# How accurate is dashboard speed when in erg mode?

I’ve today done “The Way Out” for the first time, using a Wahoo Kickr in erg mode. The workout felt exactly as the description said it would (and the accompanying video of the French and Italian Maritime Alps is great).

But I’m curious about how the app calculates the speed that it displays on the dashboard, and whether any attention should be paid to it. If the app is to be believed, while maintaining sub-threshold power and cadences between 60 and 90 rpm, I was whizzing up the climbs of the Maritime Alps at speeds from 25 to 28+ kph. Not!

I’ve noticed in other workouts that the displayed speed seemed to be a little off from what I would imagine myself doing in the situation of a given narrative, but not as far off as this; when riding on the kinds of grades that were indicated on the screen I would be probably moving at about half the indicated speed (I’m a pursuiter, after all).

Have others had a similar experience?

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Considering that you are on an indoor trainer and not moving that’s a speed of zero. Sufferspeed was created to provide a rough approximate value for speed and distance. How accurate is it? It matches my real world ability fairly well, but I’ve no idea if that’s the same for everyone.

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Hey @Salsa … it’s basically an algorithm to allow people who want it to record speed/distance equivalent.
It’s not directly related to any of the videos terrain - just based in power and a ‘standard setup’ - it’s just ‘extra’ info in case it’s useful to people. See link below on how it’s calculated.

For example, logging of ‘miles equivalent’ is popular in terms of total miles ridden in a year.

No rights and wrongs, just data points available for people to use.

It was updated the other year after a wee review of the algorithm.

Info on how it’s calculated is here:

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As described above, suff speed is a rough estimate of your speed on flat ground with no wind, based on your power output. It doesn’t take any account of slope gradient. It’s a good solution for racking up consistent mileage in Strava etc. Especially as it reports zero elevation gain in Strava too.

It would only make sense to include slope gradient in the speed calculation if it was also reporting elevation gain. Which would be a nice addition as I’m not getting realistic climbing stats in Strava since moving most of my indoor training to SUF. To achieve this SUF would need to assign a slope profile to each video, which is a bit of work, but also useful for use with the Kickr climb. I think some vids already support the climb so I presume they must already have a slope profile assigned.

There’s also the option of using your trainer reported speed (depending on what trainer you have). But that will not be realistic either. In ERG mode it will merely reflect what gear and cadence you choose regardless of your power output. In level mode it would make more sense in that you would slow down as you increased the level resistance.

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There’s probably an algorithm somewhere that can be tweaked . I use Rouvy (shh) for some endurance rides and it gives virtual mph and elevation based on their routes which are fairly accurate programmed with grade. It takes me about the same time to do a virtual climb on the same course I’ve really done it.
That may be proprietary but it’s certainly easier when you are mapping a true known road with % grade and using rider weight and power . I ignore Suf speed as it’s workout not distance that I want though I’m sure some do

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Knowing that there is no adjustment for slope resolves the discrepancy of the calculated speed. The numbers I was seeing align well with my experience of putting out a sub-threshold effort on a flat road with no wind.

Yes, it’s relatively easy to calculate speed based on a slope profile as all major cycling sims do pretty successfully. But Suff have chosen to keep it very simple so all your session speeds and distances are related to power on a perfectly flat road. It doesn’t bother me either way really since road speed has little meaning in a structured workout. Speed/distance referenced to a flat road are fine for logging mileage on Strava. That’s about the only use I can think of for speed anyway in this context.

Agree- it’s not a sim - you don’t want to be twice as long climbing mt SUF as someone else. It’s power over prescribed time or the workout work/ recovery intervals don’t work. Otherwise the video would have to skip forward depending on the speed in a climb vs flats and even speed on a flat sprint.

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Here is a link to a site that estimates speed based on slope, wind, bicycle weight, and several other parameters:

You could report a slope corrected speed without having to mess with the video timing.

The speed you see on the video doesn’t have to match your own virtual speed like sims do. Indeed your speed doesn’t match at the moment anyway as it is always reported as if it were a flat road. It’s just a number completely independent of the video.

If you did apply a slope correction then your speed would at least be proportional to the video terrain.

An earlier version of SufferSpeed did, I believe, take grade in to account. I recall the minions saying something about taking that bit out but don’t remember why. None of us are physically going anywhere, forwards or upwards, so it shouldn’t really matter.

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Agreed, but it does provide a way of logging virtual mileage in Strava etc. I’m okay with the flat earth approach currently used!

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So I use my trainer to calculate speed at the moment, not Suff Speed. I did The Scream the other day and absolutely caned it for an hour and it said I did an average speed of 9 miles per hour…if I rode like that outside I would have been doing way more than that. I know that the workout is why I am doing it but it is really demoralising when you get such silly speeds. If I swap and use Suff Speed will that likely just over estimate the speed?

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I find that Suf speed is quite accurate compared to my outdoor riding speed (given that it is quite flat around where I live).

Since I changed to Suf speed I find it a good benchmark for estimating my speed for an outdoor 20 km or 40 km ride.

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I think that’ll be fine for like for like comparisons - looks to me like it uses a fairly standard algorithm for equivalent speed for watts/weight (no idea how it actually does it but I’ve seen the other platforms and they seem to be much the same)
They’re all a bit fast to real world conditions for me but then I don’t use it for anything other than data on the screen for interest sometimes

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