Fun-is-Fast Tempus Fugit TT issue: lot slower than usual (with same power!), so less fun

Yesterday I did the Fun-is-Fast event: Tempus Fugit ITT. Although I’ve done the same TT a couple of times in the last months, despite holding a similar power (270W) I was around 2 minutes slower yesterday. One thing I observed, was that I was automatically equipped with the Fun-is-Fast revamped Zwift wheel set. And I couldn’t change them for my preferred 858/disc combo or any other wheelset for that matter. Though I did see other riders using these wheels! That seemed like a bug, but even that shouldn’t cost me 2 minutes on a 30 minutes time trial. Would love to hear the cause of this slow time. Hope that it’s not caused by a new speed calc algorithm in the latest update. If that’s the case, it’s not working correctly, because with this power output I would do a little above 40 kph (and in the previous Tempus Fugit ITT’s) irl, in stead of the 38kph I got in Zwift yesterday.


There is a bug that is likely what you saw in your race. When a rider enters the pen with a bike, it is what is displayed in the race sometimes. Hence why you occasionally see a mad TT or MTB rider in the pack. They aren’t actually riding a TT or MTB.

I haven’t done the event you speak of. But if wheelsets are auto assigned, then it’s likely the riders you saw actually had the same wheels as you.

This bug was no more obvious too me, when I was testing bikes on box Hill last week, swapping between bikes and wheelsets, my girlfriends zwift never updated my avatars bike or wheels. And unless she was in the same room as me riding, then she would not have known I was on different bikes or wheels at all.

I noticed this too! I rode a Fun is Fast event on Saturday; I tried changing to the Cervelo and Zipps, and that is what showed on the screen, but I’m not convinced it is what I was riding. I usually only do the 17.6km TTs on TF, and my best is 24:46, but I passed through that point (on a little bit less power, but not much less) in 26:30 on Saturday.

FWIW, the Fuego Flats Reverse segment took me 10:45 at 294W on Saturday; for comparison, I’ve done 10:09 at 297W on the Cervelo…

Did Anna van der Breggen ride the rubbish bike when she did her 27:44?

Oh, and the rider who beat me by 2s has lost 74kg and, impressively, 40cm, in the last three weeks!

Hi Tim,
Good to hear (or maybe not so good) I’m not alone with this issue. Anna van der Breggen herself will probably have had this issue. Her time of 27:44 equates to 42,4 km/h, which is an average speed that is a lot lower than she normally does irl. Just a few weeks back she won the Dutch national ITT champs with an average of 44,4 km/h, on a 32 km course with 2 short but steep climbs and corners. Last year at the Worlds she averaged over 47 km/h for 30km. Of course she will have been a lot more motivated to give it all at the National ITT, but the 42,4 km/h on Zwift is just too slow for her on a completely flat course without corners. Looking up the results of some other riders confirms my theory, they were also a lot slower than normal on the Fun-is-Fast ITT.

Indeed, Michiel, I’d have expected a world-class rider like AvdB to be capable of going much faster. Probably a combination of the rubbish bike and not being fully motivated to give it beans.

FWIW, 26:30 is only just faster than my first Zwift TT in January, which I averaged 265W on the Zwift TT with the bog-standard wheels, suggesting that the Fun-is-Fast bike setup is even slower than that!

Just trying to follow-up. Did an ITT race today on the felt with 858 super on the reverse Paris course. 267w got me 24mph. Checking the speeds on bikecalculator puts that in line with riding in the drops not an aerobar.

Seems like the issue isn’t limited to certain TT bikes or the fun is fast events.

Thanks for your follow-up, Blake! 24mph / 38.6 km/h does seem a little too slow for that power. Although it also depends a little on rider height/weight in Zwift. But if this issue does indeed impact more ITT’s then it should be investigated more thoroughly. I’m not planning to do any full-out TT’s in Zwift in the near future (a little too painful for me, just for science ;). But if I do, I’ll send my findings to Zwift Support, and maybe ZwiftInsider as well. Hope that other people can also share their experience with ITT’s here on the Forum.