[SOLVED] - Speed and distance are wrong for me

[Stephen1974]

I don’t think this is an issue with TD but I’m still confused and after some help

When I started using TD I noticed my speed and distance for completed workouts was off (about half what I’d expect) but being as in reality I was completely stationary for the whole time I didn’t bother about it but recently it’s been bugging me a bit as I’d prefer it to be zero or accurate for my overall stats so I tried to figure out how to correct it. I was assuming there was a setting somewhere in the turbo trainer or in TD but I’ve failed to solve it so looking for some help.

I assume the measurement comes directly from the turbo trainer (a Zwift Hub) and because I only use ERG mode via TD the only way I figure it can know how fast I’m going is to know the size of the gear I’m using and my cadence.

TD can see my cadence so it must be coming from the Zwift Hub although I’m not sure how it knows it. I have a crank mounted Garmin ANT+ cadence sensor which it might be picking up (although unlike my ANT+ HR strap it isn’t obviously paired to the Zwift hub so maybe not) or it might be trying to work it out but in any event it seems accurate (I will test it against a reading from my Garmin head unit connected directly to the cadence sensor next time I ride)

For the size of my gear I’m a bit stumped. Unlike my previous trainer there appears to be no settings in the Zwift app or companion app other than firmware update and spin down calibration so I’ve no idea how it knows the size of my gear at all. Given I only use ERG mode I obviously just stay in one gear and I’d like to set that gear to be one that gives me a reasonable real world speed/distance for the watts I’m putting out in the workout (see this site for an excellent way to estimate this An interactive model-based calculator of cycling power vs. speed - e.g. 1 hour at ave of 200w = about 34km for me in the real world so at ave 70rpm i’d need to set it up with a gear of about 8.1m to get the right sort of readings for an indoor workout)

So… any ideas on how to correct my speed/distance showing in TD with my current set up? All thoughts and ideas gladly received!

[Alex]

We don’t use speed and distance from device. Most people don’t pay attention to gears and since it does not factor in weight it can be pretty far off. We use a much more accurate version based on power and weight but we allow you to change your drag factor. As you know some people ride more aero, or are drafting and that would affect speed to power ratio.

Also if you have maps enabled in strava settings especially climbs then your speeds will be much slower. See settings below on our web based profile settings.

[Stephen1974]

Thanks for the super quick reply Alex

So TD doesn’t take speed and distance data from the trainer but works it out itself using my power from the ride and my inputted weight and drag.

I’ve checked my settings page and have it set up correctly with my actual weight (65kg’s) bike weight (7.5kgs) and I’ve left the drag at the default 0.6 but this is resulting in a speed and distance figure that seems off.

For example my ride today was 107minutes total at an average of 158w and shows an average speed of 17.6kph and 31.6km covered. This seems too slow to me. In the real world if I’d done 160w for 107 minutes I’d have been going about 31kph and covered about 56km by my estimations.

Have I got my maths all wrong here or is something off somewhere?

[Alex]

Yes we don’t use trainer speed, but that’s very slow should be closer to 30. Maybe there is a bug. Can you send me the link to your workout? Are you using strava? Can you send me a link to your strava workout? I want to make sure there is no included map with hills.

We use the same math as this calculator, but since something sounds wrong you don’t need to review it

https://www.gribble.org/cycling/power_v_speed.html

[Stephen1974]

Thank Alex - I never use Strava either (although have a free account with them) but for some reason I did link the account when I set up TD and your request prompted me to have a look. This is what I see -

Two versions of the same ride - one uploaded by TD which looks spot on in terms of distance and speed and another one that doesn’t. Both these rides show in TD and I’ve been looking at the ‘wrong’ one as it’s the most recent in the list! - so it’s all my fault!

I’ve realised the ‘wrong’ ride is caused by me recording the ride separately on a Garmin so it uploads to Garmin Connect and this is syncing to Stava and then Strava is syncing back to TD I assume… So it looks like Garmin has the problem so I’ll investigate that and leave you in peace!

I actually use a paid Training Peaks account to plan and track my activities and I think I’ve got a messy cross syncing problem between all my accounts and I need to set things up better as I seem to currently have it that Garmin syncs to TP so an easy fix is swap that around to at least get TP right by using your data not Garmin’s!

Thanks again for your help - this forum is excellent!

[Alex]

Oh great news (for me at least!!!) Yes your Garmin is recording based on what the trainer is outputting. This was my point that this value can be all over the place and why we don’t use it. Glad you found the source of your problem. You can stop syncing Garmin or you could use RunGap if you are iOS user to sync TD to garmin.