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Minimum Segment length ?

Ian
Pico de Orizaba

I noticed that someone recently asked that the minimum length of mountain bike Segments be decreased and the post was quickly archived by an admin on the basis that reverting Strava changes could not be discussed.

I have some sympathy for the poster - I was also somewhat frustrated by the recent increase in minimum length of bike Segments from 300m to 500m.  In my area there has been some good competition over Segments about 400 to 450m in length but such Segments can no longer be created or edited (the change happened as I was working on a new Segment of about 450m - it now finishes closer to a T junction than I would like but editing is no longer possible).

I don't remember seeing any requests from Strava users for such a change in the previous Strava Support forums so I wonder if someone at Strava could give some background to their reasons for making the change and their methodologies for determining minimum Segment lengths for each Activity type ?  Clearly measurement accuracy is a factor on shorter Segments, but even on a 300m bike Segment the accuracy should be within a couple of % which seems OK.

7 REPLIES 7

gnordli
Mt. Kenya

There needs to be some consideration for the time it takes to complete the segment instead of just length.  A road bike may be able to do a 500m segment in 40 seconds or so.   Whereas a 250m mountain biking segment could easily take over a 60 seconds to complete, depending on terrain.  

My suggestion is people can "submit" a segment for approval, and if let's say 50 different riders have ridden it and the top 10% avg time is greater than 45 seconds, then it should be legit.  

I just threw some numbers out there.  Strava has access to all of the data, so you can compute would looks like a legit segment for mountain bikers, before it gets approved.

There are too many mountain bike trails less than 500m -- Strava needs to figure this out. 

 

eschlange
Mt. Kenya

The new minimum segment length of 500 is especially silly when it comes to virtual segments (on platforms like Zwift, for example). On those segments, GPS is recorded consistently - Zwift records every 1s, for example. So shorter segments should be allowed, since accuracy is ensured across all users.

I wrote a thorough post about this on Zwift Insider which explains several reasons why Strava's current minimum length requirement is silly in the context of Zwift. I do hope Strava will reconsider.

https://zwiftinsider.com/strava-minimum-segment-length/

T3mppu
Mt. Kenya

I have contacted strava support on this and they told to bring it here so community would get more visibility on this.

I too had estimated the limits to be rised from 300m into 500m and support confirmed:
We have a limit in place to make sure that newly created segments would result in more accurate leaderboards and reduce segment noise overall. There are minimum distance requirements for ride segments (500m) as well as other sport types (250m).

So 500m for all cycling, 250m for running.

 

As I see, the shorter mtb segments would usually be in local forrest, where it is really difficult to get the 500m or it would be making dangerous segments if you need to cross a road or walkway to get to the 500m.

Also the speeds in such places are a lot less than on the road, so there would be more gps points recorded than on road segments that also are 500m limit.

So it would be really nice to get back the 300m (or even 250m) limit.

 

For the segment noise part, it would be also nice to be able to flag runs that clearly are not following the segment.

Ian
Pico de Orizaba

I've been prompted by Strava to identify 1 of the first 3 replies as an "accepted solution", however, I'd prefer to wait until my question has been answered and I'm still hoping to get some feedback from Strava about the reasons for their changes (which don't seem to have been led by customer requests) 

eric
Elbrus

I'd be interested in hearing strava engineers perspective also. Similar to your guess, my guess would also be that its an accuracy issue. There are some pretty big differences between various GPS tracking devices, and I suspect the margin for SOME users is much worse than a couple of % when looking at such a short segment. Say the fastest time is 30 seconds on a 300m segment (22.36MPH). Depending on a GPS ping here and a GPS ping there... I think some riders will see 5-10 seconds of variation which would render the segment pretty difficult to fairly measure. That's probably an exaggerated example, but that's my guess. My other guess is that they had to draw to line somewhere to prevent the segment database from getting overrun with tiny segments, or drowning out more "important" segments. 


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Strava member since 2013

Ian
Pico de Orizaba

As I'm sure you are aware, Strava bike Segments are numbered sequentially in the order they were created.  I started using Strava in 2017 and the first Segment I created had a number around 17,000,000.  At that time it was clear (from trial and error) that the minimum Segment length was 300m.  The latest Segments are numbered around 32,500,000.  I have completed quite a few Segments that are shorter than 300m and the highest Segment number of these is around 14,000,000.  Hence I infer that Strava set a minimum length of 300m in about 2016.  This seems perfectly reasonable - I have completed Segments that pre-date this change that are as short as 45m (the KOM is 6 seconds !) and these are clearly not suitable for meaningful competition.  

I agree that a minimum Segment length is appropriate - I'm just curious that after it being 300m for about 6 years why has it been decided to raise the limit to 500m ?  I've heard that some GPS systems only record every 5 seconds but, despite looking at many Strava Activities, I don't think I've seen an Activity with such large step intervals (by counting the data points in my Activities it seems my own GPS interval is about 1 second, despite it being from a very old phone).

The number of Strava users and Segments is no doubt increasing and so there is ever more data to be handled by Strava - however, the cost of data analysis and storage continues to fall so I doubt this would be a reason for the change. 

Strava could improve accuracy of segment timing (quite significantly) without raising the minimum segment length by implementing interpolation of segment timestamps. Even when someone uses smart recording and has recorded points further apart it is hard to imagine that person changing the speed drastically within a few seconds, so interpolation could help to determine more precisely when they went by the segment start or finish. Also, a smaller radius could be used for the interpolated points (once the initial match is found) which would help to prevent falsely matching a segment when someone didn't actually cross a segment start or finish. With the current implementation there are a lot of opportunities to cheat or misuse segments. For example, one can simply turn around 30-50 meters before the segment end, and that segment would still match and that person could cut 10+ seconds if they are running. Perhaps it isn't easy to turn around on a bike but very easy when running, and I see that happening a lot on uphill segments.

By the way, I don't know if the same 500m limit applies to running segments. If that is the case that would really hurt uphill segments and stairs. There aren't that many steep hills that are longer than 500 meters.

What Strava does with increasing the limit has nothing to do with improving the absolute accuracy of segment matching. That merely reduces the relative error which makes the timing errors less noticeable.

If Strava engineers are interested, I could suggest an interpolation algorithm that wouldn't significantly increase the computing cost of matching segments.