Time vs. Average Speed

If you look at the segment leaderboards on the SMMT Challenge website, you may notice in some cases that some efforts may have a longer time but a higher average speed. For example, if we look at the current leaderboard for the Mulholland segment it looks like this:

Note the time vs. average speed

Note the time vs. average speed

Scott has posted the fastest time while Gareth has posted the fastest speed. How is this possible?

A look at the underlying data shows that Scott’s effort on the Mulholland segment was 6.96 miles while Gareth logged a full 7.04 miles. So while Scott’s time was lower, he didn’t ride as far as Gareth did. These types of minor discrepancies happen because of a variety of reasons.

First, our GPS devices do not constantly record our locations. Rather, they take a measurement every few seconds. So you most likely do not have a GPS reading exactly on the start or end of the segment. That measurement is also not an exact measurement.

Another reason is just due to the inexact nature of the segments themselves. The start and end point depend on the ride the segment was created from. GPS is not an exact science, so the original ride may have been off and the segment might start off the road.

The result is that when it comes to Strava segments, it is an inexact science which means that luck is involved to some degree. As another example, my time on Fernwood was faster that Jon Woodbury’s time, but he posted a faster average speed. When I compared the endings of both of our efforts together, you can see why. I got lucky (or Jon got unlucky) and my segment ended before his did giving me the time advantage.

bryantvsjon

 

Normally the Fernwood segment ends where mine did, but for some reason Strava has Jon’s ending later.

So that is why you may see some discrepancies in the times vs average speed.

 

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2 thoughts on “Time vs. Average Speed

  1. Douglas Kubler

    Even if the GPS’s were perfectly accurate these situations will still occur. The fault lies with how Strava determines the start and end of an effort. Simply put Strava takes the first GPS point AFTER the start of the segment and the last GPS point BEFORE the end of the segment. If everyone used the option of recording a point every second then the total discrepancy would be limited to 1 second for the start and 1 second for the end. The troublesome cases are when someone uses so-called smart recording so that the interval between points can be much more than 1 second which makes the handicap more than 1 second. Also there are devices (iPhones) that space out the recorded points. I saw one case in which the iPhone gave a rider a 7-second gap (head start) on a segment which really hurts the competition on a short segment.

    To be fair (on average) to all competitors those using iPhones and smart-recorded rides should have a penalty of X seconds.

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