you could take? Lots of left turns on that course, so fastest time achievable would be from riding on left side of lane – but this is because it’s the shortest distance. No idea though how Zwift assigns lane position if just riding solo.

1 Like

Perhaps 100 km i=100 km +/- 1% or whatever. I wonder if we could figure out the margin of difference by looking at some data for auto steering. But how? (Do a frequency plot and stats of times on event route, except riders stop at varying spots after the banner. Does Zwift record the distance to the banner rather than end of ride?)

There’s often this strange variation of some hundreds of metres between riders in the same group in the same event that might be due to different lines or sunspots or whatever, but I don’t think I have ever seen anyone lower than the nominal distance (late joiners excepted of course). The event appears to be set for the correct distance so this one is really strange, hopefully just a one-off.

This I think was a somewhat odd event structure. ~26 laps of a 3.85km course, that eyeballing, seems to have about 17 significant turns per lap (overall over 400 somewhat hard turns). I believe it’s a fundamental geometry problem. Imagine comparing this race structure to a different 100km course that’s in a simple triangle shape with three ~33.3 km sides (and only 3 major turns over the entire distance). Gotta be huge potential distance variance between these 2 scenarios, just based on just the number of turns.

Sounds plausible, at least if the nominal distance is measured along the centre line. The number of turns per lap might not be that important per se since some of those cancel each other out as long as you can only ride on your own side of the road, but rather the number of laps (each containing a net 360-degree turn) as well as the direction of travel (inside or outside lane wrt the entire loop). This one is counterclockwise and on the non-right side of the road so that would indeed mean the inside lane overall.

Yes, and to steal a graphic from DCRainmaker, which somewhat illustrates how one road can carry different distances, depending on how you travel it.

1 Like